Biochemical properties and viable probiotic population of yoghurt at different bacterial inoculation rates and incubation temperatures
2011
Mortazarian, A. M., Shahid Beheshti Univ. of Medical Sciences, P.O. Box 19395-4741, Tehran (Iran). Dept of Sciences and Technology | Ghorbanipour, S., The International and Virtual Branch of Shahid Beheshti Univ. of Medical Sciences, P.O. Box 19395-4741, Tehran (Iran). Dept. of Food Science and Technology | Mohammadifar, M. A., Shahid Beheshti Univ. of Medical Sciences, P.O. Box 19395-4741, Tehran (Iran). Dept of Sciences and Technology | Mohammadi, M., Shahid Beheshti Univ. of Medical Sciences, P.O. Box 19395-4741, Tehran (Iran). Dept of Food Technology Research
Combined effects of inoculation rate (standard inoculation (S), 2S, 4S and 8S (representing two-fold, four-fold and eight-fold of standard inoculation, respectively)) and incubation temperature (40 or 44 deg C) on biochemical and microbiological characteristics of yoghurt milk during and immediately after fermentation were investigated. Two probiotic bacteria (Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12), along with the yoghurt bacteria Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, were used. Acidification-related parameters during fermentation, incubation time and concentrations of lactic and acetic acids, as well as probiotic bacteria viability at the end of fermentation (final pH of 4.5), were determined. Incubation time and inoculation rate showed interactive effects on biochemical parameters and incubation time, as well as on viability of both probiotic bacteria. The greatest and the lowest pH drop as the lowest pH drop, acidity increase and redox potential increase rates were observed in the treatments 8S-44 (eight-fold inoculation and fermentation at 40 deg C), and S-40 (standard inoculation and fermentation at 40 deg C, respectively. The concentration of acetic acid was significantly greater (p0.05) in the treatments incubated at 40degC compared with those incubated at 44 deg C. The longest and the shortest incubation times were observed in the treatments S-40 and 8S-44, respectively. The greatest viability for each probiotic bacteria as well as the total probiotic bacteria was observed in the treatments 8S-40. The lowest viabilities at L.acidophilus and bifidobacterium were seen in the treatments 8S-44 and S-44, respectively.
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