Effect of Drying Temperature and Air Velocity on Bioactive Compounds and Antioxidant Capacity of Germinated Kiwicha and Camu Camu Peel Flours

Drying is an essential operation for preserving plant-based raw materials; however, processing conditions may affect their bioactive compound content and antioxidant capacity. This study aimed to evaluate the effects of drying temperature and air velocity on bioactive compounds and antioxidant capacity in germinated kiwicha (Amaranthus caudatus L.) flour and camu camu (Myrciaria dubia) peel flour using response surface methodology (RSM). Kiwicha grains of the Centenario variety were subjected to germination following the methodology described by Paucar-Menacho et al. (2017). For the extraction of bioactive compounds, water and citric acid solutions at concentrations of 0.25, 0.50, 1, and 2% were evaluated, using total phenolic content (TPC) as the selection criterion. Water was selected as the extraction solvent for germinated kiwicha flour, while a 1% citric acid solution was selected for camu camu peel flour. Subsequently, two independent variables were evaluated: drying temperature (45–65 °C) and air velocity (2.5–3.5 m/s), using 11 experimental runs for each raw material. The response variables were antioxidant capacity measured by the oxygen radical absorbance capacity (ORAC) assay, total phenolic content (TPC), and proanthocyanidin content. Data were analyzed using quadratic regression models and analysis of variance (ANOVA) with STATISTICA software.

For germinated kiwicha flour, the highest experimental ORAC value (1457.95 µg Trolox equivalents/100 g) and TPC (2270.28 µg gallic acid equivalents/100 g) were obtained at 62 °C and 3.35 m/s, whereas the highest proanthocyanidin content (8462.63 µg catechin equivalents/100 g) was recorded at 48 °C and 3.35 m/s. For camu camu peel flour, the highest ORAC value (669.62 µg Trolox equivalents/100 g) and TPC (18320.35 µg gallic acid equivalents/100 g) were observed at 62 °C and 3.35 m/s, while the highest proanthocyanidin content (3576.98 µg catechin equivalents/100 g) was obtained at 65 °C and 3.0 m/s. The quadratic models explained 77.7% and 83.6% of the variability in ORAC and TPC for germinated kiwicha flour, respectively, and approximately 77% and 64% for camu camu peel flour. Nonlinear effects and interactions between drying factors were observed; however, the models exhibited significant lack of fit, and no statistically significant effects were identified for proanthocyanidin content.

In conclusion, drying conditions influenced the bioactive properties of both flours, although the quadratic models showed significant lack of fit, limiting the reliability of their predictions. The combination of 62 °C and 3.35 m/s yielded the highest experimental ORAC and TPC values for both matrices and represents a promising processing condition requiring validation. The resulting flours will be used to obtain aqueous extracts for the subsequent microencapsulation of bioactive compounds. This research was funded by CONCYTEC and PROCIENCIA under Grants E033-2023-01-BM (Contract No. PE501084298-2023-PROCIENCIA) and E077-2023-01-BM (Contract No. PE501093201-2024-PROCIENCIA).