Effects Of Freezing/Thawing Cycles On Nutritional Content,Texture Properties,and Microstructure Of Pak Choi

The freezing and thawing processes have an important influence on nutritional components,texture properties,and microstructure of fruits and vegetables.As a kind of leafy vegetables,pak choi is nutrient-rich,such as vitamins and chlorophyll.Using the test methods of texture analyzer and scanning electron microscope,the study explored the effect of different freezing/thawing temperatures and freezing/thawing cycles on nutrition,texture,and microstructure on different parts of pak choi.Besides,the relationship between nutrition and texture of pak choi was evaluated using Pearson's correlation analysis.The results provided the fundamental data for improving quality of products during processing and storage.The article included the following aspects:1)The effect of different freezing temperatures(-20?,-70? and-196?)on nutritional components and texture properties was explored.Results showed that-196? freezing process performed the best protective effect on the texture(expect for cohesiveness)of leaf stalk.For the leaf blade,-196? resulted in the minimal puncture force.Freezing at-196? best maintained the nutritional quality both of the blade and stalk.Pearson's correlation analysis showed that chlorophyll was positively correlated with the max puncture force in leaf blade(P<0.05).Dry matter,water content,total sugar,and total phenol were positively correlated with hardness,springiness,gumminess,chewiness and resilience in leaf stalk(P<0.05).Vitamin c was positively related to all the textural properties(hardness,springiness,cohesiveness,gumminess,chewiness and resilience)of leaf stalk(P<0.05).2)The effect of different thawing temperatures(4?,20?)on nutritional components and texture properties was studied.Results indicated that frozen pak choi(both blade and stalk)thawed at 4°C achieved the better effect in maintaining dry matter,water content,chlorophyll,total sugar,total phenol,and vitamin c.Thawing at 4°C performed better protective effect on the blade texture.For the leaf stalk,the texture properties(hardness,springiness,cohesiveness,gumminess,chewiness and resilience)have been destroyed significantly after both of the two different thawing temperatures(P<0.05).Pearson's correlation analysis showed that all the nutrients were positively correlated with the textural parameters,irrespective of leaf blade and stalk(P<0.05).3)The effect of freezing/thawing cycles on nutritional components and texture properties was researched.Results showed that freezing/thawing treatment significantly decreased the puncture force of leaf blade(P<0.05),and the force decreased significantly with increasing freezing/thawing cycles(P<0.05).As for the leaf stalk,hardness,springiness,cohesiveness,gumminess,chewiness and resilience have been reduced significantly after freezing/thawing treatment(P<0.05).And hardness decreased significantly with increasing cycles(P<0.05).In addition,dry matter,water content,total sugar,total phenol,and vitamin c of leaf blade and dry matter,water content,total sugar,and vitamin c of leaf stalk were subjected to loss after freezing/thawing treatment(P<0.05).Although all nutritional components were decreased with increasing cycles,only dry matter,water content,and vitamin c decreased significantly(P<0.05).Pearson's correlation analysis showed that all the nutrients(dry matter,water content,chlorophyll,total sugar,total phenol,and vitamin c)were positively correlated with the max puncture force in leaf blade(P<0.05).In leaf stalk,water content,total sugar,total phenol,and vitamin c were positively correlated with hardness,springiness,gumminess,chewiness and resilience(P<0.05).