Production and Selected Properties of Bioghurt Made from Goat Milk and Cow–Goat Milk Mixtures by Ultrafiltration and Addition of Skim Milk Powder

Abstract

In this study, bioghurt was produced from goat milk (A) and 70% goat–30% cow (B), 50% goat–50% cow milk (C) mixtures, and stored 14 days at 4 ± 1°C. Two concentration methods of ultrafiltration (UF) and skim milk powder addition (MP) were applied to milk mixtures, therefore six different bioghurt samples were obtained. Selected physical, chemical, microbiological, and sensory properties of bioghurt samples were analyzed at 1st, 7th, and 14th day of storage. Effects of milk type, concentration method, and storage period on physico-chemical and microbiological properties of samples were investigated. The effect of concentration method on titratable acidity (°SH), penetration value, and whey off values of all bioghurts was significant (p < 0.05). The milk type had no significant effects on total solids, fat content, titratable acidity, pH, and whey off values of bioghurts (p > 0.05), but only the protein contents of bioghurt concentrated with skim milk powder showed significant (p < 0.05). The sensory evaluation showed that bioghurt produced with the mixture of 50% goat milk + 50% cow milk and concentrated by addition of skim milk powder had the highest overall scores.

Introduction

According to the 1998 statistics, it has been reported that there are 8.376.000 head of ordinary and 708.000 head of Angora goat in Turkey producing 249.000 tons of milk per year. Therefore, the goats and goat milk play an important role in Turkey economy and in the components of the family diet.1

Goat milk can be digested easily in an organism due to the tiny in diameter of fat globules, and casein micelles are short and form a weak coagulum. It is utilized in the prevention of allergies on children and for nutrition of children, patients, and elder people. Goat milk mixed with other types is used in producing homemade yoghurt and some traditional cheese such as Cimi and Tulum in Turkey and in commercial cheeses and yoghurt production. Other therapeutic products and bioghurt have a big market in the countries where the milk industry has developed. In spite of the fact that these products are produced from cow's milk, it is also possible to use goat milk.2

Bioghurt, which has characteristically therapeutic benefits, is a product acidified by the fermentation of milk with Streptococcus salivarius ssp. thermophilus and Lactobacillus acidophilus. Lactobacillus acidophilus which, is found in healthy person's gut flora starting from infancy and live adhering to the epithelium cells. These bacteria are resistant to gastrointestinal secretions and low surface tension continue their development and manage the gut flora by production of organic acids like lactic acid during their activities in intestines. The bactericides produced by Lb. acidophilus such as acidophlin, lactacin B, lactacin F, and acidosin inhibit the growth of pathogenic microorganisms and give an antibiotic effect.3 4 5 6 7 Besides, it has been reported that strains of these organisms have serum cholesterol reducing effects by the help of anticholesterolemic properties8 9 and also they reduce the effects of the faecal enzymes, which stimulate the procancerogenic substances to convert cancerogenic substances in intestines and by this way, prevent the colon cancer.10 11 Experiments with human tissue showed that only l (+) lactic acid increases cell respiration up to 80%, which the d (−) lactic acid does not do. In bioghurt, the amount of desired l (+) lactic acid dominates and this fermented product contains more than 90% l (+) lactic acid.12

The consistency of fermented milk products is depended on the level of nonfat solids. For fortification of this level, addition of skim milk powder and vacuum-evaporation are the most common methods used in Turkey. Although ultrafiltration is used in the production of some fermented milk products all around the world, has become recently applicable in Turkey. The objectives of this study were to produce bioghurt from two different cow–goat milk mixtures and only from goat milk using two concentration methods (UF, MP), to determine the effects of the concentration methods, type of milk and storage period, on organoleptical properties and physico-chemical properties.

Materials and Methods

Materials

Fresh raw cow and goat milks were obtained from the dairy herds of Faculty of Agriculture farm, Ege University, Izmir. Ultrafiltration was carried out using a pilot plant type Alfa-Laval UFR-1 unit (Romicon PM 50 membrane, 100 kPa). Skim milk powder was purchased from Pinar Sut Co. (Izmir, Turkey). Bioghurt was produced by using Streptococcus salivarius ssp. thermophilus and Lb. acidophilus starter cultures obtained from Wiesby GmbH&Co.KG (Niebüll, Germany).

The Production of Bioghurt

Bulk samples of raw goat and cow milks were divided into three different portions (A: 100% goat milk, B: 70% goat–30% cow milk, C: 50% goat–50% cow milk). Afterward six different milk portions were obtained by ultrafiltration (UF) and addition (2%) of skim milk powder (MP) (A_UF, B_UF, C_UF, A_MP, B_MP, C_MP). Whole milk portions were heated to 90°C for 15 min and after cooling to 38°C, samples inoculated with 5% starter culture and incubated at 37°C until the pH reached 4.6. After pre-cooling at room temperature for 30 min, all bioghurt samples were stored for 1, 7, and 14 days at 4 ± 1°C.

Chemical and Physical Analyses

The bioghurt samples were analyzed for pH (using a Hanna 210 pH-meter), titratable acidity (°SH), fat, total solids and, total protein,13 14 whey off value at the end of 60 min (a modified method according to Harwalkar and Kalap15) and penetration value by using a Gerber penetrometer (measured in seconds after 3 mm of penetration at a product temperature of 4°C).

Microbiological Analyses

Streptococcus salivarius ssp. thermophilus and Lb. acidophilus counts and, yeasts–moulds counts were enumerated in each bioghurt samples. Each sample (1 g) was serially diluted to 10⁻⁶ using Ringers’ solution. Appropriate dilutions were plated using the following media: (i) M17 Agar (Oxoid Ltd., Basingstoke, Hampshire, England) for the enumeration of Str. salivarius ssp. thermophilus; incubated at 37 ± 1°C for 48 h. (ii) MRS Agar (Oxoid Ltd., Basingstoke, Hampshire, England) for the enumeration of Lb. acidophilus; incubated at 42 ± 1°C for 48 h. (iii) PDA plus tartaric acid (Oxoid Ltd., Basingstoke, Hampshire, England) for the enumeration of yeasts and moulds; incubated aerobically at 25 ± 1°C for 5 days.

Sensory Evaluation

Five panelists who were familiar with fermented dairy products judged sensory properties of the bioghurt samples by using a mixed-point system (rating scale of 1–5). Each panel member assessed the bioghurt samples separately, taking into account the following features: appearance, consistency in mouth and with spoon, odor and, flavor.16

Statistical Analysis

The study was repeated three times and analysis of variance (ANOVA) was performed using the General Linear Model procedure of SAS17. In all cases 0.05 probability level was considered.

Results and Discussion

The values of the compositional parameters of raw goat and cow–goat milk mixtures used in the production of bioghurt are presented in Table 1 and the physico-chemical properties of six different bioghurt samples are presented in Table 2. Average total solid content of sample B_MP (14.98%) was lower than those of other bioghurt samples. The concentration method was found effective between A_UF and A_MP samples (p < 0.05) but not statistically effective on the other samples (B_UF–B_MP, C_UF–C_MP) (p > 0.05). The total solids increased during the storage gradually, but this increase and also difference between A_UF–B_UF–C_UF, A_MP–B_MP–C_MP (effect of milk kind) was not significant (p > 0.05). These results are in agreement with the findings of Akalin18 and by the same researcher total solids in all samples were found to be more than 15% at the end of storage.

Table 1 Some properties of raw milks (n = 3)

Total solids (%)	Fat (%)	Protein (%)	Lactose (%)	Acidity (°SH)	pH
Goat milk	12.10	3.50	3.70	4.21	6.70	6.60
Aa	13.21	3.73	4.20	4.52	6.80	6.50
Bb	12.92	3.66	4.16	4.40	6.82	6.60
Cc	12.79	3.55	4.00	4.33	6.70	6.60

^a100% goat milk.

^b70% goat–30% cow milk.

^c50% goat–50% cow milk.

Table 2 Physico-chemical properties of bioghurt samples during storage for 14 days (n=3)

Samples	Storage days	Total solids (%)	Fat (%)	Protein (%)	Acidity (°SH)	pH	Penetration value (s)	Whey off value (%)
AUF a	1	15.46	3.70	4.49	34.90	4.50	10.02	32.08
	7	15.55	3.70	4.53	37.55	4.40	10.23	31.11
	14	15.57	3.75	4.51	39.80	4.35	10.30	31.08
BUF b	1	15.10	3.50	4.36	35.42	4.40	9.38	39.31
	7	15.27	3.50	4.40	37.73	4.35	9.88	34.07
	14	15.36	3.55	4.43	42.24	4.30	9.96	31.97
CUF c	1	15.13	3.60	4.49	36.80	4.45	9.19	37.76
	7	15.20	3.60	4.49	39.12	4.40	9.40	37.53
	14	15.28	3.70	4.51	40.10	4.40	10.79	34.15
AMP d	1	14.96	3.80	4.04	39.00	4.40	10.86	30.89
	7	15.00	3.80	4.66	47.50	4.35	11.12	29.44
	14	15.03	3.90	4.66	45.40	4.30	12.26	29.06
BMP e	1	14.83	3.70	4.45	38.00	4.50	10.66	32.21
	7	14.93	3.75	4.48	43.10	4.45	10.84	31.56
	14	15.19	3.75	4.50	46.70	4.40	11.74	30.34
CMP f	1	15.09	3.80	4.59	40.27	4.50	9.83	37.05
	7	15.20	3.80	4.63	41.10	4.45	9.98	35.96
	14	15.27	3.80	4.65	45.05	4.35	10.10	31.15

^aBioghurt made from 100% goat milk by ultrafiltration.

^bBioghurt made from 70% goat–30% cow milk by ultrafiltration.

^cBioghurt made from 50% goat–50% cow milk by ultrafiltration.

^dBioghurt made from 100% goat milk by skim milk powder addition.

^eBioghurt made from 70% goat–30% cow milk by skim milk powder addition.

^fBioghurt made from 50% goat–50% cow milk by skim milk powder addition.

It was found that the fat contents were not effected by concentration method, milk type, and storage period (p > 0.05). The fat contents are in agreement with the findings of Akalin,18 Desmaison et al.,19 and Akin.20 Akalin18 also reported that the effect of storage period was not significant on the fat contents of the bioghurt samples. Moreover, according to the Turkish Food Codex Fermented Milk Bulletin,21 all bioghurt samples were placed in full fat (≥ 3.8%) or fatty (≥ 3.0%) groups.

The protein content of sample C_MP was determined higher than other bioghurt samples. Significant differences were not found between the protein contents of the samples related with the effects of the milk kind and concentration method (p > 0.05) but differences between A_MP–B_MP–C_MP and A_MP–A_UF were significant. It was also found that effect of storage period was not significant on the protein contents of bioghurt samples (p > 0.05). These results are in agreement with the findings of Akalin.18 Protein contents determined in the samples were consistent with the Turkish Food Codex Fermented Milk Bulletin21 (>2.8%).

The titratable acidity (°SH) of the samples produced by UF were found to be lower than the titratable acidity of the samples produced by skim milk powder addition. Therefore differences between A_UF–A_MP, B_UF–B_MP, and C_UF–C_MP were significant (p < 0.05). Lactic acid is the characteristic substance in all fermented dairy products and it is generated by all starter microorganisms.22 But the important amount of lactose passes to permeated23 24 during the concentration of milk with UF hence, the acidity development during storage was slower in the bioghurts produced with UF. The effect of the milk type was found insignificant on the acidity of the bioghurt samples (p > 0.05), but as mentioned above the effect of the storage period was found significant for samples concentrated with UF and also for other samples (p < 0.05). Additionally, all bioghurt samples had consumable acidity (>26°SH) according to the Turkish Food Codex Fermented Milk Bulletin,21 even in 14th day. Furthermore in all bioghurt samples, effects of concentration method, milk type and storage period on pH values were found insignificant (p > 0.05). The penetration values of the samples produced by UF were found significantly (p < 0.05) lower than the penetration values of the samples produced by skim milk powder addition. The rheological properties of coagulum network in fermented dairy products vary, depending upon milk composition, total solid content, and heat treatment of milk.22 But despite the samples produced by UF contained higher total solids, consistency (Table 4) of these bioghurt samples were also noticed to be low in sensorial evaluation by the panelists, so this situation was attributed to the low acidity. However this result is in agreement with the findings of Eskici25 and Uysal.26 The increases observed in C_UF, A_MP, and B_MP samples during the storage were found significant (p < 0.05). The increase in the penetration values during the storage period can be explained by the firmer coagulum related with the development in the acidity than the other samples. The results of Eskici,25 Akalin,18 and Uysal26 support this finding.

Table 3 Microbiological characteristics of bioghurt samples during the storage for 14 days (log₁₀ cfu/g, n = 3)

Samples	Storage days	Lb. acidophilus	Str. salivarius ssp. thermophilus	Yeasts and moulds
AUF a	1	7.43	7.20	2.77
	7	7.21	6.72	2.87
	14	6.65	6.53	1.01
BUF b	1	6.30	6.34	3.16
	7	6.73	6.18	3.33
	14	6.00	7.10	1.68
CUF c	1	6.18	7.12	3.10
	7	6.11	6.32	2.39
	14	7.07	6.10	2.15
AMP d	1	7.14	7.33	3.53
	7	6.90	7.08	1.32
	14	6.11	7.13	1.38
BMP e	1	6.80	7.14	4.24
	7	6.70	6.85	2.48
	14	6.25	6.28	2.59
CMP f	1	6.21	6.90	3.12
	7	6.10	6.21	2.42
	14	5.85	6.09	2.04

^aBioghurt made from 100% goat milk by ultrafiltration.

^bBioghurt made from 70% goat–30% cow milk by ultrafiltration.

^cBioghurt made from 50% goat–50% cow milk by ultrafiltration.

^dBioghurt made from 100% goat milk by skim milk powder addition.

^eBioghurt made from 70% goat–30% cow milk by skim milk powder addition.

^fBioghurt made from 50% goat–50% cow milk by skim milk powder addition.

The whey off values of bioghurt samples produced by UF was found higher than the other samples. So, the differences between A_UF–A_MP, B_UF–B_MP, and C_UF–C_MP were significant (p < 0.05). Also significant differences were found in bioghurt samples according to milk kind used (p < 0.05) and the lowest whey off values was determined in samples produced with 100% goat milk. The whey off values of samples during the storage period was decreased gradually. Therefore, it was found significant that the storage period was effective on the whey off value of bioghurt samples (p < 0.05). Table 3 shows results of the microbiologic analyses carried on the bioghurt samples in the 1st, 7th, and 14th days of the storage. The effects of the concentration method, milk kind, and storage period were found insignificant on the number of viable cells of microorganisms (p > 0.05). The viable numbers of Streptococcus salivarius ssp. thermophilus and Lb. acidophilus are generally consistent with the counts given in Turkish Food Codex Fermented Milk Bulletin21 (total specific microorganism counts: >10⁷ cfu/g). At the beginning of the study, the number of these bacteria was used at nearly 1:1 in ratio. Table 3 indicates that this ratio was stable during the storage period. However, it was noticed that both bacteria showed a decline at the end of 14 days. This situation can be explained by the inhibition of bacteria due to the low acidity, and the metabolites formed. To have probiotic and functional properties as it is in bioghurt, a fermented product must contain starter culture at level of 10⁷ cfu/g, active and viable until the end of the shelf-life. And it is also important that the bacteria during the storage must be tolerant to acidity, biliary, and pancreatic excretions; inhibit the pathogens’ by adhesion to the intestinal cells; be resistant to antibiotics and processes and, preserve its stability.27

The yeast-mould numbers counted in the samples of bioghurt during the study were found to be higher than the counts given in the Turkish Food Codex Fermented Milk Bulletin20 (< 10² cfu/g). These counts are considered not very high and taking some measurements during the production process can eliminate this problem.

In the study, the panelists evaluated the appearance, consistency, odor, and flavor (Table 4). In this evaluation, the bioghurts produced by skim milk powder addition were liked more than the others produced by UF from the consistency and flavor point of view. However, the bioghurts produced by UF were liked in the point of appearance. Sample C_MP and C_UF were the most liked among all samples and samples concentrated by UF, respectively. In addition odor difference was not determined among the samples.

Table 4 Sensory properties of bioghurt samples during storage for 14 days (n=3)

Samples	Storage days	Appearance	Consistency in mouth	Consistency with spoon	Odor	Flavor	Total
AUF a	1	5.00	4.10	3.75	4.50	2.50	19.85
	7	4.75	4.15	3.95	4.40	2.40	19.65
	14	4.65	4.15	4.00	4.40	2.30	19.50
BUF b	1	5.00	4.00	4.10	4.80	2.50	20.40
	7	4.80	4.05	4.20	4.80	2.50	20.35
	14	4.75	4.10	4.20	4.50	2.40	19.90
CUF c	1	5.00	4.20	4.10	4.90	2.60	20.80
	7	4.95	4.25	4.25	4.90	2.50	20.85
	14	4.90	4.30	4.35	4.60	2.50	20.65
AMP d	1	4.90	4.75	4.25	4.50	3.20	21.60
	7	4.75	4.75	4.25	4.30	3.10	21.15
	14	4.75	4.80	4.30	4.30	3.10	20.95
BMP e	1	4.90	4.80	4.65	4.60	3.30	22.25
	7	4.60	4.80	4.70	4.60	3.20	21.90
	14	4.60	4.80	4.60	4.50	3.10	21.60
CMP f	1	4.90	4.90	4.75	4.70	4.50	23.95
	7	4.80	4.90	4.80	4.70	4.50	23.70
	14	4.70	5.00	4.80	4.60	4.20	23.30

^aBioghurt made from 100% goat milk by ultrafiltration.

^bBioghurt made from 70% goat–30% cow milk by ultrafiltration.

^cBioghurt made from 50% goat–50% cow milk by ultrafiltration.

^dBioghurt made from 100% goat milk by skim milk powder addition.

^eBioghurt made from 70% goat–30% cow milk by skim milk powder addition.

^fBioghurt made from 50% goat–50% cow milk by skim milk powder addition.

Conclusions

This study demonstrated that goat milk was an adequate raw material for bioghurt production according to overall properties. It was found that bioghurts differed in their selected properties like titratable acidity and penetration value, depending on concentration method. In general beside the physico-chemical and microbiological properties, sensory profiles are important parameters of fermented milk products. Thus bioghurt produced with the mixture of 50% goat milk + 50% cow milk and concentrated by addition of skim milk powder attracts attention within other bioghurts. Enumeration of viable Lb. acidophilus and Streptococcus salivarius ssp. thermophilus in six bioghurt samples for two weeks showed variable levels of these organisms. However, the count ratio of Lb. acidophilus to Streptococcus salivarius ssp. thermophilus was about 1:1 in bioghurt samples in general.