Betalain Content and Antioxidant Activity of Beta vulgaris : Effect of Hot Air Convective Drying and Storage

Beet root (Beta vulgaris) powder is a good natural food colorant because it contains significant amounts of red-colored betalain pigments. There is increasing interest in the use of natural food colors, which provide health benefits like antioxidant activity. This article reports a study of the effects of convective hot air drying on retention of betalain pigments and antioxidant activity. A wide range of drying temperatures (50–120C) was used for the study. Drying at 50–65C gave best pigment retention (betacyanin: 5.1 and betaxanthin: 2.4 mg/g dry beet powder), which was the same as that in freeze-dried samples. Total phenolic content and antioxidant activity were higher than freeze-dried samples that increased with increase in drying temperature (1.2–1.6 mg gallic acid equivalents/g and 3.9–6.4 μM trolox equivalents/g, respectively). Storage studies showed up to 50% degradation of pigments and slight increase in antioxidant activity in 5 months. Practical Applications Complexed by small land holdings, the lack of cold storage chains and unorganized transport, post-harvest losses in developing countries like India amount to nearly 40%. While farmers continue to look for improved profitability, processing of vegetables for possible value addition is almost negligible. One such option is dehydration of vegetables (for dry soup mixes, dry ready-to-cook food items) using simple convective tray drying. For commercial feasibility, there is a need to optimize the process for reduction of time and energy, achieving quality retention in terms of color, nutrients and rehydration ratio. In view of this, a small demo plant for farmers of 100 kg/batch tray drying process capacity has been set up by our group in the state of Maharashtra, India.