不同浓缩工艺对龙眼浓缩汁的色泽及挥发性成分的影响

Effects of different concentration techniques on color and volatile components of longan concentrated juice

为了探讨不同工艺条件对龙眼浓缩汁色泽和挥发性成分的影响,利用色差仪和电子鼻及顶空固相微萃取-气相色谱质谱联用技术分析常压加热浓缩、真空浓缩、真空浓缩-烘焙、桂圆浸提液-真空浓缩的龙眼浓缩汁的色泽和挥发性成分的变化。结果表明,不同浓缩工艺龙眼汁色泽指标和风味均发生显著性变化,其中真空浓缩-烘焙联用的样品,表现为龙眼浓缩汁亮度L^(∗)值变小,a^(∗)值和b^(∗)值变大(变红和变黄),褐变度增加、透明度降低。在龙眼浓缩汁的主要挥发性成分中,萜烯类物质的相对含量较高。新鲜龙眼汁检测出有24种挥发性成分,真空浓缩-烘焙联用工艺得到的龙眼浓缩汁挥发性成分增加到29种,同时还检测出烘焙风味的香气成分的2-甲基吡嗪(相对含量为6.54%),以及具有龙眼干香气成分的α-石竹烯(相对含量为0.64%)等成分。真空浓缩-烘焙联用工艺会使龙眼浓缩汁具备桂圆独特的色泽和更加丰富的香气成分。

The aim of this study was to evaluate the effects of different concentration techniques on the color and volatile components of longan concentrated juice obtained from atmospheric heating(AH),vacuum concentration(VC),vacuum concentration-baking(VC-B),and dried longan extracts-vacuum concentration(DL).Spectrophotometry and colorimeter were used to analyze the color changes of four kinds of concentrated longan juices,and electronic nose and headspace solid-phase microextraction-gas chromatography-mass spec-trometry were used to investigate the volatile components.Results indicated that the color of longan concentrated juice was altered by dif-ferent concentration processing methods,especially VC-B concentrated juice showed the decrease of L^(∗)value and the increase of a^(∗)and b^(∗)value,which resulting in a reddish-brown and decreased transparency in appearance.The relative content of terpenes was high in the main volatile components of longan concentrated juice.Twenty-four kinds of volatile components were detected in fresh longan juice.How-ever,volatile components of longan concentrated juice obtained by VC-B were increased to 29,and the baking flavor aroma composition of 2-methylpyrazine with 6.54%relativity content and dried longan aroma compound ofα-caryophyllene with 0.64%relativity content were detected in this longan concentrated juice.There are unique colors and more volatile components in longan concentrated juice obtained by the vacuum concentration-baking process.