Xiaohuang Cao1, Min Zhang1, Arun S Mujumdar1,2, Qifeng Zhong3, Zhushang Wang4. 1. State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, China. 2. Department of Bioresource Engineering, Macdonald Campus, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada. 3. Haitong Food Group Company, Cixi, Zhejiang, China. 4. Jiangsu Dingneng Food Company, Xinghua, Jiangsu, China.
Abstract
BACKGROUND: 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-1 , 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. RESULTS: 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-1 g-1 were observed in 1.5 W g-1 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-1 barley grass. Microwave heating leads to an odor change larger than that for contact heating observed for the freeze drying of barley grass. CONCLUSION: 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.
BACKGROUND: 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-1 , 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. RESULTS: 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-1 g-1 were observed in 1.5 W g-1 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-1 barley grass. Microwave heating leads to an odor change larger than that for contact heating observed for the freeze drying of barley grass. CONCLUSION: 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.