Effects Of UV-B Stress,Drying And Thermal Processing On The Contents Of Functional Components In Germinated Highland Barley

Highland barley is the main food crop in Tibet,which plays an important role in the agricultural production and economic development of the Qinghai-Tibet Plateau.Germinated highland barley has been proved to have anti-inflammatory,anti-cancer,antioxidant activity,lowering cholesterol,controlling blood sugar and assisting in lowering blood lipid and so on.These effects are mainly attributed to the active components such as polyphenols andβ-glucan in highland barley.However,how to further improve the content of active ingredients in the germinated highland barley and better retain the active ingredients in the processing process is of great significance to improve the nutrition and application value of the germinated budding highland barley.Based on the above problems,this paper studied the effects of UV-B stress,drying and thermal processing on the functional components of germinated highland barley,in order to provide theoretical basis for the comprehensive utilization of highland barley.Firstly,the contents of flavonoids,polyphenols,riboflavin,γ-aminobutyric acid andβ-glucan in germination were investigated under different UV-B radiation doses in germination,and the effects of different radiation doses on these active components were evaluated.Secondly,hot air drying,microwave drying,freeze drying,heat pump drying and vacuum drying were used to dry the germination highland barley,and the effects of drying methods on the above functional components,rehydration rate,shrinkage rate,color difference,texture and microstructure were explored.Finally,the effects of microwave,baking and steaming treatment on the functional components of germinated highland barley and their release in the simulated digestive system in vitro were investigated.The main research results of this paper are as follows:(1)Under UV-B radiation,with the extension of germination time,the contents of flavonoids,polyphenols,riboflavin andγ-aminobutyric acid showed a trend of gradual increase,while the content ofβ-glucan showed a trend of gradual decrease.Compared with the highland barley without germination under UV-B stress,the decrease ofβ-glucan content of highland barley treated with UV-B radiation was more serious.The results showed that UV-B radiation could cause the change of active components of highland barley during germination,but the effects of different radiation does on the components were not consistent.In general,the contents of flavonoids and polyphenols in highland barley were the highest after radiation treatment of 20μw/cm~2 and 6 h/d,reaching 3.63 mg/g and 3.37 mg/g.The highest content of riboflavin was 2.45 mg/g under 20μw/cm~2 and 12 h/d stress,and the highest content of gamma-aminobutyric acid was 6.72 mg/g under 10μw/cm~2 and 9 h/d radiation.(2)Different drying methods were used to treat the germination highland barley,and it was found that the drying methods had a significant effect on the quality of the germination highland barley.Freeze-drying has the minimum shrinkage rate(7.75±1.11)%,the highest rehydration rate(149.79±10.22)%and the content of functional components,and at the same time retains the complete cell structure,but the cost of freeze-drying is high,and it is difficult to be applied to the actual production.Microwave drying maintained a low shrinkage rate(8.07±0.95)%and hardness(18225.87±718.94),as well as the highest rehydration rate and polyphenols content(3.58±0.19)mg/g,but reduced the content of other components,and destroyed the complete structure of highland barley cells.The germination highland barley after hot air drying,heat pump drying and vacuum drying had higher shrinkage rate,hardness,compact microstructure and lower rehydration rate,but the decline of functional components was the lowest.The comprehensive score shows that heat pump drying(-0.052)can not only reduce the damage to the highland barley material,but also retain the chemical composition of highland barley well,which has a better application value.(3)The release amount of free amino acids of the germination highland barley without thermal processing treatment was much greater than that of the thermal processing treatment group.The complete structure of the starch granules after thermal processing treatment was damaged,while the starch granules without thermal processing treatment still maintained a good integrity.In addition,thermal processing treatment significantly reduced the contents of riboflavin and gamma-aminobutyric acid,but had little effect on flavonoids andβ-glucan.Microwave treatment increased the content of polyphenols in germination highland barley.The microwave treatment showed the highest bioavailability of riboflavin(97.8%),but the release of riboflavin was still lower than that of blank group(1.06 mg/g).The bioavailability of flavonoids and gamma-aminobutyric acid in steam-germination highland barley was the highest,which were 96.79%and 96.31%,respectively.The thermal processing had little effect on the release rate ofβ-glucan and polyphenols,and the bioavailability of the latter was higher than 90%.In addition,different thermal processing treatments had no significant effect on the viscosity of the digestive juice,and the release amount of active components in each group had no correlation with the viscosity of the digestive juice.