Evaluation of electrical and other physical properties of heated sweet potato

Abstract

Electrical impedance spectroscopy is expected to use for quality estimation of agricultural product.In this study, changes in moisture content, porosity and electrical and mechanical properties of sweet potato heated in hot water at 50, 55, 60, 65, and 70 8C were investigated. Additionally, the tissue structure was scanned by X-ray computerized tomography (CT). As a result, the porosity of the sample decreased with treatment time at every temperature while the moisture content changed at only 70 8C. This decrease in the porosity greatly affected the extracellular resistance and the elastic modulus. Moreover, the elastic modulus could be expressed by a logarithmic equation of the extracellular resistance with the high determination coefficient (R 2 5 0.91). Average CT values calculated from the scanned images of the tissue also indicated good correlations with porosity and elastic modulus. These results indicated that the extracellular resistance and the average CT value were effective for the estimation of elasticity as well as porosity. Practical applicationsSweet potato (Ipomoea batatas (L.) Lam.) is one of the most popular vegetables in Japan with its highly nutritional value and sweet taste. It is widely used for processed foods and shochu (Japanese liquor). To make these products, sweet potato is heated by hot water immersion or steaming in the process lines. Because the processes have been mechanized, technological development which enables to estimate inner state of sweet potato during heating is required. This research investigated potential of electrical impedance spectroscopy and CT scanning as the quality estimation technique for heated sweet potato. The results presented here clarified relationships between electrical properties and other physical properties, and CT value and the properties. The knowledge will contribute to design a quality control system based on the automatically quality estimation. K E Y W O R D S computed tomography, electrical property, equivalent circuit analysis, impedance, mechanical property

Effect of Heating under Pasteurization Conditions on Mechanical and Electrical Properties of Mung Bean Sprouts

“…Some studies had already investigated changes in electrical properties during heating with hot water at around 70 ℃, and they confirmed that extracellular resistance decreased by heating for 5-10 min for potato (Imaizumi et al, 2015) and sweet potato (Imaizumi et al, 2017) samples. In this study, we clarified that the extracellular resistance of mung bean sprout decreased on heating at 65 and 70 ℃ for only 15 s. Recently, Imaizumi et al (2017) have reported a strong correlation of extracellular resistance with porosity. In this case, air was recognized as an insulator and loss of porosity increased electrical conductivity in extracellular regions.…”

“…The initial elastic modulus has been suggested to reflect states of the extracellular region. It was reported that elastic modulus strongly related to porosity (Imaizumi et al, 2017). Therefore, changes in initial elastic modulus were affected by both cell membrane damage and the decrease in porosity.…”

“…In this study, we compared some models for the equivalent circuit analysis of EIS data acquired for mung bean sprouts. (Imaizumi et al, 2017), we also investigated inner structure of the mung bean sprouts by using an X-ray micro CT which enables to visualize pores in vegetables.…”

Estimating moisture content and physical properties of sweet potato based on the multiparameter of electrical impedance spectroscopy

“…Recently, as the increasing concern on drying quality, the novel methods of hyperspectral imaging, computer vision, and electrical parameter have been gained significant interest in measuring moisture content and physical properties (Imaizumi, Tanaka, Sato, Yoshida, & Uchino, 2017; Lee, Mo, Lee, & Lee, 2019; Luo et al., 2019; Onwude et al., 2018; Su, Bakalis, & Sun, 2019; Sun, Liu, et al., 2017; Su & Sun, 2016). The surface information of sweet potato which captured by the hyperspectral imaging camera and digital‐backscattering imaging system is used to reveal the changes of moisture or physical properties (Amjad, Crichton, Munir, Hensel, & Sturm, 2018).…”