The present invention relates to the preparation of a food dressing, particularly of low fat food dressings having a reduced number of auxiliary ingredients.

STATE OF THE ART

Mayonnaise is a water continuous emulsion, containing 80wt.% of dispersed oil. In order to impart proper stability and texture to mayonnaises with a reduced fat content, particularly 40wt.% or less, it iε necessary to incorporate auxiliary ingredients in the mayonnaise, particularly lipid emulsifiers and polysaccharide thickeners, such as gums and starch derivatives. Often, however, the thickeners have an adverse effect on taste and mouthfeel . Moreover, such auxiliary ingredients have to be declared on the label, unless they are considered natural. Presently, many consumers prefer industrially prepared food to have a minimum amount of added emulsifiers and thickeners. It is a problem to find natural ingredients with a functionality which can impart to low fat food dressings in general, and to low fat mayonnaise in particular, a smooth, either spoonable or pourable, rheology.

The solution mentioned in JP 06/054 662 (KAO Corp.) realizes a proper texture by using 1 to 10% of egg, milk or soyabean derived protein, which is dissolved in a water continuous emulsion containing 10 to 60wt.% of dispersed oil. For maximum thickening, the pH of the dressing is adjusted to the protein's isoelectric point which is, however, much higher than the optimum pH for microbiological stability. When lowering to the optimum pH for microbiological safety, the thickening effect quickly disappears and a dressing results which is too thin. Moreover, the oil droplets of this prior art's

dressing should be comminuted so that greater than 80% of them have an extremely small size of less than lμm, otherwise no proper texture is obtained.

The article 'Whey protein and the properties of salad dressing' in Deutsche Milchwirtschaft, 1993, 44(21) p.1054, by G. Muschiolik et al, discusses the effects of pH and salt content on protein-stabilised emulsion systems. It states that the addition of salt has little or no influence on the consistency of systems containing acid, such as salad dressings. From figure 3, it is apparent that the addition of salt either before or after high-pressure homogenisation has little effect on the consistency of systems containing acid.

Similar conclusions are reached in the article ' Investigation of the function of whey protein preparations in oil-in-water emulsions' by G Muschiolik et al, from Proc. Food Macromolecules and Colloids Symposium, 1994, Dijon, which also discusses the effects of pH and salt content on protein-stabilised oil-in-water emulsions .

The article 'Heat stability of oil-in-water emulsions containing milk proteins: effect of ionic strength and pH' by Hunt and Dalgleish, in the Journal of Food Science, Vol. 60, No. 5, 1995, p. 1120 examines the heat- stability of acidic emulsions containing whey protein and KC1.

The present invention seeks to provide a process for preparing an improved aqueous-continuous emulsion.

STATEMENT OF INVENTION

A process has been found for the preparation of aqueous continuous emulsions, containing 10 to 60wt.% of

dispersed oil. The emulsion contains a protein and less than 5wt.% of a polysaccharide thickener.

The process comprises the following steps (not necessarily in the indicated order)

a. dispersing or dissolving a protein in either an aqueous phase or an oil phase, b. mixing the aqueous phase and the oil phase so that a coarse emulsion comprising oil droplets results, c. homogenising the emulsion until the size of at least 95% of the oil droplets iε less than 5μm, d. acidifying the emulsion until a pH of from 3.5 to 4.5 is attained, e. adding electrolyte to the emulsion under shear conditions,

wherein step c precedes step e, and, in step e, the emulsion has a temperature of from 10 to 55°C.

The electrolyte addition thickens the system by the formation of flocculated oil droplets. Flocculation of oil droplets appears to increase viscoεity, and impartε an attractive texture and mouthfeel to the food dreεεing, by replacing the functionality of both emulsifiers and thickeners .

DETAILS OF THE INVENTION

Some process steps may be carried out in reverse order, but the homogenisation step preferably precedes the acidification step.

The addition of the electrolyte solution must follow the homogenisation, else no proper viscosity is obtained.

Preferably the acidification step precedes the addition of electrolyte. The temperature of the emulsion is preferably from 10 to 55°C during the acidification step.

Reversible flocculation of oil droplets, which are stabiliεed by a protein coating, εhould be diεtinguished from irreversible denaturation of protein. It is known that protein denaturation occurs at increased temperatures: this means that the molecular protein structure is changed in an irreversible way. For denaturation to occur, an extended exposure to a temperature of greater than 60°C is necessary,- also, the higher the temperature, the greater the extent of denaturation.

High temperatures, however, are not necessary when employing the present invention. Flocculation is a reversible condition; when the flocculation conditions are removed (for example, the pH is increased sufficiently) , the thick rheology disappears.

In the present invention, the addition of electrolyte solution takes place at temperatures of from 10 to 55°C. Flocculation occurs at ambient temperature, but the process proceeds much faster and results in a firmer texture when the temperature iε slightly increased. Therefore, the temperature of the emulsion is preferably from 35 to 45°C during addition of the electrolyte solution.

In general, the greater the processing temperature of the emulsion, the more stable the resulting product.

It is poεεible to poεtpone flocculation, even in the preεence of electrolyte, by adding the electrolyte ionε at a temperature of less than 10°C, and by storing the product at a temperature of less than 10°C. At a

temperature of greater than 40°C, flocculation occurs quickly and immediately. The magnitude of the effect will depend on the concentration and type of ions added. The option to postpone flocculation is advantageous, because the emulsion product can be processed and filled into containers at low viscosity. The desired thickened εtructure iε then generated in the container, for example by uεing microwave heating. Alternatively, the thickening may by effected by the consumer, so that the emulεion can be adapted to a εpecific purpoεe: for example, the emulεion iε a dreεεing which iε poured aε a relatively thin sauce on a hot dish, where it immediately turns into a thick topping.

The protein is selected from the group consisting of plant protein, fruit protein, dairy protein, egg-albumin, blood-albumin, gluten protein (which may be enzymatically-modified) , soya protein and mixtures thereof. In principle, all kindε of protein can be employed, provided the protein iε able to flocculate in the preεence of an electrolyte.

Preferably, the protein iε choεen from the group conεiεting of egg albumin, whey protein, plant protein, such as pea and bean protein, or fruit protein, such as banana and apple protein. The protein is added in either a, more or less, purified form, such as egg albumin, pea or whey protein, or as a crude product, εuch as banana puree or apple puree. The protein content may differ widely and can be as high as 84wt.% (pea protein) or aε low aε lwt.% (banana puree) . The amount of protein εubεtance should be chosen such that the final mixture contains at least 0.4wt.% of pure protein. The proper amount of protein is established easily by routine trials. The amount depends on the nature of the protein and on the amount of oil . Lesser amounts of oil require

lesεer amounts of protein and vice-versa, in order to attain the desired consiεtency.

Plant protein is suitably admixed as a mousse (puree) obtained e.g. by grinding vegetableε or fruit. Plant mouεεe εometimeε has a relative low emulsifying capacity, so it may be necessary to supplement it with an emulsion stabiliser, such as protein, preferably a vegetable or a milk (e.g. whey) protein.

Electrolytes are substances which dissolve in water and form electrically charged particles (ions) . Common electrolyteε are εaltε, such as common cooking salt. Suitable electrolytes may contain monovalent anions εuch aε chloride anions, e.g. originating from sodium chloride,- preferably, electrolytes are used which ionize in solution with divalent anions (such as sulphate, e.g. originating from sodium sulphate) or with polyvalent anionε (such as tripolyphosphate) . Such multivalent anionε can often be used in a lesεer amount than monovalent anions, whilst obtaining the same viεcoεity. Electrolyteε are added in dry form or aε an aqueouε εolution, preferably having a concentration of from 0.1 to 4wt.%.

When the electrolyte iε added, the emulεion has a temperature of from 10 to 55°C, preferably from 35 to 45°C.

Flavour components may be added at any time during the preparation, but coarse ingredients, including herbs and spiceε, are preferably added after homogenisation. The use of traditional thickeners, particularly polysaccharideε, such as starch, modified starch or gum, is superfluouε when preparing an emulsion in accordance with the present invention. Nevertheless, less than 5wt .% of a polyεaccharide may be present, as long aε it

has no adverse effect on the taste or the texture. Preferably less than lwt .%, more preferably lesε than 0.1wt.%, of a polyεaccharide is present in the final product .

The pH of the final composition should be adjusted to be from 3.5 to 4.5, but, for optimum microbiological stability, the pH is from 3.8 to 4.0.

The invention provideε an emulεion suitable for preparing dressings with an optimum pH and having the necesεary thickneεε without relying on added polysaccharides or other non-natural ingredients. Moreover, the dresεing haε a fine taεte which resembles traditional dressingε.

The invention iε further illuεtrated by the following examples :

General

The thickness of dressings is expressed in Stevens values for relatively thick consistencieε and in Boεtwick valueε for relatively thin consiεtencieε . Boεtwick valueε, aε well aε Stevens values, refer to specific and well known types of yield stress measurement.

It should be noted that an increased thicknesε iε expresεed by an increased Stevenε value, but by a decreased Boεtwick value. For comparison: Boεtwick values are in the range of 0 to 24, where a margarine/εpread has a value of 0 and a drink-yogurt haε a value of 24. Rheologieε characterised by yield stress values expressed in Nm' ² units are thicker when streεε values are higher.

Example 1 Whey protein based dressings

Table I shows the ingredients for a whey based dresεing. The aqueous phase is made by dissolving the protein in deionised water (65°C) using a high shear mixer such as a Silverεon™ mixer, followed by adding potaεεium sorbate. Sunflower oil iε heated up to 65°C and mixed with the aqueous phaεe, for five minuteε, to form a coarse "pre- emulsion" . A stable emulsion iε made by emulsification in a high pressure Crepaco™ 3-piston homogeniser, at a presεure of 1x10" kNm ^"2 (100 bar) , for a total of 5 paεεeε through the homogeniεer, followed by pasteurisation at 70°C for 1 to 2 minuteε to avoid microbiological spoilage .

The emulεion iε cooled down to 10°C, then acidified with 99.9% glacial acetic acid to pH 4. After pH adjuεtment, the emulεion iε kept at a temperature of 10°C and a NaCl solution is added, until a NaCl concentration of either 2 or 4wt .% iε attained. Table II εhowε the reεulting thick rheologieε in comparison to an emulsion which does not containing NaCl .

TABLE I

The whey protein used is a commercially available concentrate, sold under the name ' actalbumen 70' and available from Milei, Stuttgart, Germany.

Example 2 Whey protein based dressings

Example 1 iε repeated but, after paεteurising, the emulsion is maintained at 40°C for acidification and addition of NaCl. Then the emulεion is stored at 5°C. Table II shows the obtained rheologieε .

From Table II, it can be εeen that the greater the amount of an electrolyte added, the greater the yield εtreεε meaεurement of the reεultant emulεion.

TABLE II

COMPARATIVE EXAMPLE A

Example 2 is repeated but an emulsion with 2.5wt .% of NaCl is prepared. The preparation is carried out once

with the usual NaCl addition following the homogenisation and the acidification stepε, and once with the NaCl addition preceding the homogenisation and the acidification steps.

Table III shows the remarkable thicker rheology when NaCl is added after homogeniεation.

TABLE III

Example 3 Whey protein based dressing

Example 1 is repeated but sodium sulphate is added instead of sodium chloride, to achieve 5000ppm divalent sulphate ionε . Table IV shows the thickening effect on final rheology when ions of an increasing valency are used.

Example 4 Whey protein based dressing

Example 1 is repeated but sodium tripolyphosphate is added instead of sodium chloride, to achieve 5000ppm trivalent polyphosphate ionε . Table IV εhows the thickening effect on final rheology when ionε of an increaεing valency are used.

TABLE IV

Example 5 Pea protein based dressing

Table V showε the ingredientε for a pea protein baεed dressing. The oil and the protein are mixed with an Ultraturrax™ high shear mixer at a temperature of 22°C. The mixture is emulsified with the water phaεe while the temperature iε kept at 35°C. Potaεεium εorbate is added. The emulsion is homogenized at 35°C with a high pressure homogenizer (2xl0 ⁴ /lxl0 ⁴ kNm ^"2 (200/100 bar)) supplied by APV Gaulin GmbH, Lύbeck, Germany. A [D _3#2 ] ^* droplet εize of 2μm iε attained. The emulεion, whilεt having itε temperature of 35°C maintained, iε acidified with vinegar and lactic acid to achieve a pH of 3.9, and haε 1.8% NaCl added thereto, whilεt stirring. Table VI εhowε the

'see M. Alderliesten, A Nomenclature for Mean Particle Diameterε, Anal. Proc. , Vol. 21 (1984) 167-172

thickening effect by the change in Stevens value during proceεεing.

Example 6 Banana protein based dressing

Table V εhowε the ingredients for a banana protein based dresεing. The banana iε mixed with water and potasεium sorbate. After dissolving the available banana protein, oil is added while stirring with an Ultraturrax™ high shear mixer for 5 min. The mixture is emulsified while the temperature iε kept at 40°C. The emulεion iε homogenised at 35°C with an APV Gaulin high presεure homogeniεer (2xl0 ⁴ /lxl0 ⁴ kNm ^"2 (200/100 bar)) . A [D _{3 2} ] droplet εize of 1.8μm iε attained. The emulsion, whilst having its temperature of 35°C maintained, is acidified with vinegar and lactic acid to achieve a pH of 3.9, and haε 1.8wt .% of NaCl added thereto, whilst stirring. Table VII shows the thickening effect by the change in Boεtwick value during processing.

TABLE V

Notes :

1) Protein content on product resulting from the added pea or banana

2) Measured with a light scattering Helos™ device

TABLE VI

COMPARATIVE EXAMPLE B

A product was prepared with a composition identical to the product of example 6, but without any oil. The preparation was also identical. Table VII showε that no εubstantial change in Bostwick value occurred when electrolyte waε added.

Thiε comparison example clearly shows the positive relation of the presence of oil (droplets) to the flocculation effect.

TABLE VII

Example 7 Banana protein based dressing

A preparation iε carried out according to example 6, uεing the ingredientε aε indicated in Table V. The main

difference is that the amount of oil has been increased from 10 to 25wt.%. Table VIII showε the thickening effect by the change in Stevenε value during proceεεing. The Stevenε value (after three days) iε 90, which εhows a thickness greater than that of the 10% oil dressing of example 6, for which only a Boεtwick value could be eεtablished.

TABLE VIII

Examples 8 and 9 Whey protein based dressings

Example 1 is repeated up to the homogenisation step using the ingredients for a whey based dresεing εhown in Table IX, except that the deioniεed water and the sunflower oil have a temperature of 60°C, not 65°C. After each pasε through the homogeniεer, εampleε are taken for droplet measurement εize.

Table X εhowε the effect of whey concentration and the number of paεses at lxlO ⁴ kNm ^"2 (100 bar) pressure through the homogeniser on oil droplet εize and diεtribution. The mean droplet εize iε determined uεing a Maεterεizer from Malvern Instruments Ltd, Malvern, UK, with optical parameters defined by the manufacturer's presentation code 0500: 2mls of emulsion are added to a large sampling unit filled with 100ml of deionised water, and

measurements are made using a pump and a stirrer setting of 40%.

From Table X, it can be seen that 3 passeε through the homogeniεer iε εufficient for 95% of the oil droplets to have a size of leεε than 5μm when the amount of whey protein is lwt.% or 2wt .% . When the amount of whey protein is 5wt .%, only 2 passeε through the homogeniser are required.

TABLE IX

The whey protein uεed iε a commercially available concentrate, sold under the name ' Lactalbumen 70' and available from Milei, Stuttgart, Germany.

TABLE X

Examples 10 and 11 Whey protein based dressings

Example 2 is repeated but the emulsion is acidified to a pH of 3.5 or 4.5, and NaCl is added to achieve 3xl0 ⁴ ppm chloride ions. The critical stress of the resulting emulsion having a pH of 3.5 and a temperature of 5°C at tanδ=l is 363Nm ^"2 (=363Pa) . The critical stresε of the reεulting emulεion having a pH of 4.5 and a temperature of 5°C at tanδ=l is 200NtτT ² (=200Pa) .

(The critical stress is measured by a Carrimed™ controlled stress rheometer, using parallel plate geometry. The oscillation mode of the rheometer is set at a frequency of 1Hz and the applied stress is increased linearly from O.OδNm ^"2 (=0.08Pa) to an end stress which is significantly greater than that required to give tanδ=l.)

Example 12 Whey protein based dressings

Example 1 is repeated up to the homogenisation step for a whey based dreεεing εhown in Table XI; locust bean gum is added immediately after the potasεium εorbate. After homogeniεation, the emulεion iε cooled to 45°C, acidified with glacial acetic acid to pH 4, and NaCl solution is added until a concentration of 1.5wt.% is achieved.

A spoonable dressing is obtained having a Stevens value of 22.

TABLE XI

The whey protein used is a commercially available concentrate, sold under the name 'Lactalbumen 70' and available from Milei.

Example 13 Egg protein based dressing

An egg protein based dressing is prepared using the ingredients shown in Table XII and in accordance with the process described in Example 1; the xanthan gum is dissolved directly in the water without slurrying. The mixture is homogenised at 13790kNm ^'2 (2000psi) .

COMPARATIVE EXAMPLE C

A traditional dressing is prepared, using the ingredients shown in Table XII, by slurrying the xanthan gum in 10% of the oil, disεolving the remaining ingredients in the water, and adding the xanthan/oil slurry thereto. The mixture is homogenised at 13790kNπT ² (2000pεi) .

Figure 1 shows the in-mouth breakdown profiles in terms of texture for the dresεingε of Example 13 and Comparative Example C. It can be εeen that the dreεεing of Example 13 haε an advantageouε faster breakdown in the

mouth; this is a consequence of the fact that it contains lesε thickener (xanthan gum) .

The dreεεing of example 13 has a consiεtency comparable to that of the dreεsing of comparative example C, even though it contains a significantly smaller amount of xanthan gum.

TABLE XII