| Highland barley is a cereal crop of the genus barley in poaceae,which has many physiological functions such as preventing cardiovascular disease,reducing cancer risk,improving antioxidant capacity and preventing diabetes.Highland barley is the staple food of the residents of the Qinghai-Tibet Plateau.Germination is an important way to enrich selenium in cereals.The germination can significantly increase the content of organic selenium in cereals.However,the germinated grain has a high water content and is susceptible to mildew,thus needing to be dried extend shelf life.The traditional hot air drying requires long time and commonly leads to the decline of the quality of the product.When the ultrasonic technology is applied to the drying process,the drying rate can be accelerated,the drying time can be shortened,and the food quality can be better maintained.Therefore,in this thesis,the "Zangqing 2000" highland barley was used as a test material.Firstly,the process conditions of selenium-enriched germination were optimized.Secondly,ultrasonic treatment was applied to enhance the hot air drying of selenium-enriched highland barley seeds.The drying characteristics and antioxidant capacity were studied.Finally,a health-care highland barley milk beverage was developed and the changes in its quality during storage were studied.The research results are as follows:1.The effects of germination time,the pH value of culture medium and sodium selenite concentration on the content of organic selenium in highland barley seeds were studied.The changes of antioxidant substances and antioxidant abilities during the germination of highland barley seeds were studied under the optimal selenium-enriched germination process.The results showed that the optimal conditions were as follows:germination time 48 h,pH 6.0 and sodium selenite concentration 10 mg/L.Under these conditions,the content of organic selenium in highland barley seeds was 1.572 mg/kg DW,which was 16.46 times higher than that in raw material.Selenium-enriched germination could significantly increase the content of total phenolics,total flavonols,organic selenium and ABTS radical scavenging ability of highland barley seeds(P<0.05).Although ?-glucan content and ferric reducing antioxidant power(FRAP)were decreased,the degradation of?-glucan content was effectively delayed by selenium-enriched germination compared with the control.Correlation analysis showed that total phenolics content was highly positively correlated with organic selenium content and ABTS radical scavenging ability(P<0.01).Meanwhile,there were an extremely significant positive correlation relationship between ?-glucan content with ferric reducing antioxidant power(FRAP),and between organic selenium content with ABTS radical scavenging ability(P<0.01),whereas other indexes were negatively correlated or not correlated.This study showed that selenium enrichment treatment increased the content of antioxidant substances,effectively delayed the degradation of ?-glucan and enhanced the antioxidant abilities in germinated highland barley seeds.2.The effect of ultrasonic enhanced hot air drying on the drying characteristics of selenium-enriched germinated highland barley seeds was studied.The selenium-enriched germinated highland barley seeds were dried at conditions:hot air drying temperature 55? and 70?;ultrasonic intensity:125.1 W/dm2 and 180.2 W/dm2.The results showed that when the drying temperature was 55?,the ultrasonic treatment group shortened the drying time by 17.4%to 26.1%compared with the control group.At a drying temperature of 70?,the ultrasonic treatment group could reduce the drying time by 18.8%to 31.3%.Compared with the longitudinal shrinkage,the lateral shrinkage during the drying process of the selenium-enriched germinated highland barley seeds was more obvious.The greater the ultrasonic intensity was,the more obvious the lateral shrinkage of the selenium-enriched germinated highland barley seeds was.When highland barley seeds was dried at an ultrasonic intensity of 125.1 W/dm2 and a temperature of 55?,the the color of the product was improved,the rehydration rate was increased,and a better original structure was observed.Therefore,drying at an ultrasonic intensity of 125.1 W/dm2 and a temperature of 55 ? could effectively improve the drying rate,shorten the drying time,and improve the quality of selenium-enriched germinated highland barley seeds.3.The effect of ultrasonic enhanced hot air drying on the antioxidant abilities of selenium-enriched germinated highland barley seeds was studied.The results showed that the organic selenium content in selenium-enriched germinated highland barley seeds increased significantly after drying.The highest content of organic selenium was 1.580 mg/kg DW,which was 1.10 times of the hot air drying at this temperature.When the drying temperature was constant,the organic selenium content in germinated highland barley was the highest in the treatment group with an ultrasonic intensity of 125.1 W/dm2.When the ultrasonic intensity was constant,the content of organic selenium in germinated highland barley dried at 55? was higher than that dried at 70?.The phenolic content and antioxidant abilities in germinated highland barley seeds were significantly decreased after the combination of 180.2 W/dm2 ultrasound and 70? hot air drying,whereas the effect of other combined drying methods on the above indicators was not significant.125.1 W/dm2 and 180.2 W/dm2 ultrasonic enhanced hot air drying would cause ?-glucan loss.The higher the ultrasonic intensity was,the lower the ?-glucan content was.When ultrasonic intensity remained constant,the temperature of hot air drying showed no significant difference on ?-glucan content(P>0.05).Therefore,ultrasonic technology might be used to strengthen the drying process of selenium-enriched germinated highland barley seeds.The combination of 125.1 W/dm2 ultrasound and 55? hot air drying could maintain higher antioxidant abilities of the selenium-enriched germinated highland barley seeds.4.The effect of roasting time on the color and flavor of selenium-enriched germinated highland barley seeds was studied.A single-factor and orthogonal test was optimized to prepare the health-care highland barley milk beverage,and its quality changes during storage were studied.The results showed that roasting the selenium-enriched germinated highland barley seeds for 5 min could increase the aroma of the product,which showed lower browning degree,higher pyrazine flavor content and no burnt smell.The best formula for highland barley milk beverage was:the ratio of material to liquid 1:10,the amount of milk powder 2%,the amount of xylitol 1.25%,the amount of CMC 0.15%,the amount of guar gum 0.10%,the amount of xanthan gum 0.20%.The beverage had good stability,light brown color,moderate sweetness,the unique aroma of highland barley rice and the milky aroma of milk,and high nutritional value.With the prolongation of storage time,the content of organic selenium,total phenolics,ABTS radical scavenging ability and ferric reducing antioxidant power(FRAP)in the highland barley milk beverage decreased,whereas the ?-glucan content was basically unchanged.The microbial indicators of highland barley milk beverage met commercial sterility requirements. |
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