Production of animal feed supplement by edible fungi using fruit wastes as carbon source

Abstract

Fruit wastes constitute high percentage of biodegradable residues emanating from fruit processing industries where they cause environmental challenges. These fruit wastes contained sufficient carbon source that can support fungi growth for conversion to animal feed supplement through biotechnological approach. Banana peel (Bp), pineapple peel (PAp) and papaya peel (Pp) were selected as substrates and the proximate analysis of the high solid content (HSC) type and low solid content (LSC) were performed. All samples contained simple and complex sugars that support fungi growth and development. Three white rot fungi –Phanerochaete chrysosporium (P. chrysosporium), Panus tigrinus (P. tigrinus) and Schizophyllum commune (S. commune), demonstrated profound growth and protein enrichment of the substrate with high enzyme secretion and elevated substrate consumption. Composite substrate from the three peels supported growth and protein enrichment by the fungi compared with individual substrates. All three fungi cells grew together on commercial media and formulated media. P. chrysosporium/P. tigrinus interaction and P. chrysosporium/S. commune interaction were deadlocked at contact, P. tigrinus/ S. commune interaction gave mutual intermingling while cultivation of the three together gave both deadlocked at contact and mutual intermingling. All microbial mixed cultures improved the protein secretion compared with their monocultures. Combination of P. chrysosporium and S. commune synthesized highest protein, enzymes and improved substrate consumption. Product synthesis in submerged phase bioconversion (SmB) was lower than solid state bioconversion (SSB); SSB was adopted after microbial interaction study. Substrate reformulation increased metabolizable sugar from 251 mg/g to 500 mg/g consisting 0.35g Bp, 5.5g PAp and 0.15g Pp; protein content increased from 104.22 mg/g to 160.68 mg/g. Media screening with Plackett-Burman design and optimization with face-centered-central composite design (FCCCD), gave KH2PO4 (1.2g/L), CaCl2 (0.8g/L) and peptone (0.8g/L) as media components. Protein synthesis increased to 175.23 mg/g. Optimum pH (5.4), inoculum size (6.1% ) and moisture content (70.2%) was achieved by FCCCD and protein synthesis increased to 198.77 mg/g. Kinetic study of biomass growth best fit with Monod equation (R2 = 0.936), µmax of 0.641 (day-1) and Ks of 23.35 mg/g. Haldane equation had R2 of 0.931, µmax of 0.644 (day 1) and Ki of 233.37 mg/g. Luedeking-Piret equation for substrate consumption gave R² of 0.9384; growth associated co-efficient (γ) of -49.08 mg/g and non-growth associated parameter (λ) of 48.862 mg/g/day. Product formation gave R² of 0.9888, growth associated co-efficient (α) of 0.0148 mg/g and non-growth associated parameter (β) of 0.0517 mg/g/day. Hanes-Woolf model fitted α-amylase (R² = 0.9108) and cellulase enzyme (R² = 0.9882) production. Km and Vmax of both were 11.55 Units/ml and 25.19 units/ml/day and 57.47 Units/ml, 3.05 units/ml/day respectively. Validation of parameters (media, process and kinetics) in 7 kg capacity reactor increased protein synthesis (228 mg/g), enzyme production, substrate consumption and improved productivity. Optimization of substrate depth and bioconversion period gave 2.5 cm as optimum depth and six days as optimum bioconversion period. Kinetics of in-vitro digestibility of flask optimized product and reactor, fitted into zero order model while nutritional analysis of final product showed great improvement in protein, amino acids and sugars.