Vinegar Production from Gac Fruit (Momordica cochinchinensis [Lour.] Spreng.) Using Different Strains of Acetobacter sp.

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Orn anong Chaiyachet
Namfon Saikum
Ludda Klangpraphan

Abstract

Gac (Momordica cochinchinensis [Lour.] Spreng.), a local fruit/vegetable, and its fruit is the favorite part of eating. Increasing interest in Gac has gained more as a medicinal plant due to several medical studies revealing each part of Gac fruit had remarkable properties for its high antioxidant contents. Pulp and aril of Gac fruit contain high levels of lycopene, flavonoid, and total phenolic contents. This study aims to investigate the vinegar production from Gac fruit juice using three different strains of acetic acid bacteria. Vinegar production fermented with two different stages. Alcoholic fermentation was conducted by adjusting total soluble solids of Gac fruit juice to 20 °Brix and pH 4.5-4-6 and 5% of inoculum size by a commercial Saccharomyces cerevisiae strain. The alcoholic fermentation was incubated under static conditions at 30°C for 15 days. After the end of the alcoholic fermentation, obtained Gac wine had an alcohol content of 9.67±0.58% (by volume), total soluble solids content 7.00±0.00 °Brix, and pH was 4.06±0.00. Acetous fermentation, the Gac wine was fermented with a different strain of acetic acid bacteria; Acetobacter aceti TISTR 354, Acetobacter pasteurianus TISTR 102, and Acetobacter aceti subsp. xylinum TISTR 1011. The condition was adjusted the initial alcohol content 7% (by volume), the inoculum sizes starter culture of 10% (by volume), total soluble solids content 7 °Brix, and pH 4.25 under static incubation at room temperature (30±1°C) for 30 days. The results for the physicochemical analysis of Gac vinegar using three different strains of acetic acid bacteria showed the highest acetic acid content in Gac vinegar produced by TISTR 102. No statistical difference was observed for the acetic acid content between vinegar produced by the bacterial strains of TISTR 102 and TISTR 354 (p>0.05). There were found statistical differences of the acetic acid content produced by TISTR 1011 with the two other strains of acetic acid bacteria (p<0.05). The acetic acid content produced by TISTR 102, TISTR 354, and TISTR 1011 were 3.50±0.07, 3.48±0.09, and 2.27±0.04 (% by volume), respectively. Similarly, there was no statistically significant difference in alcohol content and total soluble solids between TISTR 102 and TISTR 354 (p>0.05). And there were found statistically significant differences in the alcohol content and total soluble solids content of Gac vinegar between TISTR 1011 and the two others of acetic acid bacteria (p<0.05). The alcohol content in vinegar produced by TISTR 102, TISTR 354, and TISTR 1011 were 0.47±0.06, 0.50±0.10 and 1.10±0.17 (% by volume), respectively, and total soluble solids were 11.00±0.00, 11.33±0.58, and 10.00±0.00 °Brix, respectively. The pH values of vinegar fermented by three different strains of acetic acid bacteria found statistically significant differences between TISTR 354 and the two other strains of acetic acid bacteria (p<0.05). The pH values of Gac vinegar produced by bacterial strains TISTR 102, TISTR 354, and TISTR 1011 were 3.64±0.03, 3.69±0.01, and 3.65±0.01, respectively. The results of CIELAB colorimetric measurement revealed no difference in color values L* between the three bacterial strains (p>0.05). Significant differences in a* and b* values were detected between TISTR 1011 and the two other strains of acetic acid bacteria (p<0.05). Sensory evaluation using a 9-point Hedonic scale was no statistically significant difference found between the acceptance scores of odors, color, flavor, appearance, and overall liking to the Gac vinegar produced by the different acetic acid bacteria (p>0.05). The utilization of Gac fruit as a raw material for vinegar production is an approach to promoting the applications of local medicinal plants to process products and value-added agricultural products.

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