Solar-dried fig quality: A comparative study of ultrasonic, ohmic blanching, and sulfur dioxide pre-treatments on bioactive retention, antioxidant activity, and physical properties

This study evaluated the impact of ultrasonic treatment (US), ohmic blanching (OH), and sulfur dioxide (SO₂) pre-treatments on solar-dried Izmir figs. Fresh figs were subjected to US (10 or 15 min), OH (30 or 90 s), or SO₂ treatments before solar drying. Results demonstrated that US-10 min achieved the highest rehydration ratio (3.40 ± 0.27) despite substantial shrinkage (69.81 %) and increased darkening (L* = 51.98 ± 2.65). OH-90 s enhanced flavonoid retention but increased shrinkage (63.52 ± 2.17 %) with the lowest lightness value (50.35 ± 2.61). SO₂ pre-treatment maintained superior color (highest L* = 61.10 ± 1.88; lowest ΔE = 29.34 ± 1.40) and preserved antioxidant activity, yet showed browning comparable to untreated controls. US-15 min optimally retained ascorbic acid, while OH-30 s and SO₂ treatments caused significant ascorbic acid losses. Sensory evaluation revealed SO₂-treated figs had the highest overall acceptance (4.15), while US-10 min offered balanced sensory qualities (3.29) with favorable flavor ratings (4.0). The findings position US-10 min as a promising non-thermal alternative balancing drying efficiency and quality, whereas SO₂ excelled in visual appeal but requires optimization for browning control. This research provides practical insights for dried fig production, highlighting the trade-offs between physical properties, nutritional value, and visual quality.

Industrial relevance

This research addresses critical challenges facing the fig processing industry, where postharvest losses exceed 30 % globally due to rapid deterioration and inadequate preservation infrastructure. The comparative evaluation of ultrasonication, ohmic heating, and sulfur dioxide pre-treatments coupled with solar drying offers practical solutions for small-to-medium scale processors, particularly in developing regions where energy costs and environmental sustainability are paramount. The findings enable informed pre-treatment selection based on quality-cost-sustainability trade-offs. Solar drying's scalability and low operational costs, combined with optimized pre-treatments, significantly reduce processing expenses while maintaining premium market standards. The study's insights into bioactive compound retention support value-added dried fig products with enhanced nutritional profiles, aligning with consumer demand for functional foods. The research provides evidence-based guidelines for industrial implementation, facilitating technology transfer from laboratory to commercial operations.