Effects Of Different Thawing Methods On Thawing Efficiency And Quality Of Raspberry

Raspberry is a kind of small berry with rich nutritional value and unique flavor.In recent years,it has been gradually favored by people,and the processing products of raspberry are also increasing.However,raspberry is a very seasonal and perishable fruit,the general storage period is only about 5 days,which limits the processing of raspberry,so raspberry is often frozen.In order to preserve the nutritional value of raspberries better during thawing,improve the flavor and sensory quality of raspberry products,and make the thawed raspberry processed into ideal products.Five thawing methods(refrigerator thawing,ultrasonic thawing,water bath thawing,room temperature thawing and microwave thawing)were selected to treat the quick-frozen raspberry.The processing characteristics,antioxidant properties,flavor components and sensory qualities of the raspberry after thawing were evaluated to determine the most suitable thawing method.This paper studied the effects of different thawing methods on the thawing efficiency and drip loss of raspberry.The results showed that there were significant differences in thawing efficiency and drip loss among the 5 thawing methods.The efficiency of microwave thawing was the highest,the thawing time was only 0.57 min,and thedrip loss was only 4.40%,which was the lowest among the 5 thawing methods.Sixteen processing characteristics of raspberry juice treated by different thawing methods were determined.This paper had also used Principal Component Analysis,Cluster Analysis to classify and screen 16 indicators,and used Grey Correlative Degree Analysis to comprehensively evaluate 5 kinds of thawing methods.The results showed that the weighted correlation degree of microwave thawing was the highest(0.659),and that of water bath thawing was the lowest(0.483).Therefore the most suitable thawing method for raspberry juice production was microwave thawing.The antioxidant components and antioxidant capacities of raspberry were determined in order to study the effects of different thawing methods on antioxidant properties of raspberry.The results showed that there were significant differences in antioxidant components and antioxidant capacities of raspberry treated by different thawing methods.The correlation analysis showed that the antioxidant components could directly affect the antioxidant ability of raspberry.Principal component analysis showed that most antioxidant components of raspberry were well preserved after microwave thawing.Among them,VC content was 2.62mg/100 g,anthocyanin content was 136.79 mg/g,total phenol content was 0.94 g/100 g,Catalase(CAT)activity was 1.89 U/(g.min),Peroxidase(POD)activity was 2.72 U/(g.min)and Superoxide Dismutase(SOD)activity was 706.76 U/g.The antioxidant ability ofraspberry was the strongest after microwave thawing,and hydroxyl radical scavenging rate was 19.59%,superoxide anion scavenging rate was 71.77%,DPPH radical scavenging rate was 64.88%,total antioxidant capacity was: 35.03 umol Trolox/g,total reduction capacity was0.19.The volatile components of raspberry treated by different thawing methods were determined by Gas Chromatography-Mass Spectrometry(GC-MS).The volatile components of raspberry were mainly aldehydes,esters,ketones,alcohols,fatty acids,terpenes and other compounds.The main flavor components of raspberry were evaluated by Relative Odor Activity Value(ROAV).The main flavor components of raspberry were identified as acetaldehyde,alpha-ionone,beta-ionone,raspberry ketone,alpha-terpene and alpha-pinene.The results showed that the relative odor activity of raspberry ketone was the highest after refrigerator thawing,while microwave thawing could better preserve other main flavor components of raspberry.The electronic tongue was used to evaluate the taste of raspberry after thawing.The results showed that the bitterness,astringency,umami and saltiness of raspberry decreased after thawing.The sourness of raspberry after microwave thawing was lower,the sweetness was higher and the taste was better.At the same time,consumers were invited to evaluate the color,aroma,taste,hardness and affection of raspberries.Most consumers believed that the color and hardness of microwave thawed raspberries were closer to that of fresh raspberries,and their flavor and aroma were strong.Therefore,microwave thawing was more popular with consumers.Therefore,the best thawing method of frozen raspberry was determined to be microwave thawing by the comprehensive evaluation of the processing characteristics,antioxidant properties,flavor components and sensory quality of raspberry after thawing.