Dielectric Properties of Selected Nigerian Fruit Juices in the Microwave Frequency Range: Implications for Microwave-assisted Shelf-life Extension

Abstract

Microwave dielectric heating treatment and dielectric property analysis were applied to locally produced fruit juices within the microwave frequency range of 1–20 GHz, at 2.5 GHz intervals, to evaluate their potential for shelf-life enhancement and to monitor temporal variations over 8-hour periods. To support dielectric interpretation, key physicochemical properties—pH, electrical conductivity, total soluble solids (TSS), and viscosity—were determined for each juice sample. The physicochemical results indicated that tangerine (Citrus reticulata) exhibited the highest pH value (4.60 ± 1.20), followed by Julie mango (Mangifera indica L.), while Ibadan Sweet Orange (Citrus sinensis) recorded the lowest pH (2.45 ± 0.10). Julie mango juice also showed the highest electrical conductivity (0.89 ± 0.30 mS cm⁻¹) and viscosity (145.1 ± 0.1 mPa·s). Dielectric characterization revealed that Julie mango juice possessed the highest dielectric constant and dielectric loss factor at lower frequencies and temperatures, with both parameters decreasing as frequency and temperature increased. Ibadan Sweet Orange juice exhibited intermediate dielectric values, whereas tangerine juice showed the lowest dielectric response; however, all samples followed similar frequency- and temperature-dependent trends. These variations are attributed to differences in water content, soluble solids, ionic concentration, and viscosity, which govern dipolar polarization and ionic conduction mechanisms. The observed reduction in dielectric parameters with increasing frequency and temperature reflects relaxation phenomena and thermally induced disruption of dipole alignment. Overall, the results demonstrate that the dielectric behaviour of locally produced fruit juices is strongly influenced by their physicochemical composition and relaxation dynamics, underscoring the potential of microwave-induced dielectric discharge as an effective and energy-efficient strategy for shelf-life extension while preserving quality attributes in small-scale juice processing.