烘焙與濕磨對糙米理化性質的影響

Abstract

本研究擬開發新型糙米食品原料，即為將焙炒之糙米經由微細濕磨法（micro-wet milling, MWM）研磨成焙炒糙米漿，並針對焙炒與研磨條件對糙米及糙米漿理化性質之影響進行探討。主要分為三個部分；第一部分，評估使用4種烘焙程度，分別為0、 20、30和40分鐘（即 Raw，Light，Medium 和 Dark）製備之糙米進行儲存穩定性和抗氧化活性測定，以篩選最佳烘焙度。經由水分含量，水活性和酸價的變化，評估其貯藏安定性。結果顯示，Dark 樣品穩定性最佳並具有最高的抗氧化活性。因此，以此樣品進行後續後的 MWM 處理。第二部分，使用兩個台灣稻米品種（稉米和糯米）於兩種烘焙度（Raw 和 Dark）下以 MWM 研磨成糙米漿，並評估焙炒和 MWM 的綜合效果，尤其側重於加工適用性。評估項目包括，色澤變化、冷凍貯存穩定性、糊化性質、熱性質、微細結構（SEM），DPPH 抗氧化活性等。糊化性質測定結果顯示，其成糊溫度升高，尖峰黏度、破裂黏度和回升黏度均降低，顯示焙炒糙米漿需要再經高溫蒸煮後才有可能獲得黏稠的質地，但其加工穩定性則提高。示差掃描熱分析(Differential scanning calorimetry, DSC)測定和 SEM (scanning electron microscopy)觀察結果顯示，在焙炒糙米漿中可能發生部分糊化和對澱粉粒的機械破壞。第三部分，使用兩種烘焙度的兩個日本稻米品種（稉米和糯米）製備焙炒糙米漿，評估其焙炒和 MWM 對其理化性質及生理功能性的綜合效果。評估項目包括，色澤變化、粒徑分析、質地分析、凍融穩定性等；並測定其總酚(total phenol contents, TPC) 含量和抗氧化活性。結果顯示，焙炒糙米漿的粒度變大，推測可能是粒子團聚所致。質地剖面分析(Texture profile analysis, TPA)顯示，在凍融循環中焙炒糙米漿的硬度顯著提高但其離水率顯著降低，預測其於運送貯藏之穩定性提高。在焙炒糙米漿中，其 TPC 和抗氧化活性均提高。總而言之，經焙炒及微細濕磨所製備之糙米漿可以改善食品的功能性，提供令人愉悅的香氣並調整食品質地，可以作為一種良好的食材原料。這項研究，為提高稻米產品品質和開發新型態糙米食品原料提供寶貴的參考資料。

In this study, towards development of new brown rice (BR) food material, i.e., roasted BR slurry, effects of roasting and micro wet milling (MWM) on physicochemical properties of BR were analyzed. This research was carried out in three parts. In first part, the storage stability and antioxidant activity of the BR powders prepared using 4 roasting levels 0, 20, 30, and 40 minutes (i.e., Raw, Light, Medium, and Dark, respectively) were evaluated to screen the optimal roasting levels. The dark roasted samples showed the best storage stability, evaluated by the changes of moisture content, water activity, and acid value, and the highest antioxidant activity, thus selected for the following MWM processing . In the second part, the combined effects of roasting and MWM especially focusing on processing suitability were evaluated using BR slurries with two roasting levels (Raw and Dark) of two Taiwanese rice varieties (nonwaxy and waxy). Color change, frozen storage stability, pasting properties, thermal properties, morphology, DPPH antioxidant activity, were evaluated. The results of pasting properties showed that increased pasting temperature and decreased pasting viscosity, breakdown and setback, indicating that roasted BR slurry needs higher cooking temperature to obtain viscous texture but have higher processing stability. The results of thermal properties analysis and morphological analysis indicated partial gelatinization and mechanical disruption of starch could have occurred in roasted BR slurry. In the third part, the combined effects of roasting and MWM especially focusing on functionality were evaluated using BR slurries with two roasting levels of two Japanese rice varieties (nonwaxy and waxy). As physicochemical properties, Color change, particle size distribution, texture profile, and freeze-thaw stability were measured. And as phytochemical properties, total polyphenol contents (TPC) and antioxidant activity were evaluated. Particle size became larger in roasted BR slurries, which might be attributed to agglomeration. Texture profile analysis exhibited greatly increased hardness in roasted BR slurries. Dramatically lower syneresis rate of dark roasted slurries during freeze-thaw cycle indicated the high transportation stability. In terms of phytochemical properties, increased TPC and antioxidant activity were observed in roasted samples. To conclude, the roasted BR slurry may become a good food material to improve the functionality, pleasant aroma, and to adjust food texture. I believe that this study provides valuable guidance for further quality improvements and development of new BR food materials.