Abstract

A factorial experimental design method was used to optimize the lactic acid production using Lactobacillus bulgaricus from refectory waste obtained from Istanbul Technical University mess hall, Turkey. Fermentation experiments were carried out in a batch type reactor system which contains refectory waste with Lactobacillus bulgaricus bacteria during an exposition time of 30 h. Factorial design of experiments was employed to study the effect of three factors namely temperature (30 and 45°C), substrate concentration (10 and 60 g/L) and pH (4.0 and 6.0) at two markedly different levels. The main effects and interaction effects of the three factors were analysed using statistical techniques. A regression model was recommended and it was found to fit the experimental data very well. The results were analysed statistically using Student’s t-test, and analysis of variance was used to define the most important process variables affecting the production of lactic acid by fermentation. In the present study, the most significant factor affecting lactic acid fermentation was found to be the initial substrate concentration.

Key words: Refectory waste, lactic acid, factorial design, Lactobacillus bulgaricus.