PULSED ELECTRIC FIELD, THERMOSONICATION AND HIGH-PRESSURE PROCESSING OF CLOUDY APPLE JUICE: EFFECT ON ZETA POTENTIAL AND PARTICLE SIZE DISTRIBUTION

Zeta potential (Z-potential) measurement and particle size distribution (PSD) can be used as indexes to assess the colloidal stability of cloudy apple juice as a food system. In the present study, Pink Lady apples were juiced with an 2.84 mM ascorbic acid solution (0.28 mL/g apple) and subsequently treated with different technologies: pulsed electric fields (PEF), thermosonication (TS) and high-pressure processing (HPP). For the PEF treatment, the pulse repetition rate and pulse width were set at 200 Hz and 5 µs, respectively, for a total treatment time of 100 µs. For the TS-treatment, samples were processed at 100% amplitude power for 10 min up to 70 °C. HPP treatment was carried out at 600 MPa for 5 min. Untreated cloudy apple juice was used as control. All samples were stored at 4 °C and Z-potential and PSD were measured at 25 °C in triplicate. The results showed no significant difference (P > 0.05) in Z-potential between TS-treated (-6.15 mV) and control samples (-6.06 mV). However, both HPP- and PEF-treated samples exhibited higher Z-potential values of -5.73 mV and -5.26 mV, respectively, suggesting a reduction in colloidal stability. PEF-treated samples showed the highest Z-potential value, indicating particle dispersion was the least stable among the treatments. The PSD analysis showed a monomodal distribution between 100 and 1000 µm for both control and HPP-treated samples. Nonetheless, HPP processing shifted the volume peak toward smaller particle sizes, indicating fragmentation of juice particles. For the TS-treated samples, the distribution peak decreased compared to HPP and a small new peak with a size of < 1 µm was found. In contrast, the PSD of PEF-treated juice was markedly different, with a prominent peak with size of < 10 µm, indicating significant breakdown of larger particles. Among the studied processing technologies, PEF significantly altered both the Z-potential and particle size distribution of cloudy apple juice, resulting in reduced colloidal stability and enhanced particle breakdown. HPP also promoted partial particle size reduction, while the TS had a milder effect, showing the most promising potential for application in the juice industry.