Study On Combined Drying Technique Of Chives And Its Effect On The Quality Of Dried Products

Chives(Allium ascalonicum)are mainly dried by hot air drying in industrial production,but its drying efficiency and quality is lower than other methods.Chives are mainly dried by vacuum freeze drying in experimental research,but the high cost of vacuum freeze drying is difficult to commercialize on a large scale.Combined drying can take advantage of different drying technologies to achieve the purpose of reducing energy consumption and improving product quality.This study used chives as materials to research effects of different combined drying techniques on drying characteristics and product quality of chives,and optimized the optimal drying process of leaf with microwave combined hot air drying,and established its drying kinetics model.Based on the optimal process of ultrasound pretreatment for petiole,the effects of ultrasound pretreatment on dielectric characteristics of petiole were discussed.And changes of volatile components of chives after drying was studied using SPME-GC-MS.Results of this study provided theoretical basis and technical support for industrial production of high quality dried chives.The specific research results are as follows:1.Hot air drying,microwave drying,microwave combined hot air drying,and ultrasound pretreatment assisted these three methods were used to dry chive.Results showed that rehydration ratio,chlorophyll and alliin retention rate of leaf after microwave combined hot air drying were 4.20,84.56%and 69.88%,which were significantly higher than other methods.Rehydration ratio of petiole dried by ultrasound assisted hot air drying was 4.65,which was significantly higher than other methods,and ?E was significantly lower than other methods.And thiosulfinate and alliin retention rate were significantly higher than untreated petiole.(p<0.05)2.Optimal result of microwave combined hot air drying of leaf were microwave power 3000W,moisture content at conversion point 40%,hot air temperature 75?.The kinetics model of microwave drying was Page:MR=exp(-0.03126t 1.79815)and hot air drying was Midilli:MR=0.30427exp(-0.13891t)-0.000175419t.3.Response surface method was used to optimize ultrasound pretreatment of petiole.The optimal technique were ultrasonic power 700 W,frequency 45 kHz,and time 6 min.After pretreatment,petiole were dried by hot air drying,its drying rate,rehydration ratio,L value,thiosulfinate and alliin retention rate were increased by 1.31,1.20,1.07,1.36 and 1.12 times compared with hot air drying petiole respectively.A fitting equation(y=171.953+2.273x-0.061x2+5.916 ×10-4x3-7.012×10-7x4)was established for change content of alliin in petiole during this processing.Compared with untreated samples,ultrasound pretreated petiole had a longer transverse relaxation time,it showed ultrasound pretreatment could improve drying rate of petiole.And ultrasound pretreatment could change the water state of the petiole and affected the dielectric properties.Dielectric constant of hot air drying petiole at 915 MHz was extremely significantly correlated with the moisture content and temperature;the dielectric constant of ultrasound assisted hot air drying petiole at 2450 MHz was extremely significantly related to moisture content and temperature,which can be used to predict dielectric constant during drying process of chive in a given moisture content and temperature range and provide theoretical basis for parameter setting during drying.4.SPME-GC-MS method was used to analyze volatile components of fresh and dried chives.Results showed that sulfur compounds were the main flavor substances of chives.Rrelative content of sulfur compounds in chives decreased and relative content of alkanes increased after dry.Relative content of sulfur compounds in microwave dried and microwave combined hot air dried leaf was13.93%and 15.46%,respectively,and relative content of alkanes was 47.15%and 43.18%.Therefore,the quality of leaf dried by microwave combined hot air drying was higher.Relative content of sulfur compounds in hot air dried and ultrasound assisted hot air dried petiole was 49.26%and 48.64%,and relative content of alkanes was 17.61%and 10.46%,respectively.Ultrasound assisted hot air drying produced more aldehydes and furans,which were beneficial for chives to maintain its flavor.The results also proved that optimal combined drying methods could produce high quality dried chives.