糙米發酵飲品之製造與抗氧化性質研究

Abstract

糙米雖然保存了最完整的稻米營養，但因不易消化及較難料理，在日常飲食中難加以利用。本研究擬結合營養豐富之糙米與微生物發酵等二種有益人體健康與養生之特質，開發一種機能性糙米發酵飲品。 首先以多株米麴菌(Aspergilius oryzae)製備米麴，結果顯示培養2日米麴已有良好之酵素活性，且A. oryzae BCRC 32279有較佳的澱粉酶與酸性蛋白酶活性；利用米麴之酵素活性進行糙米糖化液之製備，經過分析後，確定糖化液之最佳水解條件為50℃下反應10小時，可溶性固形物約可達20 oBrix，而胺基態氮含量約為0.03 %，破碎過的糙米比未破碎者有較高的可溶性固形物與胺基態氮含量。將糖化液分別接入酵母菌(Saccharomyces cerevisiae K901與C2109)及乳酸菌(Lactobacillus casei BCRC 14080與Lactobacillus plantarum BCRC 10069)進行發酵。酵母菌部分，發酵溫度分別為10℃、15℃與20℃，發酵至酒精度達1%停止，結果顯示發酵所需的時間依溫度由低到高分別約為40小時、25小時與10小時，各項分析值隨著發酵時間增加而下降，發酵溫度愈高則各分析值降的愈快；乳酸菌部分，結果顯示生菌數、可滴定酸與乳酸大致隨著發酵時間愈長而增加，但可溶性固形物、pH值與醣類利用則反之，而乳酸菌在37℃下發酵48小時為最佳條件。 抗氧化活性部份，酵母菌發酵液之各抗氧化力及總多酚量，皆為20℃下發酵時較低，顯示10℃及15℃下發酵有較佳的抗氧化能力，而S. cerevisiae K901略優於C2109；乳酸菌發酵液方面，各抗氧化力及總多酚量大致隨著發酵時間增加而增加，而L. plantarum略優於L. casei。測定GABA時，酵母菌之發酵液幾乎沒有GABA的生成，含量約在0.282-0.377 mg/mL之間；而乳酸菌發酵液其GABA含量則大致隨發酵時間顯著增加，含量約在0.561-1.45 mg/mL間。 本實驗之消費者感官品評以發酵液為試驗樣品，結果顯示C2109+Lc組有最高之分數，即混合發酵液之消費者喜好性比單獨酵母菌或乳酸菌發酵液好。

Although brown rice contains almost the complete nutrition of rice, it is hard to be utilized in the daily diet due to difficulty in cooking and digestibility. A new fermented beverage combining two functional food elements, nutritious brown rice and fermentation, was developed in this study. Several strains of Aspergilius oryzae were inoculated to steamed rice to produce rice-koji. High enzymatic activities were obtained when rice-koji was incubated for 2 days. Finally, A. oryzae BCRC 32279 was chosen for subsequent experiment due to its balanced activities of both amylase and acidic protease at same time. The optimal saccharifying conditions for rice-koji to hydrolyze brown rice were performed at 50℃ for 10 h. The soluble solid and amino nitrogen content of the hydrolysates were about 20 oBrix and 0.04%, respectively. Moreover, higher soluble solid and amino nitrogen content were obtained if brown rice was pulverized. Saccharified mash of brown rice were thereafter fermented with yeasts (Saccharomyces cerevisiae K901 and C2109) or lactic acid bacteria (Lactobacillus casei BCRC 14080 and Lactobacillus plantarum BCRC 10069). For yeasts, the results showed, greater amount of metabolites were produced as fermentation temperature increased from 10℃ to 20℃. The alcohol fermentation was stopped once ethanol concentration reached 1% (w/w), then it took fermented at about 10 h, 25 h and 40 h for temperatures at 20℃, 15 ℃ and 10℃, respectively. As for lactic acid fermentation, the results showed soluble solids content, pH value and concentration of sugars were decreased while titratable acid, viable count and concentration of lactic acid were increased with fermentation time. The optimal fermentation time was 48 h. Finally, the antioxidative activites of fermentation broth by yeast fermentation either at 10℃ or 15℃ was better than that at 20℃; and S. cerevisiae K901 was better than C2109. As for fermentation broth obtained with lactic acid bacteria for 48 h had the highest antioxidative activity, and L. plantarum was better than L. casei. Analyses of GABA content for fermentation broth obtained from alcohol fermentation by yeasts were from 0.282 to 0.377 mg/mL, while those from lactic acid bacteria ranged from 0.561 to 1.45 mg/mL. The results revealed that lactic acid bacteria, as compared to yeasts, were useful for the production of GABA. Finally, results of the consumer preference test showed that the score of C2109+Lc was the highest. Briefly, the fermented drink made by mixed fermentation broth from yeast with lactic acid bacterium (1:1, v/v) was more popular than the fermented drink only by yeast or lactic acid bacterium alone.