Mathematical Modeling of Drying Kinetics and Quality Characteristics of Shrimps Dried under a Solar–LPG Hybrid Dryer

Heat and Mass Transfer in Shrimp Hot-Air Drying: Experimental Evaluation and Numerical Simulation

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0-62.9 W/m2∙K and 0.007-0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10-10-8.5 × 10-10 m2/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data (R2≥ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process.

Quality evaluation of improved and traditionally dried Bombay duck (Harpodon nehereus) through biochemical, microbiological, and organoleptic analysis

The study was conducted to compare the quality and shelf life of traditionally dried (collected from the local markets) Bombay duck (Harpodon nehereus) with improved dried products (produced using a newly developed fish dryer) to assess its suitability. The quality of these products was evaluated through organoleptic, water reconstitution, nutritional, chemical, and microbiological characteristics. The organoleptic quality of improved dried fish was excellent while those produced traditionally were with grayish and dark brown color, rancid odor, and soft and fragile texture with insect infestation. The water reconstitution properties of the improved dried sample were 75.71% and 89.39% at room temperature and 80 °C, respectively, which were comparatively higher than the traditional dried products. The protein, ash, and contents were significantly higher in improved dried fish products while the lipid and total volatile base nitrogen (TVB-N) content were much lower than those of market-dried samples. The total viable counts (TVC) of bacteria were significantly higher in the traditional products which indicated poor quality. To find out the best storage method, dried fish was kept at three different conditions: in the open air at room temperature, in a sealed pack at room temperature, and a sealed pack at refrigeration temperature (4 °C). The shelf life of the products in different storage conditions was evaluated by estimating their moisture, protein, lipid, ash, TVB-N, and TVC values. The products kept at 4 °C temperature was found almost unaltered in terms of their nutritional properties after 4-months storage period. Results indicated that the newly developed fish dryer produced high-quality dried fish products with longer shelf life can be expected if the dried fish is stored at 4 °C refrigeration temperature. Our findings will be a valuable tool for the fish processors to ease the fish drying process and its storage that will enable them to commercially supply good quality dried Harpodon nehereus in the market chain at a low-cost.