Acidogenic fermentation characteristics of different types of protein-rich substrates in food waste to produce volatile fatty acids

- Two kinds of protein-rich substrates (tofu and egg white) were first investigated for producing VFA.
- Hydrothermal pretreatment had a positive impact on the VFA production from tofu but not for egg white.
- Tofu and egg white had different metabolic pathway for VFA production.

In this study, tofu and egg white, representing typical protein-rich substrates in food waste based on vegetable and animal protein, respectively, were investigated for producing volatile fatty acids (VFAs) by acidogenic fermentation. VFA production, composition, conversion pathways and microbial communities in acidogenesis from tofu and egg white with and without hydrothermal (HT) pretreatment were compared. The results showed HT pretreatment could improve the VFA production of tofu but not for egg white. The optimum VFA yields were 0.46 g/g VS (tofu with HT) and 0.26 g/g VS (egg white without HT), respectively. Tofu could directly produce VFAs through the Stickland reaction, while egg white was converted to lactate and VFAs simultaneously. About 30-40% of total protein remained in all groups after fermentation. Up to 50% of the unconverted soluble protein in the HT groups was protease. More lactate-producing bacteria, mainly Leuconostoc and Lactobacillus, were present during egg white fermentation.

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