3.2. Peroxide value (PV)
Formation of primary oxidation products was monitored by
determining PV. Changes in PV of dark chocolate with hazelnuts as
a function of active or modified atmosphere, packaging material
oxygen permeability and time of storage in the dark at 20 °C are
shown in Fig. 1. After 12 months of storage, chocolate packaged with
the oxygen absorber, irrespective of packaging material permeability,
had a very low PV ca. 1.31–1.47 meq O2/kg chocolate fat, (pb0.05).
Samples packaged in PET-SiOx//LDPE under N2 or vacuum showed a
small increase in PV value (from 0.80 to 2.19 and 2.37 meq O2/kg
chocolate fat, respectively) while for samples packaged in PET//LDPE
under N2 or vacuum packaged a fivefold increase (from 0.8 to 4.38 and
4.22 meq O2/kg chocolate fat respectively) was recorded (pb0.05).
Lastly for commercially packaged chocolate higher values of PV were
recorded (6.51 meq O2/kg chocolate fat). An observation to bemade is
that for a given packaging material (PET//LDPE or PET-SiOx//LDPE)
both atmospheres (vacuum or N2 atmosphere) showed similar rates
of hydroperoxide formation during storage. Reed et al. (2000) studied
the effect of chocolate coating (milk chocolate, white chocolate and
reduced fat chocolate vs. uncoated) on oxidative stability of normal
(NOP) and high oleic peanuts (HOP) stored for 29 weeks at intermediate
(0.6) and low (0.19) water activity (aw) values at 25 °C. They
observed an increase in peroxide value of chocolate-coated peanuts
during storage especially in chocolate bars coated with NOP compared
to HOP. Also, Vercet (2003) studied fat oxidation of almonds coated
with white chocolate during storage at 20 °C, at a relative humidity of
65%. They reported a maximum peroxide value of 9.5 meq O2/kg fat
obtained from almonds coated with white chocolate, after 15 months
of storage.