# Thin-Layer, Intermittent, Near-Infrared Drying of Two-Phase Olive Pomace: Mathematical Modeling and Effect on Recovery of Bioactive Compounds and Antioxidant Activity

## TL;DR

This study explores using near-infrared drying to efficiently process olive pomace while preserving its valuable bioactive compounds and antioxidant properties.

## Contribution

The study introduces a novel combination of near-infrared drying with analysis of bioactive retention and antioxidant activity in olive pomace.

## Key findings

- NIR drying at 140 °C reduced drying time by 68% compared to 70 °C and preserved high levels of bioactive compounds.
- NIR drying outperformed oven-drying and matched freeze-drying in preserving bioactive content, except for tyrosol.
- Midilli’s model best described the drying behavior with high accuracy (r2 ≥ 0.99839).

## Abstract

The present study examined the drying kinetics of two-phase olive pomace (OP) using near-infrared (NIR) thin layer intermittent drying at 70–140 °C. For the first time, this approach was combined with color, bioactive compound retention and antioxidant activity assessment. Among tested models, the Midilli’s semi-empirical model best described the drying behavior (r2 ≥ 0.99839, RMSE ≤ 0.01349). Effective diffusivity ranged from 1.417 × 10−9 to 5.807 × 10−9 m2/s, and activation energy was calculated at 23.732 kJ/mol. Drying at 140 °C reduced time by 68% compared to 70 °C. The corresponding sample had the highest total phenolics content, antioxidant activity (DPPH●, CUPRAC assays) and triterpenic acid (maslinic, oleanolic) content, and a significant amount of hydroxytyrosol, despite the increased sample browning. Compared to oven-drying (140 °C), NIR was equal or better and 3.2-fold faster. The same was evidenced compared to freeze-drying, except for tyrosol recovery (1.2-fold lower in NIR). These findings were obtained using two different OP industrial samples. Given that NIR is already used industrially for food drying, the present study offers proof-of-concept for its application as a rapid and eco-friendly pretreatment of OP for food and feed uses. However, scalability challenges and the limitations of semi-empirical modeling must be addressed in the future to support industrial-scale implementation.