Effect Of Different Protein On Digestibility Of Extruded Rice Starch And Preparation Of Extruded Rice

Rice,the staple food of more than half of the world’s population,with its high rapidly digestible starch content,which is not conducive to postprandial blood sugar control with long-term intake.Therefore,traditional rice staples are unable to meet the special needs of people pursuing health or abnormal glucose metabolism.The addition of nutrients in the extruded technology to prepare extruded rice with reduced digestibility provides more staple food options for special populations.Protein,the second most important component of starch-based staple foods,not only gives nutritional properties to the staple foods,but also retards digestibility through its interaction with starch.However,the effect of different proteins on starch digestibility in extruded rice is poorly studied and the mechanism is not yet clear.Based on this,this paper investigated the effects of different protein and protein hydrolysate on the physicochemical properties,structural characteristics and digestibility of extruded rice starch,revealed the mechanism of protein reducing the digestibility of rice starch in extrusion technology,and further prepared protein complex extruded rice to evaluate its digestibility,providing theoretical basis and application examples for the preparation of slow-digesting functional staple foods by extrusion technology.Firstly,the effect of different protein on the physicochemical properties and digestibility of extruded rice starch was investigated.Extruded rice starch and rice starch-protein extrusion complexes were prepared by extrusion technique.It was found that the addition of three proteins（rice protein,soybean isolate and whey protein concentrate）decreased the hydrolysis rate and rapidly digestible starch（RDS）content of extruded rice starch,and increased the slowly digestible starch（SDS）and resistant starch（RS）content.The range of decrease in RDS content was 9.21%to 13.3%,and the range of increase in SDS content and RS content was 6.17%to6.95%and 3%to 7.06%,respectively.The protein reduced the starch swelling power and the leach of amylose in the complexes,and also limited the flow of water in the system.Rapid visco analyzer（RVA）results showed that different protein reduced the peak viscosity and breakdown value of starch,where rice protein promoted the short-term regeneration of starch.Rheological results showed that protein addition enhanced the gel characteristics of the extruded complexes.Low-field nuclear magnetic resonance（LF-NMR）results indicated that protein addition limited the mobility of water in the complexes.X-ray diffraction（XRD）and Fourier infrared spectroscopy（ATR-FTIR）results indicated that protein increased the relative crystallinity of starch and enhanced the degree of order of the starch structure.Analysis of the interaction forces revealed that hydrogen bonding and hydrophobic interactions between the protein and starch mainly existed during extrusion.Secondly,the effect of protein hydrolysates on the physicochemical properties and digestibility of extruded rice starch was further investigated.According to the conclusions of the previous chapter,rice protein was selected for enzymatic hydrolysis,and extruded rice starch and rice starch-protein hydrolysate complexes were prepared by extrusion technology.It was found that rice protein hydrolysates（RPHB and RPHC）with a greater degree of enzymatic hydrolysis reduced starch digestibility more,with the RDS content,SDS content and RS content of the RPHC-containing extrusion complex being 65.54%,15.10%and 19.36%,respectively.Rice protein hydrolysates reduced the starch swelling power and the leach of amylose in the complexes.The RVA results showed that rice protein hydrolysates reduced the peak viscosity and breakdown value of starch,and RPHC inhibited the short-term regeneration of starch.LF-NMR results showed that rice protein hydrolysates converted part of the free water in the complex to weakly bound water.XRD and ATR-FTIR results showed that rice protein hydrolysates increased the relative crystallinity and 1047/1022 cm^-1 values of extruded rice starch from 11.30%to 22.10%and 0.409 to 0.462,respectively,enhancing the degree of order of the starch structure.Analysis of the interaction forces revealed that hydrogen bonding and hydrophobic interactions were mainly involved between rice protein hydrolysates and rice starch during extrusion,and the ATR-FTIR results also corroborated the presence of hydrogen bonds in the complexes.In addition,the rice protein hydrolysates showed an inhibitory effect on amyloglucosidase.Finally,based on the above study,extruded rice was prepared by compounding rice protein hydrolysate with rice flour and analyzed its quality.Taking the sensory score as the target parameter and the extrusion parameter as the factor,the protein complex extruded rice was optimized by an orthogonal experiment.The results showed that the influence of extrusion parameters on the quality of extruded rice was as follows:extrusion temperature>moisture content>screw speed.The optimum extrusion conditions are screw speed 120 r/min,extrusion temperature 105°C,and water content 40%.Then,the edible quality,digestibility,and functional characteristics of the extruded rice were compared with those of indica rice and commercial extruded rice.The results showed that the sensory quality,texture characteristics,cooking quality,and pasting characteristics of the protein complex extruded rice were better than those of the commercially extruded rice and were close to those of the indicia rice,and the antioxidant activity was significantly higher than that of the indicia rice and the commercially extruded rice.The digestibility of protein complex extruded rice has been significantly decreased（P<0.05）.Its RDS content is 62.94,SDS content is 10.67,and RS content is 26.39%.