Losses of potentially health-promoting flavan-3-ols and other phenolic compounds during various clarification treatments of novel apple juices made with the spiral filter press

Cloudy apple juices produced by spiral filter press technology have recently been reported to contain potentially health-promoting levels of flavan-3-ols. Due to the novelty of these juices, the impact of commonly applied juice clarification treatments on the concentration of flavan-3-ols and other phenolic compounds was comprehensively investigated using RP-UHPLC-DAD and HILIC-FLD. Besides cloudy apple juices with high levels of phenolic compounds, a phenolic compound extract was prepared to further enrich the juices. Subsequent clarification was performed using cross-flow ultrafiltration modules with and without prior addition of gelatin, silica sol, bentonite, and activated charcoal. Ultrafiltration alone lowered phenolic compound concentrations of the apple juice by 9%. The pretreatment with common levels of gelatine (0.2 g/L), silica sol, and bentonite caused similar losses (10%). When the gelatine dosage was doubled (0.4 g/L), the losses did not significantly aggravate and only reached 12%. In contrast, adding activated charcoal (1 g/L) reduced the phenolic compound concentration by 49%. Whereas levels of all phenolic compounds were reduced by ultrafiltration to a comparable extent, the admixture of activated charcoal primarily reduced the concentrations of phenolic compounds with small molecular weights. The treatment with gelatine, silica sol, and bentonite predominantly decreased the concentrations of flavan-3-ols with high degrees of polymerization. The clarification of model solutions of phenolic compounds revealed that interactions with apple colloids diminished the ability of gelatin, silica sol, and bentonite to reduce phenolic compound concentrations.