Regulating Effect of Exogenous Carbon Source on Microbial Growth and Metabolism in Grape Fermentation and Its Bioactivity

In this paper,the difference of growth and metabolism of yeast and lactic acid bacteria,as well as superoxide dismutase(SOD)activity and antioxidant capacity was investigated by adding extra carbon sources,including brown sugar,white sugar or honey in the grape-fermentation. The microbial count was measured by plate colony-counting method. Organic acid contents were determined by high performance liquid chromatography(HPLC). SOD activity was determined by pyrogallol autooxidation method. Antioxidant capacities were studied by(1,1-Diphenyl-2-picrylhydrazyl)DPPH free radical,(3-Ethylbenzothiazoline-6-sulfonic acid)ABTS⁺ free radical and(Hydroxyl radical)OH free radical scavenging experiments.The results showed that the addition of carbon source retarded yeast growth and ethanol metabolism,and simultaneously facilitated the growth of lactic acid bacteria and acid production. Among them,brown sugar and white sugar had strong inhibition ability on yeast growth and ethanol metabolism,the ethanol concentration reached 2.07%vol and 1.62%vol after fermentation respectively,which was significantly lower than honey group(P<0.05). Brown sugar could promote the growth of lactic acid bacteria and increase the total acid content and SOD activity. The pH value decreased from 4.16 to 3.83,and the SOD activity increased from 71.68 U/mL to 91.05 U/mL after fermentation. In comparison with white sugar,honey and control group,adding brown sugar significantly increased the DPPH,ABTS⁺,OH free radicals scavenging rate(P<0.05)in grape fermentation. The raw grape juice contained a lot of tartaric acid and malic acid,but the addition of all carbon source significantly increased the content of malic acid and lactic acid,acetic acid and citric acid. Whereas,the content of tartaric acid decreased significantly(P<0.05)by adding brown sugar,and it did not change much by adding white sugar and honey. In conclusion,the addition of brown sugar in grape-fermentation was beneficial to improve the growth and metabolism of microorganisms and enhance the nutritional value of products.