Bio-protein production by solid state bioconversion using banana peel as carbon source

Abstract

Banana peel (BP) is a lignocellulosic waste generated by many cottage and hospitality industries in Malaysia. Based on the concept of waste to wealth coupled with availability of rich carbon sugars in BP, solid state bioconversion was used to produce bio-protein from the peel. Successful production of bio-protein from BP is expected to reduce solid waste management challenges. Hot water pre-treatment operation was conducted on dried BP and this reduced the amount of saponin present in the peels. Selection of potential combination of fungi and yeast cells was done based on the amount of bio-protein produced as yardstick. Media screening was performed by selecting potential media parameters and screening them based on their contribution by adopting Placket-Burman design. The number of fermentation days was scrutinized for economical bio-processing. Following selection of positively contributing media parameters, selected media were subjected to individual optimization by one-factor-at-a- time while full media optimization was carried out by adopting face centered central composite design (FCCCD) to obtain a maximum bio-protein production. Validation was done by conducting fermentation based on the suggested values of optimized media parameters to validate the parameters. The kinetics of product synthesis was conducted by subjecting bio-protein production to zero; first and second order reaction to ascertain which reaction kinetics best describe the production rate. Saponin content reduced between raw and normal washing from 9.50 mg/g to 9.0 mg/g. It was further reduced from 9.0mg/g to 7.5 mg/g between normal washing and soaking. Drastic reduction was witnessed between 20ºC and 100ºC (from 7.90mg/g to 5.7 mg/g) and 100ºC (5.7mg/g). This amount was enough for microbial growth to take place. Microbial screening results showed highest protein synthesis (88.93mg/g) with mixed culture of Phanerochaete chrysosporium (PC) and Candida utilis (CU). Based on the significant results from Plackett-Burman experimental design, solid content, KCl, MgSO4.7H2O, sucrose and NH4H2PO4 were positively contributing media parameters. A reduction in number of days required for fermentation was reduced from ten to six days after successful bio-processing with selected media parameters. Successful OFAT experimentation showed 27.5% was optimum for solid content, 0.5% for KCl, 0.4% for MgSO4.7H2O while 5% and 0.6% were optimum for sucrose and NH4H2PO4 respectively. The trend of total soluble sugar content (TOS), total reducing sugar content (TRS), ash content and total carbohydrate content (TC) were determined to study the degradation processes involved during fermentation. Following media optimization by FCCCD, the highest bio-protein production was achieved at 5% sucrose, 0.6% NH4H2PO4 and 0.4% MgSO4.7H2O. According to the numerical solution suggestion, highest protein of 105.223 mg/g was expected at 4.79% sucrose, 0.44% MgSO4.7H2O and 0.61% NH4H2PO4. Validation result showed 143.18mg/g as the true production. Zero order and first order reaction kinetics models best described bio-protein production with 0.0592h-1 and 0.2532h-1 rate constants. Their respective coefficient of determination (R2) was 0.951 and 0.812. Second order reaction kinetics gave 0.1507h-1 and R2 (0.6) respectively to be the least fit for the bio-protein production