PACKAGED OXIDATION-STABLE OIL-IN-WATER EMULSION

TECHNICAL FIELD OF THE INVENTION The present invention relates to a packaged oxidation-stable oil-in-water emulsion containing from 0.1-10 wt . % of oil, said oil containing 0.3-80 g of polyunsaturated fatty acids per liter of emulsion. Another aspect of the invention concerns a method for the manufacture of such a packaged oil-in-water emulsion.

BACKGROUND OF THE INVENTION

It is well-known in the art of food chemistry that the application of oils containing high levels of polyunsaturated fatty acids can give rise to serious off-flavour problems. These off-flavour problems are associated with the oxidation of the polyunsaturated fatty acids, leading to the formation of volatile, potent flavour molecules, such as unsaturated aldehydes. Flavour attributes associated with oxidation products of polyunsaturated fatty acids include "fish" , "cardboard", "paint", "oily", "rancid" and "metallic".

It is also known that iron cations even at low concentration of e.g. 0.1 mg /kg behave as strong pro-oxidants . Hence, products containing appreciable amounts of polyunsaturated fatty acids in combination with significant concentrations of iron cations will very quickly develop a strong off-flavour.

It is further known that oxidation of polyunsaturated fatty acids may be inhibited through the addition of anti-oxidants . Examples of suitable anti-oxidants include tocopherols,

extracts of rosemary, ascorbyl palmitate, citric acid, ascorbic acid, TBHQ, BHA and BHT.

The oxidation of polyunsaturated fatty acids can also be prevented by ensuring that no oxygen is present in the product in which the polyunsaturated fatty acids are incorporated. This may be achieved by producing such a product under an oxygen- free atmosphere (e.g. nitrogen) and/or by packaging the product in a package with an oxygen-free headspace or no headspace at all (e.g. Tetra Pak ^® ) .

Production under oxygen-free atmosphere requires sophisticated equipment. Furthermore, the use of oxygen- free atmosphere does not adequately address the problem of oxidation of polyunsaturated fatty acids. Commercially available oils that are rich in polyunsaturated fatty acids always contain a certain level of oxidised polyunsaturated fatty acids in the form of peroxides. These peroxides are non-volatile and as such do not affect the flavour of a product. However, during processing and storage, these peroxides will degrade to potent flavour molecules, even in the absence of oxygen. In particular in the presence of pro-oxidants, such a iron and cupper cations, the degradation of these peroxides to aldehydes and other flavour molecules will proceed at a very high rate. Elevated storage temperatures also accelerate the degradation of these peroxides.

SUMMARY OF THE INVENTION

The present inventors have developed a packaged oxidation- stable oil-in-water emulsion comprising an oil with a high content of polyunsaturated fatty acids in combination with a

substantial amount of pro-oxidative metal cations. Pro- oxidative metal cations such as iron and zinc cations are advantageously incorporated in the present product to provide these essential minerals in amounts that represent a substantial fraction of the recommended daily amount (RDA) . The present packaged emulsion offers the advantage that despite the presence of high levels of polyunsaturated fatty acids and appreciable amounts of pro-oxidative metal cations, it does not exhibit off-flavour defects resulting from oxidative degradation of the polyunsaturated fatty acids. As a matter of fact, the present packaged emulsion can be stored for up to several months under tropical conditions without any significant off-flavour development.

The inventors have found that oxidation of polyunsaturated fatty acids in an emulsion that additionally contains pro- oxidative metal cations, can effectively be prevented, even if the emulsion is produced under conditions in which it is in direct contact with air, if the emulsion is packaged in a container that holds no headspace and if a very high concentration of vitamin C is incorporated in the emulsion.

DETAILED DESCRIPTION OF THE INVENTION Accordingly, one aspect of the invention relates to a packaged, oxidation-stable oil-in-water emulsion comprising:

• 0.1-10 wt. % of oil, said oil containing 0.3-80 g of polyunsaturated fatty acids per liter of emulsion;

• at least 1 mg/1 of pro-oxidative metal cations; • 10-2000 mg/1 of vitamin C; and

• up to 98 wt .% of water; wherein the container comprising the emulsion holds no headspace and wherein the molar ratio of vitamin C to pro-

oxidative metal cations exceeds 1:2.

The terminology "packaged emulsion" as used herein refers to a combination of an emulsion and a container holding said emulsion. The container holding the present emulsion can be any container that can be filled with the present emulsion in such a way that no headspace remains in the container. A particularly preferred container is a so called Tetra Pak ^® .

The term "headspace" as used herein refers to the gaseous contents of a filled container. The terminology "holds no headspace" implies that the container holds essentially no headspace. Preferably, headspace represents less than 0.1 vol.%, more preferably less than 0.01 vol . % of the internal volume of the container. Most preferably, headspace represents 0 vol.% of the internal volume of the container.

The term "oil" as used herein refers to a lipid material, preferably to a lipid material that is liquid at 30 ⁰ C, more preferably at 20 ⁰ C. Examples of lipid materials include triglycerides, diglycerides, monoglycerides and phospholipids. Most preferably, the oil is a triglyceride oil. According to a particularly preferred embodiment, the present emulsion contain at least 0.5 wt . % of oil.

The term "polyunsaturated fatty acids" as used herein refers to C12-C ₂₄ fatty acids comprising two or more double bonds. The polyunsaturated fatty acids may be present in the form of free fatty acids and/or as fatty acid residues, e.g. in the form of fatty acid esters of glycerol. Preferably, the polyunsaturated fatty acids are contained in triglycerides. The concentration of polyunsaturated fatty acids in the present emulsion advantageously exceeds 0.5 g/1.

The pro-oxidative metal cations present in the packaged emulsion are selected from the group consisting of iron cations, copper cations, zinc cations and combinations thereof. More preferably, the pro-oxidative metal cations are selected from the group consisting of iron cations, zinc cations. Most preferably, the pro-oxidative cations are iron cations. In a preferred embodiment of the present invention the emulsion contains a substantial amount of pro-oxidative metal cations, especially iron cation, e.g. at least 3 mg/1, preferably at least 5 mg/1, more preferably at least 10 mg/1 and most preferably at least 20 mg/1. Typically, the amount of pro- oxidative metal cations contained in the packaged emulsion does not exceed 130 mg/1. Preferably pro-oxidant metal cations are present in a concentration that does not exceed 100 mg/1, more preferably does not exceed 60 mg/1, most preferably does not exceed 20 mg/1.

The term "vitamin C" as used herein encompasses ascorbic acid as well as any edible salts or esters thereof. Preferably, the present product comprises an alkali metal salt of ascorbic acid, e.g. sodium ascorbate. The vitamin C concentration in the present emulsion preferably is at least 20 mg/1, more preferably at least 50 mg/1, even more preferably at least 100 mg/1 and most preferably at least 250 mg/1. The vitamin C concentration preferably does not exceed 1800 mg/1, most preferably it does not exceed 1500 mg/1.

In order to achieve high oxidation-stability it is advisable to employ a high molar ratio of vitamin C to pro-oxidative metal cations, especially iron cations. Preferably, said molar ratio exceeds 1:1, more preferably it exceeds 1.5:1 and most preferably it exceeds 2:1.

The present emulsion typically contains at least 75 wt . % of water. More preferably, the present emulsion contains at least 80 wt. of water. The amount of water contained in the present emulsion preferably does not exceed 95 wt . % .

An important advantage of the present invention resides in the fact that the present emulsion can be produced without the need of using equipment that is operated under an oxygen-free atmosphere. As a result, the present emulsion, in particular shortly after manufacture, typically contains at leastO.l ppm of oxygen, preferably at least 0.2 ppm of oxygen. The amount of oxygen contained in the present emulsion preferably does not exceed 10 ppm. More preferably said amount does not exceed 5 ppm, most preferably it does not exceed 2 ppm. Due to direct contact between the emulsion components and air, not only oxygen, but also carbon dioxide and nitrogen will be introduced into the packaged emulsion. Usually, the present emulsion contains at least 0.3 mg/1 of nitrogen, preferably at least 1 mg/1 of nitrogen. Furthermore, the emulsion typically contains carbon dioxide and nitrogen in a weight ratio of at least 1:2500.

When the present packaged emulsion is produced in the presence of air, the oil in the packaged emulsion usually contains a significant amount of oxidised polyunsaturated fatty acids in the form of peroxides. In a preferred embodiment the present emulsion is produced in the presence air, in which case the oil present in the packaged emulsion typically has a peroxide value of at least 0.5.

Vitamin C is capable of preventing oxidative degradation in that it is oxidised even more rapidly than the polyunsaturated

fatty acids and, unless it is oxidised to a very high degree, does not give rise to off-flavour development. When the present emulsion is produced without the use of an oxygen- free atmosphere, as is preferred, the oxygen present in the emulsion will oxidise a significant fraction of the vitamin C present in the emulsion. Typically, at least 5%, preferably at least 10% of the vitamin C present in the emulsion is oxidised.

The benefits of the present invention are particularly pronounced in case the emulsion contains polyunsaturated fatty acids that are extremely sensitive to oxidation. Generally speaking, sensitivity of oxidation increases exponentially with the number of double bonds present in the fatty acid. According to a particularly preferred embodiment, the polyunsaturated fatty acids contain at least three double bonds. According to an even more preferred embodiment, the present emulsion contains at least 10 mg/1, preferably at least 50 mg/1 of ω-3 fatty acids, especially of ω-3 fatty acids selected from the group consisting of DHA (docosahexaenoic acid) , EPA (eicosapentaenoic acid) and combinations thereof. Usually, the combined amount of DHA and EPA contained in the present emulsions does not exceed 3 g/1, preferably it does not exceed 1 g/1.

The present product may advantageously be used to provide an optimised balance of important nutrients. Accordingly, the present emulsion preferably contains

• 0.5-8 wt. % protein;

• 1-6 wt. % oil; • 6-20 wt. % carbohydrates;

• up to 5 wt .% of optional other nutritional components. Examples of other nutritional components that may

advantageously be incorporated include: vitamins, phytosterols, polyphenols, flavonoids, carotenoids etc.

The present emulsion preferably is a pourable liquid. Even more preferably, the emulsion is a thin liquid as evidenced by a viscosity in the range of 5-200 mPa.s at 10 s ^"1 , preferably in the range of 5-100 mPa.s at 10 s ^"1 . The viscosity of the emulsion is suitably determined by means of a Rheometer ^® AR1000, using a shear rate sweep from 0.01 to 250 s ^"1 (in 510 s.) and a cone plate measuring system with a cone angle 2:0:38 (deg :min: sec) , a cone diameter of 40 mm and a truncation of 54 microns. Preferably, the viscosity is measured at a temperature of 20 °C.

The oil comprised in the present emulsion preferably contains at least 50 wt.%, more preferably at least 80 wt . % of a highly unsaturated oil selected from the group consisting of marine oil (e.g. fish oil or algae oil), rapeseed oil, olive oil, soybean oil, sunflower oil, linseed oil, cashew nut oil, walnut oil, peanut oil canola oil and combinations thereof. According to a particularly preferred embodiment, the present emulsion contains at least 0.01 wt.% of marine oil.

In order to ensure that the present emulsion is sufficiently stable against syneresis, flocculation and creaming, it is preferred that the oil is present as dispersed droplets with a diameter D ₃ , ₂ of 0.1-3 μm, preferably of 0.3-2 μm. The D _3r2 diameter (i.e. the surface weighted average diameter) is suitably determined by means of laser diffraction, using a Helos ™ laser diffraction sensor (ex Sympatec GmbH) in combination with a 632.8 nm laser. Measurements are conducted at 20 °C using a QUIXEL ™ wet dispenser ex Sympatec GmbH (at an optical concentration between 10 and 20%) .

In accordance with another preferred embodiment the present emulsion contains between 0.1 and 15 wt.%, more preferably between 1 and 10 wt.% of a starch component selected from the group consisting of native starches, modified starches and combinations thereof. The incorporation of a starch component offers the advantage that it stabilises the emulsion and at the same time provides a digestible carbohydrate.

The present packaged emulsion does not oxidise significantly even when exposed to extreme storage conditions, such as several weeks at 40 ⁰ C. According to a particularly preferred embodiment, the packaged emulsion can be stored for more than 8 weeks, even more preferably for at least 15 weeks at a temperature of 40 ⁰ C without developing an unacceptable off- flavour .

In order to guarantee adequate storage stability the present emulsion preferably is a sterile emulsion. The pH of the emulsion preferably is within the range of 4-8. More preferably, the emulsion has a pH between 5 and 7.5, mot preferably between 6.5 and 7.

The oxidation stability of the present packaged emulsion is achieved without the need of using highly effective antioxidants such as BHA, BHT and TBHQ. Accordingly, in a preferred embodiment the emulsion does not contain an anti-oxidant selected from the group consisting of BHA, BHT and TBHQ.

Yet another aspect of the present invention relates to a method of preparing a packaged emulsion as defined herein before, said method comprising: • combining oil, pro-oxidative metal cation, vitamin C and

water in a pre-emulsion;

• homogenising the pre-emulsion;

• sterilising the homogenised emulsion; and

• packaging the sterilised emulsion in a container that holds no headspace ; wherein the pre-emulsion contains at least 0.1 ppm of oxygen.

The invention is further illustrated by means of the following examples .

EXAMPLE 1

29.9 kg of water was weighed and heated to 80 ⁰ C in an open vessel. 2.88 kg of skimmed milk powder was pre-mixed with 0.1 kg of potassium phosphate and 40 g of mono/di-glycerides (HV-52 K Danisco) . This mixture was dispersed in the hot water under high speed mixing and hydrated under proper mixing for 15 minutes. An oil blend containing 0.95% DHA was produced using Soybean oil and a DHA concentrate based on Algae oil ex Nutrinova in a ratio of 97.8:2.2%. 1.06 kg of this oil mixture was added under high speed mixing and pre-emulsified by proper mixing for 15 minutes. 3.76 kg of maltodextrin DE20 and 0.2 kg of native starch was dispersed in this pre-emulsion

Vitamins/minerals and colouring ingredients (e.g. caramel) were mixed to a blend containing 5 g of Fe-fumarate and 37.2 g of vitamin C (As sodium ascorbate) . This blend was added to the pre-emulsion. Next, 1.6 kg of sugar was added to the pre- emulsion. Flavours were added to the pre-emulsion at the desired level. The pH was checked and corrected whenever it was below < 6.7 using phosphate buffer. Final concentration of vitamin C equals 930 mg/kg and final concentration of 43 mg/kg Fe ²⁺ .

The product was homogenised at 175 - 250 bar and 65-70 ⁰ C and thereafter UHT treated at 140 ⁰ C - 4 sec. Thereafter the product was cooled to 25-30 ⁰ C and filled aseptically in aluminum bags without headspace .

The products were stored at 40 ⁰ C and evaluated on taste. Below the taste evaluation results by an expert panel are presented (average over n=5)

After 2 months the vitamin C level analysed was 554 mg/kg. These results demonstrate that the packaged emulsion was extremely oxidation stable as it did not develop significant off-flavour during prolonged storage under extreme conditions even though the product contained an appreciable amount of highly unstable polyunsaturated fatty acids. The observed reduction in vitamin C content indicates that vitamin C was preferentially oxidised during storage.