減圧含浸技術を用いた炊飯崩壊粒発生の抑制  [in Japanese] The suppression of damaged cooked rice by using vacuum infusion technique  [in Japanese]

The objective of the present research is to develop a method for inhibition of damaged cooked rice (DCR) by using vacuum infusion technique, heated water soaking, and tempering treatment. Firstly, open cracked rice (OCR) grains were sorted by crack direction, then a composition rate of DCR grain, included in cooked rice was measured. As a result, transverse and longitudinal cracked grains were derived from the OCR grain. In addition, it was suggested that unevenness of water distribution within soaked rice kernel caused a difference in swelling distribution between central part and periphery of the kernel, according generated it flatly-broadened grain. Secondly, the composition rate of DCR grain in milled rice with low moisture content was measured for each treatment. As a result, the tempering treatment clearly inhibited to generate flatly-broadened grain, and vacuum infusion combined with processes of heated water soaking and tempering suppressed to generate transverse and longitudinal cracked grain. Finally, the hardness, stickiness and balance of cooked rice were measured. The value of balance for the treatment of vacuum infusion combined with heated water soaking and tempering which is positive by correlating with eating quality was the highest among all treatments, so it appeared that this treatment maintained the eating quality of low moisture content rice. Therefore, tempering treatment was considered as the best way for keeping the appearance and eating quality of low moisture content rice. Further experiment for investigating the optimization of tempering condition and finding the generation mechanism of flatly-broadened grain by using a morphologic approach is needed.本研究は，減圧含浸処理に温水浸潰処理とテンパリング処理を組み合わせて低水分白米に施し，炊飯崩壊粒の発生を抑制することを目的とした．まず，浸漬後の白米を裂傷の有無および裂傷の方向別に分類して炊飯した際の炊飯米の形状別の構成割合を測定した．その結果，横割れ炊飯粒および縦割れ炊飯粒の多くは水浸裂傷粒から発生し，また，扁平炊飯粒は，炊飯直前の米粒中心部における水分不足によって炊飯時に米粒部位による膨潤率の差が生じ，変形を引き起こしたものと推察された．次に，減圧含浸処理に温水浸漬およびテンパリングを組み合わせて低水分白米を調製した後，炊飯して得られた炊飯米の形状別の構成割合を測定した．その結果テンパリング処理は扁平炊飯粒の抑制効果があり，また，減圧含浸と温水浸漬の組み合わせ処理により横割れ炊飯粒および縦割れ炊飯粒の抑制効果が見られた．最後に，低水分米にそれぞれの処理を施した後の炊飯米の硬さおよび粘りを測定し，バランス度を算出した．その結果，食味と正の相関があるバランス度が，最も高い値を示したのはテンパリング区であったことから，テンパリング処理は低水分米の食味低下を抑制する効果が認められた．これらの結果から，炊飯米の形状および食味に関し，テンパリング区が最も良好な結果を得た．今後は，テンパリング処理の最適処理条件の究明および形態学的なアプローチによる扁平炊飯粒の発生機構の解明を行う予定である．