Effect of solid substrate fermentation on the nutritional quality of agro-industrial residues

This study was performed to evaluate the chemical composition and in vitro gas production of five agro-industrial residues, with and without treatment, using solid substrate fermentation. Oat straw, bean straw, corn stubble, apple pomace and agave bagasse were treated using two filamentous fungi, Trichoderma harzianum and Phanaerochaete chrysosporium. Chemical analyses (crude protein, neutral detergent fiber, acid detergent fiber, lignin, cellulose and hemicellulose) were carried out. Calibrated glass syringes were used for in vitro gas production determinations and volatile fatty acid (VFA) profile was obtained by gas chromatography. In vitro data were fitted using the equations p=a+b(1-e(-ct)) by Orskov and McDonald and G=A/(1+[B/t]) by France et al (2000). Increases in CP content (P<0.05) were registered by treating oat straw (20%), bean straw (83%) and corn stubble (16%) with P. chrysosporium. Contents of NDF were reduced by 9.5% in oat straw by treatments (P<0.05). Regarding gas production parameters, the b value in agave bagasse (57.4%) and gas production rate constant c (7.5%) were higher (P<0.05) in the substrate treated with P. chrysosporium related to other treatments. Similarly, higher values for the A parameter were registered in maize straw (+22%) and agave bagasse (+13%) treated with P. chrysosporium. In spite of these isolated differences, the analysis performed showed that the chemical composition, mainly structural carbohydrates, were not modified under the conditions of this study.