Effects of temperature and foam layer thickness on collard greens powder production by foam mat drying

Abstract

Collard green is a perishable vegetable that is widely recognized for its health benefits. In this study, foam mat drying was applied to produce powdered food. The influence of Emustab® concentration on foam properties and effects of drying temperature (50–90°C) and foam layer thickness (0.5–1.5 cm) on drying kinetics, physical and bulk properties, and flowability of the powders were investigated. Response surface methodology was used to evaluate drying conditions regarding the final moisture content, hue angle, and SEC, and the desirability function was employed to optimize responses simultaneously. Shorter drying times were obtained using higher temperatures and lower foam thickness. The Midilli model best fitted the experimental data of drying with R2 = .998, RMSE = 0.020 and χ2 = 0.002. Regardless of condition, powders presented low densities, good rehydration, and flowability from poor to passable. The optimal condition was T = 72.7°C and e = 1.5 cm (D = 0.745), indicating that foam mat drying yields good quality powders with energy savings.

Practical applications: collard green is a leafy vegetable widely consumed in its fresh form, but it has a high potential for use by the food industry. Thus, this study contributes not only to the wide dissemination of knowledge about foam mat drying technique but also to the increase in the collard green consumption, due to the possibility of incorporation of the powder into different food formulations (pastas, breads, juices, etc.). The industrialization of this material can also contribute to its full use (steams are commonly discarded), reducing food waste that has been considered a problem worldwide. Therefore, the results of this study have an economic impact (full use of the food and the possibility of incorporating it into new formulations), social (increase in the producer's revenue linked to the higher added value of the food), and environmental (optimization of the process considering the reduction in consumption energy and release of CO2 to the environment).