Effects of free ammonia on volatile fatty acid accumulation and process performance in the anaerobic digestion of two typical bio-wastes

The effect of free ammonia on volatile fatty acid （VFA） accumulation and process instability was studied using a lab-scale anaerobic digester fed by two typical bio-wastes： fruit and vegetable waste （FVW） and food waste （FW） at 35℃ with an organic loading rate （OLR） of 3.0 kg VS/（m3-day）. The inhibitory effects of free ammonia on methanogenesis were observed due to the low C/N ratio of each substrate （15.6 and 17.2, respectively）. A high concentration of free ammonia inhibited methanogenesis resulting in the accumulation of VFAs and a low methane yield. In the inhibited state, acetate accumulated more quickly than propionate and was the main type of accumulated VFA. The co-accumulation of ammonia and VFAs led to an ＂inhibited steady state＂ and the ammonia was the main inhibitory substance that triggered the process perturbation. By statistical significance test and VFA fluctuation ratio analysis, the free ammonia inhibition threshold was identified as 45 mg/L. Moreover, propionate, iso-butyrate and valerate were determined to be the three most sensitive VFA parameters that were subject to ammonia inhibition.

Biotransformation of quinoa phenolic compounds with Monascus anka to enhance the antioxidant capacity and digestive enzyme inhibitory activity

This research aims to change the phenolic fractions and the bioactivities of quinoa by solid-state fermentation(SSF)with the edible fungus Monascus anka(M.anka).The contents of protein and fat increased in the fermented product,while the carbohydrate decreased.After 6-day fermentation with M.anka,the amount of phenolic compound reached the highest level.The majority of phenolic forms in fermented quinoa were phenolic acids,mainly ferulic acid,protocatechuic acid and p-hydroxybenzoic acid.Ultrahigh-performance liquid chromatography-mass spectrometry(UHPLC-MS)results showed that SSF was an effective method to transform quinoa phenolic compounds.Free fractions could be rapidly absorbed in the small intestine,suggesting that SSF with M.anka was a useful method to enhance bioavailable antioxidants.Antioxidant ability in vitro results showed that phenolic fractions from fermented quinoa were greater than the unfermented quinoa,and a significant cellular antioxidant activity(CAA)increment of 135%was obtained in the free phenolic fraction of fermented quinoa.Moreover,α-amylase andα-glucosidase inhibition activities were enhanced with fermentation.Correlation matrix analysis revealed that most of the free phenolic compounds showed strong positive correlations with antioxidant activities and digestive enzyme activities.Consequently,fermentation with M.anka was a particularly promising method to enhance the bioactivity of quinoa.