Protein hydrolysis and fermentation under methanogenic and acidifying conditions

Abstract

BackgroundMany kinds of wastewaters contain appreciable quantities of protein. Anaerobic processes are suitable for the treatment of wastewater high in organics to achieve pollution control and recovery of energy as methane and hydrogen, or intermediates for production of biofuels and valuable biochemicals. A distinction between protein hydrolysis and amino acid fermentation, especially for dissolved proteins, is needed to target which one is truly rate-limiting and to effectively harvest bioproducts during anaerobic conversion of these wastewaters. This study explored mesophilic anaerobic hydrolysis and amino acid fermentation of gelatine, as a model for dissolved proteins, at pH 7 and at pH 5.ResultsThe results showed that at pH 7, protein hydrolysis (first-order rate of 0.15 h−1) was approximately 5 times faster than acidification of the hydrolysis products (first-order rate of 0.03 h−1), implying that not hydrolysis but acidification was the rate-limiting step in anaerobic dissolved protein degradation. This was confirmed by (temporary) accumulation of amino acids. Nineteen different amino acids were detected during the first 8 incubation hours of gelatine at neutral pH and the total chemical oxygen demand (COD) of these 19 amino acids was up to approximately 40% of the COD of the gelatine that was added. Protein hydrolysis at pH 5 was 2–25 times slower than at pH 7. Shifting the initial pH from neutral to acidic conditions (pH 5) inhibited protein degradation and changed the volatile fatty acids (VFA) product profile. Furthermore, the presence or absence of methanogenic activity did not affect the rates of protein hydrolysis and acidification.ConclusionsThe findings in this study can help to set a suitable solid retention time to accomplish anaerobic degradation of protein-rich wastewaters in continuous reactor systems. For example, if the target is harvesting VFAs, methanogens can be washed-out for a shorter retention time while amino acid fermentation, instead of hydrolysis as assumed previously, will govern the design and solutions to improve the system dealing with dissolved proteins.

Bioaugmentation by Pediococcus acidilactici AAF1-5 Improves the Bacterial Activity and Diversity of Cereal Vinegar Under Solid-State Fermentation

“…Alcohol showed a negative correlation with Acetobacter and Komagataeibacter , mainly because it was rapidly oxidized to acetic acid by these AAB during fermentation. Amino nitrogen demonstrated a positive correlation with stage II, because the increase in the acidity of Cupei is favorable to the decomposition of macromolecular proteins and peptides ( Duong et al, 2019 ; Guo et al, 2019 ). The small angle between temperature and acetic acid indicated their high correlation.…”

Expanding the anaerobic digestion map: A review of intermediates in the digestion of food waste

“…experimentally determined the opposite, with 19 amino acids detected in the first 8 hours of gelatine digestion (Duong et al, 2019). Amino acids are subsequently degraded by three metabolic pathways: Stickland reaction (for pairs of amino acids), oxidative deamination and reductive deamination of single amino acids (Shen et al, 2017).…”

“…Formed during the cleavage of peptide bonds in proteins by exoenzymes, proteases or peptidases, amino acids can then be transported into bacterial cells where they are transformed to organic acids (Dalgleish et al, 2007). Alternatively, they can be used to synthesize cell proteinaceous matter if enough energy is present in the form of carbohydrates (Duong et al, 2019). Examples of amino acid intermediates include alanine, arginine, glutamate, glycine and lysine (Dalgleish et al, 2007).…”

Peruraian Anaerobik Termofilik Limbah Vinasse : Pengaruh Zeolit Alam Teraktivasi Asam dan Basa Terhadap Performa Proses

“…Perubahan komposisi NZ dan NZB pada sebelum dan setelah proses peruraian anaerobik menunjukkan bahwa beberapa kation seperti natrium (Na + ) dan kalsium (Ca 2+ ) mengalami pengurangan kadar. Hal ini dimungkinkan terjadi akibat adanya pertukaran kation dengan ion amonium (NH 4 + ) di dalam cairan yang mana ion NH 4 + ini dimungkinkan berasal dari degradasi protein (Duong et al, 2019) yang terdapat pada vinasse. Hal ini disebabkan pada zeolit, ion NH 4 + memiliki prioritas yang lebih tinggi dibanding ion Na + dan Ca 2+ sehingga ion NH 4 + dapat menggantikan kedua ion tersebut pada struktur zeolit (Lin et al, 2015).…”