Effects Of Cooking Conditions On Quality Of Cooked Rice Products

Rice,as a staple food on which billions of people live,is widely cultivated globally.Rice can be processed into numerous types of rice products and higher requirements for the nutritional quality of rice products are required nowadays.As a good source of nutrition and energy,however,rice should be cooked before consumption to improve its hardness and eating quality.Cooking conditions such as cooking temperature and time can affect the quality of the final rice product.Therefore,it is important to establish the relationship between cooking conditions and rice product quality.In order to correlate cooking conditions with qualities of cooked rice,products were prepared by cooking three rice varieties,i.e.waxy rice,rice with low amylose content and rice with high amylose content at different temperatures(50?,70?,90?)and times(15 min,30 min,45 min)respectively.The effects of cooking conditions on the structural characteristics(the ratio of amylose content and amylopectin content,hydrogen bond strength,microstructure observation by scanning electron microscope),physicochemical properties(swelling power,solubility,amylose leaching,thermal properties,pasting properties,gel texture properties,color characteristics and sensory test),rheological properties(steady shear properties,dynamic oscillatory measurements)and functional characteristics(in vitro starch digestibility,starch hydrolysis rate)of cooked rice were studied.And the quality prediction model of cooked rice was constructed by using regression and principal components analysis.It was found that for waxy rice,cooking treatment significantly increased the swelling power,peak viscosity and final viscosity.With the increase of cooking temperature,the rapid digestible starch content of all cooked rice products increased significantly,while the slowly digestible starch content and resistant starch content decreased to a certain extent.Starch digestibility had little correlation with cooking time.The gelatinization temperature,odor,appearance,palatability,taste and texture of cooked rice were positively correlated with cooking temperature and cooking time.The gelatinization enthalpy of cooked rice were negatively correlated with the two cooking parameters.Cooking treatment also significantly improved the value of L~*and decreased that of a~*and b~*.Besides,as cooking temperature increased,the shear stress increased.The comparison of stress at different sample concentrations showed the order of 15%>10%>5%.Furthermore,stress had a negative correlation with temperature.The storage modulus,loss modulus and consistency coefficient of cooked rice showed significant changes at higher temperature,which may be due to the occurrence of starch gelatinization.In summary,this study found that different cooking conditions have different effects on quality characteristics of rice products.Rice cooking in excess water at 50?may cause annealing process,representing the physical reorganization of starch granule.As cooking temperature was gradually increased to 90?,starch was gelatinized and the structure of rice products changed irreversibly.Moreover,this study established the relationship among cooking parameters,structural characteristics and quality functions of cooked rice products,and constructed the prediction model of quality characteristics of cooked rice,which provides a theoretical basis for the production and quality optimization of industrial rice products.