Infrared drying of Kinnow (Citrus reticulata) peel waste: kinetics and quality characterization

In the present work, infrared drying (IRD) technique was used to process kinnow mandarin peels at different temperatures and to check its influence on quality characteristics. The drying behavior of peels was mapped using the semi-empirical models. The moisture, water activity, total phenol content (TPC), total flavonoid content (TFC), DPPH radical scavenging activity, total carotenoids, and color attributes of fresh and dried peels were explored. The analyzed data revealed that with a rise in the drying temperature (50 to 70°C), drying time of peels decreased, and the page model was observed to fit appropriately to the drying data with the maximum R² values (0.99995–1) and the minimum RMSE (0.140 × 10⁻³ to 0.571 × 10⁻³), and χ² (0.002 × 10⁻⁴ to 0.103 ×10⁻⁴). Arrhenius equation was employed to obtain the activation energy of 34.45 kJ/mol. IRD temperature exhibited a significant effect (p<0.05) on the TPC, TFC, and total carotenoid content. The percent retention of phenols and flavonoids in kinnow peels varied from 83 to 93% and 70 to 81%, respectively. DPPH radical scavenging activity significantly increased up to 25% with increasing IRD temperature. IRD of peels at 60°C led to the retention of most of the total phenols, and enhancement of antioxidants and color characters (L* & b*). Furthermore, 10% incorporation of kinnow peel dietary fiber resulted in good overall acceptability score (8.00) of muffins. The present findings help to better understand the IRD of kinnow peels and map the drying behavior to maintain quality characters.