Test design
Test materials: fresh milk,xylo-oligosaccharides, Lactobacillus bulgaricus (Lb), Streptococcus thermophilus (St).
Strain activation: Activate Lactobacillus bulgaricus and Streptococcus thermophilus in skim milk three times until their activity is stable (judged by microscopic examination and curdled milk), then store them in the refrigerator for later use. Test method: Prepare 21 equal amounts of fresh milk samples and divide them into 3 groups, with 7 samples in each group. Add concentrations (%, w/v) of 0, 0.5, 0.6, 0.7, 0.8 to the samples in each group. , 0.9 and 1.0 xylo-oligosaccharides, and mix Lb and St in the proportions of 2:1, 1:1, and 1:2 respectively to make a starter culture, and then inoculate into 3 groups with an inoculation amount of 3%. Ferment at a constant temperature of 42°C, and take samples at regular intervals to measure the number of viable bacteria, pH value, acidity and lactic acid content in each group of milk.
test results
(1) Lb: St = 2: 1, the effect of xylo-oligosaccharides on the growth and acid production of yogurt fermentation strains
As can be seen from Figure 1, 0 to 1.5 h is the adaptation period of the strain and the initial stage of entering the logarithmic growth phase. The strain does not grow quickly, the pH value decreases slowly, and the acidity and lactic acid increase rapidly. When the xylo-oligosaccharide concentration is 0.7%, the total bacteria The maximum value is 1.94×108 CFU/mL (the control is 1.15×108 CFU/mL), and the pH, acidity and lactic acid content are similar to the control; between 1.5 h and 3.5 h, the strain enters the logarithmic growth phase and grows rapidly. The pH dropped rapidly, and the acidity and lactic acid content increased rapidly. When the xylo-oligosaccharide concentration was 0.7%, the maximum total bacterial count was 5.65×108 CFU/mL (the control was 5.41×108 CFU/mL). The pH, acidity, and lactic acid content They were 5.82, 63 and 4.93 respectively, and the pH, acidity and lactic acid content of the control were 6.05, 56 and 4.67. From 3.5 h to 4.5 h, the total bacterial count decreased, the pH dropped slowly, and the acidity and lactic acid content increased slowly.
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Post time: Nov-14-2023
