Study On Characteristics Of Lactic Acid Bacteria In Fig Pulp Fermentation

Figs are cash crops for medicine and food cultivated in subtropical,temperate region,with rich nutritions and various of phytochemicals.But their high sugar content,soft texture and inadequate skin protection make it difficult to transport over long distances.The storage period is only 1?2 days,which greatly affects their edible and economic values.Lactic acid bacteria fermentation can metabolize sugars to produce organic acids and SOD,which can improve the flavor of food,increase the content of phytochemicals and antioxidant capacity.In view of the differences in metabolic pathways and products of lactic acid bacteria,this study used fig pulp as the fermentation substrate to explore the changes of various components induced by lactic acid bacteria of different fermentative types.The study aimed to provide theoretical guidance for the follow-up study on the fermentation and transformation mechanism of lactic acid bacteria and the further development and utilization of figs resources.The main results are as follows:1.Pediococcus pentosaceus HM04 known as obligately homofermentative organism,Lactobacillus plantarum EH06 as facultatively heterfermentative organism,and Leuconostoc mesenteroides HE01 as obligately heterfermentative organism were applied in fermentation of fig pulp.Three kinds of lactic acid bacteria can produce vast of biomass in fig pulp.The number of viable bacteria during 48 h fermentation was counted at the inoculation concentration of1.5×10~6 cfu/g FW.The results showed that the three strains presented typical four-stage curves.The viable number of LP was the highest at 21 h fermentation,which was 8.39×10~8 cfu/g.LM and PP obtained the highest viable numbers of 9.20×10~8 cfu/g and 6.17×10~8 cfu/g respectively at 24 h during fermentation.2.With the progress of fermentation,the nutrients and physical and chemical indexes in the fermentative pulp changed regularly due to the growth of bacterial cells.The total sugar,reducing sugar and glucose decreased significantly after 6 h and 33%?45%of origin sugars retained at the end of fermentation.Malic acid in fruit pulp was exhausted,citric acid decreased significantly after 24 h,lactic acid began to produce from 0 h,12?24 h was a period of rapid growth,and after entering the stable period,the growth rate decreased slowly.After 36 h fermentation,the p H of the fermentative pulp was 3.25?3.35.The main chemical compositions were total sugar 42 to 46 g/100g DW,total acid 9.2 to 10.5 g/100g DW,organic acid 6.2 to 7.3g/100g DW and lactic acid 5.8 to 6.8 g/100g DW.3.In the process of fermentation,glucose and fructose were co-metabolized,malic acid was biotransformed to lactic acid,citric acid and glucose were co-metabolized in late fermentation.Biomass correlated positively with lactic acid yield during fermentation.The biomass of PP was negatively correlated with malic acid,tartaric acid and reducing sugar.The yield of lactic acid was negatively correlated with the contents of reducing sugar,malic acid,citric acid and tartaric acid.The biomass of LP was negatively correlated with fructose,malic acid and glucose in fermentative pulp.The yield of lactic acid was negatively correlated with the content of glucose,fructose and malic acid,but positively correlated with the content of succinic acid.LM biomass was negatively correlated with the contents of total sugar,malic acid,fructose and glucose,but positively correlated with the contents of succinic acid.The yield of lactic acid was negatively correlated with the content of reducing sugar,total sugar and malic acid,but positively correlated with the content of succinic acid.4.HS-SPME and GC-MS methods were used to study the changes of aroma components induced by fermentation of fig pulp by three strains of lactic acid bacteria.Pulp flavor distinguished due to different types of lactic acid bacteria utilized.The aroma of fig is dominated by?-rhodoxone,2-hexenal,(E,E)-2,4-nonadienal,hexaldehyde,linalool,1-octene-3-ol,decanal,showing composite flavor of violet,fragrance,melon and fruit oil fragrance.PP fermentation induced the increase of guaiacol,(E,E)-2,4-decadienal,1-octene-3-one,hexyl acetate,heptanone,1-amyl alcohol,hexyl alcohol,citral,iso-amyl acetate,the fermentative pulp showed aromatic and mixed fruity and mushroom flavor.After 24 h,the aroma of LP fermented pulp was stronger than that of PP fermentative pulp,which characteristic aroma composed of damasone,2-nonene-1-ol,2-methylpentaldehyde,trans-2-octenal,ethyl caproate,trans-2-decenal,2-heptanone,methyl-heptenone,benzyl acetate and l-ethyl lactate giving flavor of rose,citrus,cucumber,faint bouquet,jasmine.LM fermented pulp has a small variety of characteristic aroma,which composition was similar to that of LP fermented pulp,exceptionally with a unique grape aroma.5.The main phytochemicals and antioxidant capacity of fruit pulp changed inductively by three strains regularly.SOD activity,total phenol content and gallic acid content increased significantly,while most of total flavonoids increased during fermentation.Chlorogenic acid and ferulic acid increased firstly and then decreased,leading to the increase of total flavonoids,while coumaric acid and quercetin did not change significantly.The facultative fermentative strain LP had the strongest scavenging ability of DPPH and ABTS,while the heteromorphic fermentative strain LM had the strongest scavenging ability of hydroxyl radical,and both LP and LM had stronger total reducing ability than the homofermentative strain PP.The highest antioxidant level was presented by LP fermentative pulp,then followed by those of LM and PP.The contents of gallic acid,SOD activity,total phenol,total flavonoids and chlorogenic acid could be used as indexes to evaluate the antioxidant capacity of fermentative pulps by the three strains.