气相色谱-质谱法分析乳酸菌发酵苹果汁香气成分

摘要

In this study,changes in optical density (OD) during the fermentation of apple juice with pure and mixed cultures of lactic acid bacteria were monitored by a UV-Vis spectrophotometer.The aroma components of nine fermented apple juices were identified by head-space solid phase micro-extraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS),and the characteristic aroma components were evaluated by odor activity value (OAV) and odor threshold value (OTV).Sensory evaluation was also carried out on the samples.The results showed that the OD value of apple juice increased logarithmically with time.Forty eight aroma components were identified from nine fermented apple juices,mainly including alcohols,esters,aldehydes,ketones and phenols.Esters were the most abundant components with the highest species diversity,followed by alcohols.In addition,according to their aroma values,butyric acid ethyl ester,ethyl-2-methylbutyrate,2-methylbutyl acetate and hexyl acetate were the main aroma components in all the fermented samples.The contents of aroma components and aroma values from single and mixed culture fermentation of apple juice were significantly different (P ＜ 0.05).It was shown that the total contents of alcohols,esters and other aroma components with mixed culture fermentation were significantly higher than those of single culture fermentation and apple juice fermented with single cultures had a stronger fruity,green and flowery aroma.The overall sensory score of apple juice fermented with mixed cultures was higher than that of single culture fermentation.A mixed culture of Lactobacillus paracasei 20241,Bifidobacterium animalis 6165,Streptococcus thermophilus 6063 and Lactobacillus acidophilus 6005 at a ratio of 1∶1∶1∶1 was the optimal combination in sensory acceptance.These results can provide a theoretical basis for the research and application of lactic acid bacteria in fermented fruit and vegetable juice.%以乳酸菌单一菌种和多菌组合分别发酵苹果汁,采用紫外-可见分光光度计测定发酵过程中苹果汁光密度(optical density,OD)的变化,采用顶空固相微萃取和气相色谱-质谱联用技术检测9组发酵苹果汁的香气成分,结合不同香气物质的阈值与香气值分析特征香气成分,并对各组苹果汁进行感官评价.结果表明:在发酵过程中苹果汁的OD值呈对数上升趋势.各组苹果汁中共鉴定出48种香气成分,主要包含醇类、酯类、醛类、酮类和酚类,其中酯类是各发酵组中种类最多且含量最大的香气类别,其次是醇类.9组苹果汁的主要香气成分和香气值较大并有突出贡献的特征香气成分均为丁酸乙酯、2-甲基丁酸乙酯、2-甲基丁基乙酸酯和乙酸己酯等.多菌发酵和单菌发酵苹果汁的香气成分含量及香气值差异显著(P＜0.05),说明多菌发酵中醇类、酯类和其他类香气物质的总含量明显高于单菌发酵,且赋予苹果汁更强烈的果香、青香和花香.多菌发酵组的总体感官评分高于单菌发酵组,当副干酪乳杆菌20241、动物双歧杆菌6165、嗜热链球菌6063、嗜酸乳杆菌6005活菌数比为1∶1∶1∶1时,感官评分最优.研究结果为今后乳酸菌在发酵果蔬汁方面的研究和应用提供理论依据.