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Effect of Microwave Vacuum Drying on the Drying Characteristics, Color, Microstructure, and Antioxidant Activity of Green Coffee Beans.

ABSTRACT: The aim of this study is to investigate the effect of microwave vacuum drying (MVD) on the drying characteristics and quality attributes of green coffee beans. We specifically focused on the effective moisture diffusion coefficient (Deff), surface temperature, glass transition temperature (Tg), water state, and microstructure. The kinetics of color changes during drying, total phenolic content (TPC), and antioxidant activity (DPPH, FRAP, and ABTS) were also characterized. Microwave power during MVD affected the porosity of coffee beans, their color, TPC, and antioxidant activity. The Allometric 1 model was the most suitable for simulating surface temperature rise kinetics. Thermal processing of green coffee beans resulted in increased b*, L*, ?E, and TPC values, and greater antioxidant capacity. These findings may provide a theoretical reference for the technical improvement, mechanisms of flavor compound formation, and quality control of dried green coffee beans.

SUBMITTER: Dong W

PROVIDER: S-EPMC6100066 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Effect of Microwave Vacuum Drying on the Drying Characteristics, Color, Microstructure, and Antioxidant Activity of Green Coffee Beans.

Dong Wenjiang W Cheng Ke K Hu Rongsuo R Chu Zhong Z Zhao Jianping J Long Yuzhou Y

Molecules (Basel, Switzerland) 20180511 5

The aim of this study is to investigate the effect of microwave vacuum drying (MVD) on the drying characteristics and quality attributes of green coffee beans. We specifically focused on the effective moisture diffusion coefficient (Deff), surface temperature, glass transition temperature (Tg), water state, and microstructure. The kinetics of color changes during drying, total phenolic content (TPC), and antioxidant activity (DPPH, FRAP, and ABTS) were also ch ...[more]

PMID: 29751607

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Project description:The current study investigates the phytochemical composition of coffee plant organs and their corresponding antioxidant capacities compared to green and roasted coffee beans. HPLC analysis indicated that the investigated compounds were present in all organs except mangiferin, which was absent in roots, stems and seeds, and caffeine, which was absent in stems and roots. Total phytochemicals were highest in the green beans (GB) at 9.70 mg g-1 dry weight (DW), while roasting caused a 66% decline in the roasted beans (RB). This decline resulted more from 5-CQA and sucrose decomposition by 68% and 97%, respectively, while caffeine and trigonelline were not significantly thermally affected. Roasting increased the total phenolic content (TPC) by 20.8% which was associated with an increase of 68.8%, 47.5% and 13.4% in the antioxidant capacity (TEAC) determined by 2,2-diphenyl-1-picryl hydrazyl radical (DPPH), 2,2-azino bis (3-ethyl benzothiazoline-6-sulphonic acid) radical (ABTS) and Ferric ion reducing antioxidant power (FRAP) assays, respectively. Amongst the leaves, the youngest (L1) contained the highest content at 8.23 mg g-1 DW, which gradually reduced with leaf age to 5.57 mg g-1 DW in the oldest (L6). Leaves also contained the highest TPC (over 60 mg g-1 GAE) and exhibited high TEAC, the latter being highest in L1 at 328.0, 345.7 and 1097.4, and least in L6 at 304.6, 294.5 and 755.1 µmol Trolox g-1 sample for the respective assays. Phytochemical accumulation, TPC and TEAC were least in woody stem (WS) at 1.42 mg g-1 DW; 8.7 mg g-1 GAE; 21.9, 24.9 and 110.0 µmol Trolox g-1 sample; while herbaceous stem (HS) contained up to 4.37 mg g-1 DW; 27.8 mg g-1 GAE; 110.9, 124.8 and 469.7 µmol Trolox g-1 sample, respectively. Roots contained up to 1.85 mg g-1 DW, 15.8 mg-1 GAE and TEAC of 36.8, 41.5 and 156.7 µmol Trolox g-1 sample. Amongst the organs, therefore, coffee leaves possessed higher values than roasted beans on the basis of phytochemicals, TPC and TEAC. Leaves also contain carotenoids and chlorophylls pigments with potent health benefits. With appropriate processing methods, a beverage prepared from leaves (coffee leaf tea) could be a rich source of phytochemicals and antioxidants with therapeutic and pharmacological values for human health.

Dataset Information

Effect of Microwave Vacuum Drying on the Drying Characteristics, Color, Microstructure, and Antioxidant Activity of Green Coffee Beans.

Publications

Effect of Microwave Vacuum Drying on the Drying Characteristics, Color, Microstructure, and Antioxidant Activity of Green Coffee Beans.

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