Effect Of Different Soaking Conditions And Pressure Conditions On Cooking Quality Of Brown Rice

Brown rice has received wide attention due to its health benefits.However,cooked brown rice has the characteristics of bad palatability.The parameters of cooking procedure are closely related to the cooking quality of rice.How to improve the cooking quality by adjusting the cooking procedure has been the key to promote the consumption of brown rice,whereas little effort has been performed to systematically investigate brown rice.For this purpose,the program-adjust electric rice cooker and pressure-adjust electric pressure rice cooker were used to study the effect of different soaking conditions and pressure conditions on the eating quality and nutritional value of cooked brown rice,and explore the relationship between properties and texture characteristics of cooked brown rice.This study aims to provide information for optimizing cooking procedure and improving cooking quality of cooked brown rice.The main contents are as follows:The cooking characteristics,texture characteristics,volatile flavor compounds and sensory quality of cooked brown rice were compared and studied under soaking conditions with soaking temperature of 40℃,50℃,60℃ and 70℃ and soaking time of 30 min and 60min,and pressure conditions with cooking pressure of 30 kPa,40 kPa,50 kPa,60 kPa,70 kPa and 105 kPa.Results showed that compared with unsoaked sample,with increase of soaking temperature and soaking time,the hardness of cooked brown rice decreased from 2033 g to1639 g and the viscosity increased from 176.5 g·s to 255.6 g·s～397.2 g·s.The viscosity was positively correlated with soaking time and negatively correlated with soaking temperature.Soaking conditions had no significant effect on the composition and content of volatile flavor compounds of cooked brown rice.Soaking reduced the sensory hardness of cooked brown rice,improved the sensory viscosity and sensory elasticity,and had no significant influence on the odor.With increase of pressure from 0 kPa to 105 kPa,the hardness of cooked brown rice decreased from 2044 g to 1095 g,and the viscosity increased from 180.2 g·s to 393.7 g·s,and volatile flavor compounds contents increased firstly and then decreased,and the sensory hardness decreased,and the sensory viscosity and sensory elasticity increased,and the odor evaluation decreased firstly and then increased.Through correlation analysis of instrument results and sensory evaluation,iodine blue value,gelatinization degree,the hardness and viscosity of texture characteristics were obtained as the evaluation indexes of sensory palatability of cooked brown rice.Under pressure conditions,hexanal,2-pentylfuran and2,3-dihydrobenzofuran might be the key volatile compounds affecting sensory odor.Under the cooking procedure of this paper,soaking conditions with high temperature and long time(60℃ and 70℃,60 min),and pressure conditions of 70 kPa and 105 kPa were conductive to improve the eating quality of cooked brown rice.The moisture content,moisture binding state,crystal structure and leaching materials composition of cooked brown rice under different soaking conditions and pressure conditions were compared.Results showed that with increase of soaking temperature and soaking time,the moisture content of brown rice increased,and the interaction between moisture and brown rice components strengthened,which promoted starch gelatinization.With increase of pressures,the structural water content of cooked brown rice increased,which suggested the internal structure was broken more seriously.Soaking conditions had no significant effect on the content of amylose-lipid complex;with increase of pressure,amylose-lipid complex content decreased,which further promoted the gelatinization of starch and reduced the hardness of cooked brown rice.The composition analysis of leaching materials showed that amylopectin was the main leaching material(74.15%～77.08%),of which 87.14%～88.21%were amylopectin.The leaching amylopectin amount was negatively correlated with soaking temperature and positively correlated with soaking time;with increase of pressure,the leaching amylopectin amount increased.Correlation analysis between leaching amylopectin amount and viscosity of cooked brown rice indicated that there was a significant positive correlation between them(0.966~*,p<0.05).The phenolic compounds composition and content,γ-aminobutyric acid content,α-tocopherol content,γ-oryzanol content and antioxidant activity of cooked brown rice under different soaking conditions and pressure conditions were compared.Results showed that soaking conditions had littile effect on phenolic compounds composition and content,α-tocopherol content andγ-oryzanol content of cooked brown rice.Soaking conditions only affectedγ-aminobutyric acid content,and soaking temperature of 60℃ caused a greater retention ofγ-aminobutyric acid.Compared with low pressures,high pressures of 70 kPa and105 kPa maintained more phenolic compounds and antioxidant activity.High pressures were more effective than low pressures in terms of free phenolic compounds,and significantly increased the contents of bound ferulic acid and bound isoferulic acid.With increase of cooking pressures,the contents ofγ-aminobutyric acid andα-tocopherol decreased,whereas theγ-oryzanol content increased.Under the cooking procedure of this paper,soaking temperature of 60℃ was conducive to maintain nutritional value of cooked brown rice,and pressure conditions had different influences on bioactive compounds and antioxidant activity.In conclusion,considering the eating quality and nutritional value of cooked brown rice,the results showed that the optimal cooking procedure of electric rice cooker contained soaking stage with soaking temperature of 60℃ and soaking time of 60 min,and the optimal cooking pressure of electric pressure rice cooker was 70 kPa.