Mabel Kyei Kwofie, Valerie Orsat
Preservation of bioactive, and nutritional quality alongside microbial inactivation remains a central constraint in cranberry juice production. Thermal pasteurisation, while microbiologically effective, potentially degrades the thermolabile polyphenols fractions that define the functional value of fruit juices. Non-thermal alternatives have been widely reported for polyphenol-rich juices, but these studies almost exclusively report aggregate spectrophotometric endpoints, which cannot distinguish the release of simple phenolics from the degradation of the oligomeric proanthocyanidins that carry cranberry-specific bioactivity. The treatment-duration dependence of A-type versus B-type procyanidins under controlled high-power sonication of cranberry juice has consequently not been resolved, this study addresses that gap. Cranberry juice was treated with 20 kHz probe ultrasonication (SONICS Vibracell VCX 500; 13 mm titanium probe; 60% amplitude; 5 s on/5 s off pulse; at 25 °C for 1, 3, 5 and 7 min on a crushed-ice bath, and the physicochemical, bioactive, mineral and microbiological responses were quantified. Moderate treatment (3-5 min) increased total flavonoid content by 42.3% and total phenolic content by 33.9% relative to the untreated control, consistent with cavitation-induced disruption of the cell matrix and release of matrix-bound conjugates. Total carotenoid content rose progressively (+116.9% at 7 min), whereas total anthocyanin content, DPPH radical scavenging activity and ferric-reducing antioxidant power declined, indicating that the phenolic pool released by sonication has a lower per-unit radical-scavenging capacity than the anthocyanin and oligomeric fraction it displaces. Procyanidin A1 was stable to 5 min (within 3.4% of the control at every duration to 5 min, and within 1.1% at 3 and 5 min) while procyanidin B2 fell progressively to 20.2% below the control at 7 min, a structure-dependent divergence attributable to the additional C-O-C inter-flavan bond of A-type dimers. A 2.00 log CFU/mL (99%) reduction in total plate count of inoculated Escherichia coli K12 was achieved at 3 min, with no further measurable reduction to 7 min. Treatment for 3 min therefore represents the optimum, delivering the maximum microbial reduction observed at the point of greatest phenolic and flavonoid release and before any measurable loss of procyanidin A1. These results define a duration window for ultrasonication of cranberry juice and provide the procyanidin-resolved basis required for scale-up of the process to continuous-flow industrial configurations, mostly as a component of a combined process rather than as a standalone replacement for thermal pasteurisation.