Anaerobic protein degradation: Effects of protein structural complexity, protein concentrations, carbohydrates, and volatile fatty acids

Bovine serum albumin (BSA) and casein (CAS) were used in batch tests to compare the protein degradation in the presence and absence of carbohydrates and volatile fatty acids (VFAs). The modified Gompertz model was applied to estimate reaction rates. The results showed that deamination was the rate-limiting step, with a rate ranging between 2.7 and 12.7 mgN & sdot;h- 1. Higher protein structural complexity negatively affected protein hydrolysis, deamination, and methanogenesis by a factor of 1.6-3.8; whereas a higher protein concentration improved the conversion rates. A carbohydrate:protein COD ratio of 1 improved the hydrolysis rate of BSA from 26 mg & sdot;h- 1 to 45 mg & sdot;h- 1, and that of CAS from 98 mg & sdot;h- 1 to 157 mg & sdot;h- 1; whereas the deamination rate slightly decreased from 2.7 mg N & sdot;h- 1 to 2.5 mg N & sdot;h- 1 and from 6.0 mg N & sdot;h- 1 to 5.6 mg N & sdot;h- 1. Additionally, an initial VFAs:protein COD ratio of 1 decreased the CAS deamination rate by 17 %.