Microwave and microwave-vacuum drying as alternatives to convective drying in barley malt processing

AbstractThe possibility of using the vacuum impregnation as a pretreatment before drying apple cubes was investigated. The impregnation was carried out for 4.5 min with the vacuum pressure of 0.01 MPa. The sucrose solution or a mixture of sucrose and the citric acid were used as infiltration liquids. Apple cubes were dried by convective drying (CD) (at temperature of 50 and 70 °C) or microwave-vacuum drying (MVD) (at power of microwaves 120 and 480 W). The drying kinetics was determined and quality factors (anti-oxidant activity, mechanical–rheological properties and colour changes) were analysed. Studies proved that the vacuum impregnation causes increasing of the drying dynamics (12.50–28.57 % during CD and 12.50–18.48 % during MVD). All impregnated apples were darker, yellower and susceptible for deformation or cutting than non-impregnated. The highest level of anti-oxidant activity was observed when two-component impregnant before MVD by power of 480 W was used.

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Kinetics of Microwave Vacuum Drying of “Cat Chu” Mango in Mekong Delta - Vietnam

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.656-657.573 ◽

2015 ◽

Vol 656-657 ◽

pp. 573-579 ◽

Cited By ~ 1

Author(s):

Cuong Nguyen Van ◽

Hau Tran Tan

Keyword(s):

Mekong Delta ◽

Convective Drying ◽

Vacuum Drying ◽

Second Phase ◽

High Quality ◽

Hot Air Drying ◽

Drying Time ◽

Air Drying ◽

Microwave Vacuum Drying ◽

Hot Air

Microwave vacuum drying is one of innovative drying techniques that is today used in drying of foods, medical products and other high quality products. In this drying technology, heat is generated by directly transforming the electromagnetic energy into kinetic molecular energy of water, thus the heat is produced deep within the material to be dried under vacuum environment. This paper presents the results of research on microwave vacuum drying of “Cat Chu” mango in Mekong Delta – Vietnam. “Cat Chu” mango, with moisture content of (80 ± 1) % (wet basis - wb), was sliced into 5 cm thickness, and was dried in mWaveVac0150-lc dryer (Püschner - Germany). The drying vacuum was from 60 to 120 mbar. Three levels of microwave power were established: the first phase from 600 to 800 W, the second phase from 300 to 500 W, the last one from 150 to 250 W. The control sample was dried by convective drying method at 60 °C; and vacuum drying at 70 mbar, 60 °C. The results of this research showed that high quality product in terms of color, surface shrinkage and structure was obtained by microwave vacuum drying. The drying time was about 45 min, 450 min and 870 min with microwave vacuum drying, vacuum drying and convective hot-air drying, respectively. In addition, Fick’s equation and Crank’s solution were applied to analyze and calculate the accessibility and diffusion coefficient of microwave vacuum drying process. Starting accessibility of process was significantly increased; the diffusivity obtained was within a range from 6.44*10-10 m2/s to 16.16*10-10 m2/s. The results also indicated that there was a higher exchange in surface and a greater internal diffusion of experimental microwave vacuum drying samples compared to the control vacuum and hot-air drying samples.

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The Influence of Selected Drying Methods on the Physical Properties of Dried Apples cv. Jonagold Grown in Different Locations in Europe

International Journal of Food Engineering ◽

10.1515/ijfe-2016-0312 ◽

2017 ◽

Vol 13 (6) ◽

Cited By ~ 3

Author(s):

Anna Michalska ◽

Krzysztof Lech ◽

Adam Figiel ◽

Grzegorz P. Łysiak

Keyword(s):

Physical Properties ◽

Freeze Drying ◽

Geographical Origin ◽

Raw Material ◽

Convective Drying ◽

Vacuum Drying ◽

Drying Methods ◽

Drying Time ◽

Microwave Vacuum Drying ◽

Apple Slices

Abstract The aim of the study was to determine the influence of four different growing locations of apples cv. ‘Jonagold’ in Europe on the drying kinetics and the physical properties of dried apple slices. The drying methods applied in the study (freeze-drying, convective drying, microwave-vacuum drying and combined drying) significantly affected the drying time, which was the shortest in the case of microwave vacuum drying. The geographical origin of the apples affected the chemical and physical properties of the raw material used for drying, and, consequently, the drying time. Water activity of dried samples was connected with the final dry matter, regardless of the geographical origin of the apples. Freeze-drying resulted in the lightest in colour products (L*), whereas microwave-vacuum dried products had the highest levels of yellow pigments (b*). The highest chroma and browning index values were noted for microwave-vacuum dried samples and were strongly influenced by the drying temperature. The mechanical properties of the apple slices were more dependent on the drying method and temperature of the process than on the geographical origin when the temperature exceeded 83 °C.

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Combined Hot Air and Microwave-Vacuum Drying of Cranberries: Effects of Pretreatments and Pulsed Vacuum Osmotic Dehydration on Drying Kinetics and Physicochemical Properties

Food and Bioprocess Technology ◽

10.1007/s11947-020-02507-9 ◽

2020 ◽

Vol 13 (10) ◽

pp. 1848-1856

Author(s):

Zi-Liang Liu ◽

Izabela Staniszewska ◽

Danuta Zielinska ◽

Yu-Hao Zhou ◽

Konrad W. Nowak ◽

...

Keyword(s):

Osmotic Dehydration ◽

Drying Kinetics ◽

Convective Drying ◽

Total Phenolic ◽

Vacuum Drying ◽

Drying Time ◽

Antioxidant Power ◽

Microwave Vacuum Drying ◽

Hot Air ◽

Ferric Reducing Antioxidant Power

Abstract The aim of the study was to evaluate the effect of sonication (S), microwave-vacuum (MWV), convective freezing (F), cryogenic freezing (N), and their combinations, as well as pulsed vacuum osmotic dehydration (PVOD) on the drying kinetics, bioactive compounds, texture and color of whole cranberries during combined hot air convective drying, and microwave-vacuum drying (HACD+MWVD). Drying of berries took from 20 to 493 min. Drying rate was enhanced by 23% and drying time of non-osmotically dehydrated fruits was shortened by 33% using F treatment, while MWV decreased moisture content before drying by 68% and shortened the drying time of PVOD berries by 96%. Generally, total phenolic (TP) content increased during processing, total flavonoids (TF), and total monomeric anthocyanins (TMA) contents decreased, while the values of ferric reducing antioxidant power (FRAP) of dried fruits depended on the initial pretreatment. F and HACD+MWVD yielded fruits of the highest L* (33.8 ± 0.7), a* (25.2 ± 1.0), and b* (7.3 ± 0.6), inflated oval shape, and a small amount of wrinkles on the surface. PVOD and HACD+MWVD resulted in flat and wrinkled fruits.

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