STRAWBERRY TREE JUICE PASTEURIZATION BY HPP AND PEF COMPARED TO CONVENTIONAL THERMAL PASTEURIZATION

Strawberry tree fruit (Arbutus unedo L.) can be used in novel juices, but current use is limited by its short shelf-life and the heat sensitivity of its quality and bioactive traits. This study tested, at a pilot scale, nonthermal technologies for stabilizing strawberry tree juice and preserving quality, namely pulsed electric fields (PEF) and high-pressure processing (HPP). Juice was processed by continuous PEF (12 - 20 kV/cm, one and two cycles at temperatures between 35 – 65 °C), HPP treatments (300-600 MPa for 5 min at room temperature), and compared with conventional thermal pasteurization (70 ºC for 5-30 min, TP) and untreated juice. Experimental analyses about microbial behaviour (growth and inactivation) were conducted on (i) inoculated samples with Escherichia coli (used as a target pathogenic surrogated microorganism to optimize the thermal and nonthermal pasteurization conditions) (ii) challenge tests using pre-deteriorated (purposedly spoiled juice kept at room temperature for 16 days to induce microbial growth) were performed simulate a scenario of a juice heavily contaminated to assess the maximum microbial inactivation capacity of each treatment and, (iii) on the juices’ endogenous microorganisms (namely total aerobic mesophiles, psychrophiles, yeasts and moulds). During refrigerated storage, mesophiles, psychrophiles, yeasts and molds, and Enterobacteriaceae were evaluated, along with pH, soluble solids, water activity, color, DPPH antioxidant activity, and total phenolics. PEF 20 kV/cm (two cycles), the highest energy, gave the greatest microbial load reductions, although lower than those obtained with two cycles of PEF 17.5 kV/cm + 65°C, HPP 600 MPa, and TP. HPP, PEF, and TP kept mesophiles below detection levels up to 30 days and psychrophiles below detection levels up to 102 days. HPP also has the best-preserved appearance, with an initial ΔE* of 0.3, while thermal pasteurization caused greater color changes. Overall, HPP was the most promising option for producing safe, minimally processed, value-added strawberry tree juice with improved refrigerated stability and quality, whereas PEF, combined with moderate thermal pre-treatment, proved to be an effective treatment alternative to conventional thermal pasteurization, ensuring both microbial safety and extended shelf-life in strawberry tree juice, in shorter processing times.