Agriculture Reference
In-Depth Information
Figure 7.6.
Design of package containing a breathable window of ultra-high oxygen transmission rate (OTR)
membrane-white component (reprinted with permission from authors Kerddonfag et al., 2007; Chinsirikul
et al., 2009).
production. For very sensitive fruit commodities such as
kiwifruit, packaging with sufficient ethylene-absorbing ca-
pability may be essential in maintaining quality and shelf
life for commercial purposes (Zagory, 1995). This point has
led to extensive research studies over the past two decades
regarding the removal of ethylene from package headspaces
and/or in suppressing its effects. One relatively recent dis-
covery of 1-methyl cyclopropane (1-MCP) as an inhibitor
of ethylene action has received considerable attention for
improving the shelf life of climacteric fruits, but this subject
will not be covered in this chapter.
Potassium permanganate (KMnO
4
) has long been used
as an ethylene scavenger in a sachet form which is placed
inside the package. However, potassium permanganate has
become unacceptable for use in contact with food due to its
toxicity and color leakage (Vermeiren et al., 1999). Some
minerals or porous ceramics, including zeolite, active car-
bon, cristobalite, and clay, are considered alternative ethy-
lene control agents. Research efforts and development of
commercial products based on incorporation of these min-
erals within packaging films for fresh produce have been
reviewed by Zagory (1995) and L opez-Rubio et al. (2008).
Some commercial examples are Evert-Fresh (Evert-Fresh,
USA), Orega plastic film (Cho Yang Heung San, Republic
of Korea), and Peakfresh (Peakfresh Products, Australia).
Many of the mineralized films or bags claim to extend the
shelf life by reducing headspace ethylene, when compared
with common PE bags. However, questions remain with re-
gard to their ethylene-adsorbing capacity due to open pores
generated within the mineral-filled films, which can allow
ethylene to pass through pores rather than the plastic it-
self. Another concern involves ethylene diffusion through
the plastic matrix before coming in contact with the dis-
persed mineral. For this reason, it is understandable why
some commercial films of zeolite-filled PE contain zeo-
lite particles with diameter larger than the film thickness
(Fuongfuchat et al., 2008).
Zeolite-filled LDPE composite films possess ethylene
permeability comparable to that of neat PE film. The unen-
hanced results for ethylene permeation were attributed to
the intrinsically low permeation to ethylene of the LDPE
matrix. However, an increase in permeation kinetics was re-
ported for 10 wt% zeolite-filled LDPE, compared with neat
LDPE film. To overcome the limitation of the low ethy-
lene permeation of LDPE, Fuongfuchat et al. (2008) devel-
oped high ethylene-permeable blends of LDPE and styrene-
ethylene-butylene-styrene block copolymer (SEBS). A
70:30 blend of LDPE:SEBS offered a much higher ethy-
lene permeability of
1,780 cm
3
mm m
−
2
day
−
1
atm
−
1
,
∼
1,000 cm
3
mm m
−
2
day
−
1
atm
−
1
). Interestingly, a twofold increase in ethylene per-
meability over neat LDPE was obtained for zeolite-filled
PE/SEBS. Resulting films containing 10 wt% zeolite had
high ethylene permeability ranging from 1,900 to 2,200 cm
3
mm m
−
2
day
−
1
atm
−
1
, where desirably high oxygen per-
meability was also obtained (i.e., 220-600 cm
3
mm m
−
2
day
−
1
atm
−
1
or OTR of 5,500-15,000 cm
3
m
−
2
day
−
1
). Re-
sults also indicated the films' permselectivity to ethylene.
Zeolite-filled PE/SEBS exhibited a high ratio of ethylene
to O
2
permeability (
α
) of 6-7, where the
α
values of LDPE
and other polyolefins were reported to be approximately
1.5-2.0 (Wang et al., 1998). The ethylene-removing capa-
bility of the developed composite films versus LDPE was
also evaluated by monitoring the ethylene level inside the
bags at room temperature based on an initial ethylene con-
centration of 4 ppm. The composite films showed a higher
reduction rate of ethylene; much less ethylene (
as compared with LDPE (
∼
0.1 ppm)
remained after 4 days of testing (Fig. 7.7). Further study
showed that the modification of zeolite surface of silica-
rich zeolite (BEA)-filled membranes exhibited enhanced
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