Biorefining process of agricultural onions to functional vinegar.

Biorefinery of onion vinegar (OV) is attractive as a method for producing functional foods from onions or onion by-products. In this study, a two-stage fermentation of OV using Saccharomyces cerevisiae ATCC9763 and Acetobacter pasteurianus CICC20001 was carried out at 28 °C, the titratable acidity reached 4.01%, and the YA/E was 69.64% at 72 h. Based on this, semi-continuous fermentation was performed, proceeded to charge-discharge consisting of three cycles, and the yield, productivity, and specific production rate were 76.71%, 17.73 g/(L·d), and 20.51 h-1, respectively, which was higher than fed-batch fermentation. The in vivo antioxidant experiments showed that OV significantly increased GSH-Px, SOD, and CAT enzyme activities of Caenorhabditis elegans at 271.57, 129.26, and 314.68%, respectively. Nutritional analysis revealed that the total flavonoids and polyphenols were 3.01 mg/mL and 976.76 µg/mL, respectively. It was also shown that the acetic acid to total organic acid (A/T) ratio of OV was 79.02%, and the total free amino acid content was 262.30 mg/100 mL, 1.78-7.44 times higher than other fruit vinegar. The OV prepared in this study showed higher quality than the commercial vinegar.

Onion Vinegar Quality Evaluation and its Alleviate Oxidative Stress Mechanism in Caenorhabditis elegans Via SKN-1.

Recently, there has been renewed interest in biorefining of agricultural onion into functional products. In this study, onion vinegar (OV) are prepared by a two-stage semi-continuous fermentation method, and its content of total flavonoids (3.01 mg/mL) and polyphenols (976.76 µg/mL) is superior to other commercial vinegars. OV possesses a high radical scavenging activity and enhances the antioxidant enzyme activities in vivo, alleviating intracellular oxidative stress in Caenorhabditis elegans. Treated by OV, the 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH·), diammonium 2,2'-azino-bis (3-ethylbenzo thiazoline-6-sulfonic acid) (ABTS+·) and 2-phenyl-4,4,5,5- tetramethylimidazoline-1-oxyl 3-Oxide (PTIO·) free radicals clearance rates are 88.76, 98.76 and 90.54%, respectively in vitro. Whereas the glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT) enzyme activities in C. elegans reach 271.57, 129.26, and 314.68%, respectively. Using RNAi and RT-PCR, it has been further confirmed that OV modulates transcription factor SKN-1, the nuclear factor erythroid 2-related factor 2 (Nrf2) homologous, in C. elegans, enhancing the resistance of C. elegans against sodium arsenite stress. Lifespan analysis reveals that 1 mL OV extends the maximum lifespan of the nematode to 26 days. Evidence is presented which shows that OV increases the lifespan of C. elegans by activating the SKN-1 signaling pathway. Overall, the OV is a well functional condiment, enhancing the value-added of onion.