Study On Changes Of Protein Structure,Functional Properties And In Vitro Digestibility Of Rice During Storage

The consumption of rice is sustaining but the growth of rice is seasona,which makes the storage become an essential process for rice after harvesting.However,less attention paid to the changes in its functional properties and digestive properties during storage.Therefore,this study explored the effect of storage on the functional and structural characteristics of rice protein with simulating storage of newly harvested rice.The changes in in vitro digestion characteristics of rice protein during storage and the effects of digestion products on intestinal microbes were also analyzed.This research aims to provide quality control of rice protein during rice storage.The main research contents and results are as follows:1.An accelerated storage model of rice was used to analyzed the changes in the structure and functional properties of total protein and glutelin during 11 weeks of storage at 38°C and 80%relative humidity.The structure properties of rice protein were characterized by the subunits,secondary structure,endogenous fluorescence and UV-absorbing and the thermal stability of protein,and the content of amino acids in the primary structure.The results showed that the content of?-sheets in rice total protein and glutelin was increased,but?-helix decreased.The content of random coils increased from 14.92±1.93%in the second week to 29.04±0.55%in the seventh week and more fluorophores and UV-absorbing conjugated double bonds were exposed.After11 weeks of long-term storage,the 250 KDa protein subunit in the SDS-PAGE was significantly darker.The solubility of glutelin got a maximum of 21.14±1.71%in the fifth week,and the lowest solubility decreased to 11.09±1.23%in the following 9-11weeks,and the total protein decreased to 12.67±1.15%.The emulsification and emulsification stability of glutelin reached the highest at 315.05±10.38 m²/g and30.86±2.29 min in the 4th and 3th weeks but the total protein reached the maximum in the first 3 weeks,which were 297.15±15.75 m²/g and 30.69±3.47 min.Afterwards,the emulsification was steadily decreasing,but the emulsification showed an increasing trend in 7-11 weeks.The foamability of glutelin showed a rising in the first 5 weeks,and the foam stability increased continuously in the first 2 weeks and then continued to decline.In the final 11th week,both foamability and foam stability increased slightly.the foaming property and the foaming stability increase and decrease continuously at the beginning of storage,and reach the maximum of 115.28±15.35%and 98.61±0.056%in the 5th week,and in the following 6-10 Weeks continued to decline,and increased in the 11th week.During the storage of rice,glutelin and total rice protein are consistent in the structural changes.Long-term storage of rice not only lead to a loose and disordered change in the structure of the protein but also detracts from the functional properties of the two proteins.2.The digestion was important for the using of protein nutrition.Therefore,the changes in the in vitro digestibility of rice glutelin were further analyzed during storage.The rice glutelin was stored at 38°C and 80%relative humidity of 7 days.The digestibility of glutelin and the anti-oxidation and angiotensin-converting enzyme(ACE)inhibition ability of the digested products were analyzed.The mass spectrometry was used to identify the peptides in the digestion.The results show that storage reduces the digestibility of glutelin to 9.45±0.22%.The ACE inhibitory ability of digestion was increased in the first 2 days of storage,and the half-inhibitory concentration on the second day was the highest 0.33 mg/m L.The chelating ability of ABTS⁺,DPPH·,Fe²⁺reached the strongest on the second day of trolox of 0.16±0.01 m M,1.68±0.07 m M and4.87±0.12 Mm citric acid equivalent,respectively.Cellular anti-oxidation(CAA)ability was 16.96±0.85?mol QE/g on the second day.During the next 5 days of storage,the antioxidant capacity and ACE inhibitory capacity of glutelin hydrolysates continued to decrease.During the storage process of the first 4 days,the molecular weight of glutelin hydrolysate was mostly 700-1000 KDa,and with the prolonged storage time,the molecular weight of the hydrolysate increased to 1000-1800 KDa in 5-7 days.The hydrolysate of glutelin under different storage time contains more common peptides of LQAFEPL,LQAFEPI,QGDVVALPA,YTNIPGVV,and QGDIVALPA.It is inferred that it may be the main component that produces biological activity.In general,long-term storage reduces the digestibility of glutelin,increases the molecular weight of the digested product,and reduces the above-mentioned two biological activities of the digested product.3.Storage leads to changes in the biological activity of glutelin digestion products.Since the intestine is the main place for the production and utilization of digestion products,in order to further explore the impact of storage on glutelin digestion products,we analyzed the effects of glutelin digestion products during different storage periods on the intestines.The gluten hydrolysate under different storage times were added to a concentration of 15 mg/m L as the culture medium,and the culture time was 24 h.Finally,high-throughput sequencing was used to analyze glutelin hydrolysates impact on changes in the structure of the intestinal flora.The results show that the intestinal flora in the hydrolysate culture solution of glutelin was different under different storage time.During the first 4 days of storage of glutelin,its hydrolysate can increase the species richness of the intestinal flora.The Chao1 index increased from 20.67±5.51 to26.00±2.65,and the Shannon index increased from 1.61±0.12 to 1.71±0.04.With the extension of storage time,its hydrolysate reduces the abundance of flora.In addition,glutelin hydrolysate can promote the growth of beneficial bacteria such as Bifidobacterium,Turicibacter,Bacteroides,etc.However,as the storage time of glutelin prolongs,the probiotic continued to decrease.Further comparative analysis showed that there was a positive correlation between antioxidant indexes and Turicibacter(P<0.05).The digestion products of glutelin under different storage time can change the structure of intestinal flora.Short-term storage of its digestive products had a probiotic and improving effect on the intestinal flora,while long-term storage results in the weakening of the regulatory effect of its digestive products on the intestinal microbes.