Selection of a galactose-positive mutant strain of Streptococcus thermophilus and its optimized production as a high-vitality starter culture.

Streptococcus thermophilus (S. thermophilus) is a common starter in yogurt production and plays an important role in the dairy industry. In this study, a galactose-positive (Gal+) mutant strain, IMAU20246Y, was produced using the chemical mutagen N-methyl-N'-nitro-N-nitrosoguanidine (NTG) from wild type S. thermophilus IMAU20246 which was known to have good fermentation characteristics. The sugar content of milk fermented by either the mutant or the wild type was determined using high performance liquid chromatography (HPLC); metabolism of lactose and galactose was significantly increased in the mutant strain. In addition, we used the response surface methodology to optimize components of the basic medium M17 for survival ratio of the mutant strain. Under these optimal conditions, the viable counts of mutant S. thermophilus IMAU20246Y reached 4.15 × 108 cfu/mL and following freeze drying in the medium retained cell viability of up to 67.42%. The above results are conducive to production of a high vitality starter culture and development of 'low sugar, high sweetness' dairy products.

Influence of Different Ratios of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus on Fermentation Characteristics of Yogurt.

Lactic acid bacteria (LAB) are industrially important bacteria that are widely used in the fermented food industry, especially in the manufacture of yogurt. The fermentation characteristics of LAB are an important factor affecting the physicochemical properties of yogurts. Here, different ratios of L. delbrueckii subsp. bulgaricus IMAU20312 and S. thermophilus IMAU80809 were compared with a commercial starter JD (control) for their effects on viable cell counts, pH values, titratable acidity (TA), viscosity and water holding capacity (WHC) of milk during fermentation. Sensory evaluation and flavour profiles were also determined at the end of fermentation. All samples had a viable cell count above 5.59 × 107 CFU/mL at the end of fermentation, and a significant increase in TA and decrease in pH were observed. Viscosity, WHC and the sensory evaluation results of one treatment ratio (A3) were closer to the commercial starter control than the others. A total of 63 volatile flavour compounds and 10 odour-active (OAVs) compounds were detected in all treatment ratios and the control according to the results from solid-phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS). Principal components analysis (PCA) also indicated that the flavour characteristics of the A3 treatment ratio were closer to the control. These results help us understand how the fermentation characteristics of yogurts are affected by the ratio of L. delbrueckii subsp. bulgaricus to S. thermophilus in starter cultures; this is useful for the development of value-added fermented dairy products.

Seven new chemical constituents from the roots of Gentiana macrophylla pall.

Gentimilegenins A, B (1, 2), (6R, 8R)-6-hydroxy swerimuslactone A (3), (6R, 8S)-6-hydroxy swerimuslactone A (4), 4-hydroxy roburic acid methyl ester (5), (±) 3'-hydroxy gentioxepine (6), N-heptacosanoyl anthranilic acid (7a), N-nonacosanoyl anthranilic acid (7b), together with 40 known compounds were isolated from the roots of Gentiana macrophylla Pall. Their structures were elucidated on the basis of comprehensive analysis of HRESIMS, IR, 1D-, 2D-NMR and X-ray diffraction. The anti-inflammatory effects of selected compounds were also evaluated through the detection of their inhibitory effects on NO production in LPS-induced RAW264.7 macrophage cells.