WO2008000913A1

WO2008000913A1 - Improving of texture of dairy products

Info

Publication number: WO2008000913A1
Application number: PCT/FI2007/050397
Authority: WO
Inventors: Markku Anttila; Barbara Kankaanpää-Anttila; Matti Sepponen; Hannele Timonen; Karin Autio
Original assignee: Oy Linseed Protein Finland Ltd
Priority date: 2006-06-30
Filing date: 2007-06-28
Publication date: 2008-01-03
Also published as: FI20065456A0; EP2034849A1; WO2008000913A9; FI20065456L

Abstract

The invention relates to food technology and is concerned with dairy products, especially yoghurt that in addition to standard ingredients comprises soluble flax fiber and at least one enzyme, particularly the transglutaminase enzyme. In addition the invention is concerned with the combined use of soluble flax fiber and transglutaminase enzyme in dairy products to improve the texture and process stability of the products and to prevent syneresis.

Description

Improving of texture of dairy products

The invention relates to food technology and is concerned with the combined use of soluble flax fiber and transglutaminase enzyme in dairy products, especially in yoghurts and more specifically in non-fat yoghurts, to improve the texture and process stability of the products and to prevent syneresis. The invention is further concerned with dairy products, especially yoghurt, that in addition to standard ingredients comprise soluble flax fiber and at least one enzyme, particularly the transglutaminase enzyme.

Background of the invention

Yoghurt is the best known of milk-based sour milk products. A number of yoghurt types exist, but all of them contain the same two lactic acid bacterial species, Streptococcus ther- mophilus and Lactobacillus delbrueckii spp. bulgaricus. The starter may additionally con- tain small amounts of other species of the genus Lactobacillus as well as Bifidobacterium and Enterococcus species.

Various temperatures and ripening times can be used in the production of yoghurt. The principle is a simple one. Conditioned milk is pasteurized at 74°C for 30 minutes or at 90°C for at least five minutes, cooled to the ripening temperature, starter bacteria Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus are added and incubation is carried out for 12 to 16 hours at 30°C or for 4 to 6 hours at 41 °C. A fermentation of longer duration will increase the production of a taste typical for yoghurt. After ripening, the yoghurt is cooled and packed.

During production, yoghurt mass is susceptible to stresses due to mechanical processing, causing a possible decrease in the yoghurt's viscosity. Improvements in the stress resistance, viscosity, consistency, appearance and mouth feel of the mass have been attempted, especially in low-fat or non-fat yoghurts, by adding various stabilizers or by increasing the solid matter content of the yoghurt milk either by evaporating the milk's aqueous portion or by adding milk-based powders. As low-fat yoghurts are becoming more common, fat-free milk or whey powder has become a popular ingredient in yoghurt. The powders are used in attempts to compensate for the loss of stability of texture due to the removal of fat. A recommended amount of supplementation is 3 to 4%, a greater amount than this may lead to a powdery taste. In addition, at high concentrations the product price will begin to increase too high for the manufacturer. Stabilizers have begun to find use as substitutes for milk powder supplements, because the producers aim to produce yoghurt at a price as low as possible per kilogram. Gelatin, pectin, starch and agar are the most commonly used stabilizers in yoghurt. Of all food-grade gels the one obtained with gelatin comes closest to the ideal gel. Yoghurt manufacturers, however, would like to replace this animal-based protein with a vegetable-based stabilizer, by which an equally good final product would be achieved. Such a stabilizer has, however, not been found yet.

Non-fat yoghurt presents problems in the preservation of texture, because during produc- tion and storage of yoghurt the product exhibits syneresis, whereby whey separates from the rest of the mass to the product's surface as a transparent layer. In industrial yoghurt production the protein precipitate is stirred in a fermentation tank during the final stages of fermentation or in a cooling tank, pumped using plate or tube coolers, the yoghurt is supplemented with fruit, berries or aromas, followed by pumping to the filling or packing machine. In the manufacture of pasteurized, UHT yoghurt or yoghurt with a prolonged shelf- life, the yoghurt can also be subjected to post-fermentation heat treatments. Due to mechanical treatments the yoghurt may become less viscous or, in extreme cases, separation of whey occurs. By adding stabilizers to the yoghurt, thinning of the mass can be prevented and whey prevented from being separated. It is also intended to increase and maintain the product's de- sirable properties such as e.g. viscosity, texture, appearance and mouth feel, with stabilizers.

On the surface of a linseed there is a thick and compact mucilage layer that constitutes 4 to 8% of the seed's weight. The mucilage consists, among other things, of several polysaccharides, the pentosans, firmly attached to the seed's coat part. In recent years, a great deal of research has been conducted with regard to the isolation and use of this soluble fiber in various parts of the world (US 5,260,282. WO 93/16707, WO 96/22027). The soluble fiber of flax binds plenty of water and also functions as an emulgator. Addition of flax fiber to non-fat yoghurt has been tested because of its thickening and water-binding properties. Syneresis occurring in the product during storage has, however, presented a problem. The polymeric structure formed by caseins also flocculates, causing spon- taneous loss of water. For this reason it has been speculated how to make the flax polysaccharide function in the product more effectively than before so that the yoghurt would endure the three weeks' storage time without excessive syneresis. Accordingly, a process enhancing the functionality of flax polysaccharide should be found, whereby the substance could be used as stabilizer in yoghurt.

The transglutaminase enzyme (TG) has been utilized in food industry in improving the texture of several different products. TG forms covalent linkages between the side chains of two different amino acids, the lysine and glutamine residues, and also catalyzes the gelling reaction of the milk protein casein. With TG it is possible to influence the gelling, gel strength, elasticity and water-binding capacity of a protein.

For the expensive transglutaminase isolated from mammals a more lucrative form, the microbial transglutaminase (MTG) produced by using Streptoverticillium mobaraense has been developed. For instance the separation of whey occurring in yoghurt can be prevented by adding MTG, since MTG increases the water-binding capacity of the gel. The MTG reaction also makes it possible to produce various dairy products such as low-fat ice-cream and cheese or these same products with a low solid matter content (Motoki & Seguro, Transglutaminase and its use for food processing, Trends Food Sci. Technol. 9:204-210. 1998).

Studies in which TG has been utilized in yoghurt production, are described in the following. Fεergemand et al. (Transglutaminase: effect on instrumental and sensory texture of set style yoghurt, Milchwissenschaft, 54, 563-566, 1999) studied the effect of transglutaminase on yoghurt texture. Transglutaminase has been found to cross-link unheated milk proteins to a small extent, whereas the cross-linking effect of TG increases considerably after heat treatment of milk proteins. In the study of Lorenzen et al. (Lorenzen P. et al, Einfluss der enzy- matischen Quervernetzung von Milcheiweiss auf die Eigenschaften geriihrter Joghurt- und Dickmilcherzeugnisse, Kieler milchwirtschaftliche Forschungsberichte, 2. Vierteljahre; 97- 115) it was found that there was no significant difference in the rheo logical and organoleptic properties of yoghurts if TG had been added to the yoghurt milk or if a milk protein solution treated with TG was added to yoghurt milk before its fermentation. Instead the TG yoghurts had a higher viscosity and lower syneresis than yoghurts produced using the same methods without enzyme addition. In the study it was also found that in yoghurts produced by adding TG directly into the yoghurt milk, aggregates could be observed which had been formed through enzyme activity and not broken down upon stirring. If enzyme action had taken place in the milk protein solution that was subsequently added to yoghurt milk, the result was a product having a soft texture. The amount of enzyme used in yoghurt milk varied with the protein content. The enzyme was allowed to act in 40⁰C yoghurt milk for 120 minutes as the pH remained at the normal level of milk's pH (6.6 to 6.7). After the incubation, enzyme action was stopped by heating the milk at 80⁰C for 1 minute. Stirring of the yoghurt took place with an electrical blender bar for a total of 5 minutes. The yoghurt batches in question were, however, produced in a small scale, whereby it is not known whether the aggregates resulting from the action of TG had broken down in the pump- driven pipe transfers required to be carried out in industrial yoghurt production.

Summary of the invention

It has now been surprisingly found that dairy products possessing a good texture and process stability can be produced by incorporating both soluble flax fiber and transglutaminase enzyme into the products. The invention is thus directed to the combined use of soluble flax fiber and transglutaminase enzyme in dairy products, especially in non-fat dairy products, and most especially in non-fat yoghurt.

The invention is furthermore directed to a dairy product, especially yoghurt, and most especially non-fat yoghurt, possessing a good texture and process stability and comprising soluble flax fiber and transglutaminase enzyme in addition to standard ingredients. In the non-fat yoghurt according to the invention the separation of whey during storage is prevented or at least markedly decreased and the yoghurt's process stability is improved. Brief description of the drawings

Figure 1 depicts a production chart of flax yoghurt on the process scale. This is a process typical of mixed yoghurt, except for the addition of enzyme with the starter, as well as dif- ferent endurance tests.

Figure 2: Results of preliminary TG experiments from the mean values of compression forces for the whole monitoring and measurement period and of syneresis 14 days after production.

Figure 3: Mean values of compression force measurement results and syneresis results of preliminary LF+TG experiments 14 days after production of yoghurt batches (LF = LinoFi- bre, soluble flaxseed fiber, tA g/1 = 0.10 g/1, tB g/1 = 0.12 g/1, tC g/1 = 0.15 g/1). Figure 4: Mean values of compression force measurement results and syneresis results of preliminary LF+TG+WPC experiments 14 days after production of yoghurt batches (WPC = whey protein concentrate, wA% = 0.15%, wB = 0.25%, wC% = 0.43%). Figure 5: Results from the mean values of maximum compression forces for the whole monitoring and measurement period and from syneresis for 14 days' monitoring measurements after production, for batches produced using the same formula. The "old" batches had been produced two weeks before the fresh batches.

Detailed description of the invention

Soluble flax fiber can be isolated from linseed by a variety of methods. In the method patented by Kankaanpaa-Anttila and Anttila (WO 96/22027) the linseeds are cold pressed and hot pressed, whereby the oil is separated from the seed. After this the seeds are subjected to alkaline extraction, after which any insoluble fiber is separated. Protein and flax mucilage are next precipitated first with hydrochloric acid and then with ethanol. The isolated flax protein and mucilage is air dried and packed. In its production Oy Linseed Protein Finland Ltd currently uses a more gentle method, in which the seeds are extracted with water and soluble fiber is precipitated from the resulting flax mucilage. After drying and milling the fiber powder is ready for use. Attempts have been made to improve the solubility of the flax and simultaneously to reduce its caking upon mixing with liquid by first agglomerating the fiber into larger powder particles that have again subsequently been milled to smaller particles. When mixing directly into a liquid it is, however, beneficial to blend the flax fiber first with another powder or e.g. with sugar. This will better incorporate the fiber into the product and thus prevent formation of clots.

The flax fiber used in the experimental part of this application (LinoFibre, manufactured by Oy Linseed Protein Finland Ltd.) comprises approximately 73% of carbohydrate (of this, the total pentosan content is approximately 29 to 30%), 7% of protein, less than 0.3% of fat, less than 10% of moisture, 7% of ash. Total dietary fiber in LinoFibre constitutes ap- proximately 80% and soluble fiber 70%. Flax polysaccharide is pale-colored, odorless and tasteless. When fully dissolved, it is completely colorless.

Transglutaminase forms linkages between lysine and glutamine residues. Transglutaminase also catalyzes the gelling reaction of casein, myosin, whey protein, hen egg proteins, soya proteins etc. (Kurth and Rogers, Transglutaminase catalyzed cross-linking of myosin to soya protein, casein and gluten, J. Food Sci. 49:573-76). Previously it has not been studied to any significant extent whether flax mucilage fraction (polysaccharide) or proteins of the flax protein fraction can be cross-linked by means of transglutaminase to whey, caseinate or casein. Flax's intrinsic protein has not been tested for yoghurt applications mainly because of consequent color and flavor problems, but purified, spray-dried isolate could possibly come into question. As the research object of this study was used, however, only flax polysaccharide having a protein fraction rich in glutamic acid required for the TG reaction, whereas the lysine content is lower (Table 1).

Table 1. Amino acid composition of soluble flax fiber (LinoFibre).

Content Content

Amino acid g/kg Amino acid g/kg

Cystine 2.4 Isoleucine 2.1

Methionine 0.9 Leucine 3.2

Aspartic acid 4.1 Tyrosine 0.9

Threonine 1.6 Phenylalanine 2.0

Serine 2.7 Histidine 0.9

Glutamic acid 17.9^ Ornithine <0.1

Proline 1.4 Lysine 3.1

Glysine 6.9 Arginine 6.6

Alanine 1.8 Hydroxyproline <0.1

Valine 2.1 Tryptophan 1.0

Ammonia 2.1

' Glutamine is included in the glutamic acid content shown in the table.

In addition to conventional ingredients, the dairy product of the invention comprises both soluble flax fiber and transglutaminase enzyme. In the investigations it was observed that mere transglutaminase or, on the other hand, mere soluble flax fiber is not enough to stabilize yoghurt texture sufficiently. The soluble flax fiber participates in the transglutaminase reaction together with the casein thus strengthening the texture of enzyme-containing yoghurt.

Preferred dairy products of the invention are yoghurts and other products based on yoghurt such as beverages and desserts, especially low-fat or non-fat yoghurts. Other dairy prod- ucts, the texture and process stability of which is improved by combined use of flax fiber and transglutaminase enzyme, i.e. products, in which transglutaminase prevents phase separation of casein while flax fiber confers texture on the product, are for instance quark and other products based on quark, among other things spreads and desserts, cottage cheeses produced without rennet, sour milk products such as sour milk and curd milk and products derived therefrom, leavened cream products such as creme fraiche, sour cream and curd cream, as well as yoghurt- or quark-based sorbets used in confectioneries.

The greatest advantage by the combined use of flax fiber and transglutaminase enzyme is achieved in non-fat or low- fat dairy products. A foodstuff may be termed non-fat provided that its fat content is not more than 0.5 g/100 g or /100 ml. In foodstuffs termed low- fat the fat content is not more than 3 g/100 g or 1.5/100 ml. In dairy products, low- fat yoghurt comprises fat approximately 0.5 to 1.0%, sour milk 0.5%, sour whole milk 1% and milk usually less than 1.5%. In fat-free yoghurt the fat content is not more than 0.1%.

In order to achieve the desired texture-stabilizing effect, a sufficient amount of transglutaminase and flax fiber must be added during the production of the dairy product. The amount of the enzyme used varies with the milk's protein content and the properties of the product being manufactured, but due to the combined effects of the flax fiber and transglutaminase the amount of enzyme can be lowered from those recommended by the manufacturers. For instance, in producing the yoghurt of the invention, to the yoghurt milk with a protein content of approximately 3.5% is added transglutaminase having an activity of 100 U/g in an amount of 0.10 to 0.20 g per liter of milk, i.e. 10 to 20 U/l. More preferably, in producing the yoghurt of the invention, transglutaminase is added at 13-17 U/l to the yoghurt milk, and most especially at approximately 15 U/l. The TG concentrations recommended by the manufacturer are, however, considerably higher (35 U/l or 20 to 50 U/l, depending on the time of addition).

The amount of flax fiber in the yoghurt of the invention can be 0.04 to 0.08% (w/v) calcu- lated on the basis of the volume of milk used as starting material, at a pentosan content of the flax fiber of approximately 30%. Most preferably the yoghurt of the invention comprises approximately 0.06% of flax fiber, calculated on the basis of the milk used as starting material.

The amount of flax fiber and transglutaminase to be added into the dairy product is naturally dependent on, besides the flax fiber and the enzyme used, also on the dairy product being produced and on other components, and can be optimized in an ordinary manner for each application.

When using transglutaminase in yoghurt milk, the addition is made after pasteurization and cooling of the yoghurt milk at a time when whey proteins have already unfolded. Before addition of transglutaminase, the yoghurt milk is cooled to optimum temperature, i.e. to 50⁰C at the maximum. The enzyme addition can be made before addition of the starter in order to ensure that it will have the time to act within its optimum pH range, before the starter lowers the pH to a value close to 4.3. In practice it, however, turned out that TG has the time to act long enough before the starter lowers the pH to a range that is unfavorable to the enzyme even if the starter and the enzyme are added simultaneously.

In one embodiment, the yoghurt of the invention also comprises whey protein concentrate, for example 0.10 to 0.30% (w/v), calculated on the basis of the milk used as starting material. Preferably the yoghurt of the invention comprises approximately 0.15% of whey pro- tein concentrate calculated on the basis of the milk used as starting material, with the whey protein concentrate having a protein content of approximately 65%.

If desired, also other stabilizers, such as starch, may be added to the yoghurt according to the invention.

In organoleptic assays the texture and appearance of the yoghurt of the invention were generally considered good and even excellent. The product's process stability was also excellent.

Examples

In this study, utilization of transglutaminase in flax fiber yoghurt as one alternative ingredient in order to improve texture was elucidated. Transglutaminase was tested in flax fiber yoghurt with flax fiber alone as well as in combination with flax fiber and whey protein. By varying the concentrations of ingredients used for the yoghurt we aimed to find a combination having a durable texture and an impeccable organoleptic quality. The possible floccula- tion and granulation of the combination used as stabilizer were organoleptically studied always after completion of each set of experiments as well as after monitoring measurements.

The aim was to develop the texture and process stability of yoghurt, especially non-fat yoghurt, containing soluble flax fiber. In developing the process the aim was also to prevent the separation of whey or at least to considerably reduce it in yoghurt during storage. The intention was to develop a compensatory method for the use of gelatin in both non-fat and fat-containing yoghurts and thus confer competitive rheological properties upon the product. A requirement was also that the process would be competitive with other commercial stabilizers in the same price category.

Test materials

LinoFibre flax fiber

The flax fiber used in the study was agglomerated and milled LinoFibre manufactured by Oy Linseed Protein Finland Ltd. The particle size used was 125 to 250 μm. LinoFibre comprises approximately 71% of carbohydrate, of which the total pentosan content is approximately 30%. The powder comprises approximately 8% of flax protein. LinoFibre was added to cold yoghurt milk, mixed into crystalline sucrose before homogenization of milk. Mixing with sucrose facilitated dispersing of the flax polysaccharide and its solubility in milk.

Ajinomoto transglutaminase

In the experiments Ca²⁺-dependent ACTIVA-MP transglutaminase was used, which is manufactured by the Japanese Ajinomoto Co., Ltd. The enzyme preparation possesses an activity of 100 Ug^"1 and contains 1% of enzyme. In ACTIVA-MP, lactose at 90% and mal- todextrin at 9% have been used as carriers. The enzyme has shown to have optimal activity at 50⁰C and within a pH region of 5 to 8. The enzyme preparation was used as such without purification. TG was added to yoghurt milk at 43°C dissolved in started dilution after tank pasteurization.

Raw milk was separated using a Seital separatore sentrifugo separator (capacity 500 1/750 1/h) and tube pasteurized at 72°C for 15 seconds with a Fischer HPM (500 1/h) plate pasteurizer, after which the milk was cooled to approximately 15 degrees. The fat remaining in the milk was about 0.07% and protein content was the normal 3.5%. Whey protein powder

HIPROTAL 865 is ultrafiltered whey protein powder manufactured by Frieslands Foods Domon in the Netherlands. The powder comprises approximately 19% of lactose, 65% of protein, 6.5% of minerals, 6% of fat and 3.5% of moisture. In producing the flax fiber yo- ghurt, the whey protein powder was mixed with the other solids and added to cold yoghurt milk before homogenization of the milk.

Fat-free milk powder

The Valio fat-free milk powder manufactured by Valio Oy comprises 35% of protein, 52% of lactose, less than 1% fat and 0.42% of sodium Fat-free milk powder was used in control yoghurt batches, whose yoghurt milk was supplemented with 2.25% of milk powder. The fat-free milk powder was added to cold yoghurt milk before homogenization of the milk.

Starter YC280 The frozen mesophilic DVS starter YC280 from the Danish starter culture manufacturer CHR Hansen was used in the study for fermenting the yoghurt milk. The optimal fermentation range for the starter is at pH 4.5 to 4.8. The dosing amount recommended by the manufacturer is 0.02%. In the experiments a starter concentration was used that was slightly higher than recommended in order to ensure that fermentation was properly proceeding already at an early stage of fermentation.

Preparation of samples in fermentation bath

Preliminary experiments with transglutaminase were carried out in a fermentation bath manufactured by Tankki Oy. Heating of yoghurt milk to homogenization temperature, tank pasteurization, cooling to fermentation temperature, fermentation and cooling to 20⁰C were carried out in the fermentation bath. When necessary, sample batches were mixed manually. The experimental batches prepared in the fermentation bath were subjected to endurance tests with a small Gaulin homogenizer without pressure increase.

Test runs in fermentation bath

In the fermentation bath tests it was initially elucidated what kind of effects TG had in flax fiber yoghurts (Table 2), and the appearance of flax yoghurt containing enzyme was exam- ined. After this, the optimal enzyme concentration for flax yoghurt was screened. In the latest set of experiments, used for determining an appropriate enzyme concentration, four sample batches without addition of solids were produced in the fermentation bath (Table 3).

Table 2. Experimental design of preliminary TG experiments

Experiment Fat-free Sucrose LinoFibre TG Starter milk

Control 3.2 1 1.2% - - 0.05%

TG 3.2 1 1.2% - 0.35 g/1 0.05%

LF 3.2 1 1.2% 0.06% - 0.05%

LF+TG 3.2 1 1.2% 0.06% 0.35 g/1 0.05%

Table 3. Experimental design of preliminary experiments for screening of optimal TG concentration in LF yoghurt

Experiment Fat-free Sucrose LinoFibre TG Starter milk

LF control 3.2 1 1.2% 0.06% - 0.05%

LF+TG 0.10 g/1 3.2 1 1.2% 0.06% 0.10 g/1 0.05%

LF+TG 0.12 g/1 3.2 1 1.2% 0.06% 0.12 g/1 0.05%

LF+TG 0.15 g/1 3.2 1 1.2% 0.06% 0.15 g/1 0.05%

After finding the optimal enzyme concentration, preliminary experiments were conducted in fermentation bath with enzyme-containing flax yoghurt that also contained whey protein concentrate (WPC). With this series of experiments it was intended to elucidate whether whey protein concentrate would be suited to be used in combination with TG and which concentration would yield the best possible result. Four sample batches were produced according to the experimental design shown in Table 4. Table 4. Experimental design of preliminary WPC+TG experiments

Experiment Fat-free Sucrose WPC LinoFibre TG Starter milk

LF+TG (Control) 3.2 1 1.2% - 0.06% 0.15 g/1 0.05%

LF+TG+WPC 3.2 1 1.2% 0.15% 0.06% 0.15 g/1 0.05%

0.15%

LF+TG+WPC 3.2 1 1.2% 0.25% 0.06% 0.15 g/1 0.05%

0.25%

LF+TG+WPC 3.2 1 1.2% 0.43% 0.06% 0.15 g/1 0.05%

0.43%

After small-scale fermentation bath experiments yoghurt batches were produced on the process scale according to formulae that were considered successful.

Experimental batches on process scale

In total 24 batches of flax yoghurt and three control yoghurt batches were produced on the process scale in the experimental dairy of the milk technology department of the University of Helsinki. A flow chart of the process is shown in Figure 1. In the first experimental batches it was elucidated what kind of effects TG had in flax fiber yoghurts, and the optimal concentration of flax fiber in yoghurt was assessed.

Chemical and physical methods of analysis

Measurement of compression force

Measurement of compression force was carried out at 1, 4, 7, 14 and 21 days after production of the yoghurt with a Texture Analyser TA-XT2i^® apparatus using a "heavy duty probe adaptor" measurement probe, i.e. a piston made of vinyl and having a diameter of 40 mm. Compression force and yoghurt's sensory consistency usually show good correlation. The more consistent the sample is, the higher is the compression force.

Measurement of whey separation The separation of whey, i.e. syneresis occurring in yoghurt was measured by pouring 80 ml of yoghurt samples produced in fermentation bath into 100-ml measuring cylinders. 800 ml of process scale yoghurt samples were poured into a 1-1 measuring cylinder. Attempts were made to monitor the separation of whey at 1, 4, 7, 14 and 21 days after production of the yoghurt. Separation of whey was expressed on a volume percent basis. The allowed amount for syneresis is 2% v/v.

Results

Optimum content ofLinoFibre in yoghurt

Based on experimental batches, a LinoFibre content of 0.06% yielded the best texture in non-fat flax fiber yoghurt.

Results of preliminary TG experiments

According to preliminary experiments the amount recommended for yoghurt by the manufacturer, 0.35 g/1, was a dosage far too high, because at this concentration the texture of the mass became flocculated and "gritty". Enzyme-containing samples had a watery mouth feel and tasted more sour than corresponding samples without enzyme. This was obviously due to the fact that the difference in mass resulting from enzyme processing brought about a different sensation of sourness in the mouth. A larger amount of free fluid remained between the "grits", from which the watery and sour perception was more pronounced on the tongue. Based on the initial preliminary TG experiments a decision was made to continue preliminary experiments at lower TG contents. Shown in Figure 2 are the results of preliminary TG experiments at the considerably lower concentration of 0.10 g/1.

From the results obtained with Texture Analyser measurements it is seen that it is possible to improve the yoghurt's texture quite much with the enzyme content used in the experiment. The LF+TG yoghurt reached the highest value, i.e. it had the highest consistency. The yoghurt containing enzyme alone was the second in consistency. Differences in consistency between distinct batches remained proportionately similar regardless of whether the sample in question was one stressed by homogenizer or an unstressed one. Based on results obtained with Texture Analyser measurements it could also be established that the enzyme neither makes the yoghurt any longer more thick nor otherwise functions in yoghurt visibly during cold storage.

In organoleptic assays of the yoghurts it became clear that the yoghurt LF+TG yielded the thickest texture and fullest mouth feel. This sample had the most pleasant feel and taste compared with the other samples. Slight syneresis occurred in measuring cylinders only with the homogenized controls and the LF sample. In the organoleptic assays made during the monitoring period it was, however, noticed that some whey was present in the yoghurt bowl in all samples, to the largest extent in the TG yoghurt.

Based on preliminary TG experiments it was worthwhile to continue adding TG into flax fiber yoghurt, because the enzyme excellently improved the yoghurt's texture and it in any case required a suitable additional stabilizer, for which the flax polysaccharide seemed well suited.

Optimum enzyme content in flax yoghurt

The results of compression force measurements and syneresis are shown in Figure 3. The control yoghurt had a clearly more loose texture than batches that did not contain TG. The thickest texture and highest consistency was found in the sample that contained the highest enzyme level, LF+TG 0.15 g/1, although the batch LF+TG 0.12 g/1 was only slightly looser. In addition the batch stressed with homogenizer, LF+TG 0.15 g/1, had the best mouth feel. Flocculation was not observed in any of the batches that had undergone stress. In non- stressed samples, "grits" resulting from the action of TG could, however, be observed. When fresh, all batches were mild and brisk- tasting. Towards the end of storage the taste became slightly sour, though this is a feature very typical of yoghurt flavor. In non-stressed samples only the LF control did not exhibit syneresis, but after homogenization it exhibited a clearly stronger syneresis than the other samples. In homogenized samples containing 0.12 and 0.15 g/1 enzyme, slight syneresis occurred only after one week after production, and the level did not increase by the two weeks' monitoring measurement. Accordingly, the formula containing LF+TG 0.15 g/1 Activa MP made its way further. Optimum content of whey protein concentrate in LF+TG yoghurt

Sample LF+TG 0.15 g/1 of the previous set of experiments served as control in the four- sample set of experiments produced in fermentation bath. Shown in Figure 4 are the results obtained from maximum compression forces and syneresis.

Small "grits" and fiocculation caused by enzyme activity could again be observed in unstressed batches. In batches that had undergone homogenizer stress the mass was uniform and also otherwise impeccable in appearance. The batches containing 0.15 and 0.25% of WPC were the most pleasant in mouth feel. On the other hand the batch containing the highest amount of WPC had the most white and soft-looking appearance. Its mouth feel was also very soft, despite being slightly loose.

During the monitoring period, syneresis was not observed in any of the experimental batches. Only upon opening of the yoghurt beaker a minor streak of whey was seen on the surface. The samples of this experimental series thus showed good retention of whey. From the results of consistency measurements it could be seen that of the samples that had undergone homogenizer stress, the highest compression force was required by sample LF+TG- control. The difference to sample LF+TG+WPC 0.15% was, however, very small. In masses that had undergone homogenizer stress, the magnitude of compression force required decreased with the increasing amount of whey protein added to the sample. Based on this experimental design it is thus obvious that addition of WPC in higher concentrations results in a more loose mass.

LF+TG 0.15 g/1 and LF+TG+WPC 0.15% were thus very similar in thickness and texture. LF+TG+WPC 0.15% had a slightly softer appearance than LF+TG 0.15 g/1. Any fiocculation should, however, not be mentioned for the LF+TG 0.15 g/1 sample. With a small whey protein addition the mass will be made to look slightly smoother and have a smoother mouth feel.

It was decided to include the formulae LF+TG 0.15 g/1 and LF+TG+WPC 0.15% for further development. The formulae were executed on the process scale and stressed by a rotary lobe pump, whereby it was seen whether the masses exhibited differences in process stability.

Process scale experiments with formulae found to be best

Towards the end of the study, experimental batches on the process scale were prepared according to the experimental design described in Table 5. Using the same formula, double batches were produced for organoleptic assays so that the first batches were two weeks older than the fresh batches produced at the second time. The results of compression forces and syneresis over the monitoring measurements period are shown in Figure 5.

Table 5. Ingredients of process scale yoghurt batches

Batch Fat- SucLino- fat-free WPC TG Starch Starter free rose Fibre milk milk powder

LF+starch.ⁿ⁾ 28 1 1.2% 0.06% - - - 0.6% 0.05%

LF+TG^*2) 28 1 1.2% 0.06% - - 0.15 g/i - 0.05%

LF+TG+WPC^* 28 1 1.2% 0.06% - 0.15% 0.15 g/i - 0.05%

3)

MJ 2.25%^*4) 28 1 1.2% 0.06% 2.25% - - - 0.05%

^*l) LinoFibre+starch *²⁾ LinoFibre+Transglutaminase

^*3) LinoFibre+Transglutaminase+whey protein concentrate *⁴⁾ Milk powder control 2.25%

Results of organoleptic assays

In the assessment of organoleptic quality the samples were examined for appearance, texture as well as for odour and taste. All batches of the invention received almost full scores for appearance, the same was true for texture. Taste and odor were also considered generally good, though slightly too sour. The starch-containing flax fiber yoghurt was, however, considered slightly inferior to other presented yoghurts with regard to both appearance and texture. Among the flax fiber yoghurts, the LF+TG+WPC yoghurt and the LF+TG yoghurt were considered the best as a whole. Since these yoghurts were in all organoleptic assays considered to be very similar with regard to their properties, it is profitable to choose the less expensive one. The fewer different ingredients needs to be used for a yoghurt, the easier and more profitable will be its production.

Claims

1. A dairy product, characterized in that it comprises soluble flax fiber and transglutami- nase enzyme.

2. The dairy product according to claim 1, characterized in that it is non-fat or low- fat.

3. The dairy product according to claim 1, characterized in that it is yoghurt, another product based on yoghurt, such as a beverage or dessert, quark, another product based on quark, such as a spread or dessert, cottage cheese, sour milk product such as sour milk or curd milk or a product derived therefrom, leavened cream product such as creme fraiche, sour cream or curd cream, or a yoghurt- or quark-based sorbet used in confectioneries.

4. The dairy product according to claim 1, characterized in that it is a yoghurt comprising 0.04 to 0.08% (w/v) of soluble flax fiber and 13-17 U/l of transglutaminase enzyme, calculated on the basis of milk used as starting material.

5. The dairy product according to claim 4, characterized in that it comprises approximately 0.06% of soluble flax fiber and approximately 15 U/l of transglutaminase enzyme, calculated on the basis of milk used as starting material.

6. The dairy product according to claim 4 or 5, characterized in that it comprises whey protein concentrate.

7. The dairy product according to claim 6, characterized in that it comprises 0.10 to 0.30% (w/v) of whey protein concentrate, calculated on the basis of milk used as starting material.

8. The dairy product according to any one of claims 4 to 7, characterized in that the pro- tein content of the milk used as starting material is approximately 3.5% and the pentosan content of the soluble flax fiber is approximately 30%.

9. A process for the production of the dairy product according to any one of claims 4 to 8, characterized in that the soluble flax fiber is added to pasteurized and optionally separated raw milk before of after homogenization.

10. The process according to claim 9, characterized in that the enzyme is added to yoghurt milk before addition of starter or together with the starter.

11. The dairy product according to any one of claims 1 to 8, characterized in that due to the soluble flax fiber, the amount of transglutaminase enzyme required is smaller than in a transglutaminase-containing dairy product produced without soluble flax fiber.

12. Combined use of soluble flax fiber and transglutaminase enzyme in dairy products to improve the texture and process stability of the products.