焙炒與擠壓加工對米糠品質之影響

本研究在探討熱加工：焙炒、膨發擠壓及蒸煮擠壓，對米糠品質的影響。研究分為三部分，第一部分米糠以炒焙處理後，在不同溫度（-20、7和25℃）下進行貯藏，測定米糠油脂品質（過氧化價、酸價及游離脂肪酸含量）及以掃描式電子顯微鏡觀察其微觀結構。第二部分米糠以擠壓加工方式處理後，於7℃下貯藏56天，每隔14天進行米糠油脂品質、米糠醇含量、膳食纖維含量（可溶性及不可溶性）測定及其微觀結構觀察，並找出最佳米糠擠壓加工條件。第三部分以最佳米糠擠壓加工條件加工米糠，於溫度27~28℃下貯藏28天，每隔7天再次測定米糠油脂品質及米糠醇含量。第一部分實驗結果發現，米糠焙炒後，與控制組相比，有極顯著性差異（p <0.01）。可以有效減緩米糠過氧化價、酸價及游離脂肪酸含量上升。特別在-20℃下貯藏25天，有最低的過氧化價、酸價及游離脂肪酸含量，分別為0.43±0.23 meq/kg、2.47±0.09 mg KOH/g及1.21±0.04%。在第二部分實驗結果發現，米糠經膨發擠壓加工及蒸煮擠壓加工後，於7℃下貯藏56天，與控制組相比，有極顯著性差異（p <0.01）。可以有效減緩米糠過氧化價、酸價及游離脂肪酸含量上升。從結果說明，米糠經擠壓加工後，可以減少米糠油脂氧化。關於米糠中的米糠醇，實驗結果發現，不論米糠是否經過擠壓加工，隨著貯藏時間增加，其米糠醇含量皆隨之下降，（控制組：4.57→1.78 mg/g；膨發型：4.40→1.97 mg/g；蒸煮型：4.39→2.26 mg/g），但貯藏56天後的米糠，有經過擠壓加工，其米糠醇含量較高。另外米糠中的可溶性膳食纖維，經過擠壓加工後，發現含量會增加，原本控制組是1.74%，經過膨發擠壓加工及蒸煮擠壓加工後，最高含量分別改變為4.18%和11.35%。從掃描式電子顯微鏡影像，得知米糠微觀結構，經擠壓加工後，受到強烈扭曲，使米糠的纖維素及脂溶性物質受到影響。根據前述五項實驗結果，選出最佳擠壓加工條件為，膨發擠壓加工條件（模具溫度：130℃；螺軸轉速：320 rpm）、蒸煮擠壓加工條件（套筒溫度：150及130℃；螺軸轉速：90 rpm）。第三部分實驗，以最佳擠壓加工條件處理米糠後，於27~28℃下進行貯藏試驗。試驗結果發現，貯藏28天後，膨發擠壓加工、蒸煮擠壓加工米糠的過氧化價分別為1.11、0.85 meq/kg、酸價分別為2.81、4.76 mg KOH/g、游離脂肪酸含量分別為1.41、2.39%及米糠醇含量分別為2.81、2.34 mg/g。與相同溫度（27~28℃）下貯藏28天後的米糠，其過氧化價（1.72 meq/kg）、酸價（13.13 mg KOH/g）、游離脂肪酸（7.60%）及米糠醇（2.12 mg/g）相比，擠壓加工後的米糠氧化情形可以減少、米糠醇裂解可以減緩。綜合以上三部分的實驗結果發現，米糠經熱加工（焙炒、擠壓）可以降低油脂氧化的發生、減緩米糠醇裂解及提升可溶性膳食纖維含量，不僅維持米糠的品質，還提升其營養價值。

關鍵字

米糠；焙炒；膨發擠壓加工；蒸煮擠壓加工；油脂氧化

並列摘要

This study explored the effects of thermal processing: roasting, collet extrusion processing and cooking extrusion processing, on the quality of rice bran. The study was divided into three parts. In the first part, rice bran was roasted and stored at different temperatures (-20, 7 and 25℃) for its quality (peroxide value, acid value, free fatty acid content) and the microstructure by scanning electron microscope (SEM). In the second part, rice bran was treated by extrusion (collet, cooking) processing, and stored at 7°C for 56 days. Every 14 days rice bran’s quality, γ-oryzanol content, dietary fiber content (soluble and insoluble) were measured, and its microstructure was observed by SEM. According to the results of rice bran quality, γ-oryzanol content, dietary fiber content (soluble and insoluble), and SEM images, the best extrusion processing conditions would be determined. In the third part, rice bran was processed by the best extrusion processing conditions, and stored at temperature about 27 to 28°C for 28 days. The rice bran quality and the γ-oryzanol content were determined every 14 day. Results, in the first part of study, showed that roasted rice bran was significantly (p <0.01) different with the control group. It showed effectively slow down the peroxide value, acid value and free fatty acid content of roasted rice bran. Particularly when the rice bran was stored at -20°C for 25 days, the lowest peroxide value, acid value and free fatty acid content were 0.43±0.23 meq/kg, 2.47±0.09 mg KOH/g and 1.21±0.04%, respectively. Results, in the second part of the study, showed that the rice bran treated by collet extrusion processing and cooking extrusion stored at 7°C for 56 days were found significantly different with the control group. Extrusion processing could effectively slow down the peroxide value, acid value and free fatty acid content of rice bran. In other words, rice bran treated by extrusion processing resulted into the reducution of the happening of oxidation. Regarding γ-oryzanol of rice bran, the experimental results showed that whether rice bran was extruded or not, the content of γ-oryzanol decreased with the increasing storage times (control group: 4.57→1.78 mg/g, collet: 4.40→1.97 mg/g, cooking: 4.39→2.26 mg/g), but if rice bran treat by extrusion processing, and stored for more than 56 days, its γ-oryzanol was found higher. In addition, the rice bran treated by extrusion processing, its soluble dietary fiber was also found increased. The SDF of original control group was 1.74%, whereas it changed to 4.18% and 11.35%, respectively, when the rice bran was treated by collet extrusion processing and cooking extrusion processing. From the scanning electron microscope, the microstructure of the rice bran showed that the rice bran treated by extrusion processing, the rice bran structure was strongly distorted, which affected the cellulose and fat-soluble substances of rice bran. Based on the results mentioned in the three parts of the study, the best extrusion processing conditions were found for collet extrusion (die temperatures: 130°C, screw speeds: 320 rpm), and for cooking extrusion conditions (barrel temperatures: 150 and 130°C, screw speeds: 90 rpm), rice bran treated by extrusion processing stored at 27 to 28°C. The results found that after stored 28 days, the peroxide value of rice bran treated by collet extrusion processing and cooking extrusion processing, was 1.11, 0.85 meq/kg, the acid value was 2.81, 4.76 mg KOH/g, the free fatty acid content of rice bran was 1.41, 2.39% and the content of γ-oryzanol was 2.81, 2.34 mg/g, respectively. At same temperature (27 to 28℃) stored 28 days, compared with the peroxide value (1.72 meq/kg), acid value (13.13 mg KOH/g), free fatty acid content (7.60%) and the content of γ-oryzanol (2.12 mg/g) of rice bran. Rice bran treated by extrusion processing, its oxidation and degradation of γ-oryzanol would be reduced. Comprehensive results of the three parts of the study, the rice bran treated by thermal processing (roasting and extrusion) would reduce the happening of oxidation and the degradation of γ-oryzanol, whereas the thermal processing of rice bran would increase the soluble dietary fiber, maintaining the quality of the rice bran, but increasing the nutritional values.