Application of Fractional Calculus-Based Anomalous Diffusion Model for Drying Analysis of Large Grapes Subjected To Micro-Perforation Pretreatment

Abstract

The study aimed to assess the potential of using needle micro-perforation pretreatment at various piercing lengths as an alternative to dipping in alkaline liquor solution for the hot air drying process of large grapes at temperatures of 60, 70, and 80 degrees C. Fick's second law and anomalous diffusion model based on the fractional calculus approach were used to analyze the drying curves and estimate effective diffusivity (D-eff). Needle micro-perforation on drying kinetics and some physicochemical properties (water activity, pH, titratable acidity, rehydration rate, shrinkage ratio, and color) of hot air dried Kavacik grapes (Vitis vinifera L. cv Alphonse Lavall & eacute;e) were investigated. The anomalous diffusion model fit the experimental data better and revealed super-diffusive behavior (alpha > 1). The effective diffusivity coefficients varied between 1.00 x 10(-10) to 6.47 x 10(-10) m(2)/s. The pretreatment at various piercing lengths showed no significant impact on water activity and color (P > 0.05). However, it did have a significant effect on pH, titratable acidity, rehydration rate, and shrinkage degree (P < 0.05). MG1.5 drying conditions at 60 degrees C were found to be the most suitable process conditions for achieving energy-efficient drying (high D-eff: 3.87 x 10(-10) m(2)/s) of grapes while preserving their highest-quality attributes related to drying (a(w): 0.54, RR: 1.95, pH: 4.31, Delta E: 3.38 and SR: 0.98). The results revealed that the needle micro-perforation pretreatment provided better color and water activity properties in dried grapes, and the drying time was reduced at even low temperatures. It has been shown that micro-perforation can be an environmentally friendly alternative method to chemical pretreatment in grape drying.