Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.     

Kinetics and modeling of whole longan with combined infrared and hot air

The aim of this research was to evaluate the effects of operating variables on the drying behavior of whole longan undergoing a combined infrared and hot air drying process, to determine its kinetic parameters, and to develop drying kinetic models. The single-layer drying experiments were carried out at infrared powers of 300, 500 and 700 W, drying air temperatures of 40, 60 and 80 °C, and air velocities of 0.5, 1.0 and 1.5 m/s. The samples were dried until attaining a final moisture content of 0.2 kg water/kg dry solid. The results show that the drying had a short constant rate period followed by a falling rate period in all cases. The drying rate and product temperature were significantly influenced by infrared power, temperature and velocity of ambient air. In the constant rate period, the mass transfer coefficient varied from 3.646 × 10⁻³ to 1.914 × 10⁻² m/s. It increased with increasing infrared power, but decreased as air velocity and air temperature increased. In the falling rate period, theoretical and semi-empirical drying kinetic equations were used to describe the drying kinetics of the product. It was found that the overall effective diffusion coefficient and drying constant varied from 7.012 × 10⁻¹¹ to 6.681 × 10⁻¹⁰ m²/s and 0.026 to 0.234 h⁻¹, respectively. Both parameters increased with increasing infrared power and air temperature, but decreased with increasing air velocity. Combined regression equations developed to predict the drying kinetic parameters (h_D, D_eff and k) for all three models gave a fairly good fit.