Produção de biomassa da levedura Saccharomyces cerevisiae CMIAT 170-L7K antagônica a fungos fitopatogênicos

Abstract

Saccharomyces cerevisiae has a worldwide biotechnological importance, whether in baking, in the production of alcoholic beverages and ethanol, as a source of protein for humans and animals and in biological control. The S. cerevisiae strain CMIAT 170-L7K isolated from tropical fruits natural microbiota by Embrapa Semi-Arid (Petrolina/PE) has antagonic activity to phytopathogens of post-harvesting rot caused by Apergillus niger in table grape. The aim of the present work was to establish a fermentative process for biomass production of yeast S. cerevisiae CMIAT 170-L7K that present an antagonistic potential against phytopathogens. Therefore, 20 mL of the pre-inoculum with 24 hours of cultivation of the culture activated in YM medium was injectected in a bioreactor BioFlo 115 with a 2 L useful volume fermentation vat, which contained YM2 culture medium. Initially, discontinuous process fermentations were conducted as a control: agitation 150 rpm, aeration 8 Lair/min and temperature 30 ± 1ºC in fermenter, with two impellers Ruston. Then, the feeding process was studied with a concentrated solution containing 200 g/L of hydrolysed sugar. The feeding was initiated with 16 hours of fermentation process and the feeding rates were 12,5, 15, 20 mL/h. In a third experiment, it was performed an experimental design of factorial 2³ under the influence of the variables aeration rate (8, 9, 10 Lair/min), agitation (150, 200 e 300 rpm), and feeding rate (15, 17,5 e 20 mL/h). Samples of all fermentations were taken at regular intervals and centrifuged. In the supernatant, the concentration of reducing sugars was determined by the DNS method. The pellet was resuspended in distilled water for the quantification of the biomass concentration by spectrophotometry at 600 nm. In the discontinuous process, the biomass production was 7,65 g/L after 24 hours of cultivation. For the fed discontinuous process with the feeding rate of 12,5 a 20 mL/h, the final biomass production was slightly higher than 14 g/L after 40 hours of cultivation. In the experimental design, it was verified that increase in the production of biomass after 40 hours of fermentation to 15.65g / L. It was concluded that all variables at the maximum level with feeding rate at 20 mL / h, aeration of 10 L. ar / min and agitation rate of 200 rpm were the parameters for the production of higher biomass concentration of this S. cerevisiae strain.