Microwave Vacuum Drying for Crispy Beet Snacks: Process Development, Drying Kinetics, and Product Qualities
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With the increase in snack consumption in the modern diet and concerns over ultra-processed foods made by deep frying or baking, there is a need to develop novel processing methods to produce more nutritious options. Microwave vacuum drying (MVD) was used to develop crispy chips from beets (Beta vulgaris), an important specialty crop in the State of New York. The beet slices (Φ5 cm × 3 mm thickness) were dried under 58-62 torr vacuum and 40°C at microwave powers of 900, 1350, and 1800 W. The drying times, drying rates, and effective moisture diffusivities were experimentally determined. Under the tested conditions, crispy beet chips were dried from their initial moisture content of 80% on wet basis to under 20% on wet basis within 21-27 minutes. The drying rates ranged from 0.00326 to 0.495 kg water/kg dry mass/min with higher MVD power corresponding with larger drying rates. The effective moisture diffusivity ranged from 1.39 x 10-10 to 1.03 x 10-8 m2/s which increased as the moisture content decreased and power density increased. Puffing on the chip surface initiated between 10-15 min, corresponding to moisture content between 59.8%-68.7% on wet basis. The color metrics, water activity, texture, and microstructure were also measured across the drying time. This study provides evidence that MVD can be a promising method to produce crispy vegetable snacks.