Otimização do processo produtivo da levedura Candida pseudointermedia CMIAT 168 – L10 por fermentação descontínua simples

Abstract

The yeast Candida pseudointermedia CMIAT 168-L10 was isolated from the natural tropical fruit microbiota by Embrapa Semi-Arid (Petrolina / PE), presenting an antagonistic activity against post-harvest phytopathogens. The development of a process of biomass production of this yeast will make possible field scale studies, and future use as a biological control agent. In this way, this work aims to define conditions of the fermentation process of greater production of biomass. First, the yeast was activated in YM medium containing 3 g/L of yeast and malt extract, 2 g/L of peptone and 4 g/L of dextrose in 100 mL of medium per 24h. The growth of C. pseudointermedia was carried out in a single batch, with the modified YM culture medium, differing the carbon source, consisting of 5g/L peptone, 3g/L yeast extract, 3g/L malt extract and inverted commercial sucrose, pH corrected to 4.5. Three different concentrations of sucrose were evaluated at 20, 30 and 40 g/L. The process conditions were: temperature 30 °C, agitation at 150 rpm and aeration 8 Lar/min. Then, an experimental design was drawn with three independent variables: sucrose concentration (25, 30 and 35 g/L), aeration rate (8, 9 and 10 Lar/min) and agitation rate (150, 175 and 200 rpm). For the analysis of the fermentation process, samples with 3-hour time intervals were taken, which were submitted to the analysis of biomass by optical density, analysis of total sugars by the 3,5-dinitrosalicylic method. All fermentations were conducted in duplicate. The maximum yield of the processes with initial sugar concentration at 20, 30 and 40 g/L were after 24 hours of cultivation. As results, biomass concentrations of 13.1, 18.56 and 17.53 g / L and residual sugars of 0.392, 0.523 and 0,967 g/L were obtained and productivity of 0.434, 0.695, 0.647 g/L/h and the biomass yield of 0.646, 0.621, 0.486 g/g in fermentations with 20, 30 and 40 g/L of sucrose, respectively. The results showed that the growth of the yeast remained linear with the increase of the sugar concentration, but this when reaching high concentrations in the medium, as in the process with a sucrose concentration at 40 g/L, aeration 8 Lar/min and agitation 150 rpm, caused the repression of cellular respiration, due to the lack of adequate oxygen supply for the metabolization of this glucose in the medium. Regarding the design, it was observed that of the assays that produced more biomass was the test 5. Thus, it was concluded that the best condition for the process was with 25 g/L sucrose, 8 Lar/min aeration and 200 rpm agitation.