| For the same variety of rice,cooking method has a great influence on the eating quality of cooked rice.The formation mechanism of cooked rice eating quality is different with different cooking methods.High pressure steam cooking method could conducive to promoting moisture diffusion,improving the texture and quality stratification of rice of cooked rice and forming more flavor substances.At the same time,it could shorten the cooking time and improve the production efficiency.However,the research on the eating quality formation mechanism of cooked rice is relatively weak,and there are few reports on the influence of high pressure steam on the eating quality of cooked rice and its eating quality forming mechanism.The subject of this research are rice samples cooking under high pressure steam,to explore the effects of different steam pressures on the eating quality of cooked rice.From three aspects of microscopic morphology and structure,moisture binding and distribution state,as well as coated layer composition and state,the mechanism of rice hardness and adhesiveness changes caused by high pressure steam was explored,which could provide certain theoretical basis for the research of cooked rice processing.The main contents are as follows:First of all,the sensory evaluation combined with instrument determination was used to determine the eating quality of cooked rice,to explore the influence of high pressure steam cooking on appearance characteristics,volatile substances,texture characteristics and cooking characteristics of cooked rice.The results showed that with increase of high pressure steam from atmospheric pressure to 0.18 MPa,the hardness of cooked rice decreased from 22.26 N to 13.01 N,the chewiness decreased from 8.76 to 4.98,and the adhesiveness of cooked rice increased from 1.22 N·s to 2.15 N·s,and the springiness and the degree of gelatinization also increased.As the high pressure steam intensifies the Maillard reaction,the whiteness of cooked rice decreased from 78.19 to 73.93.At the same time,more heterocyclic volatile substances were produced,which significantly changed the flavor of cooked rice.Secondly,the mechanism of reducing the hardness of cooked rice under high pressure steam was explored from two perspectives:microscopic morphology and structure,moisture binding and distribution state.The results showed that,with the increase of high pressure steam level,the number of holes in the external and internal tissue structure of cooked rice increased,and the moisture was easier to get into the interior of the cooked rice,and the moisture relaxation time T21,T22 and T23 measured by low-field NMR also increased.The diffusion of moisture in interior of cooked rice was easier,which reduces the gradient difference between inner and outer layers of rice and makes starch gelatinized more fully in the central part of cooked rice.At the same time,the high pressure steam destroys the starch-lipid complex structure and protein network structure,further promotes the gelatinization of the starch,thereby reducing the hardness of the rice.In addition,the Pearson correlation analysis was established for the moisture distribution uniformity and hardness of cooked rice,and it was found that there was a significant negative correlation between them at the level of 0.05（-0.952*）.Finally,the mechanism of high pressure steam cooking method to improve the adhesiveness of cooked rice was explored from the distribution of the coated layer and the composition of the leaching materials in the coated layer.The results showed that with the increase of high pressure steam level,the tissue structure damage of cooked rice was aggravated,making material leaching more easily.Thus,the thickness and amount of coated layer were increased.More than 74%（m/m）of the leaching materials in the coated layer were starch,of which 80%（m/m）were amylopectin.High pressure steam could inhibit amylose dissociation and spiral structure,which could reduce the leaching of amylose content.The fine structure of the leaching starch was further analyzed,and it was found that the medium and long chains（fb2 and fb3）of leaching starch in the coated layer were increased,and the starch with longer branched chain length and larger relative molecular weight was easier to leach.Among them,the relative molecular weight distribution had greater influence on the coated layer of cooked rice than the branched chain length distribution. |
