Electroporation of stomata: effect on drying kinetics and aroma compounds of Genovese basil leaves

Abstract: The aroma components of herbs and spices are very sensitive to heat, complicating their drying process. Until now, exporters of dried herbs face the challenge of low total phenolic contents and efforts are constantly being made to improve the drying efficiency of herbs and conserve their aroma. This thesis looks at the influence of extracellular trehalose impregnated by vacuum impregnation (VI) and electroporation achieved with reversible pulsed electric field (PEF) treatment affecting stomata opening on the convective air drying kinetics, rehydration properties, colour changes and aroma preservation of basil leaves. In describing the drying kinetics of treated basil samples, attention is given to the determination of the drying rate and the effective moisture diffusivity. The results indicate that reversible electroporation of opened stomata resulted in faster drying rate (from 0.025 to 0.00039 min-1) compared to samples with opened stomata not electroporated (from 0.0202 to 0.0021 min-1) throughout the drying period. Vacuum impregnation with trehalose increased the initial drying rate of the control from 0.012 to 0.016 min-but towards the end of drying, the drying rate of the control and vacuum infused control were slightly the same (0.0025 and 0.0024 min-1) respectively. Similar trends were also observed for effective moisture diffusivity where samples with stomatal electroporation resulted in increased effective moisture diffusivity (1.857'10-9 m2 s-1) compared to samples where the opened stomata were not electroporated (1.309'10-9 m2 s-1). As a result of the increased drying efficiency, irreversible electroporation of the leaf tissue resulted in 47% reduction, reversible electroporation of opened stomata resulted in 37% reduction whilst leaves samples that were reversible electroporated but opened stomata was not electroporated resulted in 18% reduction in the drying time. The quality parameters analysed on the dried herb indicate that reversible electroporation of opened stomata resulted in less colour change, produced good rehydration properties and resulted in 1.3 to 5.7 fold increase in the major aroma compounds relative to the untreated dried samples.