Effects Of Freezing-Frozen Storage And Thawing Methods On Quality Of Blueberry

The blueberry is the research object in this study,the research was object to study the effects of different frozen storage environments(-20℃,-40℃ and-80℃)on the water migration and quality of blueberries were detailed studied;the changes of flavor components in blueberry during frozen storage period were analyzed by headspace solid-phase microextraction(HS-SPME)combined with gas chromatography-mass spectrometry(GC-MS);explore the effect of different thawing methods on the thawing rate and quality of blueberry.Reveal the law of blueberry quality deterioration in the freeze-thaw process,and provide theoretical basis for the frozen technology in blueberry storage and processing.The main results were as follows:1.The time for the blueberry to pass through the maximum ice crystals at the temperatures of-20℃,-40℃,-80℃ and liquid nitrogen(-196℃)was 35.33 min,15.68 min,0.92 min and 0.12 min,respectively.No obvious over-cooling point was found during freezing at 80℃ and liquid nitrogen;the T23 relaxation time at-80℃ was significantly higher than others(p<0.05),and was closest to fresh samples;the hardness of the frozen group at-20℃ and-40℃ were significantly lower than the treated with-80℃ and liquid nitrogen(p<0.05);the blueberries frozen at-80℃ exhibited lower drip loss and more protoplast content;the L value and ΔE of the frozen group at-80℃ had no significant difference with fresh blueberries(p>0.05).In summary,the frozen at-80℃ was relatively moderate for blueberries and has minimal effect on drip loss.It could maintain a better sensory quality of blueberries,with a-40℃freezing effect second only to-80℃.From the study we have found that proper freezing speed could better maintain the quality of blueberries.2.Moisture content of blueberry showed a downward trend in the process of frozen storage.The higher the temperature of frozen storage,the more the decline trend was more obvious.At the end of frozen storage,the T23 value of blueberries decreased from 488.67 ms to 165.13 ms,which decreased about 66.21%;the ratio of peak area of frozen blueberry after freezing in liquid nitrogen and frozen at-40℃ didn’t decrease significantly during the whole frozen storage period(p>0.05),but blueberry frozen at-20℃ begun to show significant storage on the 240th day.No matter what kind of frozen storage methods would cause damage to the blueberry cell structure,resulting in a decrease in its quality characteristics.Among them,the water content,vacuole water,and texture of blueberry frozen at-20℃ were seriously damaged,and the cell membrane damage and reddening were most serious at the end of the frozen period.The decrease was slower in water content and soluble solids content of frozen blueberry at-80℃,and the water distribution was relatively uniform,and the browning of blueberry pulp could be well inhibited.The best frozen storage effect was observed.3.After frozen storage,aldehydes were reduced and alcohols were significantly increased;the main aroma substances n-hexanal,linalool and nerol were increased in relative content after freezing and exhibited a unique aroma.On the other hand,(E)-2-hexenal,(E)-2-hexen-1-ol and eucalyptol appear different degrees of loss;compared with other groups,the content of aldehydes stored at-20℃ was the lowest,and ethanol and n-octanol were detected at the end of storage,which was unfavorable for maintaining the characteristic aroma of blueberries,and the sensory score was also lower;the blueberry aroma components have similar changes and a more stable flavor at-40℃ and-80℃.4.Ultrasound-assisted sugar immersion thawing has the highest efficiency,anthocyanin retention and retention rate of soluble solids and reducing sugar content,but its sap loss,cell membrane permeability and water loss are large,and sensory score was also low;the time of water immersion thawing was the longest,but the loss of sap and cell membrane permeability after thawing was smaller,the content of malondialdehyde was also lower,and the retention of hardness and soluble solids content was least;ultrasound-assisted water immersion thawing has better thawing efficiency,but its loss of anthocyanins and reducing sugar content was most serious;although sugar immersion thawing could reduce the loss of anthocyanins to a certain extent and has a high sensory score,its hardness is the lowest and malondialdehyde content increases significantly.