tested three types of Pliofilm liners for storing apples at 4° C. (39.2° F.). 
They obtained good results with Golden Delicious, Red Delicious, Berlepsch, and 
Canada varieties, fair results with Cox's Orange, and poor with Ontario. How- 
ever, most research has been with polyethylene, usually 1.5-mil thickness, This 
film has the desirable characteristics of being easy to handle and differen- 
tially permeable to the respiratory gases. Depending on thickness, density, 
and method of manufacture, it is usually 3 to 5 times more permeable to carbon 
dioxide than to oxygen. It is also sufficiently moisture retentive for box 
liner use. 
The original work by Gerhardt (16) on Golden Delicious apples showed 
that sealed 1,5-mil polyethylene liners maintained 3 to 4 percent carbon dioxide 
and 10 to 13 percent oxygen, which was beneficial. To avoid possible injury to 
the fruit, perforating or slitting the sealed film was recommended upon with- 
drawal from cold storage for marketing (16, 24, 27, 31, 78, 79). Commercially, 
film liners are often removed from boxes before marketing and sometimes are used 
again another season. However, reuse of liner is not recommended where sealing 
is desired, because any holes will prevent buildup of desired atmospheres (33). 
Since the early work by Gerhardt, other investigators have found that 
1.5-mil polyethylene film is not necessarily a safe film for sealed box liners 
C7, 103) 225. 275 31, 58,- 10, 73,'-17, 18, 79)! Injury in many -ditferentatorms 
has been observed, Polyethylene from different sources varies in permeability. 
If made from low density resisn, it is much more permeable than if made from 
medium or high density resins (27). A polyethylene film with a low density of 
0.914 to 0.920 was more desirable than one with a density of 0.928 or above. 
When the higher density film was used, the oxygen level sometimes dropped to l 
percent and the fruit showed low-oxygen injury. 
Polyethylene is less permeable at low temperatures than at high tempera- 
tures. It is also less permeable at 2-mil than at 1.5-mil thickness, Harden- 
burg and Anderson (27) found that Grimes Golden and Rome packed in sealed 2-mil 
film liners maintained box atmosphere of 1 to 2 percent or less oxygen and 8 to 
12 percent carbon dioxide at 32° F. This fruit was severely injured on examin- 
ation. It had a fermented flavor, and in some boxes showed 50 to 70 percent 
visible injury from the low oxygen and high carbon dioxide concentrations. 
Okamoto, Horitsu, and Harata (57) tested three thicknesses of sealed polyethyl- 
ene liners for Ralls apples, At 32° F. they had excellent results with 0.03 mm 
(1.2 mil) and 0.045 mm polyethylene, but with 0.06 mm (2.4 mil) film the storage 
life was shortened because of inadequate gas exchange. 
Even with a given lot of 1.5-mil polyethylene liners, oxygen atmospheres 
maintained were not uniform (27). Carbon dioxide concentrations were maintained 
within a narrow range of 4 to 7 percent on several varieties, but oxygen levels 
were much more variable, ranging from 1 to 14 percent. Fruit variability was 
one factor responsible, Cowell and Scott (7) explained that the variable oxygen 
levels in sealed liners is an inherent feature of this storage technique. 
Sealed liners should thus be used only with varieties that have a reasonable 
tolerance to carbon dioxide and a wide tolerance to oxygen levels. 
Perforated films have been evaluated in attempts to avoid possible injury 
from sealed liners (10, 12, 22, 27, 28). Duvekot (10) reported that Jonathan 
and Laxton's Superb apples needed one perforation in the top of sealed liners 
to avoid injury. Hansen (22) found that Golden Delicious kept very well in 
sealed polyethylene liners at 35° to 37° F., provided the liners were pierced 
to allow escape of carbon dioxide, Hardenburg and Anderson (28) showed that 
folded-top nonsealed liners maintain considerable modified atmosphere around 
54 
