Cao Xiaohuang, Zhang Min, Mujumdar Arun S, Zhong Qifeng, Wang Zhushang
State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, China.
Department of Bioresource Engineering, Macdonald Campus, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada.
J Sci Food Agric. 2018 Mar;98(4):1599-1605. doi: 10.1002/jsfa.8634. Epub 2017 Oct 23.
Young barley grass leaves are well-known for containing the antioxidant substances flavonoid and chlorophyll. However, low product quality and energy efficiency exist with respect to the dehydration of barley grass leaves. To improve energy supply and the quality of barley grass, microwave heating instead of contact heat was applied for the freeze drying of barley grass at a pilot scale at 1, 1.5 and 2 W g , respectively; After drying, energy supply and quality parameters of color, moisture content, chlorophyll, flavonoids, odors of dried barley grass were determined to evaluate the feasibility of the study.
Microwave freeze drying (MFD) allowed a low energy supply and high contents of chlorophyll and flavonoids. A lightness value of 60.0, a green value of -11.5 and an energy supply of 0.61 kW h g were observed in 1.5 W g MFD; whereas drying time (7 h) decreased by 42% compared to contact heating. Maximum content of flavonoid and chlorophyll was 11.7 and 12.8 g kg barley grass. Microwave heating leads to an odor change larger than that for contact heating observed for the freeze drying of barley grass.
MFD retains chlorophyll and flavonoids, as well as colors and odors of samples, and also decreases energy consumption in the freeze drying of barley grass. © 2017 Society of Chemical Industry.
嫩大麦草叶因含有抗氧化物质黄酮类化合物和叶绿素而闻名。然而，大麦草叶脱水存在产品质量低和能源效率低的问题。为了提高能源供应和大麦草的质量，分别以1、1.5和2 W/g的功率在中试规模下采用微波加热而非接触加热对大麦草进行冷冻干燥；干燥后，测定干燥大麦草的能源供应以及颜色、水分含量、叶绿素、黄酮类化合物、气味等质量参数，以评估该研究的可行性。
微波冷冻干燥（MFD）能实现低能源供应以及高含量的叶绿素和黄酮类化合物。在1.5 W/g的微波冷冻干燥中，观察到亮度值为60.0、绿色值为 -11.5且能源供应为0.61 kW h/g；与接触加热相比，干燥时间（7小时）减少了42%。大麦草中黄酮类化合物和叶绿素的最大含量分别为11.7和12.8 g/kg。对于大麦草的冷冻干燥，微波加热导致的气味变化比接触加热更大。
微波冷冻干燥能保留大麦草的叶绿素、黄酮类化合物以及样品的颜色和气味，同时还能降低大麦草冷冻干燥过程中的能耗。© 2017化学工业协会。
