Preparation of Quercetin-fortified Yogurt and Its Intestinal Flora-regulating Effect in Mice
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Abstract:
Using sensory evaluation score and acidity as evaluation indices, the optimal fermentation conditions and optimal formula of quercetin-fortified yoghurt were determined by the single factor and orthogonal test methods. The effect of quercetin on the microbes in the yoghurt was investigated by measuring the total number of lactic acid bacteria of yogurt. Examinations were performed on the dynamic changes in the microbial community induced by quercetin-fortified yoghurt i.e. the proliferation of Lactobacillus, Bifidobacterium, Enterobacter and Enterococcus in mice. The experiments revealed that the optimal fermentation conditions and formula of quercetin-fortified yoghurt were: fermentation time 8 h, fermentation temperature 42 ℃, inoculation dosage 0.1%, added milk powder 12%, added sucrose 4%, and added quercetin added 0.1%. The obtained quercetin-fortified yoghurt had uniform color (yellow-green color) and sweet-sour balanced taste, with a pleasant and slight bitterness (which likely came from the added quercetin and some peptides derived from protein hydrolysis). The total number of lactic acid bacteria in quercetin-fortified yoghurt was (1.475±0.005)×108 cfu/mL, which was higher than that for the unfortified yogurt (p<0.05). Observations on the dynamic microbial changes revealed the alterations in the proliferation of intestinal flora in mice: the growth of Lactobacillus and Bifidobacterium in the quercetin-fortified yogurt was stronger while the growth of Enterobacter and Enterococcus was weaker, compared with that of unfortified yogurt. The results showed that the quercetin-fortified yoghurt prepared under the optimal conditions could promote the proliferation of Lactobacillus and Bifidobacteria in vitro but inhibit the proliferation of Enterobacter and Enterococcus in vitro, with its taste better than that for the commercially available yoghurt. The results of this study provide a theoretical basis for the subsequent development and utilization of quercetin-fortified functional yogurt.
