G. S. Vijaya Raghavan

Microwave-assisted Extraction of Phenolic Compounds from Grape Seed

Abstract A microwave-assisted extraction technique was developed to optimize the extraction of phenolic compounds from grape seeds. The microwave power (300-150W) and time of extraction (20-200s) were varied during the optimization process. The polyphenol content of the resulting extracts were measured as mg of tannic acid equivalent per gram of crude extract (mg TAE/g of crude extract), using a Folin-Ciocalteau reagent. In general, neither the time nor the power had a significant effect on the overall % yield (average of 13.5%) and on the polyphenol content (392 mg TAE/g of crude extract) of the extracts. However, when the solvent polarity was changed by the addition of 10% water, the yield increased to 15.2% and the polyphenol content increased to 429 mg TAE/g of crude extract.

Electrohydrodynamic Drying—A Concise Overview

Electrohydrodynamic (EHD) drying is a novel method of non-thermal processing. The drying can be carried out using either AC or DC high voltages. The thermodynamic considerations regarding the lowering of temperature under EHD drying include rapid rates of evaporation and exothermic interaction of the electric field with a dielectric material. Multi-point and plate electrode systems are efficient in accelerating drying of agricultural materials. Compared to hot air (convective) drying systems, EHD drying systems offer lower food production costs along with superior quality in terms of physiochemical properties such as color, shrinkage, flavor, and nutrient content. Compared to convective and freeze-drying, EHD drying systems, given their simpler design and lesser energy consumption, show great potential for bulk and industrial drying applications.

Radio-Frequency Processing

Abstract Radio-frequency (RF) dielectric heating/drying has been used in various industrial applications for many years, especially in wood, textile, and some food industry processes. Since dielectric heating transfers energy directly to the product (volumetric heating), applications of RF present obvious advantages over other conventional techniques (reduction in processing time and space, improvement in product quality, etc.). The principal challenge that requires attention for the adoption of RF applications is the nonuniform heating caused by variations in size, geometry and properties of the materials. The success of an RF heating/drying setup lies in its design and in the impedance matching between the power generator and the applicator. The quality of the applicators design is very important for its efficiency. Attention must be given to the choice of materials (quality of the electric contacts, resistance to corrosion, etc.), and to the setup as a whole (durability, dielectric behavior of insulators, proper grounding, etc.). The development of new applications for RF and the design of applicators require sophisticated tools (network analyzer) and a considerable amount of expertise for fine tuning. The investment costs are high, from five to ten times higher (per kW) than for conventional means of heating. However, when used alone or in combination with conventional methods, RF energy can considerably reduce processing time, improve energy use and provide a quality product with a processing that meets new environmental constraints, and new production means.

Nutritional and rheological properties of sorghum.

Sorghum is a gluten-free cereal and forms the staple diet of a majority of the populations living in the semi-arid tropics. Sorghum contains various phenolic and antioxidant compounds that could have health benefits, which make the grain suitable for developing functional foods and other applications. It is usually consumed in the form of bread made from the grain flour. Sorghum dough has poor viscoelastic properties compared to wheat dough and mechanical methods for production of sorghum roti are scarce. This article reviews the nutritional and rheological properties of sorghum in relation to their mode of consumption.

FDTD Modeling and Simulation of Microwave Heating of in - Shell Eggs

Considering microwaves as a viable alternative for the pasteurization of In-shell eggs, preliminary trials performed had conflrmed that microwave at 2450MHz can be successfully used to raise the temperature of in-shell eggs to the required pasteurization temperatures in a few minutes. Based on these trials a flnite difierence time domain (FDTD) model was developed using C language and MATLAB to simulate the E fleld and power distribution in lossy dielectric media like that of the egg components (egg white and yolk) taking into consideration the complex shape, dielectric properties and heterogeneous composition of the in-shell egg. This can be used to assist in the design and development of an industrial microwave in- shell eggs pasteurization unit.

Optimization and characterization of hydrochar produced from microwave hydrothermal carbonization of fish waste

Fish processing results in large amounts of solid and liquid wastes that are unsustainably dumped into oceans and landfills. Alternative sustainable technologies that completely utilize seafood wastes are needed. Hydrothermal carbonization (HTC) that converts moisture-rich biomass into hydrochar is mostly employed for pure lignocellulosic biowaste. However, the suitability of HTC for pure non-lignocellulosic waste is unknown. Here, for the first time, a response surface design guided optimization of microwave hydrothermal carbonization (MHTC) process parameters, holding temperature (150-210°C) and time (90-120min), showed that a temperature of approximately 200°C and a time of approximately 119min yielded maximal hydrochar (∼34%). The atomic carbon and ash content, and calorific value of hydrochar were approximately 25-57%, 20-28%, and 19-24.5MJ/kg respectively, depending on the MHTC operating conditions. Taken together, these results confirm that MHTC produces hydrochar from fish waste of quality comparable to one produced from certain lignocellulosic, sewage and municipal wastes. Therefore, this strategy presents an exciting alternative technology that can be used either independently or in combination with other valorization techniques to completely utilize fish wastes irrespective of their quality.

Effect of Radiofrequency Heating on the Dielectric and Physical Properties of Eggs

Eggs are one of the most nutritious foods available in nature. This rich nutritive environment attracts microbes to invade, feed and multiply. Salmonella enteritidis is one such microbe that is highly pathogenic and is the causative agent for the disease salmonellosis. To ensure safety of eggs, processing them without afiecting their unique physical properties is essential. In this study, the impact of radiofrequency (RF) heating on the dielectric properties (dielectric constant and dielectric loss factor) of the egg at varying temperatures (5 - C{56 - C) and frequency (10MHz{3GHz) is evaluated. This study on the dielectric parameters is essential to devise a better heating paradigm wherein there is minimal detrimental efiect to the egg components. Based on the dielectric study, the heating process parameters were determined. The efiect of such heat treatment on the physical properties viz. Viscosity, foam density, foam stability and turbidity of the egg white were also studied. This study was conducted to provide su-cient literature and experimental background for employing RF in pasteurization of in-shell eggs. This study showed that if careful process parameter optimization and meticulous equipment design is done, RF heating can be successfully employed to pasteurize in-shell eggs.

Optimization of Radiofrequency Heating of in-Shell Eggs through Finite Element Modeling and Experimental Trials

Considering Radio Frequency (RF) heating as a viable alternative for the in-shell heating of eggs, Finite Element Modeling and simulation of RF heating of in-shell eggs at 27.12MHz were carried out to assess the feasibility and heating uniformity of the process. According to the recommendations of USDA-FSIS for the pasteurization of eggs, egg white must be heated up to 57.5 - C, and the egg yolk has to be heated up to 61.1 - C for 2min. The objective of the simulation was to determine the location of hot and cold spots generated due to non-uniform heating. A parallel plate setup for Radio Frequency heating was simulated for difierent electric fleld strength levels and orientations of the egg (long axis parallel and long axis perpendicular to the plates). The simulation results were experimentally verifled and the simulation procedure was validated using a laboratory parallel plate RF setup. A coaxial cavity design was simulated with a similar approach. Results indicated that both the parallel and coaxial cavity designs were suitable for in-shell pasteurization of eggs provided that the eggs were rotated to maintain the uniformity in heating. After the simulation of RF heating process, the process optimization was carried out to determine the most efiective procedure for the process. The varying parameters obtained by using difierent modeling techniques for radiofrequency heating of in-shell eggs, were optimized using MATLAB. Laboratory scale experimental trials were conducted to test the validity and efiectiveness of the optimized parameters. The optimal parameters set forth were found to be more e-cient in terms of heating time and uniformity.

Adapting Drying Technologies for Agri-Food Market Development in India

The adoption of new drying technologies is greatly favored by measures taken to adapt the technology to meet local needs. Drying technologies can offer opportunities for new product development, value-added features for enhanced nutrition and shelf stability for food supply management. Existing drying technologies must be modified/adapted to meet the many different properties of traditional Indian commodities and offer potential benefits for entrepreneurial developments. Much of the production and postharvest handling of products in India are done by low-income farmers in rural settings; hence, technological improvements must be based on low-cost available materials and renewable sources of energy. This article presents some of the drying developments accomplished in southern India.

MICROWAVE VACUUM DRYER SETUP AND PRELIMINARY DRYING STUDIES ON STRAWBERRIES CARROTS

A laboratory scale microwave vacuum dryer with the ability to record temporal variation of mass and temperature of a drying product was designed and built. The initial study was set up to investigate the effect of the position of a vacuum pressure control valve at two vacuum pressure levels, 6.5 and 13.3 kPa, with a fixed microwave power input of 1.5 W/g. Then, strawberry halves and carrot cubes (10 x 10 x 10 mm) were used for a preliminary study to investigate the effect on drying product temperature and the effect of input microwave powers (1, 1.5 and 2 W/g) at a fixed level of vacuum pressure (6.5 kPa). The position of the valve which allows air to pass through the vacuum container was found to provide shorter drying time and reduced the occurrence of water vapor condensation. The product temperature at the end stage of drying under continuous microwave mode was too high to ensure quality for both dried strawberry halves and carrot cubes.