Dielectric behavior of apple (var. Granny Smith) at different moisture contents

Prediction of Date Fruit Quality Attributes during Cold Storage Based on Their Electrical Properties Using Artificial Neural Networks Models

Evaluating and predicting date fruit quality during cold storage is critical for ensuring a steady supply of high-quality fruits to meet market demands. The traditional destructive methods take time in the laboratory, and the results are based on one specific parameter being tested. Modern modeling techniques, such as Machine Learning (ML) algorithms, offer unique benefits in nondestructive methods for food safety detection and predicting quality attributes. In addition, the electrical properties of agricultural products provide crucial information about the interior structures of biological tissues and their physicochemical status. Therefore, this study aimed to use an alternative approach to predict physicochemical properties, i.e., the pH, total soluble solids (TSS), water activity (a_w), and moisture content (MC) of date fruits (Tamar), during cold storage based on their electrical properties using Artificial Neural Networks (ANNs), which is the most popular ML technique. Ten date fruit cultivars were studied to collect data for the targeted parameters at different cold storage times (0, 2, 4, and 6 months) to train and test the ANNs models. The electrical properties of the date fruits were measured using a high-precision LCR (inductance, capacitance, and resistance) meter from 10 Hz to 100 kHz. The ANNs models were compared with a Multiple Linear Regression (MLR) at all testing frequencies of the electrical properties. The MLR models were less accurate than ANNs models in predicting fruit pH and had low performance and weak predictive ability for the TSS, a_w, and MC at all testing frequencies. The optimal ANNs prediction model consisted of the input layer with 14 neurons, one hidden layer with 15 neurons, and the output layer with 4 neurons, which was determined depending on the measurements of the electrical properties at a 10 kHz testing frequency. This optimal ANNs model was able to predict the pH with R² = 0.938 and RMSE = 0.121, TSS with R² = 0.954 and RMSE = 2.946, a_w with R² = 0.876 and RMSE = 0.020, and MC with R² = 0.855 and RMSE = 0.803 b by using the measured electrical properties. The developed ANNs model is a powerful tool for predicting fruit quality attributes after learning from the experimental measurement parameters. It can be suggested to efficiently predict the pH, total soluble solids, water activity, and moisture content of date fruits based on their electrical properties at 10 kHz.

Changes in unfrozen water content and dielectric properties during pulse vacuum osmotic dehydration to improve microwave freeze-drying characteristics of Chinese yam

BACKGROUND

As a pretreatment before drying, the purpose of osmotic dehydration (OD) is to reduce the initial water content of samples and shorten the drying time. When OD is combined with pulse vacuum, the mass transfer is enhanced. Furthermore, the properties of materials, which affect the absorption and dissipation of microwaves, can be changed by OD. In this work, pulsed vacuum osmotic dehydration (PVOD) with sucrose solution was adopted before microwave freeze-drying (MFD). The effects of PVOD on the drying characteristics and quality of dried products were studied.

RESULTS

Results showed that the unfrozen water content was increased by PVOD, which made the dielectric constant and loss factor of Chinese yam larger than that of untreated samples, and the difference amplified with the increasing temperature. Thus, the shortened drying time (up to 38.5%) and increased average drying rate (up to 16.8%) were achieved by MFD combined with PVOD. While in traditional freeze-drying, PVOD resulted in slightly shortened drying time but decreased drying rate. The mechanism of PVOD on improving drying rate of MFD was analyzed from the perspective of unfrozen water content and dielectric properties. Furthermore, the quality assessments indicated that PVOD treatment retained a better color and improved the total phenolic content of dried yams compared to untreated and dried samples.

CONCLUSION

PVOD using sucrose solution was an effective method to change the characteristics of yam, enhancing the MFD rate and improving the product qualities. © 2019 Society of Chemical Industry.

Frequency, moisture content, and temperature dependent dielectric properties of potato starch related to drying with radio-frequency/microwave energy

To develop advanced drying methods using radio-frequency (RF) or microwave (MW) energy, dielectric properties of potato starch were determined using an open-ended coaxial-line probe and network analyzer at frequencies between 20 and 4,500 MHz, moisture contents between 15.1% and 43.1% wet basis (w.b.), and temperatures between 25 and 75 °C. The results showed that both dielectric constant (ε') and loss factor (ε″) were dependent on frequency, moisture content, and temperature. ε' decreased with increasing frequency at a given moisture content or temperature. At low moisture contents (≤25.4% w.b.) or low temperatures (≤45 °C), ε″ increased with increasing frequency. However, ε″ changed from decrease to increase with increasing frequency at high moisture contents or temperatures. At low temperatures (25-35 °C), both ε' and ε″ increased with increasing moisture content. At low moisture contents (15.1-19.5% w.b.), they increased with increasing temperature. The change trends of ε' and ε″ were different and dependent on temperature and moisture content at their high levels. The penetration depth (d _p ) decreased with increasing frequency. RF treatments may provide potential large-scale industrial drying application for potato starch. This research offers useful information on dielectric properties of potato starch related to drying with electromagnetic energy.

Chemical composition of the flesh and the pit of date palm fruit and radical scavenging activity of their extracts

The chemical analysis of flesh and pit of two varieties of date palm fruit (Deglet nour and Alig) as well as the radical scavenging activity of their extracts was undertaken. The fruits were grown in Djerid region (Oasis of Tozeur, Tunisia). Total sugars was measured by HPLC method or with Fehling reagent, crude lipid content was obtained by Soxhlet's extraction, mineral elements were measured by atomic absorption photometer. The antioxidant activity of extracts from the flesh and pit of the date fruit was measured on the basis of the scavenging activity of the stable 1, 1-diphenyl-2-picrylhy-drazyl (DPPH) free radical. Our results showed that the total sugars could present over 60% of the dry weight of date flesh in two studied varieties. The content of reducing sugars was higher in Alig variety than Deglet nour. For the minerals content, dates flesh were a very good source of several minerals and could be an important source of potassium for regular consumer with a concentration of 0.61 and 0.72% (dry matter), respectively from flesh Deglet nour and Alig. Concerning the date pit composition, oils content was 10.13% in Deglet nour and 12.37% in Alig and the total sugars were less than 6% for the two varieties. In addition, ethyl acetate extracts from flesh Deglet nour, pit Deglet nour and pit Alig showed an important free radical scavenging activity towards 1-1-diphenyl-2-picrylhydrazyl (DPPH) free radical.