Vacuum Belt Dehydration of Chopped Beetroot (Beta vulgaris) and Optimization of Powder Production Based on Physical and Chemical Properties

Abstract

Beets contain the red and yellow pigments known as betalains, as well as nitrates and other phytochemicals that may affect human health, and have been studied for possible effects on lowering blood pressure and enhancing athletic performance. Betalains are heat-labile, so developing relatively low-temperature drying methods is one way to turn the perishable root vegetable into a value-added ingredient. The objective of this study was to determine if continuous vacuum belt drying (VBD) could be used to produce powdered ingredients with good color, physical properties, and retention of betalains. Drying studies showed that drying rate could be increased somewhat by increasing temperatures from 75 to 95 °C, with drying times ranging from 160 to 115 min. Drying times were substantially shorter than for powders produced by freeze drying (FD) (26 h) or hot air drying (HAD) (~ 6 h). Properties such as flowability or color did not depend on drying temperature. VBD beet powders had a red-purplish color that was slightly darker (L* = 25.74) than for freeze-dried powders (L* = 38.92). In contrast, HAD samples were much darker than VBD or FD powders, and showed signs of browning. Flowability was improved by the addition of maltodextrins, but at the expense of some increase in drying time. VBD powders were less hygroscopic than FD powders, but reached the same final moisture content. HAD powders were less hygroscopic. VBD samples had slightly lower betalain levels (261–273 mg betanin/g dry beet) than FD powders (291.2 mg betanin/g dry beet). Both had much greater levels than HAD powders (127.8 mg betanin/g dry beet). Powder dried at 95 °C without maltodextrin was optimal as it dried most quickly and had minimal betalain loss.