Physical Quality and Carotene Content of Solar-Dried Green Leafy and Yellow Succulent Vegetables

Abstract

The effects of vegetable type, vegetable dimensions, and solar drier load on dehydration rate; and texture, color, water activity, and carotene content of solar-dried carrots, sweet potatoes, and collard greens were studied. Mean dehydration rates (moisture loss,%/hr) for solar dried loads of 430 g/m2 and 715 g/m2 were 3.3 +/- 0.30% and 3.8 +/- 0.20% for carrots and sweet potatoes, respectively. Loads of 360 g/m2 and 465 g/m2 of collard greens had dehydration rates of 6.3 +/- 0.10% moisture loss per hr. The results showed that vegetable type accounted for significant differences (p < 0.01) in dehydration rate, and beta-carotene content. Vegetable dimensions affected (p < 0.05) water activity. Solar drier load affected water activity (p < 0.01), and hue angle (p < 0.05). Beta-carotene contents (dry basis) of dehydrated carrot, sweet potato, and collard treatments were 10.9-17.4%, 7.6-9.8%, and 11.9-21.5%, respectively. Among the carrot treatments, the 5-mm thick slices packed at a load of 715 g/m2 contained the highest beta-carotene (17.4%, dry basis) and vitamin A activity (362 IU/g, dry basis), and good physical properties. For collard greens, the 2-cm and 3-cm wide strips packed at 360 g/m2 loads had the best combinations of high beta-carotene (21.5% and 17.2%, dry basis, respectively), vitamin A activity (357.2 and 293.1 IU/g, dry basis, respectively), and optimal color, texture, and water activity. Beta-carotene losses due to solar dehydration were 48.9-67.5%, 4.0-5.8%, and 1.9-19.8% (dry basis) in carrots, sweet potato and collard greens, respectively.

Retention of Provitamin A Carotenoids in Staple Crops Targeted for Biofortification in Africa: Cassava, Maize and Sweet Potato

“…Bengtsson et al, 2008 suggested that for an equivalent drying time, cultivars with higher moisture content and with higher initial carotenoid content tended to lose more carotenoids during the drying process. Mdziniso et al, 2006, also observed that sweet potato exhibited the least b-carotene loss (5-6% dry basis) whereas carrots exhibited the highest (49-68%), and their respective fresh moisture contents were 76 and 91%.…”

“…Solar drying is achieved by direct sun radiation on the material covering the solar dryer, reaching internally higher temperatures, and similar or slightly lower humidity as the outside environment. The pVAC retention in sweet potato ranged from 77 to 96% after solar-drying (Mdziniso et al, 2006, Bengtsson et al, 2008, Bechoff et al, 2009, Bechoff et al, 2010a, and Bechoff et al, 2011a. In three studies, the pVAC retention from solar-drying was not significantly (p < 0.05) different from sun-drying (Bengtsson et al, 2008, Bechoff et al, 2009, Bechoff et al, 2010a.…”

“…In one study, solar-drying showed lower total carotenoid retention in sweet potato variety MGCL01 (89%) compared to sun-drying (95%) (Bechoff et al, 2011a). Mdziniso et al, 2006 only measured the effect of solar-drying on carotenoid retention and, therefore, cannot be compared to sun-drying. The use of UV-resistant polythene material on the solar dryer did not increase carotenoid retention as compared to solar dryer with non-UV resistant materials or sun drying (Bechoff et al, 2010a).…”

Influence of Drying Processes and Pretreatments on Nutritional and Bioactive Characteristics of Dried Vegetables: A Review

“…They concluded that blanching prevented non-enzymatic browning reaction, which resulted in a relatively high value of total carotenoids and b-carotene content, as well as redness and yellowness. Steam blanching also provided good results when applied to collard greens, which retained 55-98 % of b-carotene [57]. Artichoke byproducts Ohmic blanching was the fastest method to inactivate the peroxidase enzyme at 85°C and provided higher vitamin C and total phenolic content retention than water blanching [36] Blanching (i) Ohmic blanching (ii) (i) Water at 85 and 100°C, 120-600 s (ii) Voltage gradients of 24, V/cm, at 80°C, 0-300 s Artichoke heads Heating allowed quick and uniform heating of food product and was beneficial in terms of enzyme inactivation, colour; higher total protein and polyphenolic content in ohmically blanched samples [29] Osmotic Using lower blanching temperatures is another approach to minimizing nutrients decrease.…”

“…It usually employs water or steam at high temperatures for a short period of time. If applied under optimal conditions, blanching may improve the colour, flavour, texture, nutritional quality and overall acceptability of dried vegetables [57]. However, significant reductions in the levels of nutrients caused by blanching were reported by several authors.…”