A biologically inspired variable-pH strategy for enhancing short-chain fatty acids (SCFAs) accumulation in maize straw fermentation

• Maize straw was fermented to produce short-chain fatty acids (SCFAs) with rumen microorganisms.
• Higher inoculum ratio shows higher hydrolysis and acidogenesis rate of maize straw fermentation.
• Neutral pH is optimal pH for hydrolysis process of maize straw fermentation.
• pH between 5.8 and 7.8 does not influence acidogenesis process of maize straw fermentation significantly.
• A variable pH condition promotes acid accumulation in maize straw fermentation.

This study investigates the feasibility of varying the pH to enhance the accumulation of short-chain fatty acids (SCFAs) in the in vitro fermentation of maize straw. The corresponding hydrolysis rate and the net SCFA yield increased as inoculum ratio (VSinoculum/VSsubstrate) increased from 0.09 to 0.79. The pH were maintained at 5.3, 5.8, 6.3, 6.8, 7.3, and 7.8, respectively. A neutral pH of approximately 6.8 was optimal for hydrolysis. The net SCFA yield decreased by 34.9% for a pH of less than 5.8, but remained constant at approximately 721 ± 5 mg/gvs for a pH between 5.8 and 7.8. In addition, results were obtained for variable and constant pH levels at initial substrate concentrations of 10, 30 and 50 g/L. A variable pH increased the net SCFA yield by 23.6%, 29.0%, and 36.6% for concentrations of 10, 30 and 50 g/L. Therefore, a variable pH enhanced SCFA accumulation in maize straw fermentation.

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