WO2012046086A1

WO2012046086A1 - Method for extending the shelf-life of a foodstuff

Info

Publication number: WO2012046086A1
Application number: PCT/GB2011/051944
Authority: WO
Inventors: Bjorn E. Christensen; Kåre A. KRISTIANSEN; Sabina P. Strand
Original assignee: Ntnu Technology Transfer As; Cockbain, Julian
Priority date: 2010-10-08
Filing date: 2011-10-10
Publication date: 2012-04-12
Also published as: GB201017003D0

Abstract

Method for extending the shelf-life of a foodstuff Methods of extending the shelf-life of a foodstuff and/or for preventing or reducing microbial (e.g. bacterial) growth on said foodstuff are provided. The methods comprise coating the foodstuff with a composition comprising at least one acidic biopolymer, preferably an edible acidic biopolymer, e.g. a polysaccharide, and optionally storing said coated foodstuff. Also provided are compositions for use in said methods, processes for coating foods with said compositions and uses of said compositions.

Description

Method for extending the shelf-life of a foodstuff

This invention relates to methods for prolonging the shelf-life of foods and for reducing microbial growth on foods. The invention further relates to

compositions for use in coating foods, especially to acidic coatings which are capable of extending the lifespan of decayable foodstuffs and which possess antimicrobial properties, to processes for coating foods with said coatings and to uses of said coatings.

Foodstuffs (foods) undergo a number of changes during storage, including chemical, physical and microbial changes. These changes are a function of inherent and environmental factors acting on the foodstuff, for example temperature, exposure to light and moisture, bacterial load, etc. Early methods for stabilising foodstuffs, especially for delaying microbial growth, include pickling, e.g. placing the foodstuff in an acidic solution such as vinegar (acetic acid). Latterly, methods of coating foodstuffs with a coating material which can provide an inert protective layer have been developed. The coating material affects the rate of changes of the foodstuff on storage. As well as providing inert protective layers, coating materials may also interact with the foodstuffs to actively provide beneficial effects such as oxygen or moisture scavenging, or reduction of microbial growth. The general uses of coatings for extending the lifespan and shelf-life of decayable foods are well known. Meats, cheese and fruits are all examples of foods which may be coated to reduce contamination, dehydration and microbial growth, processes which lead to deterioration of the food and to decay.

Of the materials known for use in food coatings, biopolymers (i.e. polymeric materials derivable from natural, e.g. plant or marine, sources) have been widely investigated for use as components of coating materials, in particular because they can provide edible coatings which are cost- and waste-efficient. In many cases, the biopolymers are used only to provide desirable physical properties to the coating, e.g. owing to their gelling behaviour, and are not intended to interact with the foodstuff to provide further beneficial effects (see e.g. United Kingdom patent No. 1,055,373). An example of a class of biopolymers which are used in coatings, e.g. edible coatings, is the family of alginates, which may be extracted from Phaeophyceae (brown algae) or from bacteria and which are linear co-polymers of Z)-mannuronic (M) and Z-guluronic (G) acid monomers. The distribution of M and G monomers generally varies along the polymer chain in naturally-derived alginates. Both M and G monomers of alginates comprise a pendant carboxyl group and the nature of the counter-ion to the carboxyl group has a profound effect on the stability, structure and solubility of a polymeric alginate. Alginic acid (i.e. a protonated "alginate") has a tendency to precipitate in aqueous solution. In contrast, alginates, especially those complexed with a monovalent cation such as Na⁺, are generally soluble in aqueous

2__|_

media and will readily take up divalent cations such as Ca to form a gel. Alginates are typically isolated from natural sources as high molecular weight polymers which may be degraded, e.g. by chemical or enzymatic hydrolysis, to produce polymers of lower molecular weights. A discussion of alginates is found in Draget et al, "Polysaccharides and Poly amides in the Food Industry. Properties, Production, and Patents" - Chapter 1, (2005) WILEY-VCH Verlag GmbH, Ed. Steinbuchel and Rhee. Treatment of foodstuffs with sodium alginate biopolymer (e.g. Protanal^® LF5/60, available from FMC Biopolymer) is known, e.g. from European patent application No. 0253535.

It should be noted that the term "alginic acid" is sometimes used in older literature to refer to an alginate (in its ionic form), which may have a non-proton counter-ion, e.g. a Na⁺ counter-ion. An example of such a misleading use of this term is found in EP-0253535-A1, discussed above. The term "alginic acid" will be used herein to mean a copolymer of M and/or G monomers which carry carboxylic acid groups that are not substantially in the salt form, i.e. complexed with non- proton counter-ions. The terms "acidic biopolymer", "pectinic acid" etc. are used accordingly.

Alginic acids as such are not generally used in coatings for food because of their tendency to precipitate in aqueous solution. In contrast, alginates, especially sodium alginate (known as food additive E401), are widely used as functional

2__|_ components in food coatings, especially forming gels in the presence of Ca ions.

2__|_

Because of the solubility of sodium alginate and its ready gelation with Ca ions, the preparation of food coatings from alginates is usually carried out from an aqueous solution of the sodium salt. In a first step, a foodstuff is generally coated

2__|_

with the sodium alginate solution and, in a second step, Ca ions are brought into contact with the coated product to gel the solution and give the coating the desired physical properties (see e.g. Kampf et al, Food Hydrocolloids (2000) J_4; pp.531-

2__|_

537). Alternatively, the foodstuff may be treated with Ca ions and then sprayed with the sodium alginate solution. However, in neither of these cases is an acidic biopolymer, e.g. alginic acid, used.

Coatings formed by gelation of a biopolymer, e.g. sodium alginate, often comprise further components such as antimicrobial agents, antioxidants, acidifying agents, etc. which lend desirable properties to the coating. Various agents are known as anti-microbial agents in such coatings, including enzymes such as lysozyme, antibacterial peptides such as nisin and small organic acids such as acetic, propionic, sorbic and citric acids. However, the use of organic acids as

antimicrobial agents on certain foodstuffs, especially meat, is known to alter the appearance and texture of the food by partially denaturing the proteins in the surface of the food. This phenomenon, called acid whitening herein, can significantly affect consumer acceptance of a coated foodstuff. The small organic acids also lend a characteristically acidic, or vinegary, smell and taste to foodstuffs which some consumers find unappealing.

There exists a need for improved coating materials, especially edible coating materials, which are cheap, easy to use and which possess useful properties such as anti-microbial properties. It is an object of the present invention to provide such coating materials.

The inventors have discovered, contrary to conventional practice, that acidic biopolymers may advantageously be formulated directly into coatings for foodstuffs and that the said coatings possess surprisingly useful properties. In particular, coatings comprising acidic biopolymers possess potent anti-microbial properties and may possess a reduced capacity for acid whitening on certain foodstuffs, especially meat, when compared to coatings comprising small organic acids. Acidic biopolymer-containing coatings may also give the foodstuff a more neutral smell and taste than a coating composition comprising small organic acids. Without wishing to be bound by theory, the inventors postulate that the acidic biopolymer allows for a partially buffered delivery of protons which maintains an antimicrobial pH at the surface of the foodstuff but that, after proton delivery, the anionic component (the biopolymer) does not significantly penetrate the surface of the foodstuff and so does not flavour the food itself. In particular, the inventors' findings allow for coating compositions to be prepared in which the proton delivery potential of the coating can be fine-tuned by altering the amount of acidic biopolymer. This renders the coating compositions suitable for use on a wide range of foods.

Thus, in a first aspect, the invention provides a composition for (e.g. suitable for) coating a foodstuff, said composition comprising (e.g. consisting essentially of) at least one acidic biopolymer. The composition preferably possesses antimicrobial (e.g. bacteriostatic or bactericidal) properties when applied to the foodstuff, e.g. the composition is preferably an antimicrobial composition, especially an antibacterial composition. The acidic biopolymer is preferably an edible acidic biopolymer, e.g. a material known and approved for use in foodstuffs.

By "coating", "coated", and the like, is meant that the composition comprising the acidic biopolymer forms an essentially continuous layer on the surface of the foodstuff so as to bring the acidic biopolymer into intimate contact with the surface of the foodstuff. This contact allows protons from the acidic biopolymer to pass into the surface layer of the meat but without transferring a significant quantity of counter-ions, e.g. the biopolymer anions. Whilst the coating may be provided as a bath or dip, i.e. where the layer is part of a mass of composition such as a gel surrounding the foodstuff, it is preferred that the layer is discrete, i.e. that the layer is a thin layer, e.g. having a thickness of from several microns to several millimetres. Discrete layers may be provided by known spray techniques. The term "coating", and the like, is not intended to encompass the cooking of a foodstuff in an aqueous solution of acidic biopolymer, i.e. simply treating the foodstuff with an acidified solution at raised (i.e. above ambient) temperature.

By "acidic biopolymer" is meant a polymeric material, especially a polysaccharide, derivable from a natural, e.g. plant, bacterial or marine, source carrying chemical groups which can provide a source of H ions at the appropriate pH. Examples of such chemical groups include phosphate, sulphate and carboxylate groups. Carboxylate groups are preferred, but any acidic functionality that can provide a source of H⁺ ions at a suitable pH can be present on the acidic biopolymer. A proportion of the acidic groups of the biopolymer of the invention may be chemically modified, e.g. esterified, to abrogate proton delivery provided that the remaining groups retain sufficient proton-donating capacity to provide a

biopolymer-containing composition with beneficial properties, e.g. antimicrobial properties. Preferably, at least 50%, more preferably at least 75%, especially at least 90% of the acidic groups of the biopolymer are not chemically modified and can thus provide a source of H⁺ ions at a suitable pH. In one embodiment of the invention, the composition preferably does not comprise hydroxypropyl alginate (known as PGA and E405). The term "acidic biopolymer" is not intended to cover biopolymers having acidic functionalities substantially in the salt form, e.g. sodium alginate (known as E401) or calcium alginate (known as E404).

The properties of the compositions of the invention, especially the antimicrobial properties thereof, will depend in part on the capacity of the acidic biopolymer to deliver protons. The acid capacity (a function of the pK_a of the acidic biopolymer and the pH of the composition) and the concentration of the acidic biopolymer in the composition should be chosen accordingly. For example, it is known that the pK_a of alginic acid is typically in the range of 3.38 to 3.65, whereas that of CMC is around 4.3.

At least one pK_a value (measured under standard conditions, e.g. 25 °C in water) of an acidic group of the biopolymer of the invention is preferably between 2 and 7, more preferably between 3 and 5 especially between 3 and 4, particularly around 3.5 or around 4. Other preferred values for the at least one pK_a value of an acidic group of the acidic biopolymer are between 3.2 and 4.5, e.g. between 3.3. and 3.7 or between 4.2 and 4.4. Preferably, all of the acidic groups of the acidic biopolymer have pK_a values between the values listed above. In an especially preferred embodiment, the pK_a values of the acidic groups on the acidic biopolymer are between 3 and 4. Methods for determining the pK_a value of acid groups of a biopolymer are known in the art. The concentration of acidic biopolymer is preferably chosen such that, after coating, the pH of the surface of the foodstuff is maintained at a pH of between 2 and 8, e.g. between 3 and 7 and especially between 3 and 6, between 3.5 and 6, or between 3.5 and 5, e.g. around 4, for a period of at least 24 hours, especially for at least 48 hours, particularly for at least 3, 4, 5 or 6 days. It is preferred that the surface pH is maintained at a value which is greater than about 2.5, especially greater than about 3, 3.5 or 4. It is also preferred that the surface pH is maintained at a value which is less than about 7, e.g. less than about 6.5, 6, 5.5 or 5.

By "maintained" is meant that the surface pH retains a roughly equal value for a significant proportion of the allotted time. The pH value preferably stays within ±1.5 pH units of the said value, especially within ±1 or ±0.5 pH units. The initial surface pH is typically different to the stable value and the term "maintained" is therefore used to refer to the pH value obtained after a short period of time (e.g. 12 to 24 hours) to allow the system to reach a stable state. For example, where the foodstuff is meat or fish, the surface of the foodstuff is typically at a lower pH immediately after application of the composition. Typically, the surface pH reaches a stable pH value around 24 hours after the coating is applied, when held at low temperature, e.g. around at 4 °C. Stable pH may be obtained in shorter periods of time at higher temperatures, e.g. ambient temperatures. The surface pH is then preferably maintained at the pH values recited herein for the said periods of time.

If the composition is to be used on a foodstuff which is susceptible to acid whitening, the concentration of acidic biopolymer is preferably chosen such that, after coating, the pH of the surface of the foodstuff is maintained at a pH of between 3.5 and 7, e.g. between 4 and 6, for the periods of time specified above.

Alternatively, if acid whitening of the foodstuff is desired or if a degree of acid whitening is acceptable (e.g. if the foodstuff is to be cooked, bended or otherwise processed), the concentration of acidic biopolymer may be chosen such that, after coating, the pH of the surface of the foodstuff is maintained at a pH of less than 5 or less than 4, e.g. between 2 and 4, especially around 3 or 3.5.

In order to achieve the desired surface pH, the compositions of the invention are preferably formulated to have an initial (i.e. pre-application) pH of between 1 and 6, e.g. between 2 and 5, especially between 2.5 and 4, e.g. between 2.7 and 3.3, or greater than 2.8 such as from 3 to 4 or from 3.5 to 4.5.

The amount of acidic biopolymer (e.g. alginic acid) to be incorporated into the coating composition of the invention will vary depending on the nature of the biopolymer and its intended use (including the desired degree of proton delivery). Indeed, one advantage of the present invention is the provision of a coating composition system which may be tuned to deliver the desired effects, especially to vary the microbicidal effect of the composition. The concentration of acidic biopolymer in the composition is preferably high enough to enable the coating composition to provide the foodstuff with a surface pH according to the ranges specified above. In one embodiment, the concentration is simultaneously low enough to result in little or no deterioration in the appearance of the foodstuff after application, e.g. to result in little or no acid whitening to the surface of the foodstuff. In an alternative embodiment, the concentration of acidic biopolymer is high enough to result in a uniform acid whitening to the surface of the foodstuff, preferably high enough to cook or cure the surface of the foodstuff. Compositions having such high concentrations may be advantageous for use the coat foodstuffs intended for cooking (e.g. boiling or frying) or for foodstuffs intended to be eaten raw. High

concentrations may also impart a vinegary taste to the coated foodstuff, which is desirable in some circumstances, especially in coatings for raw vegetables and fish.

Thus, in one embodiment concentrations of acidic biopolymers in the coating compositions of the invention will generally fall in the range of 0.1-500 mg/ml (around 0.01-50% wt). Preferred concentrations include 5-250 mg/ml, e.g. 10-100 mg/ml or 15-80 mg/ml. Especially preferred concentrations include greater than 20, 25, 30, 35 or 40 mg/ml and less than 100, 80, 70, 60, 55 and 50 mg/ml, e.g. around 30-40 mg/ml (around 3-4% wt), around 40-60 mg/ml (around 4-6%> wt) and around 70-80 mg/ml (around 7-8% wt), of acidic biopolymer. Further preferred

concentrations include 0.1-10 mg/ml, especially 1-5 mg/ml, e.g. around 2, 3 or 4 mg/ml, of acidic biopolymer.

The term "biopolymer" as used herein is not considered to be limited to polymers of any particular length. The biopolymers (e.g. alginic acids) of the invention preferably have a number degree average polymerisation (DP_n) of between 10 and 1000. The acidic biopolymers of the invention may be short polymers (e.g. oligomers) having a DP_n of between 5 and 50, especially between 10 and 40, e.g. about 20. Alternatively, the biopolymers of the invention may be longer polymers having a DP_n of between 50 and 1000, especially between 75 and 500 or between 100 and 350, e.g. about 250.

Accordingly, the weight average molecular weight (M_w) of the biopolymers of the invention may vary between about 0.5 kDa and 4 MDa, especially between about 1 kDa and 2 MDa, particularly between about 5 kDa and 1 MDa, e.g. between about 10 kDa and 500 kDa. In one embodiment, the acidic biopolymers of the invention have a M_w of between 0.9 kDa and 9 kDa, preferably between 1.5 kDa and 7 kDa, e.g. about 3.5 kDa (i.e. low molecular weight). In another embodiment, the acidic biopolymers of the invention have a M_w of between 9 kDa and 1.8 MDa, especially between 15 kDa and 900 kDa, e.g. around 45 kDa (i.e. high molecular weight). The terms "low molecular weight polymer" and "short polymer" refer to the same lighter polymers, and the terms "high molecular weight polymer" and "longer polymer" refer to the same heavier polymers.

Low and high molecular weight acidic biopolymers may be present together in the compositions of the invention. Viewed from this aspect, the invention provides a composition for (e.g. suitable for) coating a foodstuff, said composition comprising at least one low molecular weight acidic biopolymer as described herein and at least one high molecular weight acidic biopolymer as described herein.

Preferably the two said biopolymers are derived from the same source, e.g. the two said biopolymers are alginic acids. Such a combination of lighter and heavier polymers allows for a greater degree of tuning of the properties of the composition of the invention. For example, the nature and concentration of the lighter polymer may be chosen to optimise the proton delivery and anti-microbial effect of the composition, whereas the heavier polymer may optimise the physical properties, e.g. the viscosity, of the composition.

According to the invention, any acidic biopolymer having the appropriate properties may be used. Suitable acidic biopolymers may be identified from lists of approved materials for human or animal consumption, e.g. the US Federal Drug Agency (FDA) Food Additives Status List. Other known sources of approved biopolymers include the "E" number codes of food labelling (especially E400-E499) and the list of important food hydrocolloids given in Food Engineering &

Ingredients, April/May 2008, Volume 33, Issue 2. Preferred acidic biopolymers of the invention include polyuronic acids, such as alginic acid (e.g. the additive designated E400) and pectinic acid, and acidic cellulose derivatives, such as acidified carboxymethyl cellulose which may be produced using known methods. Alginic acid is a particularly preferred acidic biopolymer according to the present invention, especially alginic acid obtained from FMC Biopolymer, Norway (e.g. Protacid F120NM). Sources of acidic biopolymers (e.g. alginic acids) and methods for their partial degradation and/or chemical modification are known in the art. For example, alginic acid may be obtained as an intermediate in the production of sodium alginate or may be prepared from sodium alginate, e.g. from LF/10/60 (FMC Biopolymer, Norway), by known methods. Many such acids are commercially available (e.g. from Sigma- Aldrich) or can be prepared from the corresponding salts by known methods, e.g. those set out in Example 7.

Thus in a preferred embodiment, the at least one acidic biopolymer of the invention is at least one alginic acid, e.g. one or two alginic acids.

The compositions of the invention may be provided with further components to tailor the properties of the composition for the intended use. For example, whilst the composition of the invention may comprise only the one or more acidic biopolymers (e.g. in powder form), the composition will generally further comprise an aqueous or oleaginous base with one or more additional components to tailor the physical properties of the composition. Such additional components may be active components (e.g. antioxidants, desiccants etc.) or non-active components, such as solvents or structural components. Other suitable components for incorporation in the coating compositions of the invention include stabilisers, flavourings (e.g.

spices), flavour enhancers and colourings. The further components may be acidic or non-acidic, but are preferably not acidic especially not contributing significantly to the pH or to the antimicrobial effects of the composition.

In a preferred embodiment, the composition comprises a structural polymer component (i.e. a further polymeric component) to modify the physical properties of the composition, e.g. to increase the viscosity of the composition or to gel the composition. Examples of preferred structural polymers include edible (e.g. food- grade) biopolymers such as alginates (e.g. sodium or calcium alginate), agars, carrageenans (e.g. ι-, κ- or λ-carrageenan), gums (e.g. guar gum, acacia gum, xanthan gum, locust bean gum, etc.), cellulose derivatives (e.g. ethyl or methyl cellulose), chitosans, gelatine (e.g. animal or fish gelatine), and mixtures thereof. In one embodiment, the structural polymer component does not itself provide an appreciable source of H⁺ ions. Preferably, the structural polymer component is a polysaccharide (e.g. xanthan) which comprises acidic groups (e.g. carboxyl groups) on fewer than 50% of its monomer units, especially fewer than 40% or fewer than 20%.

Particularly preferred structural biopolymers are xanthans and carrageenans (e.g. λ-carrageenan), especially xanthan. In a preferred embodiment, the

composition of the invention is an aqueous composition comprising xanthan and/or λ-carrageenan. Preferably, the composition comprises the structural polymer at a concentration of between 1-40 mg/ml. Especially preferably, the composition comprises xanthan at a concentration of between 1-10 mg/ml or between 2-7 mg/ml, especially around 2.5 or 5 mg/ml; and/or λ-carrageenan at a concentration of between 10-20 mg/ml. Guar gum, locust bean gum and water-soluble or gelling cellulose derivatives may be used at a concentration of around 1-20 mg/ml, especially around 5 or 10 mg/ml.

Thus, in a related embodiment the invention provides a composition for (e.g. suitable for) coating a foodstuff, said composition comprising at least one acidic biopolymer and at least one structural polymer. Where the acidic biopolymer is edible, the structural polymer component is also preferably edible.

Preferably, the composition is an antibacterial composition comprising at least one alginic acid as herein defined and at least one xanthan as herein defined. Especially preferred are compositions comprising alginic acid at a level of 10-80 mg/ml, especially 30-40 mg/ml, and xanthan at a level of 2-7 mg/ml, especially around 5 mg/ml.

The acidic biopolymer may be dissolved within the compositions or may form a colloidal system, e.g. an emulsion or sol, or a gel with the other components of the composition. In a first embodiment, the composition is in powder form, e.g. comprising finely dispersed particles of the one or more acidic biopolymers, optionally with a solid carrier. Dispersing the acidic biopolymer particles in a second powder may improve flowability of the composition and increase the ease of its application to the foodstuff, e.g. by sprinkling, spraying or dipping. In another preferred embodiment, the composition of the invention comprises a dispersion of an acidic biopolymer (e.g. alginic acid) in an aqueous phase, especially in a thickened or gelled aqueous phase. In an alternative embodiment, the composition comprises a dispersion of an acidic biopolymer (e.g. alginic acid) in an oil, such as a vegetable oil (e.g. olive oil, palm oil, soybean oil, corn oil, sunflower oil, safflower oil, peanut oil, or sesame oil, or a mixture of one or more of the above). In a further embodiment, the composition of the invention is an optionally thickened aqueous solution of an acidic biopolymer (e.g. pectinic acid). In a further embodiment, the composition is an emulsion, e.g. an oil-in-water or water-in-oil emulsion, wherein the acidic biopolymer is dissolved and/or dispersed in the aqueous phase. The emulsion may include an oil as defined herein. Preferably, the composition is an oil- in-water emulsion of the oil (e.g. rapeseed oil), and the aqueous phase which comprises the acidic biopolymer (e.g. alginic acid) and preferably comprises a further structural polymer (e.g. xanthan).

In one embodiment, the composition comprises a plurality of acidic biopolymers, especially having different molecular weights. In one embodiment, the composition comprises a first acidic biopolymer having a low weight average molecular weight (e.g. 0.5-10 kDa), the concentration of which may be chosen to determine the pH and buffering capacity of the composition, and a second acidic biopolymer having a high weight average molecular weight (e.g. 10-1000 kDa), the concentration of which can be chosen to determine the physical properties (e.g. viscosity) of the composition.

The coating compositions of the invention preferably possess antimicrobial properties and do not have to contain further antimicrobial agents to prevent or restrict microbial (e.g. bacterial) growth. Particularly preferred compositions are those which do not contain appreciable amounts of small organic acids. By "small organic acid" is meant a molecule of less than about 500 Da in size which is capable, at a suitable pH, of donating H⁺ ions, especially having at least a first pK_a of from 2 to 7 (when measured under standard conditions, e.g. 25 °C in water). Examples of small organic acids include acetic acid, propionic acid, sorbic acid, lauric acid and citric acid. The term is also intended to cover non carbon-containing weak acids, such as hypochlorous acid, although such acids are not preferred examples of small organic acids. An appreciable amount of a small organic acid is one which has a measurable effect on the pH of the coating composition, e.g. an amount which changes the pH by more than 0.1 units, especially by more than 0.5 or 1 units.

Thus in one embodiment, the compositions of the invention are substantially free from small organic acids and from the salts of small organic acids. The compositions of the invention are especially preferably substantially free from acetate, propionate and/or lactate anions. By "substantially free from small organic acids and from the salts of small organic acids" is meant that the small organic acid is not present in an appreciable amount as defined above. The compositions of the invention are also preferably substantially free from cations such as monovalent cations, e.g. alkali metal ions such as sodium (Na⁺) and potassium ions, and/or

2__|_

bivalent cations, e.g. alkaline earth metal ions, such as calcium (Ca ) ions.

Particularly preferably, the compositions of the invention are substantially free from

2__|_

Ca ions. By "substantially free from cations" is meant an amount of cations which is sufficient to solubilise and/or gel the acidic biopolymer, in particular, less than 10% wt, e.g. less than 5%, less than 2% or less than 1% wt cation in the

composition.

Accordingly, in a further embodiment the invention provides compositions as defined herein which do not contain any appreciable quantity of at least one of the following: antimicrobial agents (besides the acidic biopolymer); small organic acids; and Ca²⁺, Na⁺ and/or K⁺ ions.

It is important that the physical properties of the composition are such that a foodstuff can be coated with the composition to give a substantially uniform coating that affects the coated surface evenly and that possesses sufficient mechanical stability to survive post-coating steps of transport, storage, processing, etc. The physical properties of the composition will therefore depend on the intended use of the composition (e.g. the coating method), as well as any post-coating processes which are required. The nature of the properties required of the coating and of the materials which could be used to provide those properties would be evident to the skilled person, although routine optimisation by testing may be required.

Thus, in a further aspect, the invention provides a process for coating a foodstuff, the process comprising bringing the foodstuff into contact with a composition of the invention to provide a substantially uniform coating on the surface of said foodstuff. The foodstuff is preferably coated over the majority of its outer surface, especially over the entirety of any surface which will subsequently be open to the environment. Methods for coating foodstuffs are known (see e.g. WO 2007/038621) and include techniques such as dipping, soaking, spraying, etc. The foodstuff may be coated with a single layer in a single step, or may be coated with a plurality of layers, which may be the same or different compositions. However, it is important that at least the layer adjacent to the surface of the foodstuff is formed from a composition according to the invention. A multi-layer coating may advantageously provide improved properties with each layer tailored to possess specific properties, e.g. oxygen/moisture permeability, physical strength, antimicrobial properties or improved appearance. However, multi-layer coatings are generally more expensive and time-consuming to apply. The compositions of the invention can be tailored to provide many of the specifically desired properties in a single layer. Thus, the process of the present invention preferably coats the foodstuff with a single composition, especially with a single layer of a single composition.

The coating is typically applied in an amount of from 0.1 to 500 mg/cm of food surface, especially from, 1-400, 10-300 or 20-200 mg/cm , e.g. around 40-60

2 2 9

mg/cm or 70-110 mg/cm , or around 0.5-2 or 5-10 mg/cm . The coating method and the physical properties of the coating composition may be adjusted to provide the desired level of coating, as would be apparent to the skilled person.

One characteristic of preferred coatings described herein is their ability to be removed readily from the surface of the foodstuff. For example, a meat product coated with a composition according to the invention may be washed in water to remove the coating ready for sale, consumption or cooking. According to this aspect, the process comprises the further step of removing the coating, e.g. after a period of time of around 24 hours, 48 hours, 3, 4, 5, 6 or 7 days has elapsed. Where the coating is to be removed before processing or consumption, the coating may be a non-edible coating.

In a preferred embodiment, the process of the invention comprises a first step of coating the foodstuff with a composition as described herein wherein said composition is substantially free from Na⁺ ions. In a further preferred embodiment, the process of the invention does not comprise the step of contacting the foodstuff (or the foodstuff coated with at least one composition of the invention) with a

2__|_

solution comprising a significant amount of Ca ions, e.g. a solution comprising

2__|_

more than 1%, 2%, 5% or 10% wt of Ca ions. In another embodiment, the process of the invention does not comprise the step of contacting the foodstuff with an alginate gelling solution.

In another preferred embodiment, the process of the invention comprises a first step of coating the foodstuff with a composition as described herein wherein said composition is substantially free from small organic acids, especially a composition where the total amount of small organic acids is less than 2.5% wt, especially less than 1.5%, 1%, 0.5% or 0.1% wt.

The compositions of the invention preferably display antimicrobial properties towards a wide spectrum of micro-organisms. In particular, the growth both of Gram-positive and Gram-negative bacteria may be prevented or restricted on the surface of foods when coated with compositions according to the present invention. Growth of moulds and yeasts is also expected to be prevented or restricted by the coatings of the invention. In particular, the compositions of the invention can reduce the growth of bacteria selected from Staphylococcus,

Lactobacillus and Pseudomonas species. The compositions of the invention are also expected to reduce growth of Listeria species and coliforms. The compositions of the invention can therefore reduce the growth of micro-organisms of foodstuffs and can extend the shelf-life of foods.

Accordingly, in a related aspect the invention provides the use of an acidic biopolymer as defined herein (e.g. the use of a composition of the invention) for extending the shelf-life of a foodstuff. The invention also provides the use of an acidic biopolymer as defined herein (e.g. the use of a composition of the invention) as an antimicrobial coating for a foodstuff.

The invention further provides a method of extending the shelf-life of a foodstuff, the method comprising coating said foodstuff with a composition as defined herein and optionally storing said coated foodstuff. The invention also provides a method of preventing or reducing microbial (e.g. bacterial) growth on a foodstuff, the method comprising coating said foodstuff with a composition as described herein and optionally storing said coated foodstuff. Preferably, the invention provides a method as defined above for extending the shelf-life of a foodstuff and for preventing or reducing microbial (e.g. bacterial) growth on said foodstuff.

Storage may be at ambient temperatures (e.g. around 10-30 °C, especially about 20 °C), in which case the coated foodstuff is preferably stored for at least 1 day, e.g. at least 2 or 3 days, especially up to 4 days, or may be at reduced temperatures (for example less than 15 °C, especially less than 10 °C, e.g. around 4 °C), in which case the duration of storage may be longer, e.g. for at least 2 days, e.g. at least 3, 4 or 6 days, especially up to 7 days or up to 10 days.

In a preferred embodiment, the antimicrobial activity of the composition is directed towards at least one of bacteria, moulds and yeasts, especially bacteria.

Particularly preferably, the antimicrobial activity is directed towards Gram-negative and/or Gram-positive bacteria, and preferably against aerobic and/or anaerobic bacteria. Especially preferably, the antimicrobial activity is directed towards one or more of the species Staphylococcus, Lactobacillus, Listeria and Pseudomonas and coliforms.

In a preferred embodiment, the foodstuff is a decayable foodstuff such as a cereal, fruit, vegetable, milk product or meat. Preferably, the foodstuff is a foodstuff with the capacity to mobilise the protons on the acidic biopolymer, e.g. a foodstuff with a degree of water content at the surface, e.g. fruit, cheese or meat. One especially preferred foodstuff is meat, e.g. animal meat such as chicken, pork, beef, game, etc., or fish meat such as shrimp, prawns, salmon, cod, whiting, halibut, squid etc. Particularly preferred are shrimp, salmon, chicken, pork and beef, especially salmon. In a preferred embodiment, the foodstuff is a raw and/or uncooked foodstuff.

Accordingly, in a further aspect the invention provides a food product comprising a foodstuff coated with a composition as described herein. The foodstuff may be cooked before application of the coating or the food product cooked subsequent to application. The foodstuff may be coated such as to minimise the visual impact of the coating (e.g. coated with a thin layer of coating

composition) or may be immersed in the coating composition, e.g. in ajar or other container. The choice of coating will depend on the nature of the foodstuff and the preference of the consumer. As such, it can readily be determined by the skilled person on the basis of their own knowledge and the information provided herein.

Coated foodstuffs of the invention may be raw or cooked (e.g. boiled or fried). Where the foodstuff is white poultry meat (e.g. chicken) or non-white fish (e.g. salmon), application of the coatings of the invention may result in slight acid whitening of the surface of the meat. This may be desired for pre-cooking, greater preservation and/or flavouring purposes or may not be desired for reasons of aesthetic appeal and to maintain a neutral mouth-feel. However, these meats when coated according to the invention do not display any undesirable characteristics once cooked. The food product may be cooked with the coating in place or with the coating removed, as desired. For example, the coatings of the invention may be washed off with water prior to cooking.

Accordingly, in one embodiment, the food product comprises a foodstuff which is susceptible to acid whitening coated with a composition of the invention wherein the pH of the surface of the foodstuff is maintained at a pH as defined herein, e.g. at a pH of between 3.5 and 7, e.g. between 4 and 6, for a period of at least 2 days after coating. In an alternative embodiment, the food product comprises a foodstuff which is susceptible to acid whitening coated with a composition of the invention wherein the pH of the surface of the foodstuff is maintained at a pH as defined herein, e.g. at a pH of less than 5 or less than 4, e.g. between 2 and 4, especially around 3 or around 2.5, for a period of at least 24 hours after coating. In a further embodiment, the food product comprises a foodstuff which is not susceptible to acid whitening, e.g. pork, beef or prawn. The invention will now be further described with reference to the following non-limiting Examples and Figures, in which:

Figure 1 shows the change in surface pH over time for coated salmon fillets;

Figure 2 shows the levels of bacterial growth on salmon fillets coated with compositions comprising a single acidic biopolymer;

Figure 3 shows the levels of bacterial growth on salmon fillets coated with a composition comprising two distinct molecular weights of acidic biopolymer;

Figures 4 and 5 show total bacterial counts on coated and uncoated chicken fillet;

Figure 6 shows the levels of bacterial growth on coated and uncoated beef treated with acidic biopolymer;

Figure 7 shows the change in surface pH over time for coated and uncoated beef;

Figure 8 shows the levels of bacterial growth on coated and uncoated pork treated with acidic biopolymer;

Figure 9 shows the change in surface pH over time for coated and uncoated pork;

Figure 10 shows the levels of bacterial growth on coated and uncoated raw shrimps treated with acidic biopolymer;

Figure 11 shows the change in surface pH over time for coated and uncoated raw shrimps; and

Figure 12 shows the change in surface pH over time for coated and uncoated shrimps treated with an oil-in-water emulsion containing the acidic biopolymer.

Example 1 : Effect of acidic biopolymer concentration on pH

A series of coating compositions were formulated by dispersing different amounts of insoluble alginic acid (Protacid F120 NM, FMC Biopolymer AS, Norway) in a viscous aqueous solution of 0.5% w/v xanthan (Kelzan Food grade xanthan, Kelco, USA).

Pieces of fish fillet (Salma salmon, Salmon Brands AS) of approximately 10 cm by 8 cm were then coated with different compositions by dipping the fillet to provide a uniform layer of coating on each. The fillets were stored at 4 °C for 6 days and the pH of the fillet surface was measured using a surface pH-electrode

(Radiometer pHC 2441) placed in direct contact with the surface of the fillet. Two negative controls were included; a fillet without any coating and a fillet with the xanthan coating but containing no alginic acid.

Measurements of surface pH were taken at 1, 2 and 6 days after coating and the results are shown in Figure 1. The results indicate that the alginic acid has a degree of buffering capacity and that increasing amounts of alginic acid in the coating can maintain an increasingly lowered surface pH over an extended period of time.

Example 2: Effect of acidic biopolymer concentration on bacterial growth

Fish fillets were coated with a uniform layer of coating composition as described in Example 1. Compositions contained between 10 and 80 mg/ml of alginic acid. Uncoated fillets were used as a negative control with the average bacterial growth on the control fillets used as a reference.

The fillets were stored at 4 °C in non-sterile packaging and under aerobic conditions for 8 days. Small plug samples were taken every two days using a sampling device and the surface micro-organisms of the plug were transferred to 50 mM PBS in an Eppendorf tube. Serial dilutions were plated to plate count agar (PCA) plates for estimation of total bacterial load. (The sampling was done using an adapted version of NMKL method No. 91 "Sampling and pre-treatment of foods and animal feedstuff^'s, for quantitative microbiological examination", 4^th Ed., 2002)

The results are shown in Figure 2 as number of micro-organisms per square centimetre for each sample (on a logarithmic scale). The results show that the alginic acid-containing coating not only reduces overall bacterial growth, but also delays the onset of appreciable levels of bacterial growth.

Given that around 1 x 10 5 bacteria/cm 2 is an acceptable upper limit for consumption of a foodstuff, it can be seen that addition of a coating containing an acidic biopolymer can extend the storage life of a foodstuff by more than 3 days. Example 3: Effect of acidic biopolvmer coating on bacterial flora

Coated (0.5% w/v xanthan solution containing a dispersion of 30 or 40 mg/ml alginic acid) and uncoated fish fillets were prepared and incubated for 4 or 6 days at 4 °C in non-sterile packaging and under aerobic conditions to allow bacteria to grow. Samples of the fillets were taken and plated to PCA plates as described in Example 2. For the uncoated fillet, PCA plates showed individual colonies for

5 8

samples at dilutions of 1 x 10^" to 1 x 10^" . For the coated fillet, PCA plates showed

2 4

individual colonies for samples at dilutions of 1 ^x 10^" to 1 ^x 10^" .

Plates were observed for morphology of different colonies and then stored at 4-6 °C for 4 days (coated samples) or 20 days (uncoated samples). A representative selection of the colonies from PCA plates were picked out and transferred to blood agar (BA) plates for overnight incubation at 30 °C. The colonies were then tested to determine the organisms present using various techniques and kits, including: Gram staining; oxidase and catalase assays; different biochemical test panels including API plates (BioMerieux Norge AS); and ALOA plates (available from AES Laboratories, France).

Examples of micro-organisms detected on the plates include (morphology also shown): Uncoated fillet:

Lactobacillus paracasei (Gram +ve, coccoide rods)

Lactobacillus brevis (Gram +ve, short rods)

Pseudomonas fluorescens (Gram -ve, rods)

Pseudomonas aerginosa (Gram -ve, rods)

Staphylococcus hominis (Gram +ve, coccoides)

Coated fillet:

Lactobacillus plantarum (Gram +ve, coccoide rods)

Lactobacillus brevis (Gram +ve, coccoide rods)

Pseudomonas putida (Gram -ve, rods)

Pseudomonas fluorescens (Gram -ve, coccoide rods) Pseudomonas and Lactobacillus species were found both in the coated and the uncoated samples. Some differences were observed regarding the species that were identified in the different samples. However, there was no evidence that coating of the fish fillets led to specific growth of any bacteria or to selection for specific bacterial species.

The data presented above suggest that coating a foodstuff with a composition comprising an acidic biopolymer has a broad-spectrum antibacterial effect.

Example 4: Effect of compound acidic biopolymer coating on bacterial growth

A compound coating composition was formulated to contain two

biopolymers of different molecular weights. The coating composition contained 20 mg/ml of a high molecular weight alginate (LF 10/60, FMC Biopolymer, Norway) with a number average degree of polymerisation (DP_n) of 250 and 45 mg/ml of a low molecular weight alginic acid (Protacid F120NM, FMC Biopolymer, Norway) having a DP_n of 20. The low DP_n alginate was prepared by acid hydrolysis

(dispersed in water and degraded for 2 h at 95°C). The composition was pH adjusted to 4 by addition of a small amount of HC1 or NaOH.

Pieces of fish fillet (Salma salmon) of approximately 10 cm by 8 cm were then coated by dipping the fillet in coating followed by dipping in 150mM CaCl₂ (sterile filtered) to seal the coating. This treatment was performed twice to form a uniform dual layer. Uncoated fillets were used as a control.

The fillets were stored and sampled as described in Example 2 and the bacterial growth results are shown in Figure 3.

The coated fillet showed a reduction in bacterial growth relative to the control (uncoated) samples. The coated fillet also possessed an improved appearance and texture after coating, relative to coatings described in Example 1.

Example 5: Effect of acidic biopolymer coating on the sensory qualities of cooked foodstuffs

A series of tests with coated foodstuffs were performed to demonstrate that the coating materials were applicable in simple cooking and frying. The taste, smell and general appearance of coated foodstuffs were investigated. The following coatings were prepared:

Coating 0 No coating

Coating 1 A dispersion of 20 mg/ml of alginic acid in an aqueous solution of 0.5% w/v xanthan

Coating 2 A dispersion of 80 mg/ml of alginic acid in an aqueous solution of 0.5% w/v xanthan

Coating 3 A dispersion of 20 mg/ml of alginic acid in corn oil

The following foodstuffs were tested:

a) Shrimp (frozen): Thawed at 4 °C, peeled and used immediately b) Chicken fillet: Cut into cubes of approximately 10 g and used immediately

c) Salmon fillet (frozen): Thawed at 4 °C. Cut into cubes of approximately 10 g and used immediately

d) Pork fillet (fresh from food store): Kept at 4 °C. Cut into cubes of approximately 10 g and used immediately

e) Beef fillet (fresh from food store): Kept at 4 °C. Cut into cubes of approximately 10 g and used immediately

Each foodstuff was dip coated. Excess coating was allowed to drip off before continuing. Coated and uncoated foodstuffs were placed in separate plastic trays loosely sealed by taping a second plastic tray over the first. All foodstuffs were then stored at 4 °C for 24 hours.

In a first experiment, foodstuffs coated with coatings 0, 1 and 2 were boiled in lightly salted water for 1 minute (shrimp), 2 minutes (salmon) or 3 minutes (chicken, pork and beef). In each case, the taste and texture of the cooked foodstuff was the same whether coated or uncoated. A slightly acidic, but not unpleasant, taste was noted for any coating which remained on the foodstuff after boiling.

In a second experiment, foodstuffs coated with coatings 0 and 3 were fried for 30 seconds (shrimp), 60 seconds (beef) or 90 seconds (salmon, chicken and pork) on each side. In each case there was no difference in the taste or texture between the coated and uncoated foodstuff.

Example 6: Effect of acidic biopolymer coating on the storability of foodstuffs

Samples were prepared and coated as described in Example 5.

One series of foodstuffs was placed at 4 °C and a second series was placed at room temperature. The foodstuffs stored at 4 °C were inspected after 24 hours and after 6 days for general appearance and signs of putrefaction. The foodstuffs stored at room temperature were inspected after two days.

For the foodstuffs stored at 4 °C, the coated samples showed no tendency to dry out after 24 hours, whereas the uncoated samples tended to dry out. The characteristics after 6 days are shown in Table 1 , below.

Table 1

nd.: not determined

Appearance: - normal appearance

+ signs of acid whitening (whitening of flesh)

Odour: - normal odour

(+) faint acidic smell

p strong smell of putrefaction

The characteristics of the foodstuffs stored at room temperature for two days are shown in Table 2, below. Table 2

nd: not determined

Odour: - normal odour

(+) faint acidic smell

(p) smell of putrefaction

p strong smell of putrefaction

The results demonstrate that different foods respond differently to the coatings tested. Shrimp, pork and beef tolerate the 20 mg/ml alginic acid coating well, without apparent effects on appearance on application of the coating, or after boiling or frying. Chicken and salmon tend to show signs of acid whitening after coating, but coated and uncoated samples are very similar after boiling or frying.

The coatings tested clearly help prevent drying of foodstuffs and can extend the shelf-life of foodstuffs whether stored at 4 °C or at room temperature.

Example 7: Preparation of acidic biopolymer coatings with pectinic acid and carboxymethyl cellulose

Samples of pectinic acid and carboxymethyl cellulose (CMC) acid are first prepared as follows:

a) Low methoxyl pectin, obtained by treatment of a commercially available high methoxyl pectin using a pectinesterase (e.g. from an Aspergillus species) or obtained directly (e.g. Pomona's universal pectin - Workstead Industries, MA, USA), is dissolved in water to form a 1% wt solution. HCl is added to the solution to a final concentration of 0.2 M and the solution stirred at room temperature. The pectinic acid is precipitated with ethanol and dried;

b) CMC having a degree of substitution, i.e. an average number of substituted hydroxyl groups per glucose monomer, of from 0.7 to 1.4 (Sigma- Aldrich) is dissolved in water to form a 1% wt solution. HC1 is added to the solution to a final concentration of 0.2 M and the solution stirred at room

temperature. The CMC acid is precipitated with ethanol and dried.

Coating compositions are then prepared by dissolving or suspending the pectinic or CMC acids in an aqueous solution containing 5 mg/ml of xanthan such that the final concentration of pectinic or CMC acids is 10, 20, 40 or 80 mg/ml.

Example 8: Effect of acidic biopolymer coating on bacterial growth on chicken fillet

Coated (0.5% w/v xanthan solution containing a dispersion of 20 or 50 mg/ml alginic acid) and uncoated chicken breast fillets were incubated for 0 to 4 days at 4 °C in non-sterile packaging and under aerobic conditions to allow bacteria to grow. Samples of the fillet were taken and plated to PCA plates as described in Example 2. Bacterial growth data are shown in Figure 4 which indicates that the coated breast filets have a lower total bacterial count than the uncoated filets. Example 9: Effect of acidic biopolymer coating on bacterial growth on chicken fillet Coated (0.5% w/v xanthan solution containing a dispersion of 20 or 50 mg/ml alginic acid, or 20 mg/ml CMC (Walocel^™ C T2000; DS=0.9 - Dow Wolff, Germany)) and uncoated chicken breast fillets were incubated for 0 to 4 days at 4 °C in non-sterile packaging and under aerobic conditions to allow bacteria to grow. Samples (surface area 10 cm and thickness 0.5 cm) were taken from the fillets using a sterile scalpel. Each sample was transferred to a Stomacher^® bag (Seward Ltd.) and homogenised (2 x 30 seconds, 230 rpm) in 95 ml of phosphate buffer (50 mM, pH 7) containing 0.1% peptone. The total volume of sample and buffer was 100 ml. 1 ml of the sample (defined as 1 : 100 dilution) was assayed for bacterial growth as described in Example 2. Bacterial growth data are shown in Figure 5 which indicates that both alginic acid and CMC the coated breast filets have a lower total bacterial count than the uncoated filets. Example 10: Effect of acidic biopolymer coating on pH and bacterial growth on beef Whole fillets of beef were cut into slices of 1 cm thickness. Coated (0.5% w/v xanthan solution containing a dispersion of 20 or 50 mg/ml alginic acid) and uncoated slices were incubated for 0 to 4 days at 4 °C in non-sterile packaging and under aerobic conditions to allow bacteria to grow. Samples of the fillet were taken and plated to PC A plates as described in Example 2. Measurements of surface pH were taken at 0, 1, 2 and 4 days.

Bacterial growth data are shown in Figure 6 which indicates that both 2% and 5% alginic acid coatings significantly reduced the total bacterial count. Figure 7 shows the results of the surface pH measurements over time. It can be seen that all samples have a stable pH over the 4 day period, with the coated samples stabilising at a lower pH.

Example 11 : Effect of acidic biopolymer coating on pH and bacterial growth on pork fillets

Whole fillets of pork were cut into slices of 1 cm thickness and weighed. Coated (0.5% w/v xanthan solution containing a dispersion of 50 or 80 mg/ml alginic acid) and uncoated slices of fillet were incubated for 0 to 7 days at 4 °C in non-sterile packaging under aerobic conditions to allow bacteria to grow. Each fillet slice was then transferred to a Stomacher^® bag (Seward Ltd.) and an amount of buffered 0.1% peptone (50 mM phosphate, pH 7) was added to give a total weight of 100 g. The meat was homogenised and assayed for bacterial growth as described in Example 9. Measurements of surface pH were taken at 0, 1, 2, 3 and 4 days.

Bacterial growth data are shown in Figure 8 which indicates that both 5% and 8% alginic acid coatings significantly reduced the total bacterial count. This is particularly true for the 8% alginic acid coating which maintained an especially low bacterial count up to 4 days.

Figure 9 shows the results of the surface pH measurements over time. It can be seen that all samples have a relatively stable pH over the 4 day period, with the coated samples stabilising at a lower pH. Example 12: Effect of acidic biopolymer coating on pH and bacterial growth on shrimp

Coated (0.5% w/v xanthan solution containing a dispersion of 50 or 80 mg/ml alginic acid) and uncoated shrimp (peeled, raw) were incubated for 0 to 7 days at 4 °C as described in Example 8. For testing, the coated and uncoated shrimp were transferred to Stomacher^® bags, homogenised and assayed for bacterial growth as described above. Measurements of surface pH were taken at 0, 1, 2, 3, 4 and 7 days.

Bacterial growth data are shown in Figure 10 which indicates that both 5% and 8% alginic acid coatings significantly reduced the total bacterial count. This is particularly true for the 8% alginic acid coating which maintained a low and stable bacterial count up to 7 days.

Figure 11 shows the results of the surface pH measurements over time. It can be seen that all samples have a relatively stable pH over the 7 day period, with the coated samples stabilising at a lower pH.

Example 13: Powder coating of acidic biopolymer

Peeled shrimps (raw) were coated by dipping in alginic acid powder to form a visible coating layer. The coated shrimps were incubated as described in Example 9. The appearance and smell was assayed after 0, 4, 7 and 9 days. No odour developed during the experiment. Surface pH was measured at day 4 and 7.

The coating absorbed some water from the shrimps, resulting in an continuous film coating. The surface pH measured at day 4 and 7 was 4.0. No bacterial growth was detected after 4 and 7 days of incubation.

Example 14: Emulsion coating of acidic biopolymer

Peeled shrimps (cooked) were coated by dipping in oil in water (o/w) emulsions containing 5, 10 and 20% (w/w) rapeseed oil emulsified in 0.3%> w/v xanthan solution with 80 mg/ml alginic acid. The pH of the emulsions was 2.80. The surface pH of the coated and uncoated shrimps was measured at 1, 24 and 48 hours after coating. It was observed that the coatings with 5 and 10% oil (w/w) had a pleasant, smooth and homogeneous consistency and did not dry out during the test period.

Figure 12 shows the results of the surface pH after coating with the oil-in- water emulsions. It can be seen that the coated samples provide a stable and significantly lower pH over the tested period relative to the uncoated sample.

Claims

Claims:

1. A method of extending the shelf-life of a foodstuff and/or for preventing or reducing microbial (e.g. bacterial) growth on said foodstuff, the method comprising coating the foodstuff with a composition comprising at least one acidic biopolymer, preferably an edible acidic biopolymer, and optionally storing said coated foodstuff.

2. The method of claim 1 wherein the foodstuff is meat, e.g. uncooked meat.

3. The method of claim 1 or claim 2 wherein the acidic biopolymer is alginic acid.

4. The method of any one of claims 1 to 3 wherein at least one pK_a of an acidic group of the acidic biopolymer is between 3 and 5.

5. The method of any one of claims 1 to 4 wherein the pH of the surface of the foodstuff after coating is maintained at a pH of between 3.5 and 6, for a period of at least 48 hours.

6. The method of any one of claims 1 to 5 wherein the concentration of the at least one acidic biopolymer in the composition is between 10 and 100 mg/ml.

7. The method of any one of claims 1 to 6 wherein the at least one acidic biopolymer has a weight average molecular weight of between 1 kDa and 2 MDa.

8. The method of any one of claims 1 to 7 wherein the composition comprises a second biopolymer, preferably a second edible biopolymer, e.g. a polysaccharide such as a xanthan or a carrageenan.

9. The method of claim 8 wherein the second biopolymer is xanthan, present in the composition at a concentration of between 1 and 10 mg/ml.

10. The method of any one of claims 1 to 9 wherein the composition is a dispersion of the at least one acidic biopolymer in an optionally gelled aqueous phase.

11. The method of any one of claims 1 to 9 wherein the composition is in powder form.

12. The method of any one of claims 1 to 9 wherein the composition is an oil-in- water emulsion wherein the acidic biopolymer is dissolved and/or dispersed in the aqueous phase.

13. The method of any one of claims 1 to 12 wherein the composition does not contain any appreciable quantity of at least one of the following: antimicrobial agents (besides the acidic biopolymer); small organic acids; and calcium, sodium, and/or potassium cations.

14. A process for coating a foodstuff, the process comprising bringing the foodstuff into contact with a composition as defined in any one of claims 1 to 13 to provide a substantially uniform coating on the surface of said foodstuff.

15. Use of an acidic biopolymer (e.g. as a component of a composition as defined in any one of claims 1 to 13) for extending the shelf-life of a foodstuff and/or as an antimicrobial coating for a foodstuff.

16. A food product comprising a foodstuff coated with a composition as defined in any one of claims 1 to 13, wherein said foodstuff has been optionally cooked prior to or subsequent to coating with said composition.

17. The food product of claim 16 wherein the foodstuff is shrimp, prawns, salmon, chicken, pork or beef, especially salmon.

18. An antimicrobial composition for (e.g. suitable for) coating a foodstuff, said composition being a composition as defined in any one of claims 1 to 13.