Onion (Allium cepa L.) is the most widely consumed plant among the organosulfur compound-containing vegetables belonging to the Alliaceae family. Onions mainly contain sugars such as glucose, fructose, and sucrose, which give them a unique sweet taste. Onion bulbs contain sulfur compounds such as quercetin. These compounds are believed to reduce carcinogen activation, inhibit tumor growth, have antioxidant properties, and reduce cholesterol levels. The objective of this study was to investigate the optimum saccharification conditions and the efficacy of saccharized products using onion juice or pomace. In addition, alcoholic fermentation conditions for onion wine and acetic acid fermentation conditions for onion vinegar were evaluated, and salad sauce and cooking wine developed using onion were analyzed.
To determine the optimum saccharification conditions, onion juice and pomace were added at 0, 10, and 20% of the total amount. The mixed materials were then saccharized at 25, 30, and 35℃ for 72 h. After 24 h, the 20%-added onion juice or pomace and a saccharification temperature of 35℃ resulted in the highest sugar content of 13.2 ˚Brix for onion juice and 19.6 ˚Brix for onion pomace. However, sensory evaluation was not significantly different among the treatments.
The saccharized onion products from onion pomace inhibited inflammation-mediating substances (14% inhibition in histamine release). ELISA analysis for determining cytokine release showed that the saccharized onion products had a more effective blocking ability to the release of IL-8 and TNF compared to the control.
Alcohol for onion wine was fermented from onion juice and onion pomace at 25, 30, and 35℃. Acetic acid for onion vinegar was fermented from 7％ onion wine at 20, 25, and 30℃. The contents of the initial soluble solid and reducing sugar were higher in onion pomace (13.2 ˚Brix of soluble solid content, 20.07% of reducing sugar) than in onion juice (10.8 ˚Brix of soluble solid content, 15.31% of reducing sugar). During alcohol fermentation, the soluble solid contents of onion juice rapidly decreased within 3 days, while those of onion pomace gradually decreased within 15 days. The reducing sugar contents rapidly decreased within 4 days but, thereafter, gradually decreased during both alcohol fermentations. The alcohol concentrations of onion juice significantly increased within 5 days and then gradually increased by 12.8, 14.8, and 14.2％ at 25, 30, and 35℃, respectively, after 12 days. The alcohol concentrations of onion pomace significantly increased within 4 days and then gradually increased by 16.9, 15.8, and 15.4％ at 25, 30, and 35℃, respectively, after 15 days. The polyphenol contents of onion juice steadily increased during alcohol fermentation and peaked on the 12th day after fermentation; the maximum content was 368.0 mg% at 25℃. On the contrary, the polyphenol contents of onion pomace steadily increased during fermentation and peaked on the 15th day after fermentation; the maximum content was 230.0 mg% at 35℃. In addition, the metabolites of alcohol fermentation products significantly differed between onion juice and pomace.
During the acetic acid fermentation of 7% onion wine, the acetic acid contents significantly increased within 6 days and then gradually increased by 6.30, 6.42, and 6.80％ at 20, 25, and 30℃ after 14 days. Regarding organic acids, lactic acid showed a negative correlation with the overall taste preference at the 1% significance level, while acetic acid showed a positive correlation with it. The acetic acid contents of onion vinegar were the highest at 7669.8 mg%. This was followed by succinic acid, lactic acid, citric acid, and malic acid at 367.2, 364.0, 340.3, and 73.4 mg%, respectively.
To determine the fermentation conditions of cooking wine using onion, we analyzed the alcoholic content for Nuruk, yeast, and starch. The alcoholic content of Nuruk MUM-1 (13.4%) was significantly higher than that of Nuruk NAM-1 (6.5%) and NAM-2 (8.4%). The cooking wine produced by Mus-2 yeast (0.8% amount of starch) exhibited the highest alcoholic content of 16.7% for the first fermentation and 16.2% for the second fermentation. In addition, a 2 : 1 ratio of glutinous rice to starch had a significantly higher alcoholic content compared to the other source of starch (2 : 1 ratio of rice to starch). The preference investigation of the cooking wine showed the following results: medium sweet 55.6%, slightly rough 50.0%, slightly flat 44.4%, medium bodied 47.2%, normal aftertaste 36.1%, and medium harmony 52.8%. These results support the further development of fermented onion with additional benefits and functional properties.
The sugar content of onion juice extracted at 120℃ for 3 h was the highest, at 6.5 °Brix. The quercetin content of onion juice extracted at 130℃ for 3 h was the highest, at 8.4 mg/L; a content of 7.5 mg/L was obtained for extraction at 120℃ for 3 h.
With increasing addition of the onion vinegar to salad sauce (I), the pH decreased and the sugar content increased. The addition of 10% onion vinegar to salad sauce (I) resulted in the highest taste preference. Salad sauce (II), which was prepared with onion vinegar (main ingredient), olive oil, and mayonnaise, showed varied sugar content, pH, and chromaticity. The addition of 7.7% mayonnaise, 17.1% fresh cream, and 17.1% pineapple led to the highest sensory evaluation among various combinations. The flavor of the salad sauce made from the onion vinegar did not differ from that of the salad sauce made from commercial synthetic vinegar. Consequently, the use of onion vinegar in salad sauce will contribute to promoting the consumption of processed onion.