分辨米穀粉品質特性之方法

Abstract

米穀粉於食品加工領域的應用與日俱增，故須發展針對米穀粉品質檢測之參數指標。本研究之目的為建立分辦米穀粉特性之方法，藉此了解米穀粉之性質並作為米穀粉加工應用之參考。於本研究中，精白米預先被磨成粉後，測定基本組成、粒徑分佈、糊化性質、膨潤力、溶解度、滯留溶劑能力(solvent retention capacity)、破損澱粉、直鏈澱粉含量、α及β澱粉酶之活性及攪拌性質。最終以米穀粉做烘焙產品米麵包。研究結果顯示，蛋白質品質與破損澱粉為影響米穀粉攪拌性質之主要因子。添加1.5%之羥丙基甲基纖維素(hydroxypropylmethylcellulose, HPMC)至米穀粉中使能其在 farinograph檢測中達到500 FU之標準。Farinograph之指標受到滯留乳酸及碳酸鈉之能力影響，而兩者又分別與蛋白質品質與破損澱粉有關。吸水率(water absorption)和攪拌耐受指標(mixing tolerance index)與滯留乳酸和碳酸鈉(r>0.9, p<0.001)之能力呈正相關，然而擴展時間(development time)和攪拌彈性時間(stability time)與滯留乳酸(r< -0.9, p< 0.001)之能力呈負相關。 米穀粉之烘焙產品結果顯示滯留溶劑能力(solvent retention capacity), 破損澱粉, 直鏈澱粉含量皆影響米麵包之性質. 其中影像米麵包體積的重要因素藉為破損澱粉及滯留溶劑能力(solvent retention capacity)的五碳聚醣(pentosan)。米麵包之高度、比體積及體積指標皆與滯留蔗糖之能力成正相關(r> 0.8, p<0.05)，然而體積指標與滯留碳酸鈉之能力成負相關(r< -0.8, p<0.05).。本研究所使用之方法能分析米穀粉之特性並作為品工業中米穀粉品質管制之指標。

Increased use of rice flour in the food industry has necessitated it to have a set of testing methods that will reveal rice flour characteristics to indicate rice flour quality. Therefore, the objective of this study is to develop differentiating testing methods in rice flour that will help in understanding rice flour properties and that will serve as guidelines in rice flour processing properties. In this study, milled rice were ground to flour, and flour specifications such as proximate composition, particle size distribution, pasting properties, swelling power and solubility, solvent retention capacities, starch damage, amylose content, alpha-amylase and beta-amylase activity, mixing characteristics were determined. Lastly, a bake test was also conducted. Seven commercial including fresh and aged rice samples were selected for testing. Protein quality and starch damage are observed to be the main determining factors in rice flour mixing characteristics. The addition of 1.5% hydroxypropylmethylcellulose to rice flour made it possible for rice flour mixing characteristics to reach a consistency of 500 FU and be studied in a farinograph. Farinograph parameters were greatly influenced by solvent retention capacities of lactic acid and sodium carbonate which are associated with protein quality and starch damage respectively. Water absorption and mixing tolerance index were statistical (r>0.9, p<0.001) positively correlated with lactic acid solvent retention capacity and sodium carbonate solvent retention capacity, while development time and stability time were statistical (r< -0.9, p< 0.001) negatively correlated with lactic acid solvent retention capacity and sodium carbonate solvent retention capacity. Lastly, results for bake test indicated that solvent retention capacity, starch damage and amylose contentaffect rice bread properties. Pentosans and starch damage are key factors that influenced rice bread volume. Height, specific volume and volume index were statistical (r> 0.8, p<0.05) positively correlated with sucrose solvent retention capacity while volume index were negatively correlated with sodium carbonate solvent retention capacity(r< -0.8, p<0.05). Therefore, the methods used in this study reveal characteristic rice flour properties and could serve as guidelines in rice flour quality control in the food industry.