| Functional probiotic dairy products have long been a research hotspot.In this project,1 lactic acid bacterium with excellent performance was screened from 16 lactic acid bacteria with acid and bile salt resistance in vitro preserved in the laboratory.After compounding it with commercial starter culture,the optimal process conditions for the production of sea buckthorn probiotic yogurt were studied,and the changes of the characteristics and storage period of the product were comprehensively evaluated.The main results are as follows:(1)Through the detection of gastrointestinal fluid resistance,β-glucosidase activity andα-glucosidase inhibition ability,3 dominant lactic acid bacteria were screened from 16 lactic acid bacteria,and physiological and biochemical identification combined with 16S rDNA sequencing showed that 2 strains were Lactobacillus plantarum(YHG-87,YHG-133)and 1 strain was Lactobacillus fermentum(YHG-148).The determination of growth curves showed that the growth status of the three lactic acid bacteria was similar.(2)Using single-factor experiments combined with Plackett-Burman test and response surface optimization experiment,the optimal preparation process of sea buckthorn probiotic yogurt was finally determined as follows:the compound ratio of strains was commercial bacteria:Lactobacillus plantarum YHG-87=1:2,sea buckthorn added 6.0%,white sugar added 7.0%,inoculation amount 0.11%,fermentation time 6.0 h,fermentation temperature 42.0℃.The yogurt prepared under this process condition had the highest sensory score and strong antioxidant capacity in vitro.Headspace-solid phase microextraction-gas chromatography-ion mobility spectroscopy was used to detect flavor substances in different samples,and a total of 46 volatile substances were detected,mainly including esters,ketones,aldehydes,alcohols,acids,furans,pyrazines,pinenes and other volatile compounds.Compared with ordinary yogurt,the L*value of sea buckthorn yogurt was reduced,and the a*value and b*value were increased(P<0.05).Texture tests showed that compared with ordinary yogurt,the hardness of yogurt with sea buckthorn was reduced,and there were no significant differences in viscosity,elasticity,cohesion,chewing and recovery(P>0.05),and the adhesion of yogurt fermented by complex bacteria was reduced compared with that of yogurt fermented by single bacteria(P<0.05).In addition,the total phenolic content and in vitro antioxidant capacity of sea buckthorn probiotic yogurt were the highest in each sample(P<0.05).(3)The total phenolic content and antioxidant capacity of ordinary yogurt(commercial bacteria),common probiotic yogurt(commercial bacteria+Lactobacillus plantarum YHG-87),sea buckthorn yogurt(commercial bacteria),sea buckthorn probiotic yogurt(commercial bacteria+Lactobacillus plantarum YHG-87),and sea buckthorn milk(unfermented)were compared in the simulated digestion stage in vitro.The results showed that oral digestion had no significant effect on the total phenolic content and antioxidant activity in vitro of the samples(P>0.05),and the total phenolic content and in vitro antioxidant activity of sea buckthorn probiotic yogurt were the highest in the simulated gastric digestion stage,and were significantly improved after digestion;After simulated intestinal digestion,the DPPH radical scavenging capacity of sea buckthorn probiotic yogurt decreased(P<0.05),while the total phenolic content,ABTS radical scavenging capacity and iron ion reduction capacity were significantly increased(P<0.05).(4)The stability and antioxidant activity of the above four yogurt samples were studied after refrigeration at 4℃ for 28 days.The results showed that the sensory scores of all yogurt samples decreased with the increase of storage time,and the overall acceptance of sea buckthorn yogurt was consistently higher than that of ordinary yogurt.The L*value and a*value of the four yogurt samples decreased significantly with the extension of storage time(P<0.05),and the b*value did not change significantly(P>0.05),and the water holding rate of sea buckthorn yogurt was significantly higher than that of ordinary yogurt at the 28th day of storage,and the pH value of the four yogurt samples showed a downward trend,and the titration acidity showed an increasing trend.Compared with ordinary yogurt,sea buckthorn probiotic yogurt can maintain a higher viable bacteria count during storage;In terms of in vitro antioxidant activity,all samples showed a trend of decreasing first and then maintaining a stable trend,and sea buckthorn probiotic yogurt always maintained the highest total phenolic content and in vitro antioxidant activity(P<0.05). |
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