MODELLING THE DRYING KINETICS OF PRETREATED BEETROOT FRUIT (BETA VULGARIS.L).

Abstract

Beetroot is a rich source of protein, antioxidant and minerals which are vital in human nutrition but highly susceptible to spoilage due to high moisture content. An understanding of its drying kinetics will promote value addition and income obtainable through beetroot production and processing. The most common method of preservation is drying but the dried products obtained are of reduced nutritional and bioactive qualities. Hence, the need for its pretreatment. The research is aimed at modelling the drying kinetics of pretreated beet root fruit. The beetroot fruits were pretreated using osmotic dehydration with sodium chloride and hot water blanching and thin layer were dried with five different air-drying temperatures (40, 45, 50, 60, 70 °C) with the air velocity of 1.4 m/s 2 . This study was to investigate the effect of drying on nutritional, bioactive content and also the best drying thin layer model for predicting the drying kinetics of dried pretreated beetroot fruit slices. The drying data were fitted into thirteen different mathematical thin layer drying models to establish best thin-layer mathematical drying model for predicting the drying kinetics of ackee aril apple using relevant statistical tools. The drying process took place mainly in the falling rate period indicating that water removal at the initial stage of the drying process was high and there was a rapid decrease as drying continued until equilibrium was reached. The drying time reduced as drying temperature increased from 40 to 70 °C for both treated and untreated beetroot fruit samples. The longer drying time observed for sun drying give rise to products of lower quality, thus the need for the use of alternative drying methods to achieve reduction in drying time. Pre-treated beetroot fruit slices employed in this study enhance moisture evaporation and hence improves drying rate. The result showed that osmotic-dehydrated beetroot slices had the highest value of vitamin C for all dried samples than hot water blanched samples. An increase in air drying temperature generally decreased the vitaminC content and total phenolic content of the dried beetroot fruit samples. It can be concluded that the dehydration in osmotic solutions improves the quality of the final products in terms of the content of biologically active component. High temperatures and long-term drying were found to be harmful to the bioactive potential and oxidative degradation of the dried products. The important aspect of the technology in drying is the mathematical modelling of the drying processes. The modelling results showed two models Midili-Kucuk and Hii et al. models were the best models for these research work based on the higher correlation coefficient (R2) and lowest reduced chi-square (x2) and root mean square error (RMSE) value. The values of effective moisture diffusivity increased as the temperature increased and it is temperature dependent. It was observed from the result that the value effective moisture diffusivity is higher in pre-treated beetroot fruit than the untreated beetroot fruit indicating the pre-treatment had higher rate of moisture removal faster than the untreated.