Non-thermal Processing of Pineapple (Ananas comosus [L.] Merr.) Juice Using Continuous Pressure Change Technology (PCT): Effects on Physical Traits, Microbial Loads, Enzyme Activities, and Phytochemical Composition
A comprehensive study using continuous pressure change technology (PCT) for the non-thermal processing of fresh pineapple juice on pilot scale was conducted (1 L/min, 50 MPa, argon, 3 min, <35 °C). The immediate effects of a single and a twofold PCT treatment on the most important quality parameters were examined and compared with those of fresh and thermally pasteurised (90 °C) juices. In comparison to the fresh juice, both PCT-treated samples exhibited slightly brighter and less yellowish colour (CIE L*a*b*). A significant reduction in the mean particle size resulted in diminished centrifugable pulp contents and enhanced cloud stability. Moreover, a slightly improved microbial quality (−0.9 to −1.2 log10 CFU/mL) in terms of total aerobic and yeast and mould counts was attained. Noteworthy, PCT retained a high bromelain activity (−3 to −15% reduction) and efficiently inactivated polyphenol oxidase. Water-soluble vitamins, phenolic compounds, and all further constituents assessed were mostly preserved. However, the high residual peroxidase activity (−10 to −23%) and microbial loads are likely to affect juice quality during storage. In contrast, thermal pasteurisation ensured a complete reduction in both microbial counts (−4.4 to −4.5 log10 CFU/mL) and effective inactivation of peroxidase. However, bromelain activity was strongly affected (−83%) by heat treatment, and colour was darkened and even less yellowish. Overall, this study highlighted the potential of PCT for the production of fresh-like pineapple juices; however, its current limitations were revealed as well.