The Effect Of High Pressure Treatment On Sensory And Nutritional Properties Of Brown Rice

Nowadays,due to changes in consumer life style and health awareness,brown rice is receiving increased interest as a source of not only energy but also several other healthy attributes.Despite its the high nutritional content,brown rice is not accepted as wide as white rice because of the rough and tough texture that is hard to chew.And the appearance of brown rice is also not attractive due to its off-white/brownish color.Moreover,the nutrients in brown rice are loss during processing.Therefore,it is necessary to study the way to improve the quality of brown rice and keep its nutrition.High pressure treatment(HP)is a new non-thermal food processing method.Previous studies have shown that HP has advantages in starch modification,protein modification and nutrient retention.However,these studies were somewhat limited for concept testing with a single cycle HP and lacked details on the influence on sensory quality,morphology,antioxidant properties,digestibility of brown rice and market potential of HP that might be possible with a two cycle HP.In addition,due to the individual differences of rice granules,the sensory evaluation of brown rice is still lack of objective and accurate measurement.Instrumental method was improved to evaluate the texture of cooked brown rice.The taste of cooked brown rice was evaluated by instrumental method and sensory evaluation.The color,texture,water absorption and morphological characteristics of brown rice after HP(100 to 500 MPa)by single step(10 min holding time)or two step process(two cycles,5 min holding time each)were investigated.Moreover,the effect of HP on phenolics,flavonoids,antioxidant activity and digestibility of brown rice was studied.The results are as follows:1.The relative standard deviation(RSD)values for improved instrumental method was lower than those obtained by other methods which indicates that the improved instrumental method is more precise and consistent.Texture analyzer has the advantage in the evaluation of springiness,cohesiveness and gumminess of cooked brown rice,while sensory evaluation has the advantage in the taste and overall sensory evaluation.The two methods can be combined to evaluated sensory property of cooked brown rice.2.The hardness of cooked brown rice decreased by 15%with soaking temperature increased.However,the hardness of cooked brown rice was decreased by 40%after HP.The gumminess values of cooked brown rice were reduced while springiness and cohesiveness were elevated by HP.Cooked texture of brown rice were significantly improved by HP.Moreover,the two cycle HP resulted in softer texture for cooked brown rice than single cycle HP.3.Scanning electron microscopy indicated that HP improved the texture of brown rice by disrupting the structure of rice bran layer,which allowed easier water penetration into the rice grain during cooking.This also leads to better water diffusion into the grains,which could explain the changes in color of brown rice treated by HP.The more severe structural disruption of rice bran layer caused by the two cycle HP process was due to iterative compression and decompression.Cooked brown rice with HP had more network structure and small cavities which results in the higher springiness and cohesiveness.4.Water absorption ratio and lightness values(L*)of brown rice were increased while b*values of brown rice were reduced by HP.Moreover,the two cycle HP resulted in lighter color and lower water absorption ratio for cooked brown rice than single cycle HP.5.Maximum percentage retention of phenolic and flavonoid content in brown rice treated by HP was 97%.There was a significant positive correlation between the content of phenolic compounds and free radical scavenging rate obtained by DPPH and ABTS methods at the 0.01 level.6.HP reduced the hydrolysis of brown and improved its potential health benefits by lowering RDS content and increasing SDS and RS levels.Two cycle HP induced more SDS and RS content.