富含胞外多醣及益生菌酸凝酪製品之研究

Abstract

乳酸菌胞外多醣 (exopolysaccharide，EPS) 係指乳酸菌分泌於細胞外之多醣。乳酸菌來源的胞外多醣具有多項優點，它屬於食品級安全物質，且可改善產品濃稠度與組織特性，然而乳酸菌之胞外多醣應用於商業上面臨到低產量的問題。本研究的目的為探討接種不同乳酸菌元及培養溫度對胞外多醣產量的影響，以期生產富含胞外多醣及益生菌的酸凝酪產品。分別取(A) 5%酸凝酪菌元 （Lactobacillus bulgaricus與Streptococcus thermophilus），(B) 5%酸凝酪菌元與5%黏質乳酸菌L. helveticus BCRC 14030，(C) 5%酸凝酪菌元與5%益生菌（L. acidophilus、Bifidobacterium bifidum與L. casei），(D) 5%酸凝酪菌元、5% L. helveticus BCRC14030、與5%益生菌與(E) 5%酸凝酪菌元及0.17%果膠，接種於含17%脫脂乳粉之還原乳後，於30、40與50oC，培養至 pH 4.6±0.1，攪拌均勻後製成濃稠酸凝酪，其後進行胞外多醣產量、黏絲性及單醣組成分析、酸凝酪之黏度、離水性、益生菌及L. helveticus BCRC 14030菌數的分析。 結果顯示以30和40 oC進行發酵顯著會有較佳的胞外多醣產量 (0.2~0.6 g/L) (P < 0.05)。然而四種不同菌種組合對胞外多醣產量沒有顯著差異 (P >0.05)。50℃ 發酵的酸凝酪有嚴重的離水現象。此外發現使用酸凝酪菌元及黏質乳酸菌 L. helveticus BCRC 14030的組別，以30℃進行發酵培養，有最高 EPS 黏絲性 (96.0 cm)。使用 D 處理組菌元於30、40及50℃ 三種不同溫度下進行發酵培養，EPS黏絲性皆高於使用 A 處理組菌元。以30 oC 進行發酵，發現B處理組酸凝酪，其黏度雖沒有明顯高於 A 處理組 (P>0.05)，但有顯著高於 E 處理組。於30、40與50℃下生產酸凝酪，C 與 D 組產品之益生菌數在貯藏15天後，菌數不會下降；B組產品在貯藏15天後之 L. helveticus BCRC 14030菌數會下降，D組之 L. helveticus BCRC 14030菌數則維持不變；以L. helveticus BCRC 14030進行發酵，所生成之EPS會有較高含量的鼠李糖；接種酸凝酪菌元，EPS單醣組成皆不含鼠李糖。官能品評部分，B、C及D產品的濃稠度皆優於商業產品；A、C 及D組產品與商業產品有較佳的總接受度。 綜合上述結論，接種5%酸凝酪菌元、5% L. helveticus BCRC 14030、5%益 生菌組，於30 oC發酵18小時能生產富含EPS、益生菌與 L. helveticus BCRC 14030、具較佳黏絲性以及最低離水現象之酸凝酪。

Exopolysaccharides (EPS) of lactic acid bacteria are polysaccharides secreted extracellularly by lactic acid bacteria. Several advantages of producing exopolysaccharide by lactic acid bacteria include GRAS nature of the organisms and the enhanced consistency and texture of the products by EPS. However, low EPS yield limited the commercial use of lactic acid bacteria on EPS production. The objective of this study, therefore, was to investigate the effects of lactic acid bacteria and incubation temperature on EPS production for producing EPS and probiotic-rich yogurt. Each of the 4 culture strains including (A) 5% yogurt bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus), (B) 5% yogurt bacteria and 5% ropy L. helveticus BCRC14030, (C) 5% yogurt bacteria and 5% probiotics (L. acidophilus , Bifidobacterium bifidum and L. casei), and (D) 5% yogurt bacteria, 5% ropy L. helveticus BCRC14030, and 5% probiotics was inoculated into a reconstituted milk containing 17% dried milk powder. After incubated at 30, 40, and 50oC until pH reaching 4.6±0.1, the fermented medium was homogenized to yield stirred yogurt. EPS yield, ropiness value, the composition of monosaccharide, viscosity of fermented medium, vible count, syneresis and sensory evaluation were analyzed. The highest EPS yield of （0.20-0.60 g/L） was observed at 30 and 40 ℃. However, no significant difference in EPS production was found among four different culture strains. The syneresis of yogurt was severe at 50℃. Highest ropiness value of EPS (96 cm) was found in the yogurt inoculated with yogurt bacteria and L. helveticus BCRC14030 at 30oC. Treatment D was fermented under 30,40 and 50℃, and the results showed that treatment D had higher EPS ropiness value than treatment A Under 30℃ of fermentation, the viscosity of treatment B were not significantly higher than treatment A (P > 0.05), but was significantly higher than the treatment E. Under 30℃,40 and 50℃ of fermentation, probiotic counts did not decrease in treatments C and D during 15 days of storage. However, the viable count of L. helveticus BCRC 14030 decreased in treatment B. In addition, the viable counts of neither probiotics nor L. helveticus BCRC 14030 changed in treatment D during storage. In sensory evaluation, mouth thickness of treatments B,C and D were better than commercial yoghurt. Treatments A, C, D and commercial yoghurt had acceptable. In conclusion, inoculation of yogurt bacteria, L. helveticus BCRC 14030 and probiotics with a reconstituted milk and incubated at 30℃ produced the highest EPS yield, ropiness value and probiotic counts, and lowest degree of syneresis, therefore, was suggested for EPS and probiotic-rich yogurt production.