Screening And Characterizing Of Malolactic Bacteria Isolate From The Eastern Foothill Of Helan Mountain In Ningxia

Lactic acid bacteria as the main participants of malolactic fermentation which can improve the wine quality,help to improve the wine microbial stability,makes wine taste softer and increase sensory complexity.In recent years,the extensive use of several commercial strains for malolactic fermentation in wine production in China has brought about a serious problem of wine homogenization,which is not conducive to the protection,development and utilization of local wine-making microbial resources.There are obvious differences among the wine producing areas in the eastern foot of Helan Mountain in Ningxia,which are rich in wine-making microbial resources,but the "customs" characteristics of wine are not prominent.Therefore,through the study on the isolation and screening of local malolactic bacteria in the producing area,it is of great significance to screen the excellent strains suitable for malolactic fermentation in the producing area and to brew wine with the characteristics of "customs" in the producing area.In this study,malolactic bacteria strains were isolated and identified from natural malolactic fermentation of Petit Vendot wine in the eastern foot of Helan Mountain in Ningxia.Excellent Lactobacillus plantarum strains with good stress tolerance and β-D-glucosidase activity were screened.Finally,the wine-making characteristics of Lactobacillus plantarum strains were investigated.The main conclusions are as follows:1.A total of 132 native strains were isolated from the natural fermentation of Petit Vendot wine in the eastern foot of Helan Mountain in Ningxia.After morphological,physiological and biochemical identification,the isolated strains were screened under 15%(v/v)ethanol stress.The 16S rRNA sequencing and RAPD genotyping of 21 strains with 15%(v/v)ethanol stress and higher than 107 CFU/mL were carried out.Among them,20 strains were Lactobacillus plantarum,1 strain was Lactobacillus hilgardii,and 21 strains identified as polymorphic genomic DNA.2.The tolerance of 20 strains of Lactobacillus plantarum to stress in wine(ethanol,pH,SO2)andβ-D-glucosidase activity were analyzed.The results showed that strains A7,A50,A23,A18 and B28 had good tolerance to wine stress.The results of β-D-glucosidase activity of 5 strains with good tolerance showed that the β-D-glucosidase activity of A7,A50 and B28 strains was higher than that of commercial control strains.3.Three strains of Lactobacillus plantarum were inoculated into Cabernet Sauvignon wine.The malolactic fermentation rate,the changes of basic physical and chemical indexes before and after MLF,the safety of biogenic amines and aroma composition of wine were determined.The results showed that After 32 days of start-up fermentation,the L-malic acid content of strain A7 decreased to about 0.1 g/L,which showed better malolactic fermentation ability compared with the commercial control strain.After malolactic fermentation,the contents of volatile acids and biogenic amines in wine samples increased,but much lower than the international limit standard.At the same time,compared with the commercial control strain,the variety and content of volatile aroma compounds in the wine samples inoculated with strain A7 for malolactic fermentation were more,especially the contents of esters and terpenes in the wine samples increased significantly,giving the wine unique fruit aroma,flower aroma and other aroma characteristics.The above results show that strain A7 has good potential for commercial application.