GB2241503A - Edible fatty composition containing bleached fish oils - Google Patents

Abstract

The invention relates to fatty compositions, containing fish oils and to methods of preparing those compositions. It is known for methods of refining fish oil to include a bleaching step. In this step, bleaching earth is added to the oil and later separated. One problem with this process is that the earth may spontaneously catch fire due to the oxidation sensitive components contained therein. The invention solves the problem by mixing an excess of vegetable oil with the fish oil prior to the bleaching step.

Description

Edible Fattv Composition And Method of Preparing Same The present invention relates to edible fatty compositions, in particular, to edible fatty compositions containing fish oils and to methods of preparing these compositions.

Fish oil has been an ingredient of the human diet for many years. However the instability of fish oil has meant than unless the oil is very freshly extracted from fresh fish, steps such as chemical hydrogenation of the fatty acids have been required to stabilise the oil.

The attention of the medical community has for some time been focused upon the health benefits believed to be associated with the consumption of unhydrogenated fish oil, for example in "The Lancet" 1(8284) 1269-72. It is believed that these benefits are associated with the presence of omega-3 fatty acids in the unhydrogenated fish oil. Particular omega-3 fatty acids are eicosapentaenoic acid ("EPA") and docosa-hexaenoic acid ("DHA"), which are present in moderately high levels in fresh fish oil. Compositions rich in omega-3 fatty acids are disclosed in EP 311091, in which the presence of other nutritionally significant fatty acids, such as the so-called MCT fatty acids, is also discussed.

It is well known that fresh fish oil is prone to rapid spoilage rendering it unpalatable in the short term. It has long been known that hydrogenation of fish oil reduces the sensitivity to spoilage but also reduces the level of omega-3 fatty acids. Alternatives to hydrogenation have been suggested. In particular, EP 311091 discloses the use of added tocopherol antioxidants, whereas JP 61/074539 discloses the use of molecular distillation to remove off flavour precursors and JP 55/15444 discloses the addition of an off flavour masking agent such as kaolin or calcium phosphate. It is also known to add strong flavouring agents such as lemon oil to fish oils in an attempt to disguise the nauseous taste.

Published European patent specification EP 304115 discloses the preparation of bland tasting, fish oil containing compositions of improved stability by mixture of fish and vegetable oils. It was found that up to 25% (on total blend) of fish oil could be incorporated into products without the development of a characteristic and nauseous fish smell in the short term. In this citation it is believed that the presence of natural antioxidants in the vegetable oil is important in the suppression of off flavour development, and it is considered absolutely crucial that the fish oil and the vegetable oil are blended during or shortly after refining of the fish oil. EP 304115 also discloses that vegetable oils vary in their protective effect and that certain oils, notably palm oil and lauric acid oils have a poor protective effect.

One of the alternative refining methods disclosed in EP 304115 is the so-called "silicate boil" process, in which an alkali neutralised fish oil was admixed with sodium silicate solution and boiled before drying, bleaching with a bleaching earth, deodorising and blending with vegetable oil. In an alternative method the bleaching step takes place before the silicate boil.

In all the examples of the cited text the blending of the fish oil and the vegetable oil took place shortly after the final refining step of deodorising the fish oil. For the purposes of the present specification the "silicate boil" process is intended to be included within the scope of the term 'silica treatment'.

One problem in large scale refining of fish oil is that rather large amounts of bleaching earth are required during the above mentioned bleaching step. In the examples of EP 304115 up to 8% on fish oil of a commercial bleaching earth was required. This can cause difficulties when the oil is being removed from the earth, as the presses used for this process step are unable to accommodate such high levels of earth safely.

In comparison, bleaching of vegetable oils can often require less than 1% of bleaching earth.

The difficulties with fish oil take the particular form of a fire risk. It has long been recognised that spent bleaching earth containing unsaturated oil rapidly oxidizes on contact with air. Such oxidation can proceed to the point of causing spontaneous combustion on contact with air, creating a serious odour problem and a fire hazard. This is a problem with fish oil especially, as fish oil is rich in oxidation-sensitive chemical bonds. To some extent this problem can be overcome by ensuring that the earth is sufficiently blanketed for air exclusion, as mentioned in "BAILEY'6 Industrial Oils and Fats" (pub. Wiley 1982) pages 308309. Nitrogen is suitable for blanketing during pressing, and stringent fire precautions must be taken when discharging spent earth from the press.However, the process remains disadvantageous as spent bleaching earths may be used for land-fill the fire risk returns during shipping and dumping.

I We have determined that these problems can be to a large part overcome if the vegetable oil and the fish oil are mixed prior to the bleaching step and preferably prior to both the bleaching and silicate treatment steps.

One advantage of such a co-refining process is that less bleaching earth per unit oil volume is required. This facilitates operation of the presses used to separate the oil and spent bleaching earth, thereby reducing the fire risk. It is also believed that the dilution effect of a vegetable oil reduces the risk of spontaneous combustion in the highly unsaturated fish oil.

It is also believed that the advantages of EP 304115 accrue to the present invention, insofar as crude fish oil pro-oxidants such as mucilaginous gums, heavy metals etc, and the early contact between fish oil and the vegetable oil reduces the deleterious effect of these substances on the oxidation-sensitive fatty acids of the fish oil without recourse to the addition of further antioxidants. Having regard to this aspect of the invention it s preferable that the mixing of fish and vegetable oil occurs as early in the co-refine process as convenient.

Suitable vegetable oils for blending and co-refining together with fish oil are sunflower oil, soybean oil, rapeseed oil, maize oil, cottonseed oil, olive oil, linseed oil and other commonplace edible vegetable oils or fractionated vegetable oils such as fractionated palm oil.

Oils rich in oleic acid such as olive oil, palm oil fractions, technical tri-olein, high oleic rapeseed, safflower and sunflower oils are particularly preferred.

It is I A further advantage of the co-refining process emerges when one or more 'rare' vegetable oils are used in the co-refining process, either in combination with a commonplace vegetable oil or not. Such 'rare' oils are far more expensive than commonplace oils and it is important that refining losses are minimised. In a preferred embodiment of the present invention the expensive 'rare' oil is diluted with a less expensive oil and therefore minimises losses of the expensive component during plant cleaning and feedstock changeover.

The present invention is particularly suited to the preparation of oil blends comprising an unhydrogenated fish oil and at least one vegetable oil which is rich in fatty acids of particular nutritional significance.

Among these fatty acids are long chain fatty acids such as alpha-linolenic and gamma-linolenic acid. Oils comprising significant proportions of these fatty acids include borage oils, primrose oils, peanut oil, currant seed oils particularly that obtained from the blackcurrant ribes niara, hemp and hop oils, gooseberry oil and some rapeseed oils. Amongst these 'rare' oils, borage, ribes and primrose oils are particularly expensive and it is important that losses during handling and refining are minimised.

Other, non-vegetable, oils are noted for the nutritional qualities of the fatty acid contained therein. For example, oils such as "oil of javonicus" as obtained by fermentation are envisaged as suitable for incorporation in the fat blends of the present specification.

The invention is illustrated hereafter by way of examples.

l EXAMPLE 1: A blend of 28 kg of high oleic sunflower oil (free fatty acid content 0.6%) and 28 kg of canola oil (free fatty acid content 0.1%) was weighed out and drawn under vacuum into a neutralizer vessel. The vacuum was released with nitrogen gas. This blend was degummed at 850C with H3PO4 (200 mls of a 75% solution) sprayed onto the oil and held in contact while stirring for five minutes. After settling for another five minutes the oil was stirred and washed with 50 litres of hot water.

The blend was neutralised with 15 litres of 0.1N sodium hydroxide solution and again washed with 50 litres of hot water.

14 kg crude fish oil (free fatty acid content 1.4%) was drawn into the same neutralizer vessel under vacuum and the vacuum again released with nitrogen gas.

The fish oil/ vegetable oil blend was again degummed with H3PO4 (200 mls of a 75% solution under the same conditions of heat and temperature as had been employed previously. The blend was subsequently neutralised with 15 litres of 0.1N sodium hydroxide solution, washed with 50 liters of hot water and dried under vacuum.

The neutralised blend was subjected to a soda ash silicate boiling treatment. In this treatment a solution of 1.2 kg of soda ash was dissolved in 2.5 litres of water, and added, together with 2 litres of a 30% sodium silicate solution to the oil at a temperature of 100C. Boiling and stirring were continued for 20 minutes after which the mixture was washed with hot water at 95'C and allowed to settle during which time 4 kg of a black sludge was deposited.

i The fat phase was separated and dried under vacuum. As before, the vacuum was released with nitrogen gas.

Following the soda ash/silicate boiling treatment the blend was bleached for a half hour at llO'C using 1.2 kgs of an R169 bleaching earth (an acid activated "Fullers Earth"). Care was taken to introduce the earth through the nitrogen filled headspace so as to minimise oxidation. The amount of bleaching earth required was calculated at 1% for the high oleic sunflower and canola components and 4% for the fish oil component. The bleached oil was cooled to 40etc for filtering under nitrogen gas into drums purged with nitrogen.

The cooled oil was transferred from the drums into the deodorizer unit under vacuum and held overnight under nitrogen gas. The blend was deodorized for five hours at 180it. Fifteen milliliters of a 15% solution of citric acid was added at 90iC during cooling.

The oil blend was stored in glass bottles and exhibited acceptable flavour stability.

In a comparative taste trial with blends of maize oil and fish oil samples refined according to the method of the present invention were still well inside the acceptable limits of off-flavour development after ten weeks (increase of peroxide value from less than 0.9 increasing to at most 1.8) whereas blends made simply by mixing the oils were unacceptable after ten weeks storage (increase in peroxide value from less than 0.9 to at most 42).

OOMPARATIVE EXAMPLE: In order to illustrate the dangers associated with the refining of unhydrogenated fish oil the following example is given.

A sample of 1.1 tonnes Chilean fish oil was neutralised under nitrogen at 90iC with 0.1N NaOH (200 litres on still oil) and washed with water (200 litres). To stirred oil at 95*C under nitrogen gas was added 12 kgs of soda ash in 28 kg of water and 17.5 litres of 30% sodium silicate solution. The stirred mixture was brought to the boil for ten minutes. 50 kg of water at 950C was added slowly over 15 minutes and stirring continued for a total of 30 minutes. The aqueous layer was allowed to settle for 10 minutes and the still oil washed once with 100 litres of water. After settling a black aqueous phase was run off and a second wash (100 litres) was performed. The oil was blanketed with nitrogen gas throughout and stored under nitrogen gas after vacuum drying.

To the nitrogen-blanketed oil 7.5% of R169 bleaching earth was added. Bleaching was performed under vacuum for 20 minutes at 90"C with a nitrogen gas bleed to prevent initial frothing. Because of the large quantity of earth involved, the filtration was stopped about half way through to remove the filter cake from the press.

Prior to removal the press was purged (2blown) was nitrogen gas to recover as much oil as possible.

The filter cake (bleaching earth plus adsorbed materials) removed from the press in the first half of the filtration began to smoulder immediately on exposure to air. It was necessary to use a carbon dioxide extinguisher system to stop the evolution of smoke and fumes and prevent the earth from bursting into flames.

No such difficulties were encountered when carrying out the method of the present invention.

Various modifications may be made within the scope of the present invention. For example, the vegetable oil may be subjected to a bleaching step prior to admixture with the unbleached fish oil, or supplied in a prebleached form.

Claims (10)

1) A method of refining fish oil, including the step of bleaching the fish oil, CHARACTERISED IN THAT, an excess of vegetable oil is mixed with the fish oil to form an oil mixture prior to the bleaching step.

2) A method according to claim 1, wherein the vegetable oil is selected from the group comprising sunflower oil, maize oil, safflower oil, soybean oil, rapeseed oil, peanut oil, olive oil, palm oil and mixtures and/or fractions thereof.

3) A method according to claim 1 or 2, wherein the vegetable oil is selected from the group comprising borage oil, gooseberry oil, oils obtained from plants of genus ribes, hemp oil, hop oil and primrose oil and mixtures and/or fractions thereof.

4) A method according to any of the proceeding claims, further comprising a silicate treatment of the oil mixture.

5) A method according to any of the proceeding claims, further comprising a degumming treatment of the oil mixture.

6) A method according to claim 1 which comprises the steps of: a) preparing an oil mixture of fish oil and one or more vegetable oils, b) bleaching the oil mixture with d bleaching earth, and, c) separating the spent earth from the oil mixture.

7) A method according to claim 1, further comprising the step (d) of deodorising the oil mixture.

8) A method according to any one of the preceding claims wherein the oil mixture comprises at most 25% of fish oil on total oil mixture.

9) A method as claimed in claim 8 wherein the oil mixture comprises at most 20% of fish oil on total oil mixture.

10) An oil blend preparable by the method of any of claims 1-9.