Effects of mild infrared and convective drying on physicochemical properties, polyphenol compounds, and image features of two date palm cultivars: ‘Mejhoul’ and ‘Boufeggous’

Abstract

This study investigated the effect of convective (COND) and infrared drying (INRD) on key physicochemical parameters and image texture features of ‘Mejhoul’ and ‘Boufeggous’ date palm cultivars. Overall, results showed dissimilar effects of drying on the assessed quality attributes for each cultivar. COND increased significantly total polyphenols and flavonoid content as compared to fresh fruit and seems to have a stronger and nuanced effect on ‘Boufeggous’ than on ‘Mejhoul’ for the whole polyphenol profile. Whereas, INRD induced small changes. Additionally, the two drying techniques affected slightly and differently the content of glucose and fructose with a significant decrease of total sugars and glucose in infrared dried ‘Boufeggous’. Furthermore, a significant increase was observed for total soluble solids while water activity decreased significantly in the two cultivars upon convective and infrared drying. Acidity, pH, ash, and hardness seem to be more influenced by COND than INRD. For skin color, the browning index changed significantly and in an opposite manner for the two cultivars after drying. In contrast, the behavior of these cultivars under COND and INRD was complex with more influence of INRD on chroma, a∗ and b∗ features for both cultivars. The image features indicated the highest correctness level of discrimination between fresh and infrared dried fruit samples. X-ray images of fresh, convective-dried, and infrared-dried dates showed that the flesh structure/density depends on the cultivar and drying technique. Taken together, our findings highlight INRD and COND as promising drying techniques that can be employed in the processing and postharvest storage of date and food products.