pH值調整或磷酸鹽添加對超高溫瞬間滅菌羊乳熱安定性之影響

為解決台灣夏季羊乳供過於求，於應用超高溫瞬間（ultra high temperature, UHT）滅菌法製成保久羊乳延長保存期限，常因羊乳熱安定性差而無法執行，故利用添加安定劑（stabilizer）以增加羊乳熱安定性。故本篇報告旨在探討pH值調整或磷酸鹽添加對超高溫瞬間滅菌羊乳熱安性之影響，並找出滅菌羊乳最適添加磷酸鹽比例，待冬季再製羊乳加工產品使用；分析項目包括pH值、滴定酸度（titratable acidity, TA）、游離性鈣離子濃度（ionic calcium concentration, iCa）、酒精安定性、沉澱物含量（Sediment content）、色澤（L值、a值、b值）、總生菌數及感官品評。本試驗之羊乳取自於屏東縣長治鄉某阿爾拜因（Alpine）乳羊場，試驗一將混合磷酸鈉（blend of sodium phosphates, Na）、混合鈉鉀磷酸鹽（blend of sodium and potassium phosphates, Sp）及0.5 N氫氧化鈉添加於生羊乳中，並將pH值調整為6.7－7.1作為安定劑使用量之基準，利用高壓滅菌釜（Autoclave）模擬UHT條件（135℃ 4秒）進行滅菌，以探討羊乳之熱安定性。試驗二將不同比例0.05－0.11%之混合磷酸鈉及混合鈉鉀磷酸鹽安定劑，各別添加於不同季節（春、夏、秋、冬）Alpine生羊乳中，經autoclave滅菌（135℃ 4秒）後探討最適安定劑添加比例。試驗三延續試驗二結果，選用0.08－0.09%Na及Sp比例添加至羊乳中，實施UHT pilot plant 滅菌處理（135℃ 4秒），製作成UHT羊乳（product A），並再製成酸性調味羊乳（product B）。結果顯示，試驗一於生羊乳中添加氫氧化鈉之組別，於加熱前與加熱後皆會隨著其pH值上升酒精安定性亦有上升之趨勢，並使游離性鈣離子濃度下降；而添加Na及Sp之組別於經autoclave滅菌（135℃ 4秒）後皆產生凝固之現象，由試驗一結果得知，不同安定劑無法以相同pH值做為最適添加量之基準。試驗二進一步探討羊乳中添加鹽類安定劑之最適比例，結果顯示於添加0.08－0.09%之Na及Sp於不同季節生羊乳中經加熱處理後，其沉澱物含量顯著低於其他組別且皆無產生凝固之現象，表示此範圍之添加量能讓乳樣品穩定具有最佳之熱安定性。試驗三將以0.08－0.09%Na及Sp製作成UHT滅菌羊乳並貯存於4℃，結果顯示各UHT滅菌羊乳經UHT pilot plant 滅菌處理後其pH值、游離性鈣離子濃度及L值顯著較滅菌前低，酒精安定性、a值及b值則顯著較滅菌前高，各組別沉澱物含量其中以添加0.08%混合磷酸鈉及混合鈉鉀磷酸鹽顯著低於其他組別。感官品評採取7分制評分，各處理組總接受度評分皆高於4分以上，貯存期間可長達至60天；酸性調味羊乳於4℃貯21日，結果顯示酸性調味羊乳之pH值及滴定酸度於貯存期間均無顯著差異，各處理組總接受度分數皆高於5分以上。綜合上述，於羊乳中添加0.08%混合磷酸鈉或0.08%混合鈉鉀磷酸鹽應用於UHT亦能維持良好乳品質並可做為後續調味羊乳原料使用，增加保存期限進而解決台灣夏季羊乳剩餘問題。關鍵字：熱安定性、游性鈣離子、磷酸鹽、沉澱物、超高溫瞬間滅菌

關鍵字

熱安定性；游性鈣離子；磷酸鹽；沉澱物；超高溫瞬間滅菌

並列摘要

Low heat stability of goat milk limited the application of ultra-high temperature (UHT) sterilization on producing sterilized UHT goat milk from excess goat milk in summer for producing goat dairy products in winter in Taiwan. Therefore, this study aimed to add phosphates in goat milk to increase the heat stability for producing UHT sterilized goat milk in summer for making goat dairy products in winter. The quality of goat milk was measured with aNalysis of pH value, titratable acidity (TA), ionic calcium concentration (iCa), ethanol stability, sediment content, color evaluation (L* a* b*), total bacterial count (TBC) and sensory evaluation. Milk samples were obtained from an Alpine goat farm in Changzh, Pintung, Taiwan. In experiment 1, the pH of raw goat milk was adjusted to 6.7-7.1 with baseline 3 stabilizers, blend of sodium phosphates (Na) (group 1), blend of sodium and potassium phosphates (Sp) (group 2), and 0.5 N NaOH (group 3), respectively. Autoclave sterilization at 135℃ for 4 seconds was applied to investigate the heat stability. In experiment 2, 0.05-0.11% Na and Sp were added to raw goat milk at different seasons before autoclave sterilization at 135℃ 4 sec to investigate the optimal amount of stabilizers addition. In experiment 3, was focused on producing shelf life extened milk (product A) from raw goat milk, which was added with 0.08-0.09% Na and Sp sterilized using UHT pilot plant at 135℃ for 4 sec, then reproduced acid flavor milk (product B) from product A. Results of experiment 1 showed that the addition of NaOH in goat milk before heating increased the pH, ethanol stability, and decreased iCa; however, the addition of phosphates in milk resulted in coagulation after 135℃ 4 sec autoclave heating. It indicated that pH value was not a suitable indicator for adjusting the amount of stabilizers added for stabilizing goat milk. Results of experiment 2 showed that there were seasonal differences in choosing the optimal addition levels of stabilizers. After autoclaved, sediments of goat milk with 0.08-0.09% Na and Sp addition without coagulation found, significantly lower than other treatmens, it is indicated higher heat stability. Results of experiment 3 showed that all treatments after UHT sterilization significant lower L*, but significantly higher a* and b* values. Sediments of goat milk added with 0.08% Na and 0.08% Sp were significantly lower than other treatments. The sensory evaluation was scored on 7 points hedonic scale sensory evaluations results of all groups showed that overall acceptability was higher than 4 points in 60 days of storage.The pH value and titratable acidity of acid flavored goat milk of each group were not significantly different during stored at 4℃ for 21 days. Sensory evaluations all group showed that overall acceptability were higher than 5 points. In summary, the addition of 0.08% blend of sodium phosphates and 0.08% blend of sodium with potassium phosphates to raw goat milk improve heat stability of goat milk in UHT treatment, which can extend the shelf life of excess goat milk in summer for winter use, and therefore suitable for producing acid flavored milk.