Effects Of Different Thermal Processing On Main Bioactive Components,in Vitro Digestion And Fermentation Characteristics Of Qingke

Qingke(Hordeum Vulgare L.var.nudum Hook.F)is a specialty crop in Tibet,Qinghai and other plateau areas.It has a wide planting area and high yield,and is a staple food for the Tibetan people to survive.A large number of studies have shown that Qingke is rich in a variety of bioactive components.Long-term consumption of Qingke can significantly reduce the incidence of human heart disease,diabetes and other chronic diseases and metabolic syndrome.The development of Qingke is of great significance in improving the national nutritional diet structure,promoting the development of the grain industry in plateau areas,and maintaining social stability.In addition,it meets the needs of modern life for high-quality and healthy diets.Therefore,Qingke has attracted the attention and favor of people of all ethnic groups across the country and even the world in recent years.As a kind of hullless barley,Qingke has significant processing advantages.Like most grains,Qingke needs to be cooked before it can be eaten.However,different thermal processing methods have different degrees of influence on the basic nutrients and bioactive components of grains.However,the current researches on Qingke mainly focuse on the nutritional properties of Qingke raw materials and the development of functional foods.There is insufficient research on which thermal processing method is suitable for the industrial production of matured Qingke,and there are few studies on the influence of different thermal processing methods on the bioactive components and nutritional value of Qingke.In addition,there are few reports on the in vitro digestion and fermentation characteristics of different thremal processing Qingke.Therefore,this experiment first explored the feasibility of a new type of thermal processing technology-steam explosion processing Qingke,and applied the response surface principle to optimize the processing technology of steam explosion processing Qingke.On this basis,then analyze and compare the effects of steam explosion and other six common thermal processing technologies on the main bioactive components and antioxidant capacity of Qingke.Finally,the digestion characteristics and intestinal flora fermentation characteristics of Qingke after different thermal processing and maturation were explored on simulated digestion and simulated flora fermentation experiments in vitro.It was expected to provide a certain basis and reference for the processing of Qingke and its products and the development of related industries.The main findings are as follows:1.Response surface method to optimize the steam explosion processing technology of Qingke.On the basis of the single factor test,the response surface principle was used to optimize the processing technology of steam explosion processing Qingke.The test results showed that the best process conditions for steam explosion of Qingke were:steam pressure(P)of 2.3 MPa,processing time(T)of 37.0 s and initial water content(W)of 10.0%.After steam explosion treatment,Qingke expands significantly,can better maintain the content of phenolic content(PC)and flavonoid content(FC),and improve the oxidation resistance of ABTS.Under the optimal process conditions,the expansion ratio(ER)and the unpopped kernel ratio(UKR)of Qingke were 3.24±0.02 and0.19±0.02,respectively;PC and FC were 3.81±0.13 mg gallic acid equivalent(GA)/g dry weight(Dry Weight,DW),3.24±0.11 mg rutin equivalent,respectively(Ru)/g DW,ABTS free radical scavenging capacity was 15.08±1.21 mg ascorbic acid(ASC)/g DW.2.The effects of different thermal processing methods on the bioactive components and antioxidant properties of Qingke were compared.Seven different thermal processing methods of traditional roasting,steaming,boiling,steam explosion,microwave baking,far-infrared baking and deep frying had different effects on the bioactive components and antioxidant capacity of Qingke.The phenolic compounds in Qingke were analyzed,six kinds of free phenolic compounds,such as coumaric acid,chlorogenic acid and syringic acid,and twelve kinds of bound phenolic compounds,such as ferulic acid and quercetin,were detected.Dry heat treatment(roasting,microwave baking,far-infrared baking)and steam explosion had the characteristics of high temperature and short processing time,which could increase the content of soluble dietary fiber,?-glucan and water-soluble pentosan in Qingke.It was also conducive to the retention of phenolic compounds and could better enhance its reducing ability.Wet heat treatment(steaming and boiling)had a long processing time and low temperature,which made Qingke have stronger hydroxyl radical scavenging ability,Fe²⁺chelating ability and ABTS scavenging ability,but it would cause the loss of soluble biologically active components of Qingke.Principal component analysis results showed that steam explosion processing had more advantages in the retention and improvement of the main bioactive components of Qingke.3.The effect of different thermal processing on characteristics in vitro digestion and in vitro fermentation of Qingke.(1)In vitro simulated gastrointestinal digestion experiment,the content of?-glucan,pentosan,total phenols,and total flavonoids of roasting,steam explosion,steaming and microwave baking Qingke were released,and the antioxidant capacities were improved.After the simulated digestion,there were 7 phenolic compounds in the digestion solution,namely,coumaric acid,p-hydroxybenzoic acid,chlorogenic acid,coumaric acid,caffeic acid,syringic acid and quercetin.Among them,the release of?-glucan,pentosan,total phenols,and total flavonoids of roasted Qingke in vitro digestion process was the highest,while steam explosion Qingke had the largest release of phenolic compounds,and steam explosion could improve the hydroxyl radical scavenging ability,reducing ability and Fe²⁺chelating ability of Qingke in vitro digestion.In addition,steamed Qingke showed the highest ABTS free radical scavenging ability in vitro digestion.(2)In the intestinal flora fermentation experiment,roasting,steam explosion,steaming and microwave baking were conducive to lowering the p H value and ammonia nitrogen content of the fermentation broth in vitro enterobacteria fermentation of Qingke,promoting the production of short-chain fatty acids by intestinal microbes,and increasing ABTS removal ability and reduction ability of fermentation broth.Among them,roasting could best promote the production of short-chain fatty acids in vitro fermentation of Qingke,while the total phenols and flavonoids of steam-exploded Qingke were more stable in vitro fermentation.At the species level,the intestinal flora of Qingke in vitro fermentation was dominated by Megamonas?funiformis,Dialister?sp,Escherichia?coli and Prevotella?copri.Compared with the blank group,the richness of intestinal flora in the Qingke groups were reduced after vitro fermentation,the microwave-baked and steamed Qingke group had higher species similarity,while the steam explosion and roasted Qingke had greater species differences with other groups.Thermal processing treatments were beneficial to improve the metabolic function of the intestinal flora during vitro fermentation of Qingke,improved the intestinal environment of Qingke in vitro fermentation,and also promoted the growth of beneficial bacteria.Conclusion:the optimal processing conditions of steam explosion processing Qingke are as follows:steam pressure(P)of 2.3 MPa,processing time(T)of 37.0 s and initial water content(W)of 10.0%.Dry heat treatment(roasting,microwave baking,far-infrared baking)and steam explosion had more advantages in retaining the nutritional value and functional activity of Qingke.Among them,steam explosion processing and traditional roasting processing could best promote the release of bioactive components and increased the antioxidant capacity in Qingke,which were more conducive to regulating the intestinal microecological balance and promoting the growth of beneficial intestinal bacteria.