Study of fermentation flasks

Author(s)

Leonel Vasco Ferreira

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos
• Defense date: 2002-12-19

Examining board members

Gil Eduardo Serra; Clovis Parazzi; Henrique Vianna de Amorim; Dejanira de Francheschi de Angelis; Marcio Caliari

• Advisor: Gil Eduardo Serra

Abstract

Fermentation trials were performed with different levels of inoculum, initial mash pH and temperature, and using different substrate conoontrations of glucose, sucrose, industrial syrup and molasses from sugarcane production. The kinetics of carbon dioxide liberation was determined in parallel in ali experiments. The kinetic parameters of the alcoholic fermentation with glucose as substrate were also determined. Fermentation was monitored by determining ethanol, glyoorol, residual sugars, 0011mass, yeast viability and 0011count and other variables. The yield and kinetic parameters were also determined. The experiments were carried out in a laboratoryin shakenflasks. The inoculumof 108viable 0011sImL resulted in rapid fermentations (2 - 8 hours) whilst with 104oolls the fermentations were sluggish (18 to 44 hours). The initial pH values of 3.5 and 5.0 caused various responses in the physiology of the yeast, resulting in significant alterations in fermentation yield. It was observed that whenever three negative factors were present - high substrate conoontration, pH 3.5 or high temperature (38°C) - the fermentation yield and yeast viability were reduood. The determination of the kinetics of carbon dioxide liberation was shown to be an effective way of precisely determining the fermentation time and estimating the production of ethanol and sugar consumption. By way of the kinetics of carbon dioxide liberation, the final time could be monitored in order to characterize fermentation paralyzation and carry out an immediate sampling for the determination of the control variables and especially of 0011 viability. Fermentation time and substrate consumption are relevant factors in the evaluation of strains. With molasses as substrate, an inhibitory effect of this substrate was observed. Using molasses with a purity of 60%, fermentation was significantlyworse than withthat of 69% purity, although both showed considerable inhibition of the fermentation. At pH 3.5, with an inoculum of 108 or 104 viable cells/mL and a temperature of 38°C, substrate inhibition was shown to be significant as trom 160 g/L of glucose. At pH 5.0 this inhibitionwas not apparent (AU)