生牛乳低溫菌與乳品質相關

The Relationship between Psychrotrophic Bacteria in Raw Cow Milk and Milk Quality

李素珍(Sue-Jan Lee) ； 林慶文(Chin-Wen Lin)

《畜產研究》 35卷2期 (2002/06) Pp. 127-134

摘要

本試驗旨在探討牛乳低溫菌與乳品質之相關。採樣當日生牛乳之生菌數、低溫菌數、蛋白質分解菌數與脂肪分解菌數之平均分別為12.7、19.1、3.3及5.5（×10^4 CFU /ml）。生菌數低於10^5及高於10^6 CFU /ml者各佔91.2%及5.1 %；低溫菌數低於10^4及高於10^6 CFU /ml者各佔45.0%及6.6 %，蛋白質分解菌數與脂肪分解菌數低於10^4者各佔10.3%及86.7 %，超過10^6 CFU /ml者各佔58.7%及10.0%。生乳之生菌數與低溫菌數會隨貯存時間延長而增加，於3℃冷藏時，生菌數與低溫菌數仍會增殖，於第4日顯著上升（P＜0.05），且低溫菌數佔生菌數之比例也上升，兩者有密切相關r＝0.86（P＜0.001）。冷藏中主要乳成分稍降，但無顯著差異，然而，游離脂肪酸於第4日，酪胺酸於第6日均顯著上升（P＜0.05），故生乳冷藏時間最好不要超過3日。依生乳低溫菌數分為＜10^4 CFU /ml、10^4-10^5 CFU /ml、10^5-10^6 CFU /ml及＞10^6 CFU /ml等4組，經63℃、30分鐘熱處理後，未檢出低溫菌，但生乳低溫菌數較高者，生菌、蛋白質分解菌與脂肪分解菌殘留量較高，且游離脂肪酸與酪胺酸仍留於乳中，於3℃經10日冷藏，鮮乳風味以生乳低溫菌數低於10^4 CFU /ml者較佳。分離生乳低溫菌之菌屬，革蘭氏陰性及陽性菌各佔80.2%及19.8%，而革蘭氏陰性之假單胞菌屬（Pseudomonas）所佔比例最高為62 %，其次為黃質菌屬（Flavobacterium）佔25%，具分解蛋白質及脂肪之菌分別佔62.5%及30.2 %。

關鍵字

生牛乳 ； 鮮牛乳 ； 低溫菌 ； 乳品質

並列摘要

The purpose of this experiment was to understand the relationship between psychrotrophic bacteria in raw cow milk and milk quality. Means of standard plate count (SPC), psychrotrophic count (PTC), proteolytic count (PLC) and lipolytic count (LPC) for raw bulk milk were 12.7, 19.1, 3.3 and 5.5 (×10^4 CFU /ml) respectively. 91.2 % of milk had SPC less than 10^5 and 5.1 % of milk had SPC more than 10^6. 45% of PTC were less than 10^4 and 6.6% were more than 10^6 .10.3% of PLC and 86.7 % of LPC had less than 10^4 CFU/ml. 58.7 % of PLC and 10.0 % of LPC had more than 10^6 CFU/ml. There was significant correlation between SPC and PTC (r = 0.86, P＜0.001). The SPC, PTC and the ratio of PTC/SPC of raw milk increased slowly during the first 3 days, and increased significantly at 4th days (P＜0.05) during 3℃ storage. The major milk constituents decreased a little (P＞0.05). However, tyrosine and free fatty acid (FFA) increased significantly at day 6 and 4 respectively while stored at 3℃. Thus, we recommended that raw milk be used within 3 days during 3℃ storage. Raw milk was grouped into four categories based on PTC. The four categories were ＜10^4, 10^4-10^5, 10^5-10^6 and ＞10^6 (×10^4 CFU /ml) respectively. The PTC all vanished after 63℃ for 30 min treatment. However, the SPC, PLC, LTC, tyrosine and FFA survived. And flavor score of low PTC (＜10^4 CFU /ml) milk was better than higher PTC (＞10^4 CFU /ml) milk while stored at 3℃ for 10 days. Gram-negative and Gram-positive rods were identified and occupied 80.2 and 19.8 % respectively in raw milk. Bacteria in the genus Pseudomonas was mostly encountered and occupied 62% and Flavobacterium occupied 25% of Gram-negative rods. Proteolytic and lipolytic psychrotrophs occupied 62.5 and 30.2 % respectively.

並列關鍵字

Raw cow milk ； Pasteurized cow milk ； Psychrotrophic bacteria ； Milk quality