| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 93 === Abstract
Distillation is a necessary process for factories that produce spirits. Besides offering as feed, the stillage produced after distillation is often discarded as wastes. For preventing from environmental contamination and increasing the availability of the stillage, honey was used as substrate for partial fermentation with commercial yeast. The stillage obtained was further used as substrate for acetic acid fermentation. The most appropriate fermentation condition was studied by means of response surface methodology (RSM). The derived results were discussed as follows:
1. A commercial yeast ultimately produced 8.94% ethanol was screened to investigate the conditions of ethanol fermentation. Temperature (18-26℃), sugar concentration (18-26˚Brix) and pH value (3-4) were three independent variables, while ethanol concentration produced after fermentation for 15 days was a dependent variable. The highest yield of ethanol up to 10.63% was obtained under the optimum fermentation conditions, sugar concentration 26˚Brix, pH 4.0 and 22℃.
2. Acetobacter aceti BCRC 11569 showed the highest yield among the screened acetic bacteria. This strain produced up to 4.45% acetic acid in mannitol medium containing 5% ethanol after fermentation for 5 days. Thus we chose this strain to investigate the optimal condition of acetic acid fermentation. Three independent variables were temperature (27-33℃), ethanol concentration (5-7%), inoculation concentration (5-15%), while acetic acid concentration which was obtained after fermentation for 8 days was a dependent variable. The highest yield of acetic acid up to 6.63% was obtained under the optimum fermentation conditions, sugar concentration 6%, 27℃ and inoculation concentration 5%.
3. For improvement of acetic acid fermentation, various growth factors were added. As the result, 6.71%, 6.24%, and 7.35% acetic acid could be got by adding 10% sucrose as C-source, 0.1% peptone as nitrogen source, and 1% citric acid as organic acid source, respectively. Orthogonal Experimental Design verified that simultaneous addition of 5% sucrose, 0.5% citric acid and 0.15% peptone could obtain acetic acid up to 8.28%.
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