microstructure, HPP treatment produces changes in the distribution
and aggregation of phenolic compounds, and increases the
rate of mass transfer; this results in an enhanced solvent penetration
into the cells by disrupting the cell walls and hydrophobic
bonds in the cell membrane, which may lead to high permeability
and the release of some antioxidant components (Wang et al.,
2012).
At the end of the storage period at 4 C, significant losses
(p < 0.05) of TPC were observed in untreated smoothie (about
15%), followed by HPP-450 and HPP-600 (12% and 11%, respectively).
Heat-treated smoothie showed the lowest decrease (8%).
The loss of total phenols appeared to be due to the reaction of
the partially soluble polymers formed with the Folin–Ciocalteu
reagent, the oxidation of phenolic compounds and the polymerisation
of phenolics with proteins during storage (Cao, Xu, Liao, Hu, &
Zhang, 2011). Enzymatic oxidation (polyphenol oxidase and peroxidase)
plays a major role in the degradation of phenolic compounds
in HPP samples. The reduction of TPC in pasteurised sample and its
subsequent storage could be due to both enzymatic and
non-enzymatic oxidation. Non-enzymatic autooxidation of phenolics
into quinones and further degradation products occurs during
thermal processing and storage