Liposome Phase Separation as a Quantitative Readout for Procyanidin B2 in Sugar- and Acid-Containing Systems

Procyanidins are important polyphenolic compounds in apples that contribute to both nutritional value and product quality. Conventional quantification methods, such as high-performance liquid chromatography (HPLC), provide high accuracy but require costly instrumentation, time-consuming sample preparation, and skilled operators. In this study, cell-sized liposomes composed of 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC) and dipalmitoyl-phosphatidylcholine (DPPC) (1:1 molar ratio) were hydrated in aqueous solutions containing either defined sugars, organic acids, or their mixtures, with or without procyanidin B2 (PB2). Increasing PB2 concentration consistently reduced the fraction of phase-separated liposomes, yielding highly linear calibration relationships up to 30 mg/100 g. This linearity was preserved when the calibration range was extended to 40 and 100 mg/100 g. The method was evaluated using apple juices at different processing stages, commercially available juices, and vacuum-cooked apple extracts prepared from Tsugaru and Jonathan cultivars. PB2 concentrations estimated by the liposome-based method closely matched HPLC-measured values, particularly when calibration curves constructed using mixed acids or selected sugars were applied. These results demonstrate that liposome phase separation provides a robust physicochemical readout for PB2 quantification across diverse apple-derived matrices. The proposed method offers a rapid and cost-effective alternative to conventional chromatographic analysis, underscoring the importance of matrix-aware calibration for polyphenol estimation in complex food systems.