Pressurized Yoghurt as a Carrier of Probiotic Bacteria

Transcription

1 High Pressure Bioscience and Biotechnology 295 Proceedings of the 4 th International Conference on High Pressure Bioscience and Biotechnology, Vol. 1, , 2007 Pressurized Yoghurt as a Carrier of Probiotic Bacteria Arnold Reps*, Agnieszka Jankowska, Anna Proszek, Krystyna Wiśniewska Chair of Food Biotechnology, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 1, Olsztyn, Poland * arnold.reps@uwm.edu.pl Received 24 November 2006/Accepted 30 November 2006 Abstract The aim of the study was to determine the possibilities of using pressurized yoghurt as a carrier for probiotic bacteria. The experiment involved the addition of probiotic bacteria Bifidobacterium ssp. to non-pressurized and pressurized (550 MPa/15 min) yoghurt. Yoghurts were stored at 4 and 20 o C for four weeks. A higher survival rate for probiotic bacteria was found in pressurized yoghurts. Also, the increase in acidity in non- pressurized yoghurts was higher than pressurized yoghurts. Keywords: pressurization, yoghurt, probiotic bacteria 1. Introduction In recent years, a dynamic increase has been observed in the production and consumption of yoghurt, which has prompted research into various aspects of its quality and production [2]. The intake of yoghurt contributes to better assimilation of iron, phosphorus and calcium. Yoghurt contains 50% less lactose compared to milk, hence it is recommended for patients with lactose intolerance induced by a lack of β-galactosidase an enzyme hydrolyzing that carbohydrate (in some Asian and African countries this problem affects 100% of the population). In addition, in the alimentary tract bacteria release an activated enzyme β-galactosidase which simultaneously hydrolyzes lactose [8]. In modern yoghurt production technology, apart from traditional Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus bacteria, use is made of probiotic bacteria strains, i.e. Lactobacillus acidophilus and Bifidobacterium. An important trait of probiotic bacteria is the ability to proliferate and stay for a longer period of time in the alimentary tract, which has a beneficial effect on human health [9]. Therefore, the presence of live cells of probiotic bacteria in the yoghurt consumed is of the outmost significance. Providing their appropriate concentration in the end period of shelf

2 296 life is a key task of producers and a prerequisite for a beneficial effect of food products on the health of consumers [8]. Unfortunately, a number of probiotic strains are characterized by a short stationary phase, which results in a considerable shortening of the shelf life within 2-4 weeks. In addition, Bifidobacterium strains are susceptible to unfavorable conditions of the medium, i.e. lactic acid and hydrogen peroxide produced by Lactobacillus delbrueckii ssp. bulgaricus [3]. Therefore, common cultures of traditional yoghurt bacteria and probiotic bacteria are highly hindered. One of the methods to improve the survivability of probiotic bacteria in yoghurt is the application of ABT inocula containing Streptococcus thermophilus, Bifidobacterium and Lactobacillus acidophilus for its production. However, elimination of Lactobacillus delbrueckii ssp. bulgaricus extends the period of fermentation and reduces the antibacterial activity of yoghurt, since the Lactobacillus delbrueckii ssp. bulgaricus bacterium has been reported to exhibit special bacteriostatic properties and antimicrobial activity against a number of pathogenic bacteria paratyphoid fever, tuberculosis, dysentery as well as against aerobic putrefactive bacteria and saprophytic coli [1,10]. An alternative method of eliminating the negative impact of Lactobacillus delbrueckii ssp. bulgaricus on probiotic bacteria during yoghurt storage could be the addition of probiotic bacteria to yoghurt that was earlier treated with high pressures [4]. Previous studies have shown that pressurization reduces the acidifying activity of yoghurt bacteria and prevents the after-fermentation souring of yoghurt, thus extending its shelf life. The activity of pressures higher than 400 MPa results in complete inactivation of Lactobacillus delbrueckii ssp. bulgaricus bacteria. Such prepared yoghurt may be a carrier of probiotic bacteria Bifidobacterium and Lactobacillus acidophilus [4]. 2. Materials and methods The experimental material included: non-pressurized yoghurt (Ynp) and pressurized yoghurt (Yp) with the addition of Bifidobacterium sp. culture (YnpB andypb). The yoghurts were obtained using commercial inocula produced by Ch. Hansen: - YC X16 in the form of a lyophilized concentrate,(streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus). - BB-12 in the form of a frozen concentrate (Bifidobacterium sp.).

3 297 Yoghurt prepared on regenerated milk (2% fat content) according to producer s instructions was poured into plastic containers with a volume of 100 cm 3 and pressurized in a high-pressure generator (Institute of High Pressures of the Polish Academy of Sciences in Warsaw) at 550 MPa/15min, at a room temperature. Cultures of probiotic bacteria Bifidobacterium sp. were prepared on regenerated milk (2% fat content), incubated at a temperature of 37 C for 24 h, and added to the pressurized yoghurt at a dose of 1 cm 3 of the culture per 100 cm 3 of yoghurt. Freshly prepared yoghurts and those after 1, 2, 3, and 4 weeks of storage at temp. of 4 C and 20 o C were measured for the number of bacteria and acidity (ph). 3. Results and discussion The pressure treatment of 550 MPa/15 min completely inactivated the population of Lb. delbrueckii ssp. bulgaricus reaching 1.75x10 9 cfu/g, and reduced the population number of Streptococcus thermophilus by one order of magnitude. Similar results were also obtained in earlier studies [7]. In pressurized yoghurt (YpB), directly after preparation, the number of Bifidobacterium sp. was 1.23x10 5 CFU/g. At the temperature of 4 o C, the number of Bifidobacterium sp. was reduced during the storage period; after the third week of storage the number of Bifidobacterium sp. was 9.10x10 3 CFU/g. After the fourth week of storage, the presence of Bifidobacterium sp. was not found in this yoghurt. In yoghurt (YpB) stored at 20 o C, a complete reduction of Bifidobacterium sp. was found after the second week of storage. In non-pressurized yoghurt (YpB), directly after preparation, the number of Bifidobacterium sp. was 6.10x10 6 CFU/g. At the temperature of 4 o C, the number of Bifidobacterium sp. was reduced during the storage period; after the second week of storage, the number of Bifidobacterium sp. was 4.50x10 3 CFU/g, and after the second week of storage, the presence of Bifidobacterium sp. was not found in this yoghurt. In yoghurt (YnpB) stored at 20 o C, similarly to pressurized yoghurt (YpB), the complete reduction of Bifidobacterium sp. was found after the second week of storage. The survivability of lactic bacteria in fermented dairy drinks is affected by a few factors. The number of bacteria in yoghurt is determined by: the proper selection of strain,

4 298 inoculum dose, temperature and period of fermentation, oxygen availability, medium composition, interactions of bacteria and storage conditions [5]. Fig. 1a. The number of bacteria in non-pressurized yoghurt storaged at 4oC. Fig. 1b. The number of bacteria in presurized yoghurt storaged at 4oC Fig. 1c. The number of bacteria in non-pressurized yoghurt storaged at 20oC Fig.1d. The number of bacteria in pressurized yoghurt storaged at 20oC Streptococcus thermophilus Lactobacillus delbrueckii ssp. bulgaricus Bifidobacterium sp.

5 Especially susceptible to the above-mentioned factors are bifidobacteria. Their survivability is particularly negatively affected by the presence of oxygen and high acidity of the medium [6,11]. The presence of Streptococcus thermophilus has been observed to exert a positive impact on Bifidobacterium sp. during storage, since by consuming oxygen present in the medium it produced optimal conditions for the growth of strictly anaerobic bifidobacteria [3]. Acidity [ph] 4,8 4,7 4,6 4,5 4,4 4,3 4,2 YpB storaged at 4 o C YnpB storaged at 4 o C YpB storaged at 20 o C YnpB storaged at 20 o C Fig 2. The acidity of yoghurts during the storage. Pressurization at 550 MPa/15 min resulted in a slight increase in ph of the yoghurt, i.e. from 4.64 to 4.71 ph. After the addition of a probiotic bacteria culture, yoghurt (YpB) acidity was 4.81 ph. After four weeks of storage, the acidity of this yoghurt increased to 4.76 ph. The yoghurt (YpB) stored at 20 o C was characterized by higher acidity than yoghurts stored at 4 o C, which is related to the intensity of lactic acid biosynthesis. However, even in this yoghurt a significant increase in acidity during the storage period was not found. The acidity of non-pressurized yoghurt (YnpB) stored at 4 o C increased from 4.64 to 4.52 ph after four weeks of storage. In non-pressurized yoghurt (YnpB), acidity in the last week of storage was 4.20 ph.

6 4. Conclusions - Pressure treatment at 550MPa/15 min resulted in a complete inactivation of the population of Lb. delbrueckii ssp. bulgaricus, and a decrease in the number of Streptococcus thermophilus by two orders of magnitude. - The survivability of bacteria in yoghurts stored at a temperature of 20 o C was lower than that in yoghurts stored at 4 o C. - The survival rate of probiotic bacteria Bifidobacterium ssp. was higher in pressurized yoghurt compared to non-pressurized yoghurt. - The acidity of pressurized yoghurt remained at a stable level during the storage period. Higher increases in acidity were found in yoghurt stored at 20 o C. The work was supported by National Grant 2P06T04 from State Committee For Scientific Research. 5. References [1] Fooks, L. J., and Gibson, G. R. (2002) Probiotics as modulators of the gut flora. British Journal of Nutrition, 88, Suppl. 1: [2] Hammann, W. T. and Marth, E. H. (1983) Survival of Streptococcus thermophilus and Lactobacillus bulgaricus in commercial and experimental yogurts. Journal of Food Protection. 47(10), [3] Ishibashi, N., and Shimamura, S. (1993) Bifidobacteria: Research and development in Japan. Food Technology, 47(6), 126, [4] Jankowska, A., Wiśniewska, K., Reps, A. (2005) Application of probiotic bacteria in production of yoghurt preserved by the method of high pressures. High Pressure Research 25(1), 1-6. [5] Kneifel, W., Jaros, D. and Erhard, F. (1993) Microflora and acidification properties of yogurt and yogurt-related products fermented with commercial available starter cultures. International Journal of Food Microbiology, 18, [6] Rasic, J. L. (1990) Culture media for enumeration of bifidobacteria in fermented milk products. IDF Bulletin, 252,

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