Pectinase production using apple pomace as carbon source by mixed culture fermentation

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Food Engineering, Turkey

Approval Date: 2016




There is a growing interest in enzyme production from food and agricultural wastes to reduce the cost of production. Pectinases are one of the important group of enzymes used in fruit processing, alcoholic beverages, coffee and tea fermentation and textile industries. Pectinases can be produced by both solid state and submerged fermentation from various plant and microorganisms; however fungal microorganisms are the largest sources of bulk commercial enzymes and there are numerous studies on pectinase production from fungal sources. Therefore, in this study; bacterial mix culture (Bacillus subtilis and Bacillus pumilus) was used to produce pectinase by submerged fermentation using apple pomace as carbon source. Firstly, growth curves of both microorganisms (Bacillus subtilis and Bacillus pumilus) were constructed to determine the exponential and stationary phases. The cultures were used at the beginning of stationary phase during fermentation. Pre-treatment of apple pomace was carried out using one step and two step acid hydrolysis methods. Initial screening was done to fix the time variable of fermentation. A set of 15 experiments was constructed by Box-Behnken design to optimize fermentation conditions with respect to pH (7, 8 and 9), apple pomace (AP) concentration (5, 10 and 15 %) and mix culture ratio-B.subtilis/B.pumilus (1/4, 3.4/1.6 and 4/1). Further analyses at optimum condition were carried out to investigate any correlation between reducing sugar content, biomass, protein content and pectinase production. Initial screening experiments revealed that maximum pectinase production was achieved after 24 h fermentation time. One-step acid hydrolysis with 4% H2SO4 was found the best pre-treatment method. The highest pectinase activity was 11.48±0.51 IU/mL measured at 15 % AP; pH 9 and mix ratio(B.subtilis/B.pumilus) 2.125. The determination coefficient (R2=97.98) and insignificant lack of fit (p=0.124>0.05) proved that the model fitted well to the experimental data. Pectinase production kinetics was evaluated by Leudeking and Piret model. Pectinase production was found growth-related whose coefficient (α) was 8.0431. In conclusion, this study shows that apple pomace is an effective carbon source for the pectinase production and mix culture fermentation has enhanced pectinase production.