Gamma radiation in some microbiological and biochemical parameters of ethanolic fermentation

The objective of this work was to evaluate the effect of gamma radiation in reducing the bacterial population of the sugar cane must and verify its influence in the ethanolic fermentation. For this purpose, some microbiological and biochemical parameters of the ethanolic fermentation were analyzed, such as bacterial count; viability, replication and living replicates of the yeast; p H, acidity (total and volatile), glycerol and production of organic acids (acetic, lactic and succinic) during the fermentation; and fermentative yield. Bacteria of the genera Bacillus and Lactobacillus are the most common contaminants of the ethanolic fermentation and they might cause a decrease in the fermentative yield. The ionizing radiations may affect the microorganisms altering the DNA of the cells, which lose the ability to reproduce themselves and die. The experimental design was in randomized blocks (three) with one replicate in each block. The must was sugar-cane juice with approximately 5% of total reducing sugar. Bacteria of the following species were tested: Bacillus subtilis, Bacillus coagulans, Lactobacillus plantarum and Lactobacillus fermentum. The experiments were the inoculation of each bacteria separately in the must, the inoculation of the mixture of the four bacteria in the must and the use of natural sugar-cane juice with its own contaminating microorganisms. The contaminated must was irradiated with the doses of 0.0 (control), 2.0,4.0, 6.0, 8.0 and 10.0 kGy of gamma radiation (60-Cobalt) at an average rate of 2.0 kGy/h. After the irradiation, the fermentation of the must was carried out using the yeast Saccharomyces cerevisiae (Fleischmann). It was also accomplished an experiment with the inoculation of the mixture of the four bacteria in the must and, instead of using gamma radiation to decontaminate the must, it was used the antimicrobial Kamoran ID in the concentration of 3 ppm. The effects of the irradiation of the must were: reduction of the bacterial population that contaminated the must decrease of the total acidity, the volatile acidity, the p H drop and the production of the organic acids (acetic, lactic and succinic) during the fermentation; increased of the viability, the replication and the percentage of living replicates of the yeast after fermentation; and increased of the fermentative yield. The treatment of the sugar-cane must with gamma radiation reduced its bacterial population, with consequent improved of the microbiological and biochemical parameters of the ethanolic fermentation, including the fermentative yield. The irradiation of the must was a better treatment than the use of the antimicrobial Kamoran ID in the fermentation because the yeast in the experiment with the antimicrobial presented smaller viability, replication and percentage of living replicates than in the experiment with the irradiated must. (author)