Enhancement of dried salted four-finger threadfin (Eleutheronema tetradactylum) using indirect solar dryer: An experimental study on drying kinetics and product quality

• The ISD, with a 1.0 m/s air velocity, provides a more efficient, hygienic method, reducing drying time by 18 % compared to TSD. • The ISD enables low-cost fish drying as it can be locally built and operated without reliance on electricity or fossil fuels. • The ISD prevents contamination from dust, flies, and rain, thereby enhancing hygiene and the quality of dried fish products. Traditional sun drying (TSD) of salted four-finger threadfin, which primarily relies on solar radiation, requires a prolonged drying time and often leads to uneven moisture removal and an increased risk of contamination from dust and fly oviposition. This study was aimed at investigating drying kinetics, mathematical modeling, and physicochemical properties of dried salted four-finger threadfin using indirect solar drying (ISD) under natural airflow conditions and at air velocities of 1.0 and 2.0 m/s, compared to TSD. The results indicated that moisture content (MC) decreased when drying time increased. While the ISD duration at the air velocities of 1.0 m/s and 2.0 m/s and under the natural airflow was 68, 84, and 128 h, respectively, the TSD duration was 132 h. Using ISD at 1.0 m/s exhibited the most efficient moisture reduction. That is, MC was lowered from 350 % d.b. to 115 ± 5 % d.b., which was 18 % faster than it was by TSD. The drying kinetics of the salted four-finger threadfin were best described by the Modified Henderson & Pabis model when ISD was used under natural airflow and at the air velocity of 1.0 m/s, the Saniso model when ISD was used at the air velocity of 2.0 m/s, and the Logarithmic model when TSD was applied. The effective moisture diffusivity (D eff ) of the salted four-finger threadfin ranged from 6.64 × 10⁻⁷ to 7.78 × 10⁻⁷ m²/h under the investigated drying conditions. The physicochemical compositions of the dried salted four-finger threadfin exhibited insignificant differences, compared to TSD. Indeed, drying the salted four-finger threadfin using ISD provided a cost-effective solution that can be locally constructed and operated to effectively prevent contamination from dust, flies, and rain.