3.2. Effects of juice processing on total phenolics and total flavonoids
The results obtained for the spectrophotometric measurements
were calculated and compared on a dry-weight basis. The concentrations
of total phenolics (TPC) and total flavonoids (TFC) significantly
decreased by 24.9% and 40.7% following the milling
process as compared to the fresh black mulberries, respectively
(p < 0.05). On the other hand, the subsequent mashing and pressing
steps gave rise to substantial increases, resulting in significantly
higher TPC (1866 mg GAE/100 g DW, 35.7% increase
compared to the fresh fruit) and TFC (1684 mg RE/100 g DW,
14.4% increase compared to the fresh fruit) levels in the initial
(pressed) juice than in fresh fruit (p < 0.05) (Table 1). The final pasteurization
step applied to the initial (pressed) juice had hardly any
effect on the values of TPC and TFC, which gave a final juice product
with significantly higher concentrations (39.5% higher
(1919 mg GAE/100 g DW) and 16.0% higher (1709 mg RE/100 g
DW), respectively) of total phenolics and flavonoids in comparison
to the starting fruit material (p < 0.05) (Table 1). Moreover, the
press cake waste material was determined to be relatively poor
in TPC (744 mg GAE/100 g DW) and TFC (645 mg RE/100 g DW)
(p < 0.05), indicating a suitable recovery of the compounds into
the juice fraction (Table 1).