Busarakorn Mahayothee

Equilibrium Moisture Content and Heat of Sorption of Longan (Dimocarpus longan Lour.)

The equilibrium moisture contents of longan were determined experimentally using the dynamic method at temperatures ranging from 30 to 50°C and water activity ranging from 11 to 97%. The sorption isotherm curves of longan were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models were tested to fit the experimental isotherm data of longan. The GAB model fitted the best to the experimental data of longan and the modified Oswin model was the next to the GAB model. The agreement between the best-fitted models and experimental data was excellent. The isosteric heats of sorption, determined from equilibrium data using the Clausius-Clapeyron equation, were found to be a function of moisture content.

Solar Drying of Peeled Longan Using a Side Loading Type Solar Tunnel Dryer: Experimental and Simulated Performance

This article presents experimental and simulated results of drying of peeled longan in a side-loading solar tunnel dryer. This new type of solar tunnel dryer consists of a flat-plate solar air heater and a drying unit with a provision for loading and unloading from windows at one side of the dryer. These are connected in series and covered with glass plates. A DC fan driven by a 15-W solar cell module supplies hot air in the drying system. To investigate the experimental performance, five full-scale experimental runs were conducted and 100 kg of peeled longan was dried in each experimental run. The drying air temperature varied from 32 to 76°C. The drying time in the solar tunnel dryer was 16 h to dry peeled longan from an initial moisture content of 84% (w.b.) to a final moisture content of 12% (w.b.), whereas it required 16 h of natural sun drying under similar conditions to reach a moisture content of 40% (w.b.). The quality of solar-dried product was also good in comparison to the high-quality product in markets in terms of color, taste, and flavor. A system of partial differential equations describing heat and moisture transfer during drying of peeled longan in this solar tunnel dryer was developed and this system of nonlinear partial differential equations was solved numerically by the finite difference method. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5. The simulated results agreed well with the experimental data for solar drying. This model can be used to provide the design data and it is essential for optimal design of the dryer.

Finite Element Simulation of Drying of Longan Fruit

A two-dimensional finite element model has been developed to simulate moisture diffusion in longan fruit during drying and moisture diffusivities of the components of longan fruit determined experimentally are used in this simulation. Shrinkage of the flesh of longan during drying is also taken into account. The finite element model is programmed in Compaq Visual FORTRAN version 6.5. This finite element model satisfactorily predicts the moisture diffusion during drying. Moisture contents in the different components in the longan fruit during drying are simulated. Moisture content profiles of the longan fruit are also predicted. Knowledge gained from this study will be useful in the understanding of the transport processes in the different components of the longan fruit.

Moisture Diffusivity Determination of Different Parts of Longan Fruit

The components of the longan fruit were modeled as sphere for seed, cylinder for seed stalk, and slab for seed coat, shell, and flesh. The moisture diffusivities were determined by minimizing the sum of square of derivations between the predicted and experimental values of moisture content of thin layer drying under controlled conditions of air temperature and relative humidity. Experimental data were obtained from thin layer drying of the components in the form of sphere for seed, cylinder for seed stalk and slab for seed coat, shell and flesh. Air temperatures of 50, 60, 70, and 80°C and relative humidity in the range of 1.5–13.33% were used. The mean diffusivity of flesh of longan fruit increased with temperature, but the diffusivities of shell, seed coat, seed, and seed stalk were independent of temperature. The moisture diffusivities of shell and seed coat were much lower than those of the other parts of the longan.

Measurement and Modeling of Moisture Sorption Isotherm of Litchi (Litchi Chinensis Sonn.)

The equilibrium moisture contents of litchi (Litchi Chinensis Sonn.) were experimentally determined using the dynamic method at temperatures of 30, 40, and 50°C over a range of relative humidity values of 12 to 95%. Five models were tested to fit the experimental isotherm data of litchi. The GAB model fitted the best to experimental isotherm data. The agreement between experimental and predicted values of this model is excellent (RMSE 1.8 to 3.4%). The isosteric heats of sorption water were also determined from the equilibrium data using the Clausius-Clapeyron equation and it was found to be a function of equilibrium moisture content.

Compositional and functional dynamics of dried papaya as affected by storage time and packaging material.

Papaya has been identified as a valuable source of nutrients and antioxidants, which are beneficial for human health. To preserve the nutritional properties after drying, appropriate storage specifications should be considered. This study aimed to investigate the quality and stability of air-dried papaya in terms of quality dynamics and behavior of bio-active compounds during storage for up to 9 months in two packaging materials: aluminum laminated polyethylene and polyamide/polyethylene. Samples with moisture content (MC) of 0.1328 g g(-1) and water activity (aw) of 0.5 were stored at 30 °C and relative humidity (RH) of 40-50%. The MC, aw, degree of browning (DB) and 5-hydroxymethylfurfural (HMF) content were found to notably increase as storage progressed. On the contrary, there was a significant decrease in antioxidant capacity (DPPH, FRAP and ABTS), total phenolic (TP) and ascorbic acid (AA) contents. Packaging in aluminum laminated polyethylene under ambient conditions was found to better preserve bio-active compounds and retard increases in MC, aw and DB, when compared to polyamide/polyethylene.

Phenolic Compounds, Antioxidant Activity, and Medium Chain Fatty Acids Profiles of Coconut Water and Meat at Different Maturity Stages

Coconut is grown in tropical and subtropical areas worldwide. The endosperm (water and meat) is consumed and processed in different forms. This study investigated the antioxidant activities and identified the phenolic compounds existing in the water and meat of coconut fruits at three different maturity stages, i.e., 180, 190, and 225 days after pollination from two planting areas in Thailand. Total phenolic content and antioxidant activity indices increased as the coconut matured from 180 to 190 days after pollination and then decreased or remained unchanged at 225 days after pollination. Catechin and salicylic acid were the major phenolic compounds found in the water, while gallic, caffeic, salicylic, and p-coumaric acids were found in the meat. The fat content of the meat increased significantly with maturity stage. Medium chain fatty acids profiles were also analyzed. The results are important for producers, processors, and consumers to realize an optimal quality and functionality of coconut water and meat when used for specific purposes.

Experimental and Simulated Performances of a Batch-Type Longan Dryer with Air Flow Reversal Using Biomass Burner as a Heat Source

This article presents experimental performance of a batch-type longan dryer using a biomass burner with air flow reversal and also presents modeling of the longan dryer for drying of whole longan. The dryer essentially consists of a biomass burner and a drying bin with an arrangement for periodic air flow reversal. Three drying runs with loading capacity of 2,000, 1,500, and 1,000 kg of whole longan were carried out. There was no significant difference in temperatures in different positions (except inlet and outlet) inside the dryer (p < 0.05) or moisture content inside the dryer (p < 0.05). Whole longan was dried from an initial moisture content of 74% (wb) to a final moisture content of 14% (wb). The drying time of whole longan in the longan dryer was 60, 54, and 48 h for 2,000, 1,500, and 1,000 kg loading, respectively. The quality of dried product was also good in comparison to the high-quality product in markets. To simulate the performance of the longan dryer for drying of whole longan, a set of partial differential equations was developed and the equations were solved using the finite difference technique. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5 (Compaq Computer Corp., TX). The simulated moisture contents agreed well with the experimental data. This model can be used to provide the design data and it is also essential for optimal dryer design.