Agriculture Reference
In-Depth Information
Table 5.5.
Reaction kinetics parameter for PME inactivation of orange juice by PEF (monopolarity).
1
Fractional Conversion Technique
Weibull Distribution Model
Electric Field
(kV/cm)
10
3
(μsec
−
1
)
10
3
RA
∞
(%)
k
1
×
α
×
(μsec)
γ
×
10
5
89
1.3
73
5.9
15
80
2.2
28
5
25
58
1.5
4.0
7
30
28
1.3
1.5
8
35
32
3.0
1.01
5.6
1
Treatment time
=
0-1500
μ
sec; pulse frequency
=
200 Hz; pulse width
=
4
μ
sec.
Source: Adapted from Elez-Martınez et al. (2007).
where
E
h
(kV/cm) is a critical level of
E
where RA is 50%,
and the
k
F
parameter (kV/cm) indicates the steepness of the
curve around
E
h
.
Table 5.6 illustrates the parameters calculated for sim-
plified Hulsheger's model and Fermi's model. However,
simplified Hulsheger's model did not predict with enough
accuracy the dependence of HIPEF inactivation of orange
juice PME with
E.
Neither the critical electric field strength
(
E
c
) nor the rate constant (
b
E
) were affected by the treat-
ment time and the pulse polarity. The steepness parameters
(
k
F
) were significantly nondependent on treatment time and
pulse polarity.
Each model provides different information related to the
enzyme inactivation by HIPEF which is very valuable to
design the HIPEF processing of orange juice.
Inactivation of peroxidase (POD) and activities of other
enzymes, for example, lipoxygenase (LOX), PME, and
polygalacturonase (PG), in watermelon juice were studied
by Aguil o-Aguayo et al. (2010). POD was inactivated effi-
ciently after HIPEF processing (35 kV/cm for 1,727
μ
sec
applying 4 μsec pulses at 188 Hz in bipolar mode), achiev-
ing almost a complete inactivation (residual POD activity
of 1.7%) at day 0. The POD activity in the HIPEF-treated
juice increased after 28 days of storage. However, the ther-
mally processed juice at 90
◦
C for 60 sec kept the lowest
residual POD activity values beyond day 7 of storage. A
substantial loss of PME activity (
50%) was observed in
all the treated juices, whereas HIPEF-treated watermelon
juice slightly reduced the RAPME for 56 days of storage.
A slight reduction in PG activity was achieved after the
HIPEF treatment.
>
Quality attributes
Cortes et al. (2006, 2008) made a comparative study of
the evolution and modification of various carotenoids,
vitamin A, color, browning, and hydroxymethylfurfural
(HMF) in untreated orange juice, pasteurized orange juice
(90
◦
C, 20 sec) (HTST), and orange juice processed with
HIPEF (30 kV/cm, 100 μsec) during 7 weeks of stor-
age at 2
◦
and 10
◦
C. It was found that the concentration
Table 5.6.
Reaction kinetics parameter for PME inactivation of orange juice by PEF (monopolarity).
1
Simplified Hulsheger's Model
Fermi's Model
E
c
(kV/cm)
10
3
Treatment Time (μs)
b
E
×
(cm/kV)
E
h
(kV/cm)
k
F
(kV/cm)
100
5
5
46
8
300
6
12
37
7
600
3
14
35.8
11
1,000
3
19
30
9
1,500
3
21
27.4
8
1
Treatment time
=
0-1500
μ
sec; pulse frequency
=
200 Hz; pulse width
=
4
μ
sec.
Source: Adapted from Elez-Martınez et al. (2007).
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