藉由培養Lactococcus lactis subsp. cremoris T1製作之低脂乾酪其物理及機能性之變化

Abstract

乾酪是良好的蛋白質及鈣質之主要來源，但也包含豐富飽和脂肪。低脂乾酪由於含水量高導致有較差之質地、風味及機能特性，但添加脂肪取代物可改善此情況。研究指出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。此重要特性可當作脂肪取代物，自臺灣黏質發酵乳（Taiwanese ropy fermented milk）中分離出之Lactococcus lactis subsp. cremoris T1菌株（T1），先前實驗室研究指出具有產生胞外多醣體之特性，因此在乾酪製作過程中添加作脂肪取代物。因此，本研究探討添加T1菌株於低脂乾酪對質地及機能性之影響。 首先，選用特級甜性脫脂乳清粉、糖蜜酵母粉、檸檬酸鈉及磷酸氫二鉀當作原料，以反應曲面法及二次規劃法求得高產量T1菌株之最適化配方。實驗組數共得到30組而實驗結果菌數落於7.00到9.00 log CFU/mL，得到最佳結果菌數為9.00 log CFU/mL，在驗證實驗結果證實預期結果與實驗結果並無顯著性差異。在發展T1菌株之菌數最大化培養基後，於工廠產製低脂 Mozzarella乾酪。結果指出添加T1可增進乾酪保水性及改善乾酪質地；且在品評實驗結果顯示出低脂乾酪之外觀、風味、香氣與全脂乾酪並無顯著性差異。 此外更進一步探討T1菌株添加於低脂乾酪對於免疫和抗腸炎試驗之影響。對於免疫調節反應，添加T1菌株之低脂乾酪可抑制RAW 264.7少數發炎激素分泌；在抗腸炎結果顯示，添加T1菌株低脂乾酪可顯著提升Caco-2細胞單層膜之上皮細胞完整性。 總結來說，添加T1菌株之低脂乾酪在化學基本組成分、物性分析與控制組全脂乾酪相比較並無顯著性差異，而對於免疫及抗腸炎之結果也皆有影響。透過以上試驗，可作為日後產製健康乾酪之參考依據。

Cheese is a good source of protein and calcium, but it is a major source of saturated fat. Demand for cheese with less fat is growing. The reduced-fat cheeses are usually characterized as having poor body, flavor and functional properties because of high moisture. Addition of the fat replacers may provide the solution. Exopolysaccharide (EPS) could increase water-holding capacity and interfere with protein-protein interactions in food products, which are important properties required in fat replacement. Lactococcus lactis subsp. cremoris T1 (T1), isolated from Taiwanese ropy fermented milk, may act as a fat replacer in reduced-fat cheese manufacture according to its EPS-producing property. Thus, the purpose of this study was to investigate of effect of inoculating Lactococcus lactis subsp. cremoris T1 on physical and functional characteristics of reduced-fat cheese. First, the growth medium, which was proportion of whey powder, yeast extract, citrate and potassium phosphate, was optimized using response surface methodology (RSM) to first construct a surface model, with sequential quadratic programming (SQP) subsequently adopted to optimize the model and evaluate the cell counts of T1. Optimization results indicated that after 30 sets of randomly generated initial points leading to optimal cell counts (local optimal) ranging from 7.00 to 9.00 log CFU/mL, the global optimal cell count of T1 was found to be 9.00log CFU/mL (99.99% certainty). The verification experiment yielded a result close to the predicted values, with no significant difference (P > 0.05). After maximizing the T1 growth medium, we produced reduced-fat Mozzarella cheese in an industrial cheese factory. The full fat cheese and reduced-fat cheese were positive and negative controls, respectively. Results indicated that addition of T1 could enhance moisture content and improve cheese texture. The customer preferential score of the reduced-fat cheese sample showed no difference in appearance, flavour and aroma with the full-fat counterpart. Additionally, the functional characteristics including the immunoregulatory and anti-colitis effects of T1 reduced-fat cheese were also evaluated in this study. For immunoregulatory effect, the T1 samples could stimulate the production of TNF-α, IL-10, IL-1β and IL-6 in murine macrophage cell line RAW 264.7. For anti-colitis effect, the T1 samples could also strengthen the epithelial barrier function in vitro by increasing the transepithelial electrical resistance（TEER）but not significantly upregulated the level of the chemokine CCL-20 at both the apical and basolateral sites of Caco-2 cell monolayer. In conclusion, this study demonstrated that the reduced-fat cheese made with T1 shows no significant difference in chemical properties, textural characteristics when compared with the full fat cheese control. The T1 cheese also demonstrated the immunoregulatory and anti-colitis effects. These findings will help develop new healthy cheese products.