Evaluation of Physicochemical Characteristics, Bioactive Properties, Drying Kinetics, and Rehydration of Convective Dried Autumn Olive Berries as a Source of Functional Food Ingredients

Abstract

Autumn olive berries (AOBs) are a good source of natural antioxidants and compounds associated with protective effects on health. The current study investigated the possible impacts of the convective drying process on textural, morphological, phenolic compounds, and antioxidant properties of AOBs. Four drying temperatures (50, 60, 70, and 80 degrees C) in addition to three air velocities (0.5, 1.0, and 1.5 m/s) were applied. The fresh AOBs contained 77.90% moisture, 4.37 pH, and 16.90% total soluble solids. The phytochemical data of the fresh sample revealed that it contained 1739.95 mg/kg total phenolic (TPC), 4370.69 mg/kg total flavonoid (TFC), 150.69 mg/kg lycopene content (LC), 50.20 mmol/g DPPH and 37.38 mmol/g FRAP. Furthermore, the TPC, TFC, lycopene, DPPH, and FRAP values of dehydrated AOBs were evaluated. It was observed that the convective drying increased the TPC, TFC, and antioxidant properties under all the drying conditions, giving the highest values at 80 degrees C. The AOBs dried at 80 degrees C contained the highest level of 96,592.22 mg/kg TPC, 476.97 mg/kg LC, 6.57 mg/kg gallic acid, 9.66 mg/kg catechin, 1.80 mg/kg benzoic acid, 2.13 mg/kg salicylic acid, 37.24 mg/kg ellagic acid, and 8.83 mg/kg quercetin-3-glucoside. Fruits dried at 60 degrees C contained 1873.09 mg/kg, a higher flavonoid content. The TPC, TFC, LC, and DPPH, increased with dried compared with fresh state. The color values (L*, a*, and b*) of AOBs were decreased by drying, and the highest level of increment E (10.89) was detected at 50 degrees C. Furthermore, the dried autumn olive at 80 degrees C and 1.5 m/s air velocity provided high hardness, chewiness, and gumminess of 6764.23, 1691.83, and 2989.16, respectively. The result of drying air velocities revealed no significant effects on rehydration, textural properties, and total color change. The air velocity of 1.5 m/s presented the highest values of shrinkage, hardness, antioxidant contents, and antioxidant activity for all dried samples than other air velocities. Midilli model was the best-fitted model describing the drying kinetic of AOBs, and the Weibull model described well the rehydration behavior of dried AOBs. The dried AOBs were statistically much more hardness, gumminess, and chewiness than the fresh AOBs. The present study highlighted the potential of dried AOBs as a good source of various nutrients that maintain human health with higher antioxidant properties compared with fresh fruit. These results indicate that the best drying conditions to have dried AOBs with high antioxidant properties were at 80 degrees C and 1.5 m/s. The dried AOBs obtained at these drying conditions can be used on the industrial scale for multi-purposes.