不同干燥温度对南京椴花品质影响的综合评价

Comparative evaluation on the quality of Tilia miqueliana flowers under different drying temperatures

【目的】研究不同干燥温度对南京椴花营养物质的影响,寻求较理想的南京椴花干燥温度,为南京椴花的干燥保存和推广提供理论信息和技术支撑。【方法】以南京椴盛开期花朵为供试材料,采用35、40、45℃热风干燥和真空冷冻干燥4种干燥温度加工南京椴花,通过测定复水比、含水量、多酚、黄酮、原花青素、可溶性糖、有机酸、γ-氨基丁酸、可溶性蛋白和16种游离氨基酸含量(以上营养物质均以干基计算),基于熵值法对南京椴花营养物质进行综合评价,选择保留营养物质最多的干燥温度。【结果】结果表明真空冷冻干燥复水比高于热风干燥,且热风干燥温度越高复水比越高。干花多酚含量高于鲜花,其中45℃热风干燥和真空冷冻干燥后干花多酚含量显著高于鲜花(P<0.05),45℃热风干燥含量最高,为34.27 mg·g^(-1),较鲜花增加24%;干燥后原花青素含量增加,真空冷冻干燥原花青素含量最高,为76.05 mg·g^(-1),较鲜花增加41%;45℃热风干燥次之,含量为72.01 mg·g^(-1),较鲜花增加34%;黄酮、可溶性糖、γ-氨基丁酸含量在不同处理间均没有显著性差异(P<0.05);干燥后有机酸、可溶性蛋白以及除蛋氨酸、精氨酸外的14种游离氨基酸含量均显著降低(P<0.05);干燥后游离氨基酸总量显著降低(P<0.05),其中热风干燥游离氨基酸总量为951.16~1064.32μg·g^(-1),降低64%~68%,真空冷冻干燥为594.48μg·g^(-1),降低80%。相关性分析结果表明南京椴花内营养物质间存在不同程度的相关性,酚类化合物之间呈正相关;有机酸、γ-氨基丁酸、可溶性蛋白、除蛋氨酸外的15种游离氨基酸之间普遍呈正相关;酚类化合物与有机酸、γ-氨基丁酸、可溶性蛋白、除蛋氨酸外的15种游离氨基酸普遍呈负相关。主成分分析共提取3个主成分,占总方差的85.7%,能较好地区分鲜花和不同干燥温度下的干花。熵值法综合评价结果表明,鲜花综合得分最高,45℃热风干燥次之。【结论】南京椴花干燥后品质降低,但45℃热风干燥是较理想的干燥方法。

【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°C 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°C 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°C 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 andγ-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 951.16μg·g^(-1) to 1064.32μg·g^(-1),decreasing by 64%-68%,and vacuum freeze drying resulting in 594.48μg·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.