Wenchuan Guo

Dielectric Properties of Honeydew Melons and Correlation with Quality

Dielectric properties of three honeydew melon cultivars, grown and harvested to provide a range of maturities, were measured with an open-ended coaxial-line probe and impedance analyzer over the frequency range from 10 MHz to 1.8 GHz. Probe measurements were made on the external surface of the melons and also on tissue samples from the edible internal tissue. Moisture content and soluble solids content (SSC) were measured for internal tissue samples, and SSC (sweetness) was used as the quality factor for correlation with the dielectric properties. Individual dielectric constant and loss factor correlations with SSC were low, but a high correlation was obtained between the SSC and permittivity from a complex-plane plot of dielectric constant and loss factor, each divided by SSC, for both the external surface and internal tissue measurements. However, SSC prediction from the dielectric properties by these relationships was not as high as expected. Permittivity data (dielectric constant and loss factor) for the melons are presented graphically to show their relationships with frequency for external surface and internal tissue measurements. A dielectric relaxation for the external surface measurements, which is attributable to bound water and Maxwell-Wagner relaxations, is also illustrated. Coefficients of determination for complex-plane plots, moisture content and SSC relationship, and penetration depth are also shown graphically. Further studies are needed for determining the practicality of sensing melon quality from the dielectric properties.

Peach variety identification using near-infrared diffuse reflectance spectroscopy

NIR spectroscopy was successfully used to identify peach varieties.Peach variety identification models established on PCA reached 100% accuracy.LSSVM performed better than ELM in identifying peach varieties.NIR spectroscopy had potential in developing peach variety detector. More than 1000 peach varieties with significant differences in qualities are cultivated in China. Distinguishing peach varieties is not only needed by peach sellers, but also demanded by consumers. To offer information on identifying peach varieties, near-infrared (NIR) diffuse reflectance spectra between 833 and 2500nm were collected for four peach varieties, 100 samples for each variety. Kennard-Stone algorithm method was used to divide all samples into calibration set (320 peaches) and prediction set (80 peaches). Eight principal components (PCs), 1067 and 10 characteristic wavelengths were extracted by principal component analysis (PCA), uninformative variable elimination based on partial least squares (UVE-PLS) and successive projections algorithm (SPA) from full spectra (FS) with 2074 initial wavelengths, respectively. Least squares support vector machine (LSSVM) and extreme learning machine (ELM) were used to establish peach varieties identification models using the FS, selected PCs and characteristic wavelengths as input variables. Experimental results showed that all models based on PCA reached 100% accuracy for identifying the four peach varieties. The accuracy of LSSVM models based on UVE-PLS also reached 100%. This study indicated that peach varieties could be distinguished successfully by using NIR spectroscopy.

Permittivities of Watermelon Pulp and Juice and Correlation with Quality Indicators

Permittivities from 10 to 4500 MHz at 24°C were measured on pulp and juice of watermelons of different maturities with an open-ended coaxial-line probe and network analyzer. The dielectric constant of both materials decreased monotonically with increasing frequency and loss factor had a minimum at about 1000 MHz. Moreover, the pulp and juice had very similar loss factor values at each frequency. Ionic conduction is the major loss mechanism at lower frequencies in this range, while dipolar losses are dominant at the higher frequencies. The best linear coefficients of determination, 0.8 and 0.69, were found at 4500 MHz for correlations between the loss tangent of juice and soluble solids content and between loss tangent of juice and soluble solids content/pH, respectively. The penetration depth of electromagnetic energy in pulp and juice at 4500 MHz was 4 mm. The study offers useful information in assessing watermelon quality from dielectric properties.

Study of Fruit Permittivity Measurements for Quality Detection

Permittivities of honeydew melons and watermelons, grown to provide a range of maturities, were measured with an open-ended coaxial-line probe and impedance analyzer at frequencies from 10 MHz to 1.8 GHz. Measurements on fresh apples were also made over a ten-week storage period. Data were taken on the external surfaces of the fruit and on tissue samples from the edible internal tissue. Soluble solids content (SSC), indicative of sweetness, was used for melons as the quality factor for correlation with permittivity. Dielectric constant and loss factor correlations with SSC were low, but a high correlation was obtained between the SSC and permittivity from a complex-plane plot of dielectric constant and loss factor, each divided by SSC. However, quality prediction from this relationship was not very high. Dielectric properties of apples were relatively constant during the ten-week storage period even though firmness of apple tissues decreased significantly over that period.

Nondestructive determination of soluble solids content of persimmons by using dielectric spectroscopy

ABSTRACT To explore the feasibility of dielectric spectroscopy in predicting soluble solids content (SSC) of persimmons during postharvest storage period, the dielectric constant spectra and dielectric loss factor spectra of 105 ‘Shui’ persimmons were measured from 20 MHz to 4500 MHz. Based on the joint x-y distances algorithm, the persimmon samples were divided into two sets: 70 samples in calibration set and 35 samples in prediction set. One hundred and seventy-four, 14, and 24 variables were extracted as characteristic variables from full dielectric spectra (FS) by uninformative variables elimination (UVE), successive projection algorithm (SPA), and competitive adaptive reweighted sampling (CARS), respectively. Partial least squares (PLS) and least squares support vector machine (LSSVM) were applied to build SSC prediction models using FS and characteristic variables extracted by UVE, SPA, and CARS. The results indicated that LSSVM models offered better performance than PLS models at same input variables. CARS-LSSVM had the best SSC determination performance with the correlation coefficient and root-mean-square error of prediction set of 0.970 and 0.494°Brix. This study indicates that dielectric spectroscopy technique combined with characteristic variables selection methods is promising for determining SSC of persimmons.

Sensing the water content of honey from temperature-dependent electrical conductivity

In order to predict the water content in honey, electrical conductivity was measured on blossom honey types milk-vetch, jujube and yellow-locust with the water content of 18–37% between 5 and 40 °C. The regression models of electrical conductivity were developed as functions of water content and temperature. The results showed that increases in either water content or temperature resulted in an increase in the electrical conductivity of honey with greater changes at higher water content and/or higher temperature. The linear terms of water content and temperature, a quadratic term of water content, and the interaction effect of water content and temperature had significant influence on the electrical conductivity of honey (p < 0.0001). Regardless of blossom honey type, the linear coefficient of the determination of measured and calculated electrical conductivities was 0.998 and the range error ratio was larger than 100. These results suggest that the electrical conductivity of honey might be used to develop a detector for rapidly predicting the water content in blossom honey.

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

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.

Sensing quality of watermelons through dielectric permittivity

Dielectric spectroscopy studies on honeydew melons revealed a high correlation with soluble solids content for a complex-plane plot of the dielectric properties. In this paper, a new dielectric spectroscopy measurements were carried out on watermelons to study the correlation of dielectric properties, measured on the surface of the melons and on the internal tissues, with soluble solids determinations on tissues from the same melons.

Dielectric Properties of Chickpea

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.

Sensing Egg Quality during Storage by Radiofrequency Complex Permittivity Measurement

Dielectric properties of albumen and yolk of eggs were measured at 24degC over the frequency range from 10 MHz to 1800 MHz to monitor quality changes during a 5-week storage period at 15degC. Quality factors such as Haugh unit, yolk index, moisture content and egg weight were also measured during the same period. On average, the Haugh unit, yolk index and egg weight decreased with time indicating quality deterioration. Albumen moisture content increased at first and then decreased after the third week of storage. The opposite trend was observed for the yolk moisture content. Variations of the measured dielectric properties of albumen and yolk with frequency, moisture content, and quality indicators are presented.