Comparative evaluation on the quality of Tilia miqueliana flowers under different drying temperatures
[Objective]Study the effects of different drying temperatures on the nutrient content of Tilia miqueliana flowers,seek an ideal drying temperature for T.miqueliana flowers,and provide theoretical information and technical support of T.miqueliana flowers for drying,preservation and promotion.[Method]This research used the blooming flowers of T.miqueliana as the experimental materials,hot air drying at 35℃,40℃,or 45℃,and vacuum freeze-drying were used to process T.miqueliana fresh flowers.The rehydration ratio,water content,polyphenols,flavonoids,proanthocyanidins,soluble sugars,organic acids,γ-Aminobutyric acid,soluble protein,and 16 free amino acids are determined(all nutrients were calculated on a dry basis),and comprehensively evaluated the nutrients of T.miqueliana flowers based on entropy value method,selecting the drying temperature that retains the most nutrients.[Result]The results indicate that the rehydration ratio of vacuum freeze-drying was higher than hot air drying,and as the temperature of hot air drying increases,so does the rehydration ratio.The content of polyphenols in dried flowers was higher than in fresh flower.The content of polyphenols in flowers by 45 ℃ hot air drying and vacuum freeze drying was significantly higher than that in fresh flower(P＜0.05).Meanwhile,the highest content was found in flowers by 45 ℃ hot air drying,reaching 34.27 mg·g-1,which was 24% higher than that in fresh flower.The content of proanthocyanidins in dried flowers increased,with the highest content found in vacuum freeze-dried flowers,reaching 76.05 mg·g-1,which was 41% higher than that in fresh flower.The content of proanthocyanidins in flowers by 45 ℃ hot air drying was 72.01 mg·g-1,which was 34% higher than that in fresh flower.There was no significant difference in the content of flavonoids,soluble sugars and γ-aminobutyric acid among different treatments(P＜0.05).The content of organic acids,soluble proteins and 14 kinds of free amino acids(except for glutamic acid and aspartic acid)decreased significantly after drying(P＜0.05).The total content of free amino acids also decreased significantly after drying(P＜0.05),with the content of flowers by hot air drying ranged from 951.16 μg·g-1 to 1 064.32 μg·g-1,decreasing by 64%-68%,and vacuum freeze drying resulting in 594.48 μg·g-1,decreasing by 80% .The correlation analysis results indicated that there were varying degrees of correlation between the nutrients in T.miqueliana flowers,and there was a positive correlation between phenolic compounds;Principal component analysis extracted three principal components,accounting for 85.7% of the total variance,which could distinguish between fresh and dried flowers at different drying temperatures.The comprehensive evaluation results of the entropy value method indicated that the flowers had the highest comprehensive score,followed by hot air drying at 45℃.[Conclusion]After drying,the quality of T.miqueliana flowers decreases,therefore,compared to other temperatures,45℃hot air drying is an ideal method.
Tilia miquelianaflowerhot air dryingvacuum freeze dryingquality
万方数据
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