Experimental study on the hygrothermal dynamics of peanut (Arachis hypogaea Linn.) in the process of superposition and variable temperature drying

Abstract

In order to protect the quality of peanuts after harvest and increase the efficiency of hot-air drying, a dryer based on superposition and variable temperature control technology was built. Samples layered with a thickness of 60 mm were dried with hot air temperatures of 70 °C, 90 °C, and 110 °C. Variable temperature drying was performed in three stages, including 110 °C hot air with a sample layer thickness of 30 mm, 90 °C hot air with a sample layer thickness of 60 mm, and 70 °C hot air with a sample layer thickness of 120 mm. The change in the temperature, moisture ratio, and state were monitored during the drying process. It was found that the temperature distribution for peanuts was uneven at the beginning stage of hot-air drying, but gradually became uniform as the drying proceeded. Low-field nuclear magnetic resonance and magnetic resonance imaging (LF-NMR/MRI) analysis showed that the water in fresh peanuts was mainly distributed inside the cotyledons. The amount of free water, immobilized water, and bound water varied during the drying process, when the signal amplitudes of the free water and total water were significantly reduced, and the moisture state moved in the direction closely associated with the organic components. The results of infrared thermography and MRI showed that there was satisfactory moisture and heat diffusion uniformity for peanuts during the process. This study will provide a reference for improving the hot-air drying technology of agricultural products.

Keywords:

• Peanuts
• hot-air drying
• nuclear magnetic resonance
• superposition
• variable-temperature

Acknowledgments

We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.

Additional information

Funding

We acknowledge the financial support provided to us by the Science and Technology Plan Project of Guangdong Province of China (2018B020241003-02), the National Key R & D Plan Project of China (2017YFD0400900), the National Natural Science Foundation Project of China (31901823), and the Special Fund Project for Basic Scientific Research Business Expenses of Central University of China (2020TC074), all of which have enabled us to carry out this study.