Gasa Siyabonga, Sibanda Sipho, Workneh Tilahun S, Laing Mark, Kassim Alaika
Institute for Agricultural Engineering, Agricultural Research Council, Private Bag X519, Pretoria, South Africa.
Discipline of Bioresources Engineering, School of Engineering, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg, South Africa.
Heliyon. 2022 Feb 12;8(2):e08949. doi: 10.1016/j.heliyon.2022.e08949. eCollection 2022 Feb.
The drying of agricultural produce is an important food preservation measure. However, high energy requirements for drying, limited access to energy sources, small-medium scale farmers experience high post-harvest losses of their produce. Therefore, there is a need to develop and optimize low-cost food preservation technologies. In this study, eleven mathematical models were used to estimate the drying coefficients following non-linear regression method, in hot-air oven and naturally-ventilated solar-venturi drying to find the best fit of the moisture ration models. Sweet potato tubers were sliced at 3, 5 and 7 mm thickness sizes with and without pre-drying treatments. The prepared sweet potato slices were dried in a hot-air oven dryer at a constant temperature of 70 °C in comparison to the naturally-ventilated solar-venturi dryer with a heated ambient air that varied according to the outside environmental conditions. The drying rate of the samples in a hot-air oven dryer was higher than for those in the naturally-ventilated solar-venturi dryer. The results showed that the drying time was significantly (P < 0.05) affected by the thickness size of sweet potato slices (SPS) and that the drying took place at the falling rate period and a constant drying time. The Midilli et al. model was the best fit for predicting the moisture ratio of SPS dried in hot-air oven dryer and naturally-ventilated solar-venturi dryer based on statistical analysis (R = 0.982-0.999, χ = 4.60 × 10-5.56 × 10 and RMSE = 0.011-0.067). The D was 3.32 × 10- 6.31 × 10 m s for the naturally-ventilated solar-venturi dryer and 1.02 × 10 - 2.19 × 10 m s for the hot-air oven dryer. According to the results obtained, naturally-ventilated, solar-venturi dryer and lemon juice pre-drying treatment are the suitable application for small-medium scale drying of SPS under Pietermaritzburg conditions.
农产品干燥是一项重要的食品保鲜措施。然而，干燥所需能量高、能源获取受限，中小型农户的农产品收获后损失严重。因此，有必要开发和优化低成本的食品保鲜技术。在本研究中，采用11种数学模型，通过非线性回归方法估算热风烘箱和自然通风太阳能文丘里干燥条件下的干燥系数，以找出水分比模型的最佳拟合。将甘薯块根切成3毫米、5毫米和7毫米厚的薄片，分别进行预干燥处理和不进行预干燥处理。将制备好的甘薯片在热风烘箱中于70°C恒温干燥，与自然通风太阳能文丘里干燥器进行对比，后者的加热环境空气会根据外部环境条件变化。热风烘箱干燥器中样品的干燥速率高于自然通风太阳能文丘里干燥器中的样品。结果表明，干燥时间受甘薯片厚度尺寸显著影响（P < 0.05），干燥发生在降速期且干燥时间恒定。基于统计分析（R = 0.982 - 0.999，χ = 4.60 × 10 - 5.56 × 10，RMSE = 0.011 - 0.067），Midilli等人的模型最适合预测热风烘箱干燥器和自然通风太阳能文丘里干燥器中干燥的甘薯片的水分比。自然通风太阳能文丘里干燥器的扩散系数D为3.32 × 10 - 6.31 × 10 米²/秒，热风烘箱干燥器的扩散系数D为1.02 × 10 - 2.19 × 10 米²/秒。根据所得结果，自然通风太阳能文丘里干燥器和柠檬汁预干燥处理适用于彼得马里茨堡条件下中小型规模的甘薯片干燥。
