Polyphenol
oxidase from apricot (Prunus armeniaca) (PaPPO) was purified in its latent form (L-PaPPO), and the molecular weight was determined to be 63
kDa by SDS-PAGE. L-PaPPO was activated in the presence
of substrate at low pH. The activity was enhanced by CuSO4 and low concentrations (≤ 2 mM) of SDS. PaPPO has its pH and temperature optimum at pH 4.5 and 45 °C for
catechol as substrate. It showed diphenolase activity and highest
affinity toward 4-methylcatechol (KM =
2.0 mM) and chlorogenic acid (KM = 2.7
mM). L-PaPPO was found to be spontaneously activated
during storage at 4 °C, creating a new band at 38 kDa representing
the activated form (A-PaPPO). The mass of A-PaPPO was determined by mass spectrometry as 37 455.6
Da (Asp102 → Leu429). Both L-PaPPO and A-PaPPO were identified as polyphenol oxidase corresponding
to the known PaPPO sequence (UniProt O81103) by means
of peptide mass fingerprinting.
The aim of the work was to explore the feasibility of using acorn flour as a novel and healthy ingredient in biscuits. The physico-chemical characteristics of acorn flour obtained from three different Quercus species were compared. Acorns of Quercus coccifera L. were the most antioxidant and were therefore used for preparing biscuits at two levels of addition, 30 and 60 g 100 g À1 on wheat flour basis. The physico-chemical and sensory characteristics of the obtained biscuits were then assessed. Acorn-added biscuits showed significantly (p < 0.05) higher content of phenolics, antioxidant activity and oxidative stability than control biscuits, prepared without acorn flour. These features improved as the level of acorn flour increased. As for appearance, the acorn-added biscuits were darker, larger, more voluminous and more friable than control biscuits. Higher levels of fermentative alcohols and esters, as well as Maillard reaction volatile compounds (particularly furans), were observed in the acorn-added biscuits.
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