利用不同直鏈澱粉含量之系列稻米品種為模式 探討影響澱粉膠體特性之因子

Abstract

摘要 為探討影響米澱粉膠體特性之因子，選擇18種含有不同直鏈澱粉含量之稻米品種澱粉樣品，分別以質地分析儀(TPA)、快速連續黏度分析儀(RVA)、動態流變儀(DR)量測其回凝膠體性質、糊化成糊性質、膠體之黏彈特性，為增加分析樣品母本之數量，將研究室已有之26種台農67號同源化學誘變稻米之分析結果也一併納入；並同時分析此44種米澱粉(一般品種及化學誘變品系)之視直鏈澱粉含量、去分支澱粉分子(由鏈長由長至短，區分為F1、F2、F3)之鏈長分佈澱粉分子結構參數，進一步利用逐步複迴歸之統計方法，來分析上述澱粉理化性質與分子鏈長之關係。結果發現，經碘呈色法測定18種一般稻米品種之視直鏈澱粉含量為0.30-29.37%，與現有之26種化學誘變稻米品系(1.48-28.48%)同樣為具有直鏈澱粉含量系列分佈之樣品。經去分支處理並以高效能分子篩層析法分析之一般品種與誘變品系稻米澱粉分子其鏈長分佈比較，在F2、F3(支鏈澱粉長鏈與短鏈)兩區分無顯著差異，但F1(直鏈澱粉與支鏈澱粉超長鏈鏈長)區分上之鏈長比較，發現化學誘變品系稻米澱粉之鏈長較長。以膠體之硬度而言，對於TPA測定膠體性質的預測上，直鏈澱粉含量(F1)此一推測變數可提供最大的解釋量為55.8%，是影響膠體特性的主要因素，其餘的四個推測變數分別為直鏈澱粉鏈長、支鏈澱粉長鏈之鏈長、支鏈澱粉長鏈之含量、視直鏈澱粉含量，亦提升部分的解釋力(分別為18.8%、5.5%、4.3%、1.9%)，此五個推測變數共可解釋TPA膠體硬度總變異量的86.3%。另外，在膠體之硬度研究上，除了先前選定之澱粉分子鏈長參數外，若再多加入動態流變參數為迴歸模式之推測變數，可發現先前迴歸模式中最大解釋力之直鏈澱粉含量會被於25℃量測之貯存模數值(G’25℃)所取代，其最大解釋力的部份會由55.8%改變為84.3%，整體解釋力由86.3%提升到92.9%。即澱粉在低剪力環境中加熱糊化冷卻之膠體形成初期之強度與澱粉顆粒之強韌度為主要的貢獻因子，滲離之澱粉分子貢獻程度遠低於膨潤顆粒。

Abstract To understand the roles of starch molecules, amylose and amylopectin, plays in gel-forming properties, starch samples with wide range of amylose content from 18 rice cultivars of were selected to study the relationship between molecular structural characters and their gel texture, pasting properties, and viscoelastic properties measured by using texture profile analysis (TPA), rapid visco-analysis (RVA), and dynamic rheolometry (DR). In order to increase sample population for statistical analysis, other 26 starch samples from rice mutant were also included in this study. Chain-length distribution values of starch molecules were used as independent parameters for multivariate stepwise regression analysis to elucidate the correlation between the textural properties mentioned. High-performance size-exclusion chromatographic peaks of debranched starch were designated as F1, F2 and F2 according its eluting order. The results showed that apparent amylose content of starch samples from rice cultivars (ranged from 0.30% to 29.37%) as well as samples from mutants (1.48% to 28.48%) had covered a wide range and had no significant difference in mass ratio of all three fractions and in chain-length of F2 and F3 fractions, but found significant difference in chain-length of F1 (represents the amylose and extra-long chains of amylopectin). The mutants had longer F1 chain-length than selected cultivars. Function of multiple regression analysis could be used to predict TPA hardness using starch molecular structural parameters. Mass ratio of F1 and chain-length of F1explained most of the variance attributed to the models (55.8%, 18.8% ), but chain-length of F2、mass ratio of F2、apparent amylose content had little effect on the amount of variance attributed to the models (5.5%, 4.3%, 1.9%, respectively). The full multiple regression models explained 86.3% of the variation in TPA hardness. After adding dynamic rheologic parameters, storage modular force at 25℃, as extra predictor into the multiple regression model, it will increase most of the variance (from 55.8% to 84.3%) and full variance (from 86.3% to 92.9%). The results implied that the stiffness of swollen starch granules in the starch gel at early stage of gel-forming contributed more than those leached molecules for hardness attributes of starch gel.