AU2001262232A1

AU2001262232A1 - Water in oil emulsion

Info

Publication number: AU2001262232A1
Application number: AU2001262232A
Authority: AU
Inventors: Wim Agterof; Marinus Adriaan E Bakker; Robert Vreeker
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 2000-05-26
Filing date: 2001-04-25
Publication date: 2001-12-11
Also published as: MXPA02011607A; CZ20023887A3; PL359665A1; WO2001091570A1; SK16692002A3; EA200201261A1; EP1283679A1; BR0111143A; HUP0301926A2; CA2410316A1

Description

Water in oil emulsion

The present invention relates to emulsions comprising a continuous fatty phase in an amount of from 50 to 85 wt% on total product, a dispersed aqueous phase and an emulsifier system. The invention especially relates to such water in oil emulsions which are suitable for use as shallow frying agents .

Background of the invention

Water in oil emulsions used for shallow frying include butter, margarine, pourable and spoonable margarine.

Upon storage these products desirably are stable and thus do not show separation in two phases; an aqueous phase and an oil phase. This separation, also sometimes referred to as destabilisation of the emulsion, oil exudation or oil separation, if an oil layer is clearly distinguished, or water exudation if a water layer is clearly distinguished, is believed to decrease the product's attractivity for a consumer.

Spreadable water in oil emulsions can show instability in that an oil layer is formed on the surface of the emulsion. In pourable products instability is even more often encountered, and it is visible in the form of an oil layer on top of a water in oil emulsion. Also sedimentation of water droplets on the bottom of a water in oil emulsion is an indication of instability. The method to determine instability is described in the examples .

Another problem which is encountered with water in oil emulsions is the spattering which is associated with use as a frying agent. Spattering during frying is not desired.

G. Hoffman discloses (in "the chemistry and technology of edible oils and fats and their high fat products", chapter 4, Academic press 1989) that the stability of emulsions can be increased effectively by the use of emulsifiers.

In recent years it has also been disclosed, for example in US 5,756,142 to use hardened rapeseed oil to stabilise pourable water in oil emulsions.

US 3,338,720 discloses a fluid margarine stabilised by an emulsion-stabilising amount of a hard fat.

DE 2055036 discloses a method to produce a pourable margarine with alleged increased stability, by the presence of 1 to 5% of a crystallising hard fat component with a fat particle size of 0.1 to 5 μ. It is alleged that the three dimensional triglyceride network imparts stability to the final product.

The requirement for pourability however, sets a limit to the amount of hardened, solid, fat that can be added to the compositions. The higher the solid fat content, the lower the pourability of the product will be.

This problem is addressed in GB 1,359, 639 which discloses a pourable margarine wherein the stability is increased by incorporating in the fatty phase a minor amount of an ester of a polycondensed polyhydric alcohol and a polycondensed aliphatic hydroxycarboxylic acid. The aqueous phase of these compositions optionally comprises a hydrophilic emulsifier such as a phosphatide.

However these products still do not show the desired rheology in combination with the desired stability over time. Hence the invention aims at a product which is both stable over time and wherein the rheology can be set to the desired one; spreadable spoonable or pourable, in combination with a reduced amount of hardened fat, preferably less than 3 wt% hardened fat.

It has now surprisingly been found that water in oil emulsions comprising an emulsifier system which comprises a stabilising emulsifier and a destabilising emulsifier and wherein the aqueous phase comprises a gelling agent and wherein the water droplets forming the aqueous phase are essentially present as a flocculated water droplet network, show the desired storage stability and can be set to the desired rheology. Statement of the invention

Accordingly the invention relates to an emulsion comprising a continuous fatty phase in an amount of from 50 to 85 wt% on total product, a dispersed aqueous phase, and an emulsifier system which comprises a stabilising emulsifier and a destabilising emulsifier, wherein the aqueous phase comprises a gelling agent, and wherein the aqueous phase is essentially present in the form of a flocculated water droplet network.

The invention further relates to a process to prepare such products .

Detailed description of the invention

The invention relates to water in oil emulsions suitable for frying which can be of varying rheology. For example spreadable, spoonable, squeezable or pourable products are included. As mentioned above, the problem of oil separation is most significant for pourable and spoonable emulsions. Therefore the invention especially relates to pourable or spoonable emulsions.

Pourable emulsions show a Bostwick value of at least 15 cm per 15 seconds at 15 °C. The method to determine Bostwick value is described in the examples.

According to a further preference the viscosity of the water in oil emulsion according to the invention is such that the product is pourable or at least squeezable and can easily be dosed, even in small portions. Therefore the water in oil emulsions preferably have a viscosity at 10 °C and 2 s^"1 of from 250 to 1.500 Pa.s, whereby the viscosity can be adjusted within this range.

Products according to the invention are stable during storage. This implies that preferably products according to the invention do not show separation in layers of fat and water upon storage at 20 to 25 °C for at least 4 weeks. Some oil separation, for example up to 20 vol% oil separation on total product volume is tolerable, but should preferably not occur for products according to the invention. Oil separation is preferably less than 20 vol%, more preferred less than 15 vol%, most preferably less than 10 vol% for stable products.

The aqueous phase of the emulsion according to the invention is essentially present as a flocculated network. To illustrate this network, reference is made to figure 1 which shows a theoretical drawing of flocculated water droplets in a continuous fatty phase. To obtain this network, the presence of a stabilising emulsifier and a destabilising emulsifier is required. The stabilising emulsifier is believed to be present at the sides of the water droplets where there is no contact with another water droplet. This is the water/oil interface. Destabilising emulsifier is believed to be present at the interface between flocculated water droplets. The network is believed to impart stability and rigidity to the products according to the invention. The partial replacement of stabilising emulsifier by destabilising emulsifier is believed to cause a destabilisation of the 5 emulsion such that at least part of the water droplets stick together. This is called flocculation of at least part of the water droplets. Flocculation is different from coalescence. Coalescence of water droplets leads to a merge of the inner contents of one water droplets with the inner

10 contents of another water droplet. Flocculated droplets are separated by an emulsifier layer.

The phrase "essentially present as" implies that most of the water droplets are part of a network of water droplets which is formed as described above. Preferably at least

15 50%, more preferred at least 75% of the total number of water droplets is situated in a network of water droplets. Coalescence of the flocculated water droplets is precluded by the presence of a gelling agent in the aqueous phase as is described further below.

20

Within the network individual water droplets can still be identified.

The water droplets are preferably characterised by a D3,3 of from 0.1 to 10 μm, more preferred from 0.1 to 8 μm, most

25 preferred from 1 to 5 μm.

Network formation is further illustrated in the examples. As mentioned above, it was found to be essential for network formation, that the emulsifier system comprises a stabilising emulsifier and a destabilising emulsifier.

For the purpose of the invention the term stabilising emulsifier is defined as an emulsifier which when present in a water in oil emulsion contributes positively to the formation of such an emulsion. A stabilising emulsifier can reduce the surface tension to support the formation of an emulsion and serves to reduce coalescence of individual water droplets which form the dispersed aqueous phase.

An emulsion comprising only stabilising emulsifier was found to still show considerable oil separation of about 50 vol%, probably due to sedimentation of water droplets under gravity. Such emulsions often show an undesired inhomogeinity.

A destabilising emulsifier is a compound which shows inferior emulsifying properties compared to a stabilising emulsifier. Generally a destabilising emulsifiers does not act as a good reductor of coalescence of water droplets forming the dispersed aqueous phase. Destabilising emulsifiers are preferably of low molecular weight and therefore usually cause less steric repulsion than stabilising emulsifiers.

Preferably the stabilising emulsifier is characterised by an HLB value of less than 4, preferably from 1 to 3. According to a very preferred embodiment the stabilising emulsifier is selected from the group comprising polyglycerol polyricinoleates, sucrose esters or combinations thereof. Examples of suitable esters of sucrose are esters of sucrose and palmitic acid or stearic acid.

The amount of stabilising emulsifier is preferably from 0.1 to 4 wt%, more preferred 0.1 to 2 wt%, most preferred from 0.2 to 0.7 wt% on total product. Amounts below 0.1 wt% of stabilising emulsifier may lead to instable products which even after storage of a day at room temperature show oil separation.

Preferably the destabilising emulsifier is characterised by an HLB value of more than 4.

According to another preferred embodiment the destabilising emulsifier is selected from the group comprising citric acid esters, unsaturated monoglycerides such as Dimodan^(tm) , and phosphatides such as lecithins like native lecithin (Bolec ZT^(tm)), fractionated lecithin, (cetinol^{tm) ) and hydrolysed lecithin (Bolec MT^(tm))-

Lecithins are very suitable destabilising emulsifiers as lecithins are known to positively influence frying properties like spattering behaviour of water in oil emulsions . The amount of destabilising emulsifier is preferably from 0.1 to 5 wt%, more preferred from 0.1 to 1 wt%, even more preferred from 0.2 to 0.7 wt%, most preferred from 0.2 to 0.5 wt% for pourable products.

It will be appreciated that the amount of destabilising emulsifier is dependent on the amount of stabilising emulsifier used, and on the specific destabilising emulsifier that is employed.

The emulsifier system is preferably present in an amount of from 0.2 to 7 wt%, more preferred 0.4 to 3 wt% on total product weight for pourable products.

The aqueous phase of products according to the invention comprises a gelling agent.

If the aqueous phase does not comprise a gelling agent, coalescence of water droplets forming the dispersed aqueous phase occurs, and oil separation results. Hence products that do not comprise a gelling agent in the aqueous phase, are not stable upon storage.

Preferred gelling agents are selected from the group comprising gellan gum, gelatin, whey protein, pectin, especially low methoxy pectin, alginate and combinations thereof.

The composition of the aqueous phase is such that the prerequisites for gelling of the gelling agent, for example the presence of a salt, are fulfilled. For example if gellan is used as gelling agent, the aqueous phase comprises about 0.08 wt% on weight of the aqueous phase, of a calcium salt like calciumdichloride dihydrate (CaCl₂.2H₂0) .

The amount of gelling agent on aqueous phase is preferably such that the yield stress of the aqueous phase after gelling is at least 50 Pa at 20 °C.

Suitable amounts of gelling agents are between 0.1 and 10 wt%, more preferred 0.5 to 5 wt% on aqueous phase.

The gelling agent can be used to set the desired rheology of the emulsion according to the invention. For spreadable water in oil emulsions, gelatin or heat denatured whey protein are the preferred gelling agents.

In case pourable water in oil emulsions are desired, gellan gum or alginate are the desired gelling agents.

It has been found that especially good pourable products are obtained if the aqueous phase comprises gellan gum and the ratio between the stabilising emulsifier and the destabilising emulsifier is from 3:1 to 1:1 if the destabilising emulsifier is lecithin, and from 1:1 to 1:4, preferably 1:1 to 1:2, if the destabilising emulsifier is Dimodan.

The products according to the invention are water in oil emulsions. These products are generally suitable for use in shallow frying. Preferably, these products should not lead to severe spattering when they are heated in a frying pan.

Spattering of a water in oil emulsion is believed to be caused by superheating of water droplets. At a certain point after heating said water droplets explosively evaporate, whereby oil can be spread all over the surroundings of a frying pan wherein the emulsion is heated.

Spattering can be measured by determining the spattering value according to the method illustrated in the examples. Preferably food products according to the invention show a primary spattering value (spattering upon heating of a frying product such as margarine, without incorporation of a food product to be fried) of from 5 to 10, preferably from 8 to 10. The secondary spattering value (spattering upon incorporation of food product such as a snack in a hot frying product) for products according to the invention is preferably from 5-10. The use of lecithin as destabilising emulsifier leads to improved spattering behaviour.

Preferably, products according to the invention when used as frying medium lead to little or no residue in the pan after frying. Residue formation may for example be caused by the presence of biopolymers, starches, or protein in the product. Therefore in a preferred embodiment the products according to the invention comprise less than 5 wt%, more preferred less than 3 wt%, of compounds capable of residue formation upon use in frying. Emulsions according to the invention comprise from 50 to 85 wt% fat. Although lower amounts of fat are possible, e.g. 30 wt.% fat, the advantages of the invention compared to systems without a flocculated water droplet network are less evident, since at these lower fat contents, the systems are stable without a flocculated water droplet network. The emulsifier system is especially suitable for products comprising from 50-70wt.% oil.

In this specification the terms fats and oils are used interchangeably .

The fat can be any fat or oil, but triglycerides with (poly) unsaturated fatty acids are preferred.

The products according to the invention comprise reduced amounts of hardened oils, or no hardened oils at all, but they are still stable upon storage.

Especially suitable oils are for example selected from the group comprising sunflower oil, soybean oil, rapeseed oil, cottonseed oil, olive oil, corn oil, groundnut oil, or low melting butterfat fractions and/or combinations thereof. These fats may be partially hydrogenated.

The fatty phase can also comprise sucrose polyesters (SPE's) . Optionally the product comprises in addition to these fats a hard fat component selected from the group comprising: hardened rapeseed oil, hardened soybean oil, hardened rapeseed oil, hardened cottonseed oil, hardened corn oil, hardened groundnut oil, palmoil, hardened palmoil, palmoil fractions, hardened palmoil fractions, butterfat or butterfat fractions. These fats are optionally partly or fully hydrogenated to obtain the desired structuring properties . This hard fat may partly serve to impart stability to the products, in addition to the stability obtained by the aqueous phase water droplet network. In view of the potential disadvantages of the presence of hard fat such as increased viscosity and reduced pourability, it is preferred that the amount of hard fat is below 3 wt%, more preferred below 1 wt%. Most preferred hard fat is essentially absent in products according to the invention.

Optionally other ingredients may be added to the emulsion such as flavour, salt, herbs, particles.

The invention further relates to a process that is suitable for the preparation of the products according to the invention.

The process preferably is a process wherein an aqueous phase comprising a gelling agent and/or other ingredients is mixed into an oil phase comprising at least part of the emulsifier system. To facilitate homogeneous mixing, the mixing is preferably carried out at a temperature of from 30 to 80 °C, preferably 50 to 60 °C, whereby both the oil phase and the aqueous phase are at about the same temperature before mixing.

According to a preferred embodiment in a first step an aqueous phase is mixed with a gelling agent. The conditions of mixing are preferably such that gelling does not yet take place. In a separate vessel, an oil phase comprising the emulsifier system is prepared. The aqueous phase is mixed with the oil phase. At the moment of mixing the aqueous phase is still pourable but gelation should be instant once emulsification mixing is taking place.

This can for example be ensured by mixing simultaneously in the oil phase an aqueous phase (I) comprising gelling agent and an aqueous phase (II) comprising an ingredient which triggers gel formation. Upon mixing, water droplets of aqueous phase (I) will collide with water droplets of aqueous phase (II) , whereby gelation is triggered.

After preparing the water in oil emulsion, it may be cooled and stored at a temperature of from 0 to about 20 °C. Preferably the storage temperature is from 5 to 15 °C.

According to another, less preferred method, in a first step an emulsion is prepared of an aqueous phase comprising gelling agent and an oil phase comprising stabilising emulsifier. A destabilising emulsifier is subsequently mixed into the emulsion. The destabilising emulsifier is then causing flocculation and network formation of water droplets forming the dispersed aqueous phase.

Other ingredients such as flavour components, salt, herbs, and particles can be introduced in the products at any stage of the process.

The addition of these ingredients before the optional cooling to 0 to 20 °C is highly preferred.

Examples

General methods

• Instability in the form of oil separation

Oil separation was measured as a function of time for samples stored at ambient temperature (18-22 °C) . In general three layers could be observed if oil separation took place; one clear oil layer on top, followed by a diffuse layer being a diluted water in oil emulsion, and a third layer being intact emulsion. For the measurement of oil separation the height of the top layer and middle layer was divided by the sum of the height of the three layers .

Droplet size

Droplet size was measured as the D3,3 value, which is described in M. Alderliesten, Anal. Proc. Vol 21, May 1984, page 167-172.

• Bostwick value

Pourability is measured according to the standard Bostwick protocol. The Bostwick equipment consists of a 125 ml reservoir provided with a outlet near the bottom of a horizontally placed rectangular tub and closed with a vertical barrier. The tub's bottom is provided with a 25 cm measuring scale, extending from the outlet of the reservoir. When equipment and sample both have a temperature of 15°C, the reservoir is filled with 125 ml of the sample after it has been shaken by hand ten times up and down. When the closure of the reservoir is removed the sample flows from the reservoir and spreads over the tub bottom. The path length of the flow is measured after 15 seconds. The value, expressed as cm per 15 seconds is the Bostwick rating, which is used as yard stick for pourability.

• Viscosity

Viscosity was measured at a shear rate of 2 s^"1 at 10 °C. using a Bohlin reometer, type CS-50, measuring cells C40s.

• Yield stress at 20 °C of the aqueous phase and gelling agent was determined by using a Bohlin reometer, type CS-50, measuring cells C40s.

• Spattering behaviour

The spattering behaviour of emulsions according to the invention was evaluated after storage of the products for 1 or 8 days at 5 °C.

Primary spattering (SVl) was assessed under standardised conditions in which an aliquot of the emulsion was heated in a glass dish and the amount of fat spattered onto a sheet of paper held above the dish was assessed after the water content of the emulsion had been driven off by heating.

Secondary spattering (SV2) was assessed under standardised conditions in which the amount of fat spattered onto a sheet of paper held above the dish is assessed after injection of a quantity of 10 ml water into the dish.

In assessment of both primary and secondary spattering value about 25 g of the emulsion was heated in a glass dish on an electric plate to about 205 °C. The fat that spattered out of the pan by force of expanding evaporating water droplets was caught on a sheet of paper situated above the pan. The image obtained was compared with a set of standard pictures number 0-10 whereby the number of the best resembling picture was recorded as the spattering value. 10 indicates no spattering and zero indicates very bad spattering. The general indication is as follows.

Score Comments

10 Excellent

8 Good

6 Passable

4 Unsatisfactory for SVl, almost passable for SV2

2 Very poor

Typical results for household solid margarines (80 wt% fat) are 8.5 for primary spattering (SVl) and 4.6 for secondary spattering (SV2) under the conditions of the above mentioned test.

Microscopy

CSLM microscopy was used with FITC coloured gelatin. Example 1-6 and C1-C3 Pourable water in oil emulsion

An aqueous phase (I) comprising 0.4 wt% of gellan gum (Kelcogel LS) (on aqueous phase) was prepared at 65 °C and cooled down to 50 °C. A second aqueous phase (II) comprising 0.08 wt% Calciumchloride on aqueous phase was prepared.

An oil phase was prepared by dissolving Admul Wol (polyglycerol polyricinoleate, Quest, Netherlands) and Dimodan LS/Lecithin (Bolec ZT^tm) (Danisco) in sunflower oil at 60 °C.

An emulsion was prepared by dispersing both aqueous phases in the oil phase in an UltraTurrax at 60 °C. The emulsions contained in total 40 wt% of the aqueous phases. The gellan gum concentration in the aqueous phase (after mixing) was 0.4 wt% and the calcium chloride concentration was 0.08 wt.%. The emulsions were stored at 10 °C. During cooling the dispersed water droplets became solid as a result of gel formation of the gellan gum.

The amount of emulsifier was varied as indicated in table

1.

In comparative examples cl-C3, processing and product composition were as indicated for example 1 except that no destabilising emulsifier was present (CI) or low levels of destabilising emulsifier were present (C2 and C3) . Table 1 product composition example 1-6 and comparative examples C1-C3.

* (wt% on total product)

** measured after storage for 6 weeks at 20 °C *** i r _aγ after preparation Nd. Not determined

The storage stability in terms of reduced oil separation of the emulsion in example 1-6 is clearly improved compared to a product that only comprises stabilising emulsifier and gelling agent (example CI) or products that comprise low levels of destabilising emulsifier (C2 and C3) . The use of lecithin as destabilising emulsifier leads to improved spattering behaviour. Example 7

A spreadable water in oil emulsion was prepared by the method used in example 1. The final emulsion contained 40 wt% aqueous phase, 5 wt% gelatin on aqueous phase, 3 wt% Dimodan on oil phase and 2 wt% Admul Wol on oil phase. Figure 2 shows the CSLM microscopic picture with FITC colouring of gelatin of example 7 wherein flocculation of water droplets, leading to a water droplet network is clearly visible.

Comparative example C4

Example 7 was repeated with 0 wt.% Dimodan on oil phase. Figure 3 shows the CSLM microscopic picture with FITC colouring of gelatin of comparative example C4, which shows that without destabilising emulsifier (Dimodan) no water droplet network is formed.

Examples 8-11 Water in oil emulsion with 40 wt.% water were prepared by the method used in example 1. An amount of 0.4 wt% Admul WOL (stabilising emulsifier), and 3.5 wt.% Dimodan LS (destabilizing emulsifier) was used. The gelling agents (biopolymers) given in table 2 were added to the water phase in the amounts given in table 2. The appearance of the emulsions was evaluated. Table 2: Influence of the aqueous phase composition on the consistency of products according to examples 8-11.

Claims

1. Emulsion comprising a continuous fatty phase in an amount of from 50 to 85 wt% on total product, a dispersed aqueous phase, and an emulsifier system which comprises a stabilising emulsifier and a destabilising emulsifier, characterised in that the aqueous phase comprises a gelling agent, and in that the aqueous phase is essentially present in the form of a flocculated water droplet network.

2. Emulsion according to claim 1, comprising a continuous fatty phase in an amount of from 50 to 70 wt% on total product .

3. Emulsion according to claim 1, wherein the emulsion is a pourable or spoonable emulsion.

4. Emulsion according to claim 1, wherein the stabilising emulsifier is characterised by an HLB value of less than 4, preferably from 1 to 3.

5. Emulsion according to claim 1, wherein the stabilising emulsifier is selected from the group comprising polyglycerol polyricinoleates, sucrose esters or combinations thereof.

6. Emulsion according to claim 1, wherein the amount of stabilizing emulsifier is 0.1 to 4 wt.% on total product .

7. Emulsion according to claim 1, wherein the destabilising emulsifier is selected from the group comprising citric acid esters, unsaturated monoglycerides and phosphatides .

8. Emulsion according to claim 1, wherein the amount of destabilizing emulsifier is 0.1 to 5 wt.% on total product.

9. Emulsion according to any of the preceding claims, wherein the amount of gelling agent is such that the yield stress of the aqueous phase after gelling is at least 50 Pa at 20 °C.

10. Emulsion according to any of the preceding claims, wherein the gelling agent is selected from the group comprising gellan gum, gelatin, whey protein, pectin, especially low methoxy pectin, alginate and combinations thereof.

11. Emulsion according to claim 2, wherein the gelling agent is gellan gum or alginate or a combination thereof.

12. Emulsion according to any of the preceding claims, wherein the water droplets have a D3,3 of from 0.1 to 10 μm, more preferred from 0.1 to 8 μm, most preferred from 1 to 5 μm.

13. Process for the preparation of a water in oil emulsion according to any of the previous claims, wherein an aqueous phase comprising a gelling agent and/or other ingredients is mixed into an oil phase comprising at least part of the emulsifier system.

14. Process according to claim 10, wherein the mixing is carried out at a temperature of from 30 to 80 °C, preferably 50 to 60 °C.