由碎米提取米蛋白之可行性

Abstract

蛋白質為食品中三大營養素之一，亦在食品加工上賦予產品加工功能性。稻米中的米蛋白是生產米糖漿之副產物，具有高營養價值、低致敏性、產量大且價格低廉等優勢。稻米研磨加工過程中會產生 15% 至 30% 的碎米，其原料成本為白米的一半，因此本研究以碎米作為原料，評估碎米提取米蛋白之可行性。第一部分探討不同規格之碎米提取米蛋白之產物性質，結果發現碎米中broken kernel及chips之原料蛋白質含量高於完整米whole kernel，利用澱粉酶提取方法提取米蛋白，顯示出broken kernel rice protein (BRP) 及chips rice protein (CRP) 之蛋白含量及收率皆略低於whole kernel rice protein (WRP)，但若於酵素水解澱粉前去除油脂，所製得BRP及CRP 之蛋白含量增加，然而蛋白收率下降。第二部分為不同規格碎米蛋白之品質分析，在顏色方面，脫脂米蛋白之白度指數皆高於WRP、BRP及CRP，且具顯著差異 (P < 0.05)，在油脂氧化揮發物方面，顯示碎米蛋白在油脂氧化揮發物上相對含量高，但經過脫油後其含量相對降低，此外，分析不同規格碎米蛋白於pH 7下之水溶性、乳化性及發泡性等加工功能性，各樣品間皆無顯著差異 (P > 0.05)。第三部分為加熱處理對於米蛋白功能性及雙硫鍵含量之影響，結果顯示米蛋白經加熱與否之雙硫鍵含量無顯著影響，實驗也發現鹼萃取法及澱粉酶提取法所提取出之米蛋白，其水溶性及加工功能性並無顯著差異 (P > 0.05)。 本研究結果發現碎米中油脂會使米蛋白之蛋白含量、收率及白度指數下降，但可以利用碎米作為原料提取米蛋白降低生產成本，並增加碎米之經濟效益以提升產業競爭優勢。

Protein provides functional properties for food products and essential nutrients for human body. Rice protein, a by-product from the processing of white rice for syrup production, is a low-cost protein source. Broken rice, whose price is half of that for the white rice, is produced during the milling process and is probably a more cost-efficient material for rice protein production. In this study, the feasibility of extracting rice protein from broken rice using enzyme extraction method was evaluated. In the first section, the protein content and recovery of the rice protein from broken rice were determined. The protein content within whole kernel was lower than that within broken kernel and chips. However, higher protein content and recovery was observed in the rice protein extracted from whole kernel (WRP) when compared to that from broken kernel (BRP) and chip (CRP). The protein content of BRP and CRP could be increased by removing the lipids in the rice kernel with hexane before the extraction of rice protein. Nevertheless, removing the lipids in the rice kernel could result in a decreasing in the protein recovery of all the samples. In the second section, the quality of rice protein in samples was evaluated. The whiteness indices of deoiling rice proteins were significantly lower than that of WRP, BRP and CRP (p < 0.05). In terms of volatile compounds, BRP and CRP showed relatively high content of fatty volatiles, but those volatile compounds decreased after deoiling. Among WRP, BRP and CRP, no significant differences in protein solubility, emulsifying activity, foaming activity and other functional properties were observed at pH 7.0 (p > 0.05). In the last section, we focused on the effects of heat treatment on the functionality and the amount of disulfide bonds. No significant differences in functional properties and the amount of disulfide bonds was observed for rice protein underwent thermal processing (p > 0.05). In conclusion, the lipids of broken rice were the main factor leading to the decrease in rice protein contents, protein recovery and its quality. However, rice protein could be produced from broken kernel and chips, and could reduce the production cost of food and enhance the competitiveness in the food industry.