INFLUENCE OF DRYING PROCESSES ON QUALITY ATTRIBUTES, BIOACTIVE COMPOUNDS AND ANTIOXIDANT ACTIVITIES OF GRAPE SWEET SAPPHIRE

The grape is one of the most consumed fruits in the world, with an intense purple color, high sugar content, and phenolic compounds. It is considered an economically important raw material for developing many products. The grape is a perishable product like the other fruits. It is necessary to adopt conservation methods to reduce the moisture content, improve storage and prevent the deterioration of these foods. Drying is one of the oldest food preservation methods, reducing moisture content and changing the raw material in a new product. Many changes occur in food during drying. It is necessary to evaluate or improve drying conditions. The present study evaluated the convective drying in grapes Sweet Sapphire. Grapes were dried in a convective dryer at 45, 55, and 60 °C. The Page Model was adjusted to represent the drying kinetics. The quality of grapes was determined for physical-chemical (soluble solids; moisture; water activity; hardness; color), total phenolics (TPC; Folin-Ciocalteu method), anthocyanins content (pH differential method), and antioxidant characteristics (ABTS; DPPH; FRAP) before and after drying. The drying process was stopped when it reached the final moisture of 20%. At 60 °C, the value was reached in 24 h, and time increased to 30 h at 55 °C and 55 h at 45 °C. The drying process performed at 55 °C and 60°C compared to drying at 45 °C reduced 45% and 56%, respectively. A good fitting was achieved for the Page model (R2 > 0.99). Results indicated that the different temperatures did not affect the k and n constant. Furthermore, the n values (0.848-1.454) suggest that grape drying presents other mechanisms apart from the purely diffusive (n > 1). The values of effective moisture diffusivity ranged between 2.64 × 10−10 and 6.18 × 10−10 m2/s and increased with temperature. In addition, the activation energy of 49.97 kJ/mol was obtained. Regarding the quality properties and color of grape samples, significant differences were found between temperatures for hardness, L*, and color difference. During drying, TPC was evaluated at different times until the drying process was completed. The higher values obtained with total phenolic content were at 55°C (963,53 mg GAE/100g) and used for anthocyanin and antioxidant capacity. Total anthocyanins for fresh samples were 68.01 mg M-3-G /100g. This value increases with drying (94.69 mg M-3-G/100g). The same occurs with ABTS (600.89 mM TEAC/g) and FRAP assays (7.722.83 µM FeSO4/g). No significant increase in DPPH assays was found between fresh and dried samples. Removing water by the drying process concentrated bioactive compounds such as phenolics and anthocyanins and consequently increased the antioxidant capacity of dried grapes, except for the DPPH assay. The results of this study suggest that the use of higher temperatures (55°C and 60°C) positively influences the drying of grapes, with a reduction in drying time and an increase in moisture diffusivity. Therefore, evaluating the drying process, quality parameters, and the phenolic compounds were essential to determine the best temperature (55°C) for drying sweet sapphire grapes without damaging the quality of the final product.