| China is a big country in melon production,but melons in the market are mainly fresh food,canned melons,pickled melons,etc.The processing method is relatively simple and the utilization rate is low,while melons are not easy to store,resulting in great waste.Reasonable development and utilization of melon and moderate processing can solve the problems of storability and product simplification at the same time.Lactic acid bacteria fermentation of fruit and vegetable juice is a research hotspot in recent years.It can not only improve the flavor of products,increase nutrients,but also extend the shelf life of fruits and vegetables.In this study,a fermented juice was made of the Yangjiaocui sweet melon juice with lactic acid bacteria,which had good flavor and laxative activity.The main results are as follows:(1)Preparation of croissant sweet melon juice fermented by lactic acid bacteria:Taking sweet melon as raw material,Lactobacillus plantarum C17 and Lactobacillus pentosus Lp-B as strains,the production of γ-aminobutyric acid(GABA)as index,fermentation time,fermentation temperature and inoculum amount as research conditions,and the ratio of 1:1,the fermentation process was optimized.The optimum fermentation conditions were determined by single factor and orthogonal experiments as follows:fermentation time 18 h,fermentation temperature 40℃,inoculum 7%(1 × 108 CFU/ml).Under these conditions,the maximum yield of GABA was 2.01 mg/ml.(2)Study on volatile flavor of sweet melon juice fermented by lactic acid bacteria:Headspace solid phase microextraction-gas chromatography-mass spectrometry(HS-SPME-GC-MS)and headspace gas chromatography-ion mobility spectrometry(HS-GC-IMS)were used to measure the changes of volatile components before and after fermentation.By GC-MS analysis,45 volatile components were detected in sweet melon juice before and after fermentation.Before fermentation,the main components were nonanol,(6Z)-Nonen-l-ol and(Z)-3-Nonen-l-ol and after fermentation,the main components were 2,3-butanediol-diacetate,2-methoxy-3-propenylphenol and 2-methoxy-3-propenyl phenol.After fermentation,the aroma similar to rose and orange in the juice did not weaken,and the pungent acetic acid smell was removed,which increased the fruit aroma.GC-IMS analysis showed that 49 volatile components were detected in sweet melon juice before and after fermentation,including alcohols(6 kinds),esters(14 kinds),aldehydes(17 kinds)and ketones(8 kinds).The fermented melon juice reduced the bad flavor brought by pretreatment process and increased the aroma similar to banana,pineapple,apple and rose.GC-IMS technology is more sensitive.(3)Study on the laxative function of sweet melon juice fermented by lactic acid bacteria in mice:Lactic acid bacteria fermented sweet melon juice was prepared under the optimal fermentation conditions,mice with constipation induced by loperamide hydrochloride were given different doses by gavage.The results showed that lactic acid bacteria fermented sweet melon juice could reduce the first black stool time of constipation mice,increase the number and weight of defecation in 6 hours,improve the intestinal propulsion rate of constipation mice,increase the fecal water content,regulate the gastrointestinal active peptide,promote the production of short chain fatty acids in the intestine,restore the integrity of colon tissue.Adjust the intestinal flora from α diversity,βdiversity,phylum level and genus level.Among them,the high-dose group and sterilization group of lactic acid bacteria fermented sweet melon juice had the best effect on relieving constipation in mice.In this study,GABA-rich lactic acid bacteria fermented sweet melon juice with laxative function was prepared,which improved the flavor,and provided a new idea for the study of flavor and functionality of fruit and vegetable juice. |
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