چكيده لاتين :
Introduction: Kombucha syrup is obtained by fermentation of tea and sugar and the symbiotic coexistence of acetic acid bacteria and yeasts (Santos-Jinor et al. 2009). Kombucha syrupis considered as product with probiotic and functional properties. The health benefits of Kombucha syrup include boosting immune system, increasing digestion, cancer prevention, fat, blood pressure and cholesterol reduction, prevention of heart disease, treatment of fatty liver, reduction of diabetic symptoms and weight loss (Dufresne and Farnworth E 2000). Kombucha syrup can be used in some other types of tea or soft drinks such as coca, whey and lactose (Lončar et al. 2006). Spasenija et al. (2012) investigated the possibility of cultivating Kombucha with two types of black tea and thyme tea in combination with probiotics for fermenting milk at different temperatures. The results showed that inoculation of Kombucha culture with different types of tea in combination with probiotic starter culture can be used for milk and fermented products. Since the microorganisms present in Kombucha are highly beneficial and resistant especially in acidic conditions, they can replace harmful microorganisms in the gastrointestinal tract. Therefore, Kombucha beverage can be considered as a probiotic and functional product (Dufresne and Farnworth 2000). Regarding the benefits of Kombucha syrup for consumer’s health, the aim of this study was to evaluate the effect of Kombucha syrup on the survival of Bifidobacterium bifidum as well as quality of Doogh during storage.
Materials and methods: Kombucha syrup was prepared by method described by Blanc (1996), and added to Doogh in the level of 0-20%. Doogh was prepared by the method described by EbrahimzadeganandZomorodi (2014). Then Doogh samples were kept at 4°C cold room for 41 days and were analyzed at intervals of 5, 23 and 41 days during storage. Count of bifidobacterium was performed in RCA agar culture medium under anaerobic conditions prepared by gas pack A in anaerobic jar and incubated at 37°C for 72 hours (Krasaekoopt et al. 2003). The pH was measured using a digital pH meter calibrated with commercial buffers of 4 and 7, dry matter was obtained by drying the samples in oven at 103 ± 2°C until a constant weight, density was measured using a picnometer (National Iranian Standard No. 2453) and syneresis of Doogh determined by the method descirbed by EbrahimzadeganandZomorodi (2014). The color evaluation of the samples was determined by determining colorimetric factors including b*, a*, and L* using digital colorimetric method and image J software (Zomorrodi, 2012). The overall acceptance of the samples was determined using consumer liking and preference experiment and 5-point Hedonic method by 15 trained panelists. For this purpose, the score of 5 represented the desirable quality and 1 indicated undesirable quality (EbrahimzadeganandZomorodi 2014).
Results and discussion: According to Fig.1, the number of Bifidobacterium bifidum bacteria increased by increasing Kombucha syrup and decreased during storage time (P <0.05). The reason for the increase in the survival of Bifidobacterium bifidum by increasing level of Kombucha syrup can be such justified that during the fermentation and oxidation process of Kombucha syrup, the fungi and yeasts consumed sugar, and produced valuable substances such as glycerol, some B group vitamins (B1, B2, B6, B12) and vitamin C, some minerals, amino acids and other products (Jayabalan et al. 2014). Probably, some of these compounds, including vitamins and amino acids, have been caused to maintain survival of probiotic bacteria in Doogh (Gomez and Malcata 1999). The reason for the decrease in probiotic count during storage can be attributed to more sensivity of this genus to oxygen, high acidity and low pH, the need for growth supplements, namely small molecules organic nitrogen and vitamins, as well as, the need for low reduction potential (Krasaekooptet al. 2003). Vinderolaet al. (2002) reported that pH 4.5 or less had a negative effect on the survival of bifidobacteriumbifidum in yogurt stored at of 5 °C, which is in consistent with the results of this research. According to the recommendation of the International Dairy Federation, the number of live and active probiotic bacteria at the end of the expiration date of the product must be at least 107Cfu/g. Also, by increasing the level of Kombucha syrup, the dry matter and specific gravity increased significantly (P <0.05). This is due to the high brix of the Kombucha syrup. Spasenija et al. (2012) reported that the viscosity of fermented milk produced with Kombucha syrup made of black tea was significantly higher than that of control sample. These results show the positive effect of black tea ingredients on sample gel during storage. Syneresis of Doogh decreased with increasing Kombucha syrup level (P <0.05). Wu et al. (2013) reported that the Kombucha fungus is able to produce exopolysaccharide. Therefore, increase of dry matter of Doogh due to the increasing Kombucha syrup level and the presence of exopolysaccharides in the syrup, is the reason of the syneresis reduction in Doogh. Also, with increasing kombucha syrup level, the pH decreased (P <0.05). Because in this research the pH of kombucha syrup was about 2.89. The pH reduction can be due to the increased concentration of acetic acid and a small amount of lactic acid, gluconic and glucuronic acids produced by bacteria and yeast in tea fungus (Sreeramulu et al. 2000). Also, due to the use of black tea in the production of the kombucha syrup, addition of this syrup to Doogh, caused to decrease yellowness and to increase redness. On the other hand, Kombucha syrup had no negative effect on overall acceptance score of Doogh.
Conclusion: According to the experimental model obtained by the response surface method, the correlation between the studied variables detected appropriate. The results of this research showed that, the optimum points for production of Doogh was determined kombucha syrup level 20% and storage time 23 days. In optimum conditions, the number of Bifidobacterium bifidum, 7.6 log cfu/g, specific gravity, dry matter, syneresis and pH were 1.025, 8. 21. 29% and 3.95 respectively. The score of overall acceptance was 4.5 of 5.
