Evaluation of freeze crystallization on pomegranate juice quality in comparison with conventional thermal processing

The objective of the present study was to evaluate the potential of freeze crystallization (FC) as concentration technology for pomegranate juice. By comparing with conventional thermal treatment (evaporation), the effect on quality parameters (physicochemical properties, bioactive compounds, antioxidant activity, and aromatic profile) at three cycles was investigated. In the last cycle, the results showed that both FC and evaporation technologies, concentrate similar total soluble solids (≈48 °Brix). However, FC maintained a comparable color to the initial sample (red color), while the evaporated samples presented a browning color. FC efficiently retained higher bioactive compound concentration than heat treatment (50 °C), with values close to 87%, 71%, 69% and 67% for total polyphenol, anthocyanin, tannin, and flavonoid content, respectively. A similar behavior, with highest values in FC, was observed in the antioxidant capacity, since FC resulted in an increase of 5.19, 5.12, 5.29 and 4.05-fold versus 3.11, 3.60, 3.87 and 1.97-fold in relation to the initial value, for 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) (ABTS), ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) assays, respectively. In aromatic profile, FC allowed preservation of volatile compounds from the fresh juice. Instead, heat treatment only retained 68% of the volatiles components present in the initial sample. Therefore, compared with evaporation, our results suggest that FC is a potential alternative as non-thermal technology to preserve diverse and interesting components from fresh juice.