doi: 10.1111/1471-0307.12130
ORIGINAL RESEARCH
Effect of production season on protein fraction content in milk of various breeds of goats in Poland A N E T A B R O D Z I A K , 1 * J O L A N T A K R Ó L , 2 J O A N N A B A R Ł O W S K A 2 and ZYGMUNT LITWIŃCZUK1 1
Department of Breeding and Protection of Genetic Resources of Cattle, University of Life Sciences in Lublin, Akademicka 13, Lublin 20-950, Poland, and 2Department of Commodity Science and Processing of Raw Animal Materials, University of Life Sciences in Lublin, Akademicka 13, Lublin 20-950, Poland
Milk of various goat breeds was analysed to assess the effect of production season on content of basic chemical components, with regard to whey proteins. Milk of goats in the productive herds (white and coloured coat) contained significantly (P < 0.01) more total protein, casein, fat, dry matter and functional whey proteins. The production season significantly determined the content of total protein (P < 0.01), casein (P < 0.01) and whey proteins (P < 0.05), including a-lactalbumin (P < 0.01) and lactoferrin (P < 0.01). A higher content of total protein and casein was found in the autumn–winter season and the content of whey proteins was higher in the spring–summer period. Keywords Goat’s milk, Protein fractions, Whey proteins, Technological suitability.
INTRODUCTION
*Author for Correspondence: E-mail:
[email protected]. pl © 2014 Society of Dairy Technology
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Cow’s milk dominates global milk production, but milk from other animals is important in specific regions, countries and local contexts. Goat’s milk constitutes only 2.1% of global milk production (i.e. approximately 15 million tons), but is relatively significant in sub-Saharan Africa, accounting for 10% of the total, and parts of South Asia and of East and South-East Asia (excluding China) (Gerosa and Skoet 2012). Europe produces only 2.5% of the world’s goat’s milk, but it is the only continent where goat’s milk production has significant economic importance and organisation. In European countries, such as Poland, goat’s milk production takes place on a small scale and most of the milk is used by households or families (Trancoso et al. 2010). In Poland, goat’s milk is the second most important dairy product after cow’s milk. The size of its production in 2011 amounted to 19.8 thousand tons, which represents a small part (approximately 0.7%) in the production of this raw material in Europe (FAOSTAT 2013). Interest in a healthy diet has resulted in increased interest in goat’s milk, which is considered to be a
dietic and therapeutic product of high nutritional value and is classified as a functional food (Michaelidou 2008; Silanikove et al. 2010; Renna et al. 2012). In terms of the content of basic components, goat’s milk is similar to cow’s milk; however, it differs in the qualitative composition of protein and fat (Silanikove et al. 2010; Renna et al. 2012). Goat’s milk, in comparison with cow’s milk, is less allergenic due to a smaller proportion of as1-casein (5% of total casein proteins), and in individuals with mutations that determine the ‘null’ as1-casein alleles (CSN1S1), there is complete elimination of the casein fraction (Ramunno et al. 2001). Lara-Villoslada et al. (2005) have also argued that the lower allergenicity of goat’s milk compared with cow’s milk results from the fact that the lower proportion of as1casein reduces sensitivity to a second protein allergen, that is the b-lactoglobulin (b-LG). According to Wroblewska and Jez drychowski (1999), in comparison with cow’s milk, the allergenicity of goat’s milk is approximately 72–73% lower in relation to a-lactalbumin (a-LA) and appro-ximately 96% lower in relation to b-LG. Furthermore, due to the differences in casein micelle structure and the size of fat globules, goat’s milk is characterised not only by faster
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digestion but also by higher digestibility than bovine milk. It may therefore be a valuable raw material for the production of food for infants and the elderly, as well as for people with allergies to cow’s milk (Kondyli et al. 2007; Ribeiro and Ribeiro 2010). It should also be mentioned that goat’s milk protein is digested faster and is easier to digest, and its amino acids are absorbed at a higher level by the human body (Ribeiro and Ribeiro 2010). Nevertheless, goat’s milk is unpopular amongst consumers due to restricted distribution and specific organoleptic characteristics. It is mostly consumed in the form of drinking milk and rennet cheeses. In Poland, the production of cheeses from goat’s milk occurs on a small scale, using traditional methods. The whey obtained, which is a rich source of a variety of proteins, is most often treated as a useless waste product and is discarded away (Kr ol et al. 2011). The nutrient content of goat’s milk depends on many factors that determine the productivity of the animals, such as genotype, reproduction, agrienvironmental and socioeconomic conditions, as well as management strategies, including feeding system and the associated production season (Barłowska et al. 2011; Mestawet et al. 2012). In Poland, the goats are mainly used for milk production, and mixed breed animals have been improved with imported breeds. The aim of this study was to assess the effect of the production season on the content of basic chemical components, particularly casein and whey proteins, in milk from goats of various breeds. MATERIALS AND METHODS
Animals and samples The research was conducted in 2010–2011. Six farms from the area of South-East Poland (the Podkarpacie region) were included in the study. At one of the farms, Alpine and Saanen goats were included in the control of milk utilisation. The goats at the remaining farms were not subject to milk recording but they were divided into two groups by coat colour, that is, coloured or white. The study included 475 samples of goat’s milk, including 259 samples from the spring–summer season (May–July) and 216 from the
autumn–winter season (October–November) (Table 1). The production season was predominantly associated with the lactation phase of goats. At all farms, the beginning of lactation fell on average in March and ended at the turn of October and November. In the spring–summer season, animals at all farms were grazed on pastures. However, in the autumn–winter season, goats were fed mainly with haylage. Animals were milked twice a day and the milk was measured individually. During milking, goats received ground grain in both seasons. Representative samples (350 mL) for analyses were collected from two entire milking procedures. All milk samples collected in plastic containers were transported under cold conditions to the laboratory of the Department of Commodity Science and Processing of Raw Animal Materials at the University of Life Sciences in Lublin (Poland). Milk samples from goats with a visually sick mammary gland were not collected.
Analysis of milk samples In all milk samples, the following parameters were determined: pH value – measured by the Pioneer 65 pH meter (Radiometer Analytical); density – measured by a lactodensimeter; rennet coagulation time – measured according to Shern’s method, expressed as the time of formation of casein flakes; somatic cell count (SCC) – measured with Somacount apparatus (Bentley Instruments Inc., Chaska, MN, USA); basic chemical composition, that is, the content of fat, protein, lactose and dry matter – measured with Infrared Milk Analyzer apparatus (Bentley Instruments Inc.); and the percentage of casein – measured according to the AOAC (2000). The concentrations of whey proteins, that is, a-LA, b-LG, lactoferrin and lysozyme, were analysed using reverse-phase high-performance liquid chromatography (RPHPLC). All samples were prepared as follows: 50 mL of raw milk was adjusted to pH 4.6 with 0.1 M HCl and allowed to stand at room temperature for about 1 h to allow the acid precipitation of caseins. Then, whey (7 mL) was taken from each of the samples separately and centrifuged at 5,600 g for 15 min. Finally, whey solutions were filtered through paper quality filter discs (diameter: 125 mm, density: 65 g/m2, grade: 3 h; Munktell, Germany) and 0.20-lm disposable sterile filters (Millipore type, GSTF, USA). The
Table 1 Distribution of analysed milk samples Season
Research year
Coloured goats in productive herd
White goats in productive herd
Alpine
Saanen
Total
Spring–summer
I II Total I II Total
57 57 114 50 21 71 185
52 48 100 50 46 96 196
13 13 26 13 12 25 51
10 9 19 12 12 24 43
132 127 259 125 91 216 475
Autumn–winter
Total
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supernatants in vials were kept refrigerated until further analysis, and 20 lL was injected into the chromatograph at the suitable time. The procedure of whey protein separation was based on the method elaborated by Romero et al. (1996) with modifications (Kr ol et al. 2011). Protein analysis was performed using the ProStar 210 model liquid chromatography system and UV-Vis ProStar 325 detector (Varian, USA). The measurements were carried out using the water/acetonitrile mobile phase by gradient elution and using the column NUCLEOSIL 300-5 C18 (Varian) of 250 mm length and 4.6 mm diameter. The mobile phase was solvent A (90% water, 10% acetonitrile) and solvent B (90% acetonitrile, 10% water), purchased from Sigma (Germany). The solvents were filtered through 0.45-lm filters (Millipore, USA) and degassed by using ultrasound. All chemicals were of HPLC analytical grade. The total analysis time for a single sample was 35 min, at a wavelength of 205 nm and column temperature of 37 °C. The analysis of reference substances was conducted under the same conditions. On the grounds of the obtained chromatograms, using program Star 6.2 Chromatography Workstation (Varian), qualitative and quantitative identification of each substance was performed. Calibration of the chromatographic system for whey protein determination was carried out by the external standard method. For this purpose, each protein was calibrated individually by injecting solutions of the standards (20 lL). These were purified proteins, that is, a-LA (≥85%), b-LG (90%) and lactoferrin (90%), all from bovine milk, as well as lysozyme (95%) from hen egg whites, which were purchased from Sigma (Germany).
Statistical analysis The results were analysed statistically using the general linear model (GLM)-factorial analysis of variance (ANOVA) procedures of Statistica, 6th version (StatSoft Inc, 2003), on the ground of one- and two-way ANOVA with interaction. Means and standard deviations were given for the individual traits analysed. The significance of differences between means was estimated by Tukey’s test at the level of P < 0.05. Statistical analysis included the effect of production season and goat breed, using the following linear model: Yij ¼ l þ ai þ bj þ eijk where: Yij – dependent variable; l – effect of total mean; ai – effect of goat breed (i = 1..4); bj – effect of production season (j = 1, 2); and eijk – random error. RESULTS AND DISCUSSION The results showed that purebred goats (i.e. Alpine and Saanen) produced significantly more milk in both seasons 412
compared with the mixed breed goats, by 0.52 kg in the spring–summer season and by 0.58 kg in the autumn–winter season (Table 2). The biggest differences (P < 0.01) were between the milk yield of coloured and Saanen goats kept in a productive herd (0.85 kg in the spring–summer season and 0.89 kg in the autumn–winter season). Nevertheless, it should be noted that in both production seasons, in the group of mixed breed goats white goats had higher milk yield, which might have resulted from their improvement by the Saanen breed. According to Morand-Fehr et al. (2007), Alpine and Saanen goats, next to Toggenburg and Swiss Alpine (Oberhasli), are classified as typical dairy breeds, distinguished by a high milk performance. In European countries, when these breeds are maintained in an intensive system, they are able to produce up to 3–4 kg of milk per day (Morand-Fehr et al. 2007). The studies of other authors also point to the higher productivity of Saanen goats (Mioc et al. 2008; Norris et al. 2011). In the research of Barłowska et al. (2011), similarly to this study, a higher milk yield of goats in the spring–summer season (by 0.14 kg) relative to autumn–winter season was demonstrated. According to Auldist et al. (2013), higher milk performance in the spring–summer season is related to maintenance of animals on the pasture. It may also result from the stage of lactation because in goats, its peak usually falls in the spring–summer season (Mioc et al. 2008; Barłowska et al. 2013). However, a more favourable chemical composition, both in the spring–summer and in autumn–winter seasons, was characteristic for milk obtained from goats kept in the productive herds. Nevertheless, the milk of animals with a coloured coat contained the highest levels of the analysed components (Table 2). A significantly lower content of basic components was found in the milk of highly productive goats, that is, Alpine and Saanen (P < 0.05 and P < 0.01, respectively). These differences in the concentrations of individual components, in favour of the mixed breed goats, in the spring–summer season were as follows: dry matter – 0.5%; protein – 0.28%, including casein – 0.20%; and fat – 0.31%. However, these differences were lower in the autumn–winter season, that is, dry weight – 0.4%; protein – 0.19%, including casein – 0.15%; and fat – 0.28%. No statistically significant differences in the percentage of lactose were found. Nevertheless, it should be noted that the milk of purebred goats, despite a lower content of protein including casein, was characterised by a significantly higher proportion of casein in the total protein (above 82% in both seasons) which is illustrated in Figures 1 and 2. This milk also coagulated faster enzymatically, by an average of 20 s. The longer clotting time of the milk of mixed breed goats could be associated with the higher content of dry matter, especially protein, which has been shown by other authors (Clark and Sherbon 2000; Barłowska et al. 2013). According to Martin and Addeo (1996), the short time of enzymatic clotting of caprine milk © 2014 Society of Dairy Technology
24 2.25C 2.95A 125A 3.45 4.62 11.7A 6.76b 1.028 870a
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Values are given as mean standard deviation of triplicates. S-S – spring–summer season; A-W – autumn–winter season. SCC – somatic cell count. Differences within season for breeds: lowercase letters, significant at P < 0.05; uppercase letters, significant at P < 0.01.
0.41 0.38 101 0.49 0.27 0.9 0.07 0.006 790
71 1.36A 3.21C 163B 3.85 4.49 12.2B 6.78b 1.028 960ab
goats in
A-W
productive
0.49 0.52 91 0.69 0.37 1.7 0.11 0.002 800
100 1.99B 2.96B 165ab 3.52b 4.47 11.6B 6.64 1.028 960b
0.74 0.30 83 0.49 0.23 0.9 0.06 0.003 730
96 1.54B 3.14BC 143AB 3.72 4.50 12.1AB 6.69a 1.028 1200b
A-W
114 1.72A 3.05B 174b 3.58b 4.41 11.7B 6.71 1.028 840ab No. Daily yield (kg) Total protein (% w/v) Rennet coagulation time (s) Fat (% w/v) Lactose (% w/v) Dry matter (% w/v) pH value Density (g/cm3) SCC (thousand/mL)
0.48 0.36 97 0.46 0.28 0.7 0.08 0.002 850
26 2.20B 2.75A 155a 3.29ab 4.43 11.3AB 6.65 1.027 690a
S-S S-S S-S
Breed Production season
Alpine White goats in productive herd Coloured herd
Table 2 Daily yield and physical–chemical properties of milk of goat breeds analysed with regard to production season
0.85 0.30 72 0.58 0.36 0.9 0.09 0.001 520
25 1.81B 3.02AB 134A 3.55 4.52 11.9AB 6.66a 1.028 820a
A-W
0.53 0.36 82 0.46 0.54 0.9 0.07 0.001 640
19 2.57C 2.69A 152a 3.19a 4.47 11.1A 6.73 1.028 710a
S-S
Saanen
0.47 0.21 59 0.39 0.12 0.5 0.10 0.002 540
A-W
0.80 0.26 55 0.40 0.18 0.6 0.09 0.002 430
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results in a curd with a lower consistency, which can lead to pulverisation of the clot and lower yield, particularly during mechanised production. The research of Greyling et al. (2004) and Mestawet et al. (2012) also showed a lower concentration of basic components in the milk of highly productive improved goats in comparison with mixed breed animals and local breeds. Numerous authors attribute the significantly higher level of protein, including casein, in the milk of mixed breed goats to a specific genotype of these animals. The population of local (indigenous) goats is generally characterised by a higher frequency of A, B and C genes of as1-casein, that is, the so-called strong genes, which determine the higher synthesis of this protein fraction and, consequently, casein and total protein (Strzałkowska et al. 2004; Devold et al. 2011). In the study of Mayer and Fiechter (2012a), which included six breeds of goats (coloured, Pinzgau, Saanen, Strahlen, Toggenburg and white) maintained in Austria, only small (statistically insignificant) differences in the chemical composition of milk were found. The production season had a significant effect on the percentage of basic milk components (Table 2). A higher content was recorded in the autumn–winter season, which was related to the stage of lactation. In the final stage of lactation, which in goats is mostly associated with the autumn–winter season, milk production is reduced, while the concentration of basic components is increased. Fekadu et al. (2005), analysing milk obtained from Alpine goats for the production of a hard cheese, found a higher content of basic components, that is, dry matter (by 0.69%), fat (by 0.38%), total protein (by 0.43%) and casein (by 0.13%), in the autumn (October) compared with the summer (June). Similar results were also obtained in our own and other authors’ studies (Barłowska et al. 2011, 2013; Norris et al. 2011). The results obtained indicated slight breed differences in the somatic cell count. However, it should be noted that a lower level of somatic cells was observed in the milk of purebred goats, that is, Alpine and Saanen. In all groups of goats, a lower cytological quality of milk was found in the autumn–winter season. It was probably associated with the stage of lactation because at the end of the lactation period, with a reduction in milk production, an increase in somatic cell count occurred. Deterioration of the cytological quality of goat’s milk with a following lactation was also shown by Fekadu et al. (2005). Milk obtained in the productive herd, compared with milk from purebred goats (Alpine and Saanen), proved to be a richer source of bioactive whey proteins (Figure 1–7). Both in the spring–summer and in autumn–winter seasons, their content was significantly (P < 0.05) higher in the milk of the productive herd, by over 0.60%. Similar to the results of the present study, Mayer and Fiechter (2012a) showed the content of whey proteins in the milk of Saanen goats to be 0.59 g 100/g. In the milk of the five remaining breeds (coloured, Pinzgau, Strahlen, Toggenburg and white), the 413
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Figure 1 Content of total protein, casein and whey proteins (% w/v) in milk of goat breeds analysed with regard to production season.
Figure 2 Percentage of casein and whey proteins in total protein in the milk of goat breeds analysed with regard to production season.
percentage of the whey proteins discussed was similar to the results for the milk of mixed breed goats (0.62–0.66%). A considerably lower percentage of whey proteins was found in bulk milk obtained in the Czech Republic – 0.43 g 100/g (Hejtmankova et al. 2012), and Austria – 0.52 g 100/ g (Mayer and Fiechter 2012b). However, the milk of goats kept in Ethiopia contained considerably more of these proteins (0.77–0.95%) (Mestawet et al. 2012). 414
The greatest proportion of the whey proteins, representing more than 50%, is b-LG, which shows mainly antioxidant and anticarcinogenic activities, as well as retinol-binding capacity (Krol et al. 2011). In both seasons, the smallest quantity of this protein (2.82–2.94 g/L) was found in the milk of Alpine and Saanen goats (Figure 4). The mixed breed goats produced milk containing significantly more bLG (on average, by 0.25–0.34 g/L, depending on the © 2014 Society of Dairy Technology
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Figure 3 Content of a-lactalbumin (g/L) in milk of goat breeds in relation to the production season.
Figure 4 Content of b-lactoglobulin (g/L) in milk of goat breeds in relation to the production season.
season). The milk of mixed breed goats also had the highest concentration of a-LA (1.81–2.08 g/L), the protein responsible for controlling milk secretion and transport of calcium, zinc and manganese ions (Kr ol et al. 2011; Bullut-Solak and Akin 2012). The smallest amount of this protein, as in the case of b-LG, was found in the milk produced by purebred goats. The concentration of a-LA in the milk of mixed breed goats was higher by the following amounts: 0.38 g/L © 2014 Society of Dairy Technology
in the spring–summer season and 0.32 g/L in autumn–winter season. Maotsou et al. (2006), analysing milk from the most primitive goat breed in Greece, that is, Skopelos (covered by legal protection), showed that it was characterised by a higher content of total protein (3.67%), casein (2.97%) and albumins (a-LA – 1.37 g/L, and b-LG – 2.14 g/L) compared with milk of highly productive breeds of international importance. Similar results were found in our own 415
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Figure 5 Proportion of a-lactalbumin to b-lactoglobulin in milk of goat breeds analysed in relation to the production season.
Figure 6 Content of lactoferrin (mg/L) in milk of goat breeds analysed in relation to the production season.
research, with the highest concentration of proteins in the milk of mixed breed goats. Moreno-Indias et al. (2009) found 1.99 g/L of b-LG and 1.36 g/L of a-LA (the average for 60 Spanish farms) in whey obtained during traditional production of goat’s cheese. A crucial component of the whey fraction is lactoferrin. It has multiple effects on the human body, such as antibacterial, antiviral, antioxidant or anticancer effects. Lactoferrin 416
is also responsible for the absorption and bioavailability of iron. Furthermore, this protein is an essential element of nonspecific innate immunity of humans and other mammals (Hiss et al. 2008). As with b-LG and a-LA, a higher concentration of lactoferrin was also characteristic of milk from the productive herds compared with milk from Alpine and Saanen goats. The difference in lactoferrin content depended on the production season, from 5.5–6.5 mg/L in the © 2014 Society of Dairy Technology
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Figure 7 Content of lysozyme (lg/L) in milk of goat breeds analysed in relation to the production season.
Table 3 Effect of selected factors on analysed traits (P-value) Effect of selected factors Specification
Breed
Production season
Interaction of breed x production season
Daily yield Total protein Casein Proportion of casein in total protein Rennet coagulation time Fat Lactose Dry matter pH value Density SCC Whey proteins a-Lactalbumin b-Lactoglobulin Lactoferrin Lysozyme Proportion of a-lactalbumin to b-lactoglobulin
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.307
0.712 0.206 0.332 0.015
0.000
0.003
0.000
0.000 0.694 0.000 0.000 0.348 0.000 0.021 0.000 0.000 0.000 0.001 0.000
0.048 0.000 0.000 0.000 0.907 0.029 0.038 0.000 0.384 0.000 0.125 0.000
0.752 0.014 0.260 0.000 0.427 0.15 0.239 0.033 0.040 0.049 0.245 0.154
SCC – somatic cell count.
autumn–winter season to 14–17 mg/L in the spring–summer season. Moreno-Indias et al. (2009) found a higher concentration of lactoferrin in whey from rennet cheese production © 2014 Society of Dairy Technology
from the milk of goats kept in the Canary Islands. The whey obtained during industrial milk processing contained 115 mg/L of lactoferrin, while with a traditional method of processing unpasteurised milk, the content was three times higher (390 mg/L). However, Hiss et al. (2008) reported several times lower concentration of the protein in the milk of German Improved Fawn and German Improved White goats. At the beginning of lactation (from the 2nd to 32nd week), the lactoferrin content ranged from 10 to 28 lg/mL and then began to increase progressively, reaching more than 100 lg/mL in the 44th week. Besides lactoferrin, lysozyme is also one of the most crucial components of the nonspecific humoral immune response. The antibacterial properties of lysozyme have led to considerable interest in its practical utilisation in many sectors of food industries. It is used primarily as an additive in food, due to its preservative properties (Benkerroum 2008). In the milk evaluated in the present study, the lysozyme content ranged from 7.0 to 8.3 lg/mL, and significantly more of this protein was found in the milk of goats from the productive herds (Figure 7). The production season significantly determined the total whey protein content (P < 0.05) as well as a-LA (P < 0.01) and lactoferrin (P < 0.01) contents, which is shown in Table 3. Milk produced in the spring–summer season contained more whey proteins (by 0.02% on average), a-LA (by 0.17 g/L on average) and lactoferrin (by 14.5 mg/L on average). A higher percentage of whey proteins in the spring–summer season compared with the autumn–winter season was also found in research performed on cow’s milk (Litwinczuk et al. 2011). According to Mackle et al. (1999), the concentration of milk whey proteins might be 417
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influenced to a large extent by the energy supplied in the feed ration. They found a decrease in a-LA and b-LG levels in the case of limited access to pasture. The research of Hejtmankova et al. (2012), carried out on the milk of 400 goats of the Czech White Short-Haired breed, showed a decrease in whey protein content during the course of lactation (March–October). The concentration of major albumins, that is, a-LA and b-LG, decreased in total by more than 100 mg 100/g of milk, being 0.356 g 100/g of milk in October. However, there was an increase in b-LG concentration during the course of lactation (at the expense of a-LA content), reaching a value of 0.235 g 100/g of milk in October. Similar tendencies were shown by Krol et al. (2013) in the milk of six breeds of cows used in Poland. According to Heck et al. (2009), a decline in a-LA levels during lactation may be associated with a reduction in milk production because this protein is a component of the lactose synthase complex. Turner et al. (2007), analysing the lactoferrin content of the milk of cows using a pasture to various degrees, found a significantly (P < 0.05) higher yield of this protein (in g per day) in the milk of cows having unrestricted access to pasture (ad libitum). It can be assumed that the bioactive compounds contained in green forages, which have immunomodulatory properties, have an indirect effect on lactoferrin levels. Drackowa et al. (2009) reported, however, the lowest concentration of this protein in April (98 mg/L), whereupon its concentration gradually increased in the following months, reaching the maximum value in the autumn period (144–149 mg/L). CONCLUSION In conclusion, it can be stated that a lower milk yield was characteristic of goats maintained in the productive herds (both white and coloured goats), compared with the highly productive goat breeds. However, the milk of goats in the productive herds contained more basic nutrients, including total protein and casein. It also constituted a valuable source of functional whey proteins, especially in the spring–summer season. Existing higher potential of mixed breed goats shows unique qualities of milk for cheese production (due to the higher casein content). Moreover, this milk is suitable for the production of specific dairy products because it is rich in biologically active components of the protein fraction. Nevertheless, the milk of goat breeds of international importance (Alpine and Saanen), despite having a lower content of total protein including casein, was distinguished by a significantly higher percentage of casein, which is crucial in the dairy industry. ACKNOWLEDGEMENTS This work was conducted as part of the Ministry of Science and Higher Education project No. N N311 633838.
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