Novel Processing Technologies for Fruits - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 82

Temperature
Sensor

Reflex

Oven opening

Microwave oven

Fruits
PTFE grid

Computer

Fruit juice

« Easy Wave »
software package Oven opening

Column

Graduated cylinder

Chronograph

Figure 5.8. Schematic for the extraction of fruit juice using microwave heating (source: Cendres et al., 2011).

selected temperatures ( D -values at 60 ◦ C: batch microwave
=

( z -value) of MW-assisted carotenoid degradation at selected
temperatures are presented in Table 5.7. The z -value for to-
tal carotenoids was 14.2 ◦ C; for single compounds, z -values
ranged between 10.9 ◦ Cfor

7.37 sec, continuous microwave = 22 sec, and con-

ventional 150 sec). The authors claimed that some

enhanced-thermal effects during microwave heating largely
contributed to greater PME inactivation.
The effects on orange juice batch pasteurization in an im-
proved pilot-scale microwave (MW) oven were evaluated
by monitoring PME activity (Cinquanta et al., 2010). The
heat sensitive fraction of PME was inactivated after about
1minat70 ◦ C of MW heating. This point, corresponding
to 5.5

=

-carotene and 16.7 ◦ Cforan-

β

theraxanthin.
Cinquanta et al. (2010) used an improved pilot-scale mi-
crowave (MW) oven for pasteurization of orange juice and
studied effects of MW heating on juice quality parame-
ters namely color, carotenoid compounds and vitamin C
content. Total color differences ( E ) increased significantly
with temperature and the value set to 11.2 after 1 min at
85 ◦ C. More significant carotenoid losses were recorded in
orange juice processed at higher temperatures: the heat
treatment caused losses ranging from 41% at 75 ◦ Cfor
1 min to 52% at 85 ◦ C for 1 min. A total of seven carotenoid

10 − 5 PMEU, was lower than values recommended
for orange juice pasteurized. The MW thermal behavior
of PME in orange juice was estimated at different times
and temperatures (60 ◦ ,70 ◦ ,75 ◦ , and 85 ◦ C), to calculate
the decimal reduction time ( D )and z -values. The D -values
of PME were 23.2 min (60 ◦ C), 10.6 min (70 ◦ C), 2.9 min
(75 ◦ C), and 1.7 min (85 ◦ C), with a z -value equal to 22.1 ◦ C.

×

Table 5.7. Thermal kinetic parameters of
carotenoids in MW-treated orange juice.

Quality attributes
Degradation of carotenoids in orange juice was stud-
ied by Fratianni et al. (2010) during microwave (MW)
heating at different time/temperature conditions. Degra-
dation rate of carotenoids was influenced by MW heat-
ing temperatures. Degradation of violaxanthin and anther-
axanthin were clearly detected after 10 min of heating
at 60 ◦ and 70 ◦ C, while compounds with provitamin ac-
tivity (

D Value (min)

60 ◦ C ◦ C ◦ C z Va l u e ( ◦ C) Carotenoid

Violaxanthin 21.3 8.2 8.7 11.7

Antheraxanthin 28.9 8.5 3.6 16.7

Lutein 130.1 31.7 5.0 11.2

Zeaxanthin 37.0 13.9 3.3 15.1

-cryptoxanthin) and lutein were
more stable at these temperatures. At 85 ◦ C a decrease of
about 50% was observed for almost all carotenoids after
1 min of MW heating. Thermal degradation of carotenoids
followed first-order reaction kinetics. The decimal reduc-
tion time ( D -value) and thermal resistance temperature

β -carotene and β

β -Crytoxanthin 45.1 21.3 4.0 11.8

α -Carotene 99.3 29.8 5.9 12.9

β -Carotene 99.7 24.6 3.5 10.9

Total carotenoids 56.6 4.5 14.2

Source: Fratianni et al. (2010).