| Highland barley(HB)is the main grain crop in Qinghai-Tibet Plateau of China.However,the major restrictive cause for the application of HB is the deterioration of lipids during storage.HB was susceptible to lipid hydrolysis and autoxidation due to the lipase with high activity and a high content of polyunsaturated fatty acids(PUFA),which reduces its nutritional value.Therefore,radio frequency(RF)heating technology was applied to inactivate lipase in HB,optimized the RF treatment parameters from the perspective of controlling free radicals intensity,and the effects of different RF treatment parameters on the storage stability of HB were studied.The effects of different packaging methods on the storage characteristics of RF stabilized HB were also studied.The purpose of this study was to use RF heating technology to delay the quality deterioration of HB,and provide theoretical basis for the application of RF in extending the shelf life of HB by inactivating lipase.The main research contents and results are as follows:Firstly,the effect of lipase deactivation were studied by changing the RF plate spacing,water supplementation,RF temperature and holding time.The results showed that the operating conditions to reach the maximum inactivation ratio of lipase were as follows: plate spacing 120 mm,RF temperature 125°C with holding for 0 min,and water supplementation4%.Under this conditions,the maximum inactivation ratio of lipase reached 75.58%.Secondly,The lipid rancidity of HB with the maximum inactivation ratio of lipase was evaluated during storage.The results showed that the lipase activity of RF-treated HB increased gradually,while that of the untreated HB fluctuated at a higher level during storage.The fatty acid value reduced by 61.49% after RF treatment and did not change significantly during storage,while that of the untreated HB fluctuated at a higher level.The hexanal content increased by 155.80% after RF treatment and then increased by 134.46% during storage,while that of the untreated HB increased rapidly during storage.The free radical intensity increased by 58.19% and then increased by 23.98% during storage,while that of the untreated HB also increased significantly during storage.The above results show that not only all the indicators of the untreated HB showed a deteriorating trend during storage,but also the indicators of the RF-treated HB except the fatty acid value showed a deteriorating trend,among which the hexanal content and free radical intensity were worse than the untreated HB.The reason for this phenomenon may be the unilateral pursuit of the maximum inactivation ratio of lipase,which leading to significant increase of free radical intensity in RF-treated HB.Afterwards,the operating parameters for lipase inactivation were optimized again by reducing free radical intensity,and the reduction of free radical intensity was realized by changing the RF treatment temperature.Four RF-treated HB samples at different temperatures were obtained based on free radical control,and the storage stability of the four group HB samples were evaluated.The results showed that the free radical intensity of the RF 75°C-10min-0% and RF 115°C-0 min-0% samples increased,and the RF 95°C-0 min-2% and RF105°C-0 min-3% samples decreased compared with the untreated HB.The free radical intensity of the above four samples showed an increasing trend during storage,among which the first two samples increased rapidly and the latter two samples increased slowly.The lipase activity of RF 75°C-10 min-0% sample was significantly higher than that of the other three samples,and increased significantly during storage.The hexanal content and its increasing rate of RF 105°C-0 min-3% and RF 115°C-0 min-0% samples was higher,while that of RF75°C-10 min-0% and RF 95°C-0 min-2% samples was lower and no obvious increase was found during storage.The optimal operating conditions were RF 95°C-0 min-2%.Under these conditions,the inactivation ratio of lipase reached 44.19%.Finally,the effects of three packaging methods,namely ziplock bag packaging,vacuum packaging,and vacuum combined with oxygen absorber packaging,on the storage qualities of RF-stabilized HB were studied at ambient temperature for 8 months.The results showed that:(1)No significant change in fatty acid value was found among the three RF samples after 8months of storage,and they were almost 74.49%,75.19% and 72.88% of ziplock bag,vacuum and vacuum combined with oxygen absorber packaged conrtol samples,respectively.The peroxide values of the ziplock bag,vacuum and vacuum combined with oxygen absorber packaged RF samples were 18.52%,34.48% and 71.43% lower than the corresponding controls,respectively.The free radical intensity of the three RF samples was significantly lower than that of control group(p<0.05),and it showed a decreasing trend during storage.The lowest free radical intensity was observed in RF-treated HB samples packaged by vacuum combined with oxygen absorber.The hexanal content of HB in the control group and the ziplock bag and vacuum packaged RF-treated samples increased rapidly during storage,and the hexanal content in vacuum combined with oxygen absorber packaged RF sample only increased slightly,which indicated that the combination of RF treatment and vacuum combined with oxygen absorber packaging could effectively inhibit the lipid oxidation of HB.Compared with the control group,the fatty acid composition of RF-treated HB samples changed more slowly.The lowest decreases in linolenic acid content showed in vacuum combined with oxygen absorber packaged RF samples.(2)The peak viscosity,breakdown value,final viscosity,and setback value of HB were significantly increased after RF stabilization.During the first 6 months of storage,the setback value of the RF treated samples decreased with increasing storage time(p<0.05),while the opposite trend was found in control groups.The setback value decreased sharply after storage for 6 months.There was no significant difference in breakdown value,final viscosity,and setback value disintegration value between RF and corresponding control samples after 8 months of storage.(3)After 8months of storage,the β-glucan content of the ziplock bag,vacuum and vacuum combined with oxygen absorber packaged RF samples was 4.75%,6.67% and 3.21% higher than that of the control group,but showed no significant difference compared with the samples stored for0 d.(4)The sensory evaluation grades of RF-treated HB under the three packaging methods were significantly better than those of the control samples(p<0.05),and no unpleasant flavor was smelled during 8 months of storage period,while the unpleasant flavor was smelled after stored for 6 months in control group. |
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