藉由臺灣黏質發酵乳及其分離菌株 Lactococcus lactis subsp. cremoris T1製作機能性低脂乾酪之研究

Abstract

本實驗室自臺灣黏質發酵乳（Taiwan ropy fermented milk, TRFM）中分離出之Lactococcus lactis subsp. cremoris T1菌株（T1）及Lactococcus lactis subsp. cremoris T4菌株（T4），前者可產生胞外多醣體後者則無，而胞外多醣體具有良好保水能力，可增加乳製品之保水性並干擾蛋白質分子聚合，因此本研究將以TRFM及其分離菌株T1與T4添加於低脂乾酪中，探討儲存期間其對低脂乾酪乳酸菌數、理化特性、質地及抗氧化、抗高血壓、免疫等機能性之影響。實驗以全脂生乳及低脂生乳為對照組，以添加TRFM、T1及T4菌元，各發酵4小時及8小時之低脂生乳為實驗組，最終乾酪產品在4℃、相對溼度80%之條件下熟成14天，再以真空包裝後保存於4℃冰箱中14天。於儲存期結束後進行試驗，結果顯示，各實驗組乾酪的乳酸菌數皆達108 cfu/g以上；實驗組乾酪其水分含量顯著高於對照組（P < 0.05），於儲存期間之變化，對照組乾酪之水分含量下降14-17%，實驗組之乾酪僅下降9-12%；在質地分析之硬度（hardness）部分，添加T1及TRFM為菌元的實驗組乾酪，皆顯著低於添加T4為菌元的實驗組乾酪及對照組之低脂乾酪，且各組乾酪之硬度會隨儲存時間延長而上升。本研究顯示，TRFM及其分離菌株T1所產生之胞外多醣體可改善低脂乾酪之保水性及質地等特性，期能發展新風味且質地良好之低脂乾酪以增加乳製品多樣性。在機能性試驗部分，以添加TRFM、T1及T4菌元各發酵4小時的實驗組，其螯合金屬離子之能力顯著高於對照組乾酪（P < 0.05）；添加TRFM、T1及T4菌元之各實驗組乾酪，其抵抗自由基（DPPH）及血管緊縮素轉換酶之抑制能力亦顯著優於對照組乾酪；最後品評試驗部分則以T1發酵8小時之乾酪較受品評員青睞。由於直接添加由TRFM中分離之T1做為發酵菌元，其保水性、乾酪質地、品評結果、抗氧化力及抑制血管緊縮素轉換酶之能力皆優於對照組及以TRFM與T4做為發酵菌元之實驗組乾酪，因此本研究結果顯示，添加T1做為低脂乾酪的菌元，有改善低脂乾酪質地且提高低脂乾酪機能性的可行性。

Fat reduction in cheese is associated with many textural and functional defects. Low-fat cheeses have low intensity of typical flavor and may develop a bitter off-flavor and hard, rubbery, dry and grainy texture. Exopolysaccharide (EPS) could increase the water-holding capacity and interfere with protein–protein interactions in food products, which are important properties required in fat replacement. In our previous study, EPS producing strain, Lactococcus lactis subsp. cremoris T1 (T1), was isolated from TRFM. This strain may act as a fat replacer in low fat cheese. Thus, the purpose of this study was to manufacture a new functional low fat cheese with TRFM、T1 and T4 strain and investigate the effects of TRFM、T1 and T4 (EPS-negative genetic variant, Lactococcus lactis subsp. cremoris T4, was isolated from TRFM) strain on the chemical, microbial, functional, physical and sensory characteristics of this low fat cheese. Skim milk was pasteurized at 65℃ for 30 min, inoculated with T1 strain/ T4 strain/ TRFM as starter cultures, and added rennet to form milk curd. The cheeses were then produced by cooked, cut and released whey from the milk curd. The full fat cheese and low fat cheese were positive and negative controls, respectively. The microbial analysis indicated that the cell counts of lactic acid bacteria in the low fat cheese samples inoculated with T1, T4 and TRFM were above 108 cfu/g. The low fat cheese inoculated with T1 and TRFM also showed a significantly higher moisture contents than the low fat cheese control. The moisture/protein ratios of the low fat cheese inoculated with T1 and fermented for 4 hrs (4-T1 sample) showed no significant differences with the ratio of the full fat cheese control. The further texture analysis verified that the 4-T1 and 8-T1 samples demonstrated a very similar texture profile to the full fat cheese control. In addition, the 8-T1 sample had the highest customer preferential scores in appearance, texture and flavor than other cheese samples. Additionally, the functional characteristics including antioxidation, antihypertension and immunoregulation were evaluated. The cheese samples made with TRFM、T1 and T4 have significantly higher ability of scavenging free radical than the control full-fat and low-fat cheeses during ripening period. The reactive oxygen species play an important role related to the degenerative or pathological processes of various serious diseases. This finding indicated that the cheese samples made with TRFM、T1 and T4 might possess natural antioxidants and compounds with radical scavenging activity. The cheeses made with T1、T4 and TRFM also showed a significantly higher inhibition in angiotensin-converting enzyme (ACE). ACE is known to associate with hypertension and congestive heart failure. ACE inhibitors in the TRFM、T1 and T4 samples may reduce the activity of the renin-angiotensin-aldosterone system. In conclusion, this study demonstrated that the low fat cheese made with TRFM and T1 not only gives a positive impact on the low fat cheese quality, but also provide the functions of a radical scavenging activity and ACE inhibition.