Effect Of High Pressure Treatment On Storage Quality Of Cooked Rice

Rice made product is prone to loss of quality during storage, so its industrialization development is restrained. In order to evaluate the effect of high pressure treatment on storage quality of cooked rice, ‘Panjin’ rice materials that had been soaked at 40 for ℃40min with ratio of rice and water(w/w) as 1/2 was treated under 200, 400 or 600 MPa respectively for 10 min at 15 ℃before being steamed for 15min; the rice without high pressure processing was used as control. The cooked rice was packaged with plastic wrap and then stored at 4 ℃or-18℃. The texture, iodine blue value, light transmittance, color, water content, pH value, flavor compotent, sensory quality and spin-spin relaxation time of cooked rice were determined every one(at 4℃) or two(at-18℃) days during storage.The analysis of basic physicochemical properties of cooked rice showed that compared with the control, during 4 ℃storage, the hardness of high-pressure treated rice rose slowly; its adhesiveness, iodine blue value and pH decreased rapidly; and its light transmittance and whiteness rose quickly. During-18 storage, the ℃ b* value of high-pressure rice was lower; The hardness and adhesiveness of 400 MPa rice were the lowest and highest among the treatments with slowest hardness rising rate and adhesiveness decline rate. The whiteness and iodine blue value of 400 MPa rice was at a relatively higher level. From the above, the edible quality of cooked rice made of rice treated with 400 MPa was evaluated during-18 storage. ℃The electronic nose analysis results showed that pressure treatment affected the production of methane, sulfide, ethanol, aromatic compounds and organic sulfide in the cooked rice during storage. During 4 ℃storage, the contents of methane, sulfide and ethanol in the 200 MPa rice were the highest, while that of sulfide, aromatic compounds and organic sulfides in the 600 MPa rice were the lowest in the pressure treatments. W5 S and W1 W were more effective for identifying the flavor of the cooked rice. During-18 ℃storage, W1 S, W1 W and W2 S were more effective for identifying the flavor of the cooked rice. The contents of methane, sulfide, ethanol, aromatic compounds and organic sulfide in the control sample and 200 MPa rice were the lowest and highest in the pressure treatments, respectively.Low-field nuclear magnetic resonance(NMR) measurement, sensory evaluation and the correlation analysis between sensory and NMR indexes of cooked rice revealed that T21, T22 and T23(0ms<T21<2ms, 2ms<T22<6ms, 25ms<T23<45ms) were observed in cooked rice. The sensory scores of cooked rice all decreased during storage. High-pressure treatment enhanced the mobility of bound water and promoted the conversion from other state water to bulk water in cooked rice. During 4 storage, 200 ℃and 600 MPa treatment accelerated the sensory quality deterioration of cooked rice. A close correlation was established between relaxation parameters including T22 peak area, T23 peak area, T22 peak area percentage, T23 peak area percentage and sensory quality indexes. During-18 ℃storage, the 400 MPa treatment could improve the sensory quality of cooked rice, elevate the flavor, form, color scores of cooked rice. The sensory index have positive correlation with T23, T21 peak area, T22 peak area, T23 peak area, T22 peak area percentage, but have negative correlation with T23 peak area percentage.In conclusion, 400 MPa treatment improve the sensory and edible quality of cooked rice stored at-18℃. High pressure treatment has potential application of quality improvement for cooked rice.