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Featured researches published by G. Tiwari.


International Journal of Fruit Science | 2013

Investigating Alternative Strategies for Managing Bacterial Angular Leaf Spot in Strawberry Nursery Production

William W. Turechek; Shaojin Wang; G. Tiwari; Natalia A. Peres

This article discusses some of the approaches we have tested for managing the bacterial pathogen Xanthomonas fragariae in infected strawberry nursery stock. X. fragariae causes angular leaf spot in strawberry and is transmitted to production fields almost exclusively through infected nursery stock. Of the methods that we have investigated over the past several years, a modified heat treatment has proven to be very effective at reducing systemic infections in propagation material, but cultivar selection affected the outcome. Surface-sterilizing treatments also had an effect on angular leaf spot. We tried procedures from dipping plants in a solution of 10% chlorine bleach to the use of UV-C radiation to reduce the severity of angular leaf spots in the field. Lastly, a sanitation-type treatment, namely removing or trimming remnant leaf and petiole tissue from nursery-trimmed plants, was found to have a significant impact on angular leaf spot. No one method completely eliminated X. fragariae from the planting stock, but there is good indication that a strategic combination of control practices that includes heat treatment should help to reduce significantly the initial amount of bacteria introduced into a field.


2008 Providence, Rhode Island, June 29 - July 2, 2008 | 2008

Effect of Water Assisted Radio Frequency Heat Treatment on the Quality of ‘Fuyu’ Persimmons

G. Tiwari; Shaojin Wang; Sohan Birla; Juming Tang

Water assisted radio frequency (RF) heat treatment was evaluated as a potential alternative to chemical fumigation for providing quarantine security against Mexican fruit fly (Anastrepha ludens) in ‘Fuyu’ persimmon. Three holding times were chosen for each of the three treatment temperatures (46, 48 and 50 °C), one time at, one above and another below 100% mortality. Heat treatment protocols included preheating the fruit in 40°C water, followed by RF heating in 12 kW, 27.12 MHz RF system, holding at the target temperature for the required time and then hydro cooling at 4°C for 30 min. The preheating time at 40°C was determined based on the final RF heating uniformity over the fruit cross-section. Quality parameters, including weight loss, firmness, soluble solids, titratable acidity, peel and pulp color, and calyx browning of persimmons, were evaluated after 7 days of room (22°C) and cold storage (4°C). All treatments except for one condition (48°C + 8 min holding) had no significantly adverse effects on quality attributes. Slight calyx browning was observed in the treated samples and the degree of browning increased with treatment time for each treatment temperature. Results suggested that water assisted RF heat treatments provided potential for disinfestation of persimmons with acceptable product quality.


2009 Reno, Nevada, June 21 - June 24, 2009 | 2009

Temperature and Moisture Dependent Dielectric Properties of Legume Flours Associated with Dielectric Heating

Wenchuan Guo; Shaojin Wang; G. Tiwari; Judy A. Johnson; Juming Tang

Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean) at four different moisture contents were measured using an open-ended coaxial probe and impedance analyzer at frequencies of 10 to 1800 MHz and temperatures of 20 to 90°C. The dielectric constant and loss factor of the legume samples decreased with increasing frequency but increased with increasing temperature and moisture content. At low frequencies and high temperatures and moisture contents, negative linear correlations were observed between the loss factor and the frequency on a log-log plot, which was mainly caused by the ionic conductance. At 1800 MHz, the dielectric property data could be used to estimate the legume sample density judging from high linear correlations. Loss factors for the four legume samples were similar at 27 MHz, 20°C and low moisture contents (e.g. <15 %). At the highest moisture content (e.g., 20%) soybean had the highest loss factor at 27 MHz and 20°C, followed by green pea, lentil and chickpea. The difference in loss factor among the four legumes did not show clear patterns at 915 MHz. Deep penetration depths at 27 MHz could help in developing large-scale industrial RF treatments for postharvest insect control or other applications that require bulk heating in legumes with acceptable heating uniformity and throughputs.


2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010 | 2010

Developing Postharvest Disinfestation Treatments for Legumes Using Radio Frequency Energy

Shaojin Wang; G. Tiwari; S. Jiao; Judy A. Johnson; Juming Tang

There is an urgent need to develop technically effective and environmentally sound phytosanitary and quarantine treatments for the legume industry to replace chemical fumigation. The goal of this study was to develop practical non-chemical treatments for postharvest disinfestations of legumes using radio frequency (RF) energy. A pilot-scale 27 MHz, 6 kW RF unit was used to investigate RF heating and consequent quality attributes in treated chickpea, green pea, and lentil samples. Only 5-7 min was needed to raise the central temperature of 3 kg legume samples to 60°C using RF energy, compared to more than 275 min when using forced hot air at 60°C. RF heating uniformity in product samples was improved by adding forced hot air, and back and forth movements on the conveyor at 0.56 m min-1. The final temperatures exceeded 55.8°C in the interior of the sample container and 57.3°C on the surface for all three legumes, resulting in low uniformity index values of 0.014-0.016 (ratio of standard deviation to the average temperature rise) for the interior temperature distributions and 0.061-0.078 for surface temperature distributions. RF treatments combined with forced hot air at 60°C to maintain the target treatment temperature for 10 min followed by forced room air cooling through a 1 cm product layer provided good product quality. No significant differences in weight loss, moisture content, colour or germination were observed between RF treatments and unheated controls.


2008 Providence, Rhode Island, June 29 - July 2, 2008 | 2008

Dielectric Properties of Chickpea

Wenchuan Guo; G. Tiwari; Shaojin Wang; Juming Tang

Dielectric properties of compressed chickpea samples, matched with true kernel density, were studied over the frequency range from 10 to 1800 MHz. Both dielectric constant and loss factor of chickpea, measured with an open-ended coaxial-line probe and an impedance analyzer, decreased monotonically with increased frequency at the measured temperatures from 20 to 90 oC and moisture content from 7.9 to 20.9% (wet base). Those values also increased with increasing temperature and moisture content at any given frequency. The increase rate was more at higher temperatures and higher moisture levels than at lower temperatures and lower moisture levels. The penetration depth of electromagnetic energy in compressed chickpea flour decreased with increasing frequency, and influenced by moisture content. It was higher in lower moisture content chickpea than in higher moisture content samples. Lower frequency and drier material are preferred for drying or killing pests in host material.


Biosystems Engineering | 2010

Developing postharvest disinfestation treatments for legumes using radio frequency energy

Shaojin Wang; G. Tiwari; S. Jiao; Judy A. Johnson; Juming Tang


Lwt - Food Science and Technology | 2010

Temperature and moisture dependent dielectric properties of legume flour associated with dielectric heating.

Wenchuan Guo; Shaojin Wang; G. Tiwari; Judy A. Johnson; Juming Tang


Biosystems Engineering | 2008

Frequency, moisture and temperature-dependent dielectric properties of chickpea flour

Wenchuan Guo; G. Tiwari; Juming Tang; Shaojin Wang


Journal of Food Engineering | 2011

Analysis of radio frequency (RF) power distribution in dry food materials

G. Tiwari; Shaojin Wang; Juming Tang; Sohan Birla


Journal of Food Engineering | 2011

Computer simulation model development and validation for radio frequency (RF) heating of dry food materials

G. Tiwari; Shaojin Wang; Juming Tang; Sohan Birla

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Shaojin Wang

Washington State University

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Juming Tang

Washington State University

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Judy A. Johnson

Agricultural Research Service

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Sohan Birla

University of Nebraska–Lincoln

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S. Jiao

Washington State University

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Aurelio López-Malo

Universidad de las Américas Puebla

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