發芽及熟化處理對國產有色米機能性質之影響

Abstract

稻米中天然存在之機能性物質可能因為不同加工程序而流失，本篇旨在探討發芽及熟化處理對於有色米中機能性成分（總可溶性酚類化合物、花青素、總可溶性原花青素、γ-氨基丁酸(GABA)、慢速消化澱粉及抗解澱粉）之影響，並設法在加工過程中保留或獲得較高的機能性物質含量。試驗分為稻米發芽、熟化及去分支三部分。米粒在發芽前須經過浸泡處理，此過程會讓糙米中的水溶性機能成分流失，而在接下來的發芽過程中，總可溶性酚類化合物含量會稍微提升，花青素及原花青素逐漸流失，而GABA含量則大幅提升；若使用稻穀樣品進行發芽處理，因稻殼形成物理性保護，可有效減少水溶性機能成分流失，但也因為稻殼阻礙穀粒吸水效率，造成發芽稻穀之GABA含量低於發芽糙米之現象。熟化處理分成濕熱熟化與乾熱熟化，濕熱熟化對於米中機能性成分造成不同程度之破壞，以GABA之熱穩定性最高，其次為總可溶性酚類化合物、總可溶性原花青素，而花青素則在加熱後破壞殆盡；乾熱熟化不會對紅米中總可溶性酚類化合物含量造成影響，且可溶性原花青素含量經乾熱處理後可增加為2-3倍，然而，所有樣品之GABA含量均在加熱過程中大幅下降。黑米樣品建議採用濕熱熟化以保留較高的酚類化合物及GABA含量；紅米樣品若以GABA含量為考量亦應採取濕熱熟化，若以較高的酚類化合物含量為考量則以乾熱熟化為佳。糯米樣品經過濕熱熟化保留的慢速消化澱粉(SDS)含量為0-2.91%，乾熱熟化保留的SDS含量提升至3.49-11.78%，採用的兩種熟化方式都無法從糯米樣品中獲得抗解澱粉(RS)，且SDS含量也有限，因此採用支鏈澱粉之去分支處理以進一步提升SDS及RS含量。將熟化米穀粉進行去分支處理後離心，分離出上清液後加以濃縮，經回凝儲藏可獲得38-42%之SDS及RS含量，並且RS含量隨著溫度循環儲藏之天數增加而上升，因此，支鏈澱粉進行去分支後回凝可作為提升糯性有色米之SDS及RS含量之有效方法。

The amount of bioactive compounds in rice may be lost during processing. The objective of this study is to investigate the changes of contents of bioactive compounds (including total soluble phenolics, anthocyanins, total soluble proanthocyanins, γ-amino butyric acid, slowly digestible starch, and resistant starch) in colored rice via germination and cooking, and try to enhance and maintain the amounts of these compounds after processing. Three major parts, including germination, cooking, and debranching, are included. The soaking process required for rice germination would cause the loss of water soluble phytochemicals in brown rice. The contents of total soluble phenolics slightly increased and GABA significantly increased while the anthocyanins and proanthocyanins gradually decreased during germination. The husk of paddy could effectively prevent the loss of water soluble compounds, but it retarded the water absorption, resulting in the low degree of germination and low GABA content of germinated rough rice. In the second part, the effects of both moist-heating and dry-heating treatments were conducted. Moist-heating caused various degradations of phytochemicals. The thermal stability of bioactive compounds from high to low were GABA, total soluble phenolics, total soluble proanthocyanins, and anthocyanins. The total soluble phenolics content of red rice remained constant after dry-heating, while the total amount of soluble proanthocyanins was increased by 2-3 times. However, GABA content of all rice cultivars significantly decreased by dry-heating. Black rice was suggested to be moist-heated for keeping higher amounts of phenolics and GABA. Moist-heating treatment was suitable for retaining GABA in red rice as well. But, the dry-heating treatment was chosen for obtaining higher amount of phenolics. Slowly digestible starch (SDS) content of moist-heated and dry-heated waxy rice were 0-2.91% and 3.49-11.78%, respectively, while no resistant starch (RS) could be detected after both thermal treatments. Debranching treatment of waxy rice flour suspension with debranching enzyme, pullulanase, followed by centrifugation, condensation, retrogradation, and freeze-dried could obtain 38-42% SDS and RS contents in total. The RS content gradually increased with the increasing time period of retrogradation. Hence, enzymatic debranching treatment followed by the retrogadation treatment could be a way to produce SDS and RS in rice.