Gopu Raveendran Nair

Microwave Drying of Corn (Zea mays L. ssp.) for the Seed Industry

Microwave drying of corn (Zea mays L. ssp.) was conducted in this study and its germination was tested after drying. The objective of the test was to determine an optimum microwave drying method for corn seeds to achieve maximum germination and minimum drying time, as well as to obtain the maximum temperature that can achieve the best results without reducing the viability. The different methods used for drying included constant temperature drying at 30, 40, and 50°C; intermittent power microwave drying; and fixed power microwave drying at 2, 3, 3.5, and 4 W/g. The drying was started with an initial moisture content of 33% (wb) and ended with a final moisture content of 16% (wb). In the constant temperature method, the microwave power was automatically controlled to keep the temperature constant throughout the drying period. A control cycle of 20 s was used for intermittent drying in which the microwave generator was on for 12 s and off for 8 s throughout the drying process. In fixed power microwave drying, the power was constant throughout the process. The germination tests were conducted on all samples with the rolled blotting paper method. The minimum drying time was reached with 4 W/g fixed power where 0% germination resulted. The optimum method for drying of corn seeds for maintaining a high germination rate was 4 W/g intermittent power microwave drying, which took 110 min to dry from 33% moisture content to 16% (wb). The germination percentage of 4 W/g intermittent power was 93.3%. The maximum permissible temperature of corn seeds when subjected to intermittent microwave power resulting in maximum germination was 67°C.

Effect of Dielectric Properties of a Solvent-Water Mixture Used in Microwave-Assisted Extraction of Antioxidants from Potato Peels

The dielectric properties of a methanol-water mixture were measured at different temperatures from 20 to 80 °C at two frequencies 915 MHz and 2450 MHz. These frequencies are most commonly used on industrial and domestic scales respectively. In this study, the dielectric properties of a methanol-water mixture were found to be dependent on temperature, solvent concentration, and presence of plant matrix. Linear and quadratic equations were developed to establish the dependency between factors. At 2450 MHz, the dielectric constant of methanol-water mixtures was significantly affected by concentration of methanol rather than by temperature, whereas the dielectric loss factor was significantly affected by temperature rather than by methanol concentration. Introduction of potato peel led to an increase in the effect of temperature on the dielectric properties of the methanol fractions. At 915 MHz, both the dielectric properties were significantly affected by the increase in temperature and solvent concentration, while the presence of potato peel had no significant effect on the dielectric properties. Statistical analysis of the dissipation factor at 915 and 2450 MHz revealed that both temperature and solvent concentration had a significant effect on it, whereas introduction of potato peels at 915 MHz reduced the effect of temperature as compared to 2450 MHz. The total phenolic yield of the microwave-assisted extraction process was significantly affected by the solvent concentration, the dissipation factor of the methanol-water mixture and the extraction time.

Effect of Static High Electric Field Pre-Treatment on Microwave-Assisted Drying of Potato Slices

Dehydration of fruits and vegetables affects their physical, biochemical, and organoleptic properties. In the present study, the effect of static high electric field intensity of 4 kV/cm on drying kinetics of microwave-convective and hot air drying systems was evaluated. The studied electric field intensity had minimal to no effect on the drying kinetics of the potato slices. Less to no curling was observed for high electric field pre-treated samples compared to microwave-convective and hot-air-dried samples. This characteristic was attributed to membrane permeabilization induced by application of a high electric field.

Electrohydrodynamic Drying of Sand

ABSTRACT This study analyzes the electrohydrodynamic (EHD) drying characteristics of sand. Effect of process parameters (independent variables) including air speed, electrode gap, and applied voltage on drying kinetics and dependent variables including percentage water removed (%), Sherwood number, EHD number, and specific energy consumed (SEC) (kJ/kg) were also investigated using a central composite design and response surface methodology. Maximum drying was obtained for process parameter combination of air speed (2 m/s), electrode gap (1.5 cm), and applied voltage (15 kV). Air speed and electric field intensity (ratio of applied voltage to electrode gap) were found to have a significant effect on percentage water removed (%) and Sherwood number. In case of EHD number and SEC during the EHD drying process, all process parameters had a significant effect on them. The SEC increased with an increase in applied voltage but reduced with an increase in air speed at any given applied voltage suggesting that the EHD drying process, in combination with cross flow, will lead to higher drying rate and low energy consumption under ambient conditions. Regression models were also developed describing the relation between independent and dependent variables.

Effect of microwave and hot air drying on flax straw at controlled temperatures

Flax stems were subjected to microwave drying at controlled temperatures. The rate of drying was then compared with conventional hot air drying. The product temperature was maintained at 40°C, 60°C and 80°C for both microwave and hot air drying. The moisture content of flax stem was about 70% (wet basis). The microwave drying was conducted in a microwave apparatus which recorded mass, product temperature, incident microwave power, reflected microwave power and inlet/outlet air temperature. The final moisture content for experiment was set to 9% (wet basis). Microwave-convective drying ensured about 30% to 70% reduction of drying time for drying flax straw as compared to hot air drying. Curve fitting with different mathematical models were carried out and all the models were fitted well for both hot air and microwave drying. The tensile strength of flax straw, measured with an Instron apparatus, increased with an increase in the processing temperature of both processes. Hot air dried flax straw showed the greatest tensile strength and modulus of elasticity at processing temperatures of 60°C and 80°C with a significant difference.

Electro-osmotic dewatering of soaked hemp stems

ABSTRACT Hemp stems were immersed in water as a pretreatment to enhance the production of hemp fiber. To reduce the high moisture content, the soaked hemp stems were dewatered using a bench-type electro-osmotic roller press. Variables like applied voltage (12, 24, and 36 V), roller pressure (1000, 2000, and 3000 kPa), and duration of soaking of hemp stems (12, 24, and 36 h) were subjected to investigation and the percentage of total water expelled due to electro-osmotic dewatering (EOD) at various levels of experiments was recorded. Hemp stems soaked for 24 h treated at a roller pressure of 2,000 kPa at an applied voltage of 36 V showed the maximum water removal after EOD process. The water removal was found to be increasing with increase in applied voltage and roller pressure. Soaking time up to 32 h leads to an increase in water removal and then it started decreasing. The probable reason for that was the penetration of surface water into micropores and its adhesion to the lignocellulosic bonds. Electro-osmotic permeability of hemp stems at various levels of voltages, roller pressures, and soaking times was studied and the result proved that electro-osmotic permeability was inversely proportional to applied voltage and it was independent of the applied pressure.

Comparative evaluation of steam-assisted treatments of biomass components and sweet sorghum bagasse

A process originally used for the fractionation of sweet sorghum bagasse powder was evaluated using biomass components such as cellulose, xylan and lignin. The autohydrolysis of the substrates was conducted at 121±0.5°C with isothermal treatment time of 90 min. The lime treatment of the autohydrolysed substrates was conducted at 121±0.5°C for 106 min with 0.1 g Ca(OH)2 dosage per gram of the substrates. The responses from the treatment of the biomass components were used to evaluate the responses observed during the treatment of the sweet sorghum bagasse. Carbon dioxide gas at a flow rate of 17 mL*min−1 was used for the precipitation of lignin and lime from the liquid obtained from the lime treatment process. The process responses were also compared and confirmed using the Fourier transform infrared spectrophotometry and the differential scanning calorimetry of the sweet sorghum bagasse and the treated and untreated biomass components.