DRYING OF ZUCCHINI AND CARROT SLICES: INFLUENCE OF TISSUE STRUCTURE ON MASS TRANSFER PARAMETERS

The present work aimed mainly at investigating the influence of tissue structure on dehydration characteristics of zucchini and carrot. Microwave power levels of 100, 350, 550 and 750 W used to dehydrate the samples with thicknesses of 3, 5, 7 and 9 mm. The results showed that moisture removal from the slices occurred in a short accelerating period at the process beginning followed by a falling rate period. The moisture diffusivity increased with both increasing microwave power and the samples thickness where the average values for zucchini and carrot slices changed from 1.17×10-8 to 9.42×10-8 and from 0.73×10-8 to 5.51×10-8 m2 s-1, respectively. The average activation energy for zucchini and carrot slices varied in the range of 1.22–1.68 and 1.57–1.84 W g-1, respectively and decreased with increasing samples thickness.

Mathematical models to describe the drying process of Moringa oleifera leaves in a convective-air dryer

Drying kinetics of Malaysian Moringa oleifera leaves was investigated using a convective-air dryer. The drying parameters were: temperature (40, 50, 60, 70 °C), air velocity (1.3 m s^–1, 1.7 m s^–1). The drying process took place in the falling rate period and there was an absence of a constant rate period in this experiment. Six mathematical models (Lewis, Henderson and Pabis, Wang and Singh, Peleg, Page, and logarithmic) were selected for the description of drying characteristics of the leaves. The Wang and Singh model was determined as the best model based on the highest overall coefficient determinant (R²) and the lowest overall root mean square error (RMSE). The effective diffusivity (D_eff) was also calculated which was in the range of 3.98 × 10^–11 m² s^–1 to 1.74 × 10^–10 m² s^–1.An Arrhenius relation was constructed to determine the activation energy for the samples in the convective air dryer. The activation energy for M. oleifera leaves was 39.82 kJ mol^–1 and 33.13 kJ mol^–1 at drying velocities of 1.3 m s^–1 and 1.7 m s^–1, respectively.

Thin layer drying kinetics of Freshwater Clawed Lobsters (Astacus astacus)

Fresh-water Clawed Lobsters is seafood consumed in its cooked, dried or semi-dried state. Drying is a veritable technology for its storage beyond immediate consumption. This study thus, investigated the drying behaviour of the lobster on thin-layers. A laboratory convective oven dryer was used as the heating source, on the temperature range of 50 – 100°C applied in a varying manner on multiples of 10°C. The layer thickness was about 20-mm. As with high moisture sea foods, the drying profile showed a typical falling rate period with no distinct constant rate period for all the temperature levels used in this work. Moisture loss (diffusion) data obtained from the experiments were fitted to three popular semi-empirical thin-layer models of Page, Lewis, and Henderson-Pabis, respectively, and their suitability was validated using statistical parameters (of R2, RMSE and χ2). This was done to select thin-layer model that would suitably describe the drying kinetics of the samples over the range of temperature levels chosen in this work. Consequently, the Page model and that of Henderson-Pabis respectively were taken to have reliably predicted the drying behaviour of the samples at the chosen temperature levels. The effective diffusivity and the temperature-related activation energy values ranged from 2.239 × 10−8 m2/min - 4.005 × 102/min and 28.5kJ/mol, respectively. Drying rates along with characterizing drying constants and curves also showed an exponential increase with temperature.

Anticipated Reductions in Tax Rates and Earning Management of Listed Companies: Evidence from China

The effects of tax rate changes on corporations’ earning management are not fully understood. As a transitional economy, China has listed companies with different ownership and special regulatory rules. We explore under the expectation of tax reduction whether there are differences in the way and degree of earnings management implemented by different types of companies. Our study shows that firms under the anticipation of tax reduction make use of earning management, including delaying sales, taking unusual income-decreasing discretionary accruals, and so on, which leads to lower income in higher tax rate period. We find that private enterprises have more attention to reduce earning in the higher tax rate period than state-owned enterprises (SOEs), indicating that the ownership has effect on the extent of earning management. Moreover, under the specific regulations in Chinese stock market, we find that for those listed companies with negative net profit in the previous year, the priority is how to reverse losses rather than tax saving.

MATHEMATICAL MODELLING OF HOT AIR DRIED APPLE AND EFFECTS OF VARIETY, SHAPE AND TEMPERATURE ON DRYING BEHAVIOR AND QUALITY CHARACTERISTICS

In this study, drying kinetics and quality characteristics of apple cv. Starking, Gala and Granny Smith circles and squares were studied at two different drying temperatures, 60 °C and 70 °C. Drying times were varied between 85-165 min. Depending on variety, shape and temperature. The falling rate period was observed and drying rate changed depending on the drying parameters. Four mathematical models were fitted to experimental data and Logarithmic model was found to be the best for all the samples. Total phenolic contents and antioxidant capacities of dried apple samples varied in the range of 4.11-8.36 mg GAE/g dry matter and 4536.43-7370.47 mmol AEAC 100/g dry matter, respectively and showed a tendency to increase or decrease after drying depending on the variety and shape interaction. Shape had also significant effect on antioxidant capacities of samples as well as the variety (p<0.05). The results of variance analysis demonstrated that there were significant differences among color values of apple samples dried at 60 ºC and 70 ºC.

Drying kinetics and thermodynamic analysis of tomato in a tunnel dryer

In this study, drying kinetics and thermodynamic analysis of tomato were conducted in a tunnel dryer. Drying experiments were performed at three temperatures (100, 115, and 130 °C) and an air velocity of 1.45 m/s. From the drying curves, only a falling rate period was observed. Under these conditions, a characteristic drying curve was determined. It is observed that at the 40 minutes of the drying process, the outlet gas enthalpy achieved a maximum value that is very close to the inlet value and remained constant until the end of the process. Entropy exhibited similar behaviour to enthalpy. The maximum value of the exergy efficiency curve corresponds to the maximum value observed within the drying rate curves. This maximum value represents the stage when the available energy is efficiently used in moisture removal. As the drying rate decreases the available energy is started to be less employed.

EFFECT OF THE DRYING METHOD ON THE QUALITY AND DRYING CHARACTERISTIC OF MINT LEAVES (Mentha spicata L.)

Mint leaves are vegetables used for tea especially in the northern part of Nigerian because of their nutritional and medicinal values. Fresh mint leaves are perishable and to extend their shelf-life drying the leaves is a common practice among the people. The application of a proper drying method is essential to preserve its nutritional and medicinal values. Lack of information on the drying characteristic that could be used for the design of its dryers is a major bottleneck in its processing. This accounts for the poor colour, taste, flavour of dried mint leaves found in the market.In this study, three methods were used to dry mint leaves, sun, oven and shade drying methods. Proximate analyses were carried out on the samples dried with the three methods. Samples drying characteristics were investigated using an oven at 40, 50, 60 and 70 °C. The results show that the drying method significantly affected all the proximate compositions at 5% level. Shade drying has the highest crude protein and ash contents of 7.74% and 8.48% respectively. Carbohydrates were more (30.13%) when open sun drying was employed. Oven drying favoured lowest moisture content of 7.20%, highest crude fiber of 49.34% and highest crude fat contents of 9.22%. To dry mint leaves to equilibrium moisture content, it took 140 min for samples at a drying temperature of 40 °C, 120 min at 50 °C, 90 min at 60 °C and 70 min for 70 °C. Drying of the leaves occurred in a falling rate period.

Isothermal drying characteristics and kinetics of human faecal sludges

Background: Drying is an important step for the thermochemical conversion of solid fuels, but it is energy-intensive for treating highly moist materials. Methods: To inform the thermal treatment of faecal sludge (FS), this study investigated the drying characteristics and kinetics of various faecal wastes using thermogravimetric analysis and isothermal heating conditions. Results: The findings show that FS from the anaerobic baffled reactor (ABR) and ventilated improved pit latrines (VIP) exhibit similar drying characteristics, with maximum drying rates at 0.04 mg/min during a constant rate period that is followed by a distinct falling rate period. On the contrary, fresh human faeces (HF) and FS from urine diversion dry toilets (UDDT) exhibited a falling rate period regime with no prior or intermittent constant rate periods. The absence of a constant rate period in these samples suggested limited amounts of unbound water that can be removed by dewatering and vice versa for VIP and ABR faecal sludges. The activation energies and effective moisture diffusivity for the sludges varied from 28 to 36 kJ/mol and 1.7·10-7 to 10·10-7 m2/s at 55°C and sludge thickness of 3mm. The Page model was consistent in modelling the different sludges across all temperatures. Conclusions: These results presented in this study can inform the design and development of innovative drying methods for FS treatment.

Modelling the Thin-Layer Drying Kinetics of Marinated Beef during Infrared-Assisted Hot Air Processing of Biltong

Biltong is a dried meat product that is widely consumed in South Africa. The marinated meat is traditionally dried under ambient winter conditions while commercial biltong producers use hot air driers. Hot air drying is time-consuming and energy-intensive. A combined infrared and hot air drying (IRHAD) is an alternative method of drying meat during biltong processing. The aim of this study was to establish the effect of the infrared (IR) power, the temperature, and velocity of the drying air on the drying kinetics of marinated beef and subsequently select the best thin-layer drying model for IRHAD during biltong processing. Marinated beef samples were dried at IR power levels of 500, 750, and 1000 W; drying air temperatures of 30, 35, and 40°C; and air velocity of 1.5 and 2.5 m∙s-1. Results indicate that increasing the IR power and the drying air temperature increased the IR emitter temperature and the core temperature of the marinated beef sample. Consequently, increasing the drying rate thus reduced drying time. The air velocity had an inverse relationship with the IR emitter temperature, the core temperature of the marinated beef sample, and the drying rate. The drying process was characterised by a rising rate period in the first half an hour, followed by a falling rate period which implies that moisture transport occurred partly by surface evaporation and predominantly by diffusion. The effective moisture diffusivity ranged from 4.560 × 10 − 10 to 13.7 × 10 − 10 m 2 ∙ s − 1 , while, the activation energy ranged between 40.97 and 59.16 kJ∙mol-1. The IRHAD of marinated beef during its processing to biltong was best described by the two-term model since it had the highest R 2 (0.9982-0.9993) and the lowest RMSE (0.0062-0.0099). The power level of the IR emitter of 1000 W combined with a drying air temperature and velocity of 40°C and 1.5 m∙s-1, respectively, showed the highest improvement in the drying kinetics and the lowest drying time of 5.61 ± 0.35 hours; hence, it is recommended as a possible drying alternative for the processing of biltong.