以反應曲面法探討糖質克弗爾多醣/小麥澱粉混合膜之物理及機械特性

Abstract

The sugary kefir polysaccharide (K) was extracted from sugary kefir grains and mixed with wheat starch (S) to form composite edible films. The effect of total solid, K/S ratio and glycerol content in the mixed system on the mechanical and other physical properties as well as water vapor permeability (WVP) of the resulting films were investigated by using Box-Behnken design of response surface methodology. The results revealed that the mechanical strength (including tensile strength and puncture force) of K/S films was enhanced with increasing total solid content and decreasing K/S ratio or glycerol content, accompanied with a decrease in elongation and puncture deformation. Moreover, the WVP of edible films decreased with increasing total solid content or decreasing glycerol content. However, the WVP of composite films decreased when K/S ratio decreased from 75/25 to 50/50, then increased when K/S ratio further decreased to 25/75. Edible films with lower total solid and glycerol content and higher K/S ratio generally showed larger water contact angle. Moisture sorption isotherm results revealed that edible films with a total solid-K/S ratio-glycerol value of 1.25-50-20 and 0.75-50-10 had the highest and lowest equilibrium moisture content among the treatments, respectively. Edible films with higher glycerol content and lower K/S ratio generally showed higher moisture content and solubility, accompanied with enhanced opacity and lightness. Microstructural examination by using scanning electron microscopy (SEM) revealed that films prepared under lower K/S ratio showed grainy surface and occasional pores. However, films with different glycerol content did not show a significant difference in terms of microstructure. Optimization analysis based on the mechanical strength and WVP results revealed that the optimal film forming condition could be obtained under a total solid content of 1.25%, K/S ration of 37/63, and glycerol content of 10%. Validation test revealed that films prepared under the optimal condition showed a tensile strength of 20.60±2.19 MPa, puncture force of 3.01±0.40 N and WVP of 3.86±0.18×10-11 gm-1s-1Pa, which were not significantly different from the prediction results by response surface model. Such results implied the appropriateness of the response surface model obtained.

本研究萃取糖質克弗爾粒中之糖質克弗爾多醣與小麥澱粉混合製成混合可食膜，利用反應曲面法之Box-Behnken Design實驗設計，探討總固形物、多醣/澱粉混合比例及甘油量對可食膜機械、物理性質及水氣阻隔性之影響。實驗結果發機械強度(包含抗張強度及穿刺強度)皆隨總固形物量提高、多醣/小麥澱粉混合比例及甘油添加量降低而增強，但卻造成延展度及穿刺形變量降低。此外，WVP會隨著總固形物提高及甘油添加量降低而下降；當多醣/澱粉混合比例由75/25降至50/50時，可食膜水氣阻隔性(WVP)首先降低，當比例再降至25/75時，WVP則提高。可食膜於低總固形物含量、甘油添加量及多醣/澱粉混合比例高時擁有較大的水接觸角。可食膜之等溫吸濕曲線以總固形物1.25%、多醣/澱粉比例50/50及甘油添加20% 組別(1.25-50-20)之平衡水分含量最高；以0.75-50-10組別最低。可食膜水分含量及溶解度皆隨著甘油添加量提高及混合比例降低時，有提高趨勢，亦會提高可食膜之不透明度及提高薄膜亮度。以SEM觀察可食膜之微結構發現，混合比例低的可食膜其結構越粗糙且有些微孔洞產生，而不同甘油添加量之間對於微結構並無明顯影響。以機械強度及阻隔性作為可食膜之重要應用因子，得出最適合製膜條件為1.25-37-10組別，實驗值分別為抗張強度20.60±2.19 MPa、穿刺強度3.01±0.40 N以及水氣透過性3.86±0.18×10-11 gm-1s-1pa，其預測值及實驗值之間並無明顯差異，顯示反應曲面模式對於可食膜機械性質及水氣透過性之適切性。