Vijaya Raghavan

A Comprehensive Review on Electrohydrodynamic Drying and High-Voltage Electric Field in the Context of Food and Bioprocessing

Increasing global energy demand and the application of more energy-consuming processes has forced food industries to investigate alternative processes. This article pertains to one such novel and promising alternative drying process called electrohydrodynamic (EHD) drying. EHD is a method of inducing electric wind that is generated by gaseous ions under the influence of a high-voltage electric field. This article evaluates the available literature and discusses the experimental investigations carried out to explain the effect of operating parameters on the drying rate and specific energy consumption (kJ/kg water) of the EHD process. Through the review it was established that the corona current increased linearly with an increase in applied voltage (kV) for both positive and negative polarities and a negative corona discharge produced a larger corona current compared to a positive corona discharge. It was also revealed that the specific energy consumption increased with an increase in applied voltage for both polarities but was lower compared to conventional drying processes such as fluidized bed drying; however, it was observed that the specific energy consumed by the EHD process was lower than that of latent heat of vaporization, indicating the removal of water from the surface of the sample by other means in addition to evaporation. Electrode configuration plays an important role in determining the efficiency of the EHD process; the multiple-needle electrode configurations had better efficiency than wire and single-electrode configurations. Recent and past studies on application of EHD both postharvest and in food processing were also reviewed and the benefit of using EHD for food and bioprocessing due to its unique properties supported the feasibility and applicability of EHD as a suitable alternative for processing thermally sensitive biological materials.

Advancements in Drying Techniques for Food, Fiber, and Fuel

Removal of moisture from biological materials, popularly called drying, has numerous benefits, including ease of handling due to reduction in bulk, resulting in reduced handling costs. Moreover, drying prevents microbial growth and spoilage. Though different drying techniques share a common objective, conceptually they are different and require modification/adaptation based on the biomaterial that is dried. There have been significant scientific advancements in the past century in the field of drying of foods, fibers, and fuel. This article will provide an extensive review of various drying pretreatments and different hybrid drying techniques, including supercritical and fluidized bed concepts, microwave drying, superheated steam drying, and heat pump drying to meet tomorrows food and energy needs.

Inactivation of Escherichia Coli O157:H7 in Liquid Dialyzed Egg Using Pulsed Electric Fields

Pulsed electric field (PEF) pasteurization may be used either to replace or supplement conventional processing of heat-sensitive products such as liquid egg. The objective of this study was to investigate inactivation characteristics of Escherichia coli O157:H7 in liquid egg products at low temperature using square waveform pulsed electric fields. Dialyzed liquid egg products, namely whole egg, egg white and egg yolk, were exposed to an electric field of lSkVcm −1 at a low temperature of 0°C. The square voltage fields were generated across parallel plate treatment chambers. A pulse frequency of 1 Hz was used. Up to 500 pulses were applied. Product temperature during the PEF treatment was controlled using a water cooling system. About 1, 3 and 3.5 log reductions were obtained for the dialyzed egg white, egg yolk and whole egg products, respectively. The results showed that microbial inactivation rate increased with increasing number of pulses, especially for the egg yolk and whole egg products. The inactivation kinetics was exponential with some tailing. A new kinetic model for the bacteria inactivation was proposed.

Soil biochar amendment as a climate change mitigation tool: Key parameters and mechanisms involved

Biochar, a solid porous material obtained from the carbonization of biomass under low or no oxygen conditions, has been proposed as a climate change mitigation tool because it is expected to sequester carbon (C) for centuries and to reduce greenhouse gas (GHG) emissions from soils. This review aimed to identify key biochar properties and production parameters that have an effect on these specific applications of the biochar. Moreover, mechanisms involved in interactions between biochar and soils were highlighted. Following a compilation and comparison of the characteristics of 76 biochars from 40 research studies, biochars with a lower N content, and consequently a higher C/N ratio (>30), were found to be more suitable for mitigation of N2O emissions from soils. Moreover, biochars produced at a higher pyrolysis temperature, and with O/C ratio <0.2, H/Corg ratio <0.4 and volatile matter below 80% may have high C sequestration potential. Based on these observations, biochar production and application to the field can be used as a tool to mitigate climate change. However, it is important to determine the pyrolysis conditions and feedstock needed to produce a biochar with the desired properties for a specific application. More research studies are needed to identify the exact mechanisms involved following biochar amendment to soil.

Soybean Hydrophobic Protein Response to External Electric Field: A Molecular Modeling Approach

The molecular dynamic (MD) modeling approach was applied to evaluate the effect of an external electric field on soybean hydrophobic protein and surface properties. Nominal electric field strengths of 0.002 V/nm and 0.004 V/nm had no major effect on the structure and surface properties of the protein isolate but the higher electric field strength of 3 V/nm significantly affected the protein conformation and solvent accessible surface area. The response of protein isolate to various external field stresses demonstrated that it is necessary to gain insight into protein dynamics under electromagnetic fields in order to be able to develop the techniques utilizing them for food processing and other biological applications.

Electrical Conductivities of Liquid Egg Products and Fruit Juices Exposed to High Pulsed Electric Fields

Electrical conductivity can be used to monitor important changes in a food product during pulsed electric field (PEF) processing. Electrical conductivities of selected fruit juices (namely apple, orange, and pineapple juices) and liquid egg products (namely whole egg, yolk, and egg white) were determined online during a PEF treatment. The property was measured at broad processing temperatures ranging from 5 to 55°C. Electrical conductivity increased linearly with increasing temperatures for all the products. The liquid egg products have the highest overall electrical conductivity varying from 0.22 to 1.1 S/m whereas fruit juice products have the lowest electrical conductivity ranging from 0.13 to 0.63 S/m. Regression equations of electrical conductivity as functions of temperature were developed. This paper provides a database and equation correlations of food electrical conductivity that could be used to design and optimize PEF process.

Foam-Mat Freeze Drying of Egg White—Mathematical Modeling Part II: Freeze Drying and Modeling

Foam-mat freeze drying is one of the promising methods of drying, which utilizes advantages of both freeze drying and foam-mat drying. Egg white with its excellent foaming properties makes a suitable candidate for foam-mat freeze drying. Experiments were conducted to study foam-mat freeze drying of egg white, in an effort to determine the suitability of this method. Xanthan gum (XG) at 0.125% concentration was used as stabilizer for foaming. The results showed that the addition of xanthan gum during foaming has a positive impact in reducing the total drying time and also produces excellent quality egg white powder. The addition of stabilizer also plays an important role in improving drying. Simple models were applied for determining drying time and diffusion coefficients during freeze drying.

Carbon neutral electricity production by Synechocystis sp. PCC6803 in a microbial fuel cell

The aim of this work was to illustrate the use of photosynthetic microbes in a microbial fuel cell to produce electricity without the requirement of an external carbon source. This research here describes the use of a cyanobacterium Synechocystis PCC6803, to produce electricity without any net CO(2) production in a two-chambered MFC. Conditions for optimum electricity production were determined through standardizing operating parameters. A maximum power density of 6.7mWm(-3)(anode chamber volume) was achieved under high intensity lighting (10,000lux). Light intensity and wavelength directly affected electricity production, indicating the pivotal role played by photosynthesis. The maximum removal of CO(2) was 625mmolm(-3) over 20h under high intensity light. The results presented here will contribute to the understanding of how cyanobacteria can be exploited for the direct conversion of CO(2) to electric current.

Comparative shotgun proteomic analysis of Clostridium acetobutylicum from butanol fermentation using glucose and xylose

BackgroundButanol is a second generation biofuel produced by Clostridium acetobutylicum through acetone-butanol-ethanol (ABE) fermentation process. Shotgun proteomics provides a direct approach to study the whole proteome of an organism in depth. This paper focuses on shotgun proteomic profiling of C. acetobutylicum from ABE fermentation using glucose and xylose to understand the functional mechanisms of C. acetobutylicum proteins involved in butanol production.ResultsWe identified 894 different proteins in C. acetobutylicum from ABE fermentation process by two dimensional - liquid chromatography - tandem mass spectrometry (2D-LC-MS/MS) method. This includes 717 proteins from glucose and 826 proteins from the xylose substrate. A total of 649 proteins were found to be common and 22 significantly differentially expressed proteins were identified between glucose and xylose substrates.ConclusionOur results demonstrate that flagellar proteins are highly up-regulated with glucose compared to xylose substrate during ABE fermentation. Chemotactic activity was also found to be lost with the xylose substrate due to the absence of CheW and CheV proteins. This is the first report on the shotgun proteomic analysis of C. acetobutylicum ATCC 824 in ABE fermentation between glucose and xylose substrate from a single time data point and the number of proteins identified here is more than any other study performed on this organism up to this report.

Foam-Mat Freeze Drying of Egg White and Mathematical Modeling Part I Optimization of Egg White Foam Stability

Egg white (albumen) is a rich source of protein and is widely used in confectionary industry for its wonderful foaming ability. Foam-mat freeze drying is one of the promising methods of drying, which tries to utilize the advantages of both freeze drying and foam-mat drying to produce better quality egg white powder. Preliminary experiments showed that the stability of foams made with egg white alone is not adequate for foam-mat freeze drying. Experiments were thus conducted using different stabilizers (methyl cellulose, propylene glycol alginate, and xanthan gum) to optimize foam stability. Bubble size distribution was determined using microscopy to understand foam structure. This article will discuss the effect of stabilizers on the stability of egg white foam and possible mechanisms involved. The results showed that xanthan gum at 0.125% provided sufficient stability for freeze drying.