Study on Fermentation Process of Mushroom Yogurt by a Strain of Lactobacillus paracasei and Analysis of Volatile Components
In order to integrate the nutrition of yogurt with that of mushrooms,improve the nutritional value of yogurt,and increase the types of deeply processed products of mushrooms and the taste of yogurt,in this study,with mushroom juice and milk as the main raw materials,the patented microorganism Lactobacillus paracasei separated and screened is inoculated for fermentation.Single factor experiment is conducted on the ratio of raw materials,sugar addition amount,inoculation amount and fermentation temperature.Based on the results of single factor experiment,response surface optimization experiment is used to determine the optimal process for the fermentation of mushroom yogurt by Lactobacillus paracasei.The results show that the optimal ratio of milk to mushroom juice is 2∶1,the addition amount of sugar is 7％,the starter inoculation amount is 4％and the fermentation temperature is 28 ℃.Under these conditions,the obtained mushroom yogurt has uniform milky white color,with the flavor of natural mushrooms and yogurt fermentation.The sensory score reaches 81 points.The physical,chemical and microbiological indexes are detected,and the results show that the products produced using this microorganism and fermentation process meet the national standards for fermented milk.At the same time,the volatile components are determined and analyzed using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry(HP-SPME/GC-MS).A total of 26 volatile flavor components,including ketones,acids,alcohols,olefins and alkanes are detected,among which,the relative content of ketones is the highest,accounting for 57.18％,and the relative content of acids accounts for 13.69％.Meanwhile,the main volatile compounds of mushrooms,such as l-octen-3-ol(mushroom alcohol)and 1,2,3,5,6-pentathiepane(mushroom essence)are detected,and the relative content accounts for 9.17％and 1.96％respectively,which is consistent with the sensory evaluation that mushroom yogurt has a strong mushroom flavor.
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