Study Of The Effects On Coffee Flavor Of Lactic Acid Bacteria Inoculation

In this study,two strains of Lactobacilli with pectinase activity were selected from 4 strains of flavor-producing lactic acid bacteria and used to study the modulation of coffee flavor by inoculating lactic acid bacteria under the condition of keeping the natural microbial strains.The changes of p H,the macroscopic changes of coffee beans and the microbial populations of fermentation system,have been studied to explore the influence on fermentation by lactic acid bacteria inoculation.The study further explored the changes of non-volatile components and volatile aroma components in green beans and roasted beans obtained from different fermentations and the changes of volatile aroma components in different cupping extracts.The sensory evaluation was carried out by professional sensory graders according to the standard of Specialty Coffee Association of America(SCAA),evaluating the changes of coffee flavor by the inoculated fermentation of the two lactic acid bacteria,which can provide some guidance for the related research and industrialization of the application of lactic acid bacteria in coffee inoculated fermentation.The main results of the study are as follows:(1)The lactic acid bacteria strains with good pectinase and pectin esterase activity were screened out by the pectin medium combined with Congo red staining method.L.plantarum115(LP)and L.mesenteroides 57(LM)were selected for the inoculated fermentation of coffee beans.(2)The inoculated fermentation of LP and LM brought significant changes(p<0.05)to the microbial population and p H of the coffee fermentation system.The inoculation of LP enabled LP to always maintain an absolute growth advantage in the system,making the number of lactic acid bacteria up to 6.90×10~8 CFU/g,decreased the acidity of the system continuously,reaching the lowest p H 3.35 at the end of the fermentation,and reduced the growth of miscellaneous bacteria,leading the whole system to have highly concentrated dominant microbial strains.The inoculation of LM enabled LM to always maintain a relative growth advantage in the system,making the number of lactic acid bacteria up to 2.80×10~8 CFU/g,made rapid acidification of the system,reaching the lowest p H 3.56 in 36 hours,and reduced the growth of miscellaneous bacteria while induced the growth of specific microbial strains,leading the whole system to have more kinds of dominant microbial strain than the LP fermentation system.(3)The inoculated fermentation of LP and LM brought significant changes(p<0.05)to the non-volatile components of green coffee beans and roasted coffee beans,including carbohydrates,phenolic acids,organic acids and amino acids.Inoculated fermentation changed green beans by reducing the glucose and fructose content and increasing the sucrose content;it increased the total amount of chlorogenic acid,LP fermented green beans increased by about49.70%compared with generally fermented green beans while LM fermented green beans increased by about 36.17%;there were significant differences(p<0.05)in the content of most of the organic acids,among then the lactic acid content of LM fermented green beans was greatly increased,approximately 220 times as many as in generally fermented green beans;amino acids had significant differences(p<0.05)both in composition and content.In roasted beans,inoculated fermentation enhanced the aroma properties of coffee;in addition,inoculated fermentation made the acidity properties of roasted coffee beans softer,LM fermented roasted beans contained the most malic acid,about 3.09 mg/g,and LP fermented roasted beans contained the most lactic acid,about 8.28 mg/g.(4)The inoculated fermentation of LP and LM brought significant changes(p<0.05)to the volatile components of both green coffee beans,roasted coffee beans and coffee extracts.Alcohols,aldehydes,acids,and esters were the main volatile components in green beans,and the inoculation of LP brought more aromatic compounds,heterocyclic substances,and ketones while the inoculation of LM brought more furans,acids and alcohols.Furans and pyrazines were the main volatile components in roasted beans.Inoculated fermentation resulted in different substituents of these two types of substances.In addition,the inoculation of LP brought some characteristic aromatic aldehydes and esters,giving the soft acidic fruit aroma to the coffee roasted beans and the inoculation of LM brought some characteristic acids,aldehydes,esters and the high content of pyrroles,giving not only the typical roasting aroma but also the rich floral and fruity aroma to the coffee roasted beans.Furans,pyrazines,aldehydes and ketones were the main volatile components in the coffee extract and the inoculation of LP brought the characteristic products with creamy aroma for the coffee extract while the inoculation of LM brought the characteristic products with fruity aroma for the coffee extract.(5)The inoculated fermentation of LP and LM improved the sensory scores(p<0.05)of roasted coffee beans.The final score order was LP fermented roasted beans>LM fermented roasted beans>generally fermented roasted beans.Among the descriptions of aroma characteristics,LP fermented roasted beans had unique cream aroma,and LM fermented roasted beans had unique strong cinnamon and starfruit aromas.