有色米米糠之生物活性成分分析及阿拉伯木寡醣製備

Abstract

本研究分為兩大部分，第一部分對花蓮太巴塱黑糯米1 (HB1)、台灣西部黑米(WB)、泰國黑米(TB)、花蓮太巴塱紅糯米1 (HR1)、光復紅米(HR)及泰國紅米(TR)等六種有色米米糠中所含的生物活性成分進行分析，第二部分則以花蓮太巴塱黑糯米2 (HB2)及花蓮太巴塱紅糯米2 (HR2)之米糠為材料，藉由球磨與酵素水解製備阿拉伯木寡醣(arabinoxylan oligosaccharides, AXOS)。有色米米糠生物活性成分分析中，依碾白時去除的先後順序，將米糠分為一次及二次碾白米糠兩個劃分(RB-1st及RB-2nd)；出麩率分別為10-19與6-11 wt%)。結果顯示，總酚含量、總類黃酮含量、DPPH自由基清除力與還原力等抗氧化性質，皆以游離態者(如RB-1st依序為17.89–36.70 mg ferulic acid equiv/g、11.72–12.17 mg catechin equiv/g、18.94–49.99 mg trolox equiv/g及13.27–28.18 mg ascorbic acid equiv/g)高於結合態者(如RB-1st依序為2.92–6.92 mg ferulic acid equiv/g、0.79–2.85 mg catechin equiv/g、2.40–6.86 mg trolox equiv/g及2.13–5.51 mg ascorbic acid equiv/g)；RB-1st高於RB-2nd，此外，在紅米RB-1st中游離態之總酚含量及抗氧化活性皆顯著高於黑米。花青素及原花青素分別在黑米(如RB-1st為6.28–11.27 mg Cy3glc equiv/g)及紅米米糠(如RB-1st為12.16–19.13 mg catechin equiv/g)中具有豐富的含量，亦主要分布於RB-1st。有色米米糠中的酚酸多以結合態存在，黑米中含量較高者依序為阿魏酸、原兒茶酸與香草酸；紅米中亦是以阿魏酸含量最高，而香豆酸次之。此外，利用串聯質譜技術，鑑定出紅米的HPLC圖譜中一未知化合物為原兒茶醛。有色米米糠中的維生素E以α-生育酚(13.12–67.30 μg/g)及γ-生育三烯酚(16.91–53.09 μg/g)含量較高。AXOS的製備再分為兩小部分，一是以生產機能性食品配料為導向，透過球磨處理，提升米糠中的水溶性阿拉伯木聚醣(water-extractable arabinoxylan, WE-AX)含量；另一是藉由聚木醣酶水解米糠不可溶性膳食纖維(RBIDF)中的阿拉伯木聚醣，以生產AXOS，並探討在木聚醣酶水解前預先施以球磨處理，對酵素水解效率的影響。結果顯示，有色米米糠經過乾式或濕式球磨後，粒徑皆大幅降低，而其WE-AX含量皆大幅提升，以濕磨增加速度較快，但可到達的極限值較乾磨低，另在球磨過程中對於酚類化合物、花青素、原花青素等生物活性成分的破壞，乾磨相對較低。RBIDF的球磨處理中，採用濕磨可使其WE-AX大量增加，而使用乾磨則增加的量極低，且難以達到細磨的效果。經濕磨處理之RBIDF，進一步以木聚醣酶水解後，其還原糖的增加量(29.5 μmol Xyl equiv/g RBIDF)高於未經濕磨預處理者(15.3 μmol Xyl equiv/g RBIDF)，因此，濕磨預處理應有助於提高木聚醣酶的水解效率。

This study consisted of two parts. First, bioactive compounds in rice bran from six colored rice samples (Hualien Taibalang black waxy rice 1, HB1; Western black rice, WB; Thai black rice, TB; Hualien Taibalang red waxy rice 1, HR1; Guangfu red rice, GR; Thai red rice, TR) were analyzed. Second, arabinoxylan oligosaccharides (AXOS) were prepared from the rice bran of Hualien Taibalang balck waxy rice 2 (HB2) and Hualien Taibalang red waxy rice 2 (HR2). Ball milling and enzymatic hydrolysis was used for AXOS preparation. In the first part, the colored rice bran was collected from first and second milling periods (RB-1st and RB-2nd, respectively) and used for analyses. Total phenolic content, total flavonoid content, DPPH radical scavenging activity, and reducing power of colored rice bran were higher in free form (e.g. 17.89–36.70 mg ferulic acid equiv/g, 11.72–12.17 mg catechin equiv/g, 18.94–49.99 mg trolox equiv/g, and 13.27–28.18 mg ascorbic acid equiv/g according to the order above in RB-1st) than in bound form (e.g. 2.92–6.92 mg ferulic acid equiv/g, 0.79–2.85 mg catechin equiv/g, 2.40–6.86 mg trolox equiv/g, and 2.13–5.51 mg ascorbic acid equiv/g according to the order above in RB-1st) and higher in RB-1st than in RB-2nd. In addition, total free phenolic content and antioxidant activities in the RB-1st of the red rice bran were significantly higher than that of the black one. There were plentiful anthocyanins and proanthocyanidins in black (e.g. 6.28–11.27 mg Cy3glc equiv/g in RB-1st) and red rice bran (e.g. 12.16–19.13 mg catechin equiv/g in RB-1st), respectively, especially in RB-1st. Phenolic acids in colored rice bran were mainly in bound form. Ferulic, protocatechuic, and vanillic acids were the dominant phenolic acids in black rice. In red rice, ferulic acid was also the most abundant phenolic acid followed by p-coumaric acid. Moreover, one novel phenolic compound, 3,4-dihydroxybenzaldehyde, was the first time to be identified in the bound phenolics extract from RB-1st of red rice bran by using HPLC-DAD/ESI-MS-MS. α-Tocopherol (13.12–67.30 μg/g) and γ-tocotrienol (16.91–53.09 μg/g) were the most abundant forms of vitamin E in the colored rice bran. The potential of colored rice bran to be used as a functional food ingredient through ball milling was examined in the second part. Besides, the effect of ball milling pretreatment on the efficiency of enzymatic hydrolysis of AX in rice bran insoluble dietary fiber (RBIDF) was also investigated. After either dry or wet ball milling of colored rice bran, the particle size decreased dramatically while water-extractable arabinoxylan (WE-AX) bran increased significantly. Compared to the dry ball milling process, WE-AX in colored rice bran increased more rapidly during wet ball milling. However, the maximum amount of WE-AX after wet ball milling was lower than that from the dry ball milling. In addition, the degradation of some bioactive compounds was severer in wet milling process than that in the dry ball milling. WE-AX in RBIDF increased substantially in wet ball milling process but not in dry ball milling process. Both untreated and wet ball milled RBIDF were further hydrolyzed with xylanase. The increase of reducing sugar was higher in wet ball milled RBIDF (29.5 μmol Xyl equiv/g RBIDF) than in the control sample (15.3 μmol Xyl equiv/g RBIDF). As a result, wet ball milling pretreatment could improve the efficiency of enzymatic hydrolysis of AX in RBDIF.