| As a staple food,industrial production of cooked rice requires quick production,energy-saving techniques and stable quality of the cooked rice,with good taste and flavor.Different varieties of rice and different storage periods can cause differences in the properties of the cooked rice during processing due to variations in their compositions,making it necessary to study the physical and structural changes of rice during the cooking process.Water plays a critical role in the cooking process of rice,directly affecting the gelatinization process of rice and its degree of retrogradation during storage.Weak alkaline electrolytic water has characteristics such as small water molecule clusters,strong permeability,alkaline p H and negative oxidation-reduction potential.Using it to soak rice can quickly diffuse water into the inside of the rice,promote rapid water absorption by the rice,and make the starch in the rice easy to gelatinize,which is beneficial to the processing of cooked rice.In this study,weak alkaline electrolytic water was used instead of traditional tap water for cooked rice processing,to develop a low-cost and industrially producible technology for processing cooked rice.Hyperspectral imaging technology was applied to develop intelligent discrimination technologies for visualizing water and gelatinization degree during the cooking process of rice,realizing standardized production of cooked rice.This research was divided into four parts.(1)Under the action of an electric field,weak alkaline electrolytic water had a smaller cluster system,with a 17.30%decrease in DDAA-OH and a 22.89%increase in Free-OH compared to tap water.Therefore,fewer hydrogen bonds were formed between water molecules,and there were more free proton donors and acceptors,making it more likely to form hydrogen bonds with other substances.During the soaking process of rice,weak alkaline electrolytic water effectively increased the water absorption rate,maximum water content,and diffusion rate of water in different types of rice,with a maximum increase of 41.16%,3.98%,and 12.24%,respectively.As weak alkaline electrolytic water formed more hydrogen bonds with substances in rice,it was easier to combine with the substances inside the rice to form more bound water(a maximum increase of 8.35%).Under the combined effects of the alkaline environment of weak alkaline electrolytic water and its own molecular properties,erosion occurred on the surface and interior structure of rice,leading to the shedding of surface layers and the formation of numerous porous structures.With the increase of water absorption,more substances such as starch and protein dissolved from the rice,resulting in a maximum increase of 52.92%in the content of leachate.(2)Weak alkaline electrolytic water could increase the hardness of cooked rice prepared from four types of rice,namely glutinous rice,japonica rice A,japonica rice B,and indica rice,with values respectively increasing from 29.88 N,44.29 N,30.99 N,and 42.38 N to38.58 N,47.52 N,40.15 N,and 55.81 N.It also increased the adhesiveness from 6.61 N·s,3.71 N·s,2.99 N·s,and 3.68 N·s to 7.97 N·s,5.57 N·s,3.77 N·s,and 3.69 N·s,resulting in higher gel strength of the cooked rice,thus improving its sensory quality and textural properties.The rheological properties of rice exhibited a pseudoplastic fluid behavior(with a non-Newtonian index of n<1).Due to the more compact structure and higher gel strength of rice prepared with weak alkaline electrolytic water,it possessed a larger zero-shear viscosity and stronger shear resistance.The analysis of flavor components showed that 49kinds of volatile components were detected,weak alkaline electrolytic water hydrolyzed lipids in rice,generating more free fatty acids that promoted lipid oxidation and produced more aldehydes.Additionally,the hydrolysis of soluble sugar and protein yielded more flavor components through the Maillard reaction.Weak alkaline electrolytic water also promoted the hydrolysis of starch during the cooking process,resulting in more amylose(increased by 24.11%,2.51%,6.66%,and 10.75%,respectively for glutinous rice,japonica rice A,japonica rice B,and indica rice)and soluble sugar(increased by 38.42%,59.90%,45.50%,and 12.76%,respectively).Cooked rice prepared with weak alkaline electrolytic water had more rapidly digestible starch(52.13%)and slowly digestible starch(32.88%),less resistant starch(14.99%),and a higher glycemic index(74.19).Fourier-transform infrared spectroscopy analysis confirmed that weak alkaline electrolytic water enhanced the breakdown of starch granules during cooking.Microstructure analysis demonstrated that cooked rice prepared with weak alkaline electrolytic water had a denser network structure.(3)During the constant temperature storage of cooked rice,the change in water content was not significant due to the sealed state,but the mobility of water decreased,especially after 5 hours of storage.Weak alkaline electrolytic water reduced the decreasing trend in water mobility within a certain period of time.During constant temperature storage,the hardness of cooked japonica rice A prepared with weak alkaline electrolytic water and tap water increased by 13.54%and 16.50%,respectively,while its adhesiveness decreased by 20.90%and 18.60%,respectively.The hardness of cooked glutinous rice prepared with weak alkaline electrolytic water and tap water increased by 2.88%and 1.05%,respectively,while its adhesiveness decreased by 27.87%and 20.90%,respectively.Rheological analysis showed that during constant temperature storage,the storage modulus(G’)of glutinous rice first decreased and then increased due to the more sensitive water-hydrolyzing effect of amylopectin,leading to continuous hydrolysis and retrogradation caused by the hydrolyzed amylose.In contrast,due to its higher amylose content,the G’of cooked japonica rice A continued to increase during constant temperature storage.A total of 63 volatile components were detected in cooked rice during constant temperature storage,with aldehyde compounds and furan compounds being the main flavor substances.The Maillard reaction produced more flavor substances in cooked rice,which was promoted by weak alkaline electrolytic water.However,the flavor of cooked rice decreased as the storage time prolong.The content of amylose in cooked japonica rice A prepared with weak alkaline electrolytic water and tap water decreased by 26.07%and 20.36%,respectively,during constant temperature storage.Weak alkaline electrolytic water reduced the content of amylose in cooked glutinous rice during constant temperature storage by 66.26%,while tap water reduced it by 12.39%.The content of soluble sugars decreased in cooked rice prepared with weak alkaline electrolytic water,while it first increased and then decreased in cooked rice prepared with tap water.The content of soluble sugars in cooked glutinous rice increased during constant temperature storage.In-vitro digestion results showed that during constant temperature storage,the digestibility of cooked japonica rice A decreased significantly,with a decrease in rapidly digestible starch,slowly digestible starch,and glycemic index,and an increase in resistant starch,while the changes in cooked glutinous rice were relatively small.Weak alkaline electrolytic water maintained the better digestibility of cooked rice within a certain period of time.The changes in starch ordered structure and microstructure of cooked rice indicated that retrogradation occurred during constant temperature storage.Therefore,weak alkaline electrolytic water maintained the sensory quality and nutritional characteristics of cooked rice for a certain period of time.(4)Using hyperspectral imaging technology,hyperspectral images of the soaking process of rice were collected and analyzed.A total of 35 characteristic wavelengths were obtained,and the reflectance values corresponding to these 35 characteristic wavelengths were taken as independent variables,while the water content was taken as the dependent variable.A partial least squares regression model was established to predict the water content,with a correlation coefficient R~2 of 0.9673 and a root mean square error RMSE of 0.5300.This model was used to visualize the water content during the soaking process of rice,resulting in clear images that comprehensively reflect the water absorption process of rice soaking.Additionally,through hyperspectral imaging of the gelatinization process of rice,35characteristic wavelengths were obtained,and a partial least squares regression prediction model was established to predict the gelatinization degree,with an R~2 of 0.9534 and an RMSE of 4.5046.This model was used to visualize the gelatinization degree during the rice gelatinization process.After applying pseudo color and logarithmic transformation to the visualization image,more visible results were obtained.Based on the modeling and visualization results,data discrimination for water content and degree of gelatinization during soaking and cooking could be achieved,the uniformity of water absorption and gelatinization could be detected,and dynamic adjustments to the process parameters could be madeaccording to the obtained data and image information,combined with practical production conditions.Research findings could solve the difficult problem of standardization in industrialized production of cooked rice. |
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