Continuous and Intermittent Drying of Rough Rice: Effects on Process Effective Time and Effective Mass Diffusivity

Joan Carlos Alves Pereira,Antonio Daniel Buriti De Macedo,Bruno Adelino De Melo,Wilton Pereira Da Silva,Josivanda Palmeira Gomes,Antônio Gilson Barbosa De Lima,Rossana Maria Feitosa De Figueirêdo,Ângela Maria Santiago,Alexandre José De Melo Queiroz

doi:10.3390/agriculture10070282

Joan Carlos Alves Pereira, Antonio Daniel Buriti De Macedo + Show 7 more

Open Access

https://doi.org/10.3390/agriculture10070282

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Abstract

The choice of the drying process plays a key role in reducing the costs of electricity consumption in the food industry. Thus, this study aimed to evaluate continuous and intermittent drying of rough rice, using empirical and diffusion models to describe the drying kinetics, considering only effective time of operation to compare and evaluate these processes. Experiments were carried out during the month of April 2018, in Campina Grande, Paraiba Brazil, and were conducted with continuous and intermittent drying of rough rice grains (about 20 g, each experiment) using a fixed-bed dryer with constant power, at temperatures of 50 and 70 °C. For the intermittent experiments, the intermittency ratio was α = 2/3 and the drying periods were 10 and 20 min, with intermittency periods of 20 and 40 min, respectively. Comparison between continuous and intermittent drying kinetics indicated reduction in the effective time of all intermittent drying experiments, reaching up to 32.2%, hence promoting energy saving. It was also found that a one-dimensional diffusion model with boundary condition of the first kind properly described all rough rice drying processes and that the effective mass diffusivity is higher in intermittent drying, compared to continuous drying at the same temperature.

Highlights

Among the cereals produced in Brazil and in the world, rice (Oryza sativa L.) is considered a crop of great economic and food importance, being considered as the main food of more than half of the world population, occupying the second place in production and extension of cultivated area, only behind wheat [1]
The mean values of equilibrium moisture content, Xeq, obtained for each experiment at 50 ◦ C were 0.072, 0.084 and 0.066 (d.b.) for continuous drying, intermittent drying with tin = 10 min and intermittent drying with tin = 20 min, respectively; and 0.036, 0.043 and 0.031 (d.b.)
122 min for intermittent drying with tin = 10 min

Summary

Introduction

Among the cereals produced in Brazil and in the world, rice (Oryza sativa L.) is considered a crop of great economic and food importance, being considered as the main food of more than half of the world population, occupying the second place in production and extension of cultivated area, only behind wheat [1]. In order to reduce post-harvest waste of agricultural products and increase their shelf life, several techniques are used, such as pasteurization, cooling, osmotic dehydration, among others. Among these techniques, drying is one of the oldest, most simple and most widely used methods in food preservation [3,4,5,6,7]. Drying is considered to be a fundamental operation to maintain the quality terms of energy consumption, improving the quality of the dried material, when compared to of products for long periods of time, which is not completely possible for a fresh product

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