524 Part V: Fruits, Vegetables, and Cereals
compounds in fruit juice by naturally present en-
zymes.
Apple Juice Processing
Apple juice is processed and sold in many forms
including American apple cider, European apple
cider, and shelf-stable apple juice. American apple
cider is the product of sound, ripe fruit that has been
pressed and bottled or packaged with no form of
preservatives added and stored under refrigeration.
This is a sweet type of cider, which has not been fer-
mented. Because of an increased number of food-
borne outbreaks of E. coli0157:H7 and Crypto-
sporidium parvumin apple cider, many jurisdictions
are working toward implementation of a kill step in
the processing of apple cider. The recent outbreaks
make apple cider not suitable for children, the el-
derly, and immuno (1) compromised people.
European-type apple cider is a naturally fermented
apple juice, usually fermented to a specific gravity
of 1 or less (Anonymous 1980). Shelf-stable apple
juice includes clarified and crushed apple juice and
concentrates. The most popular type of apple juice is
the one that has been clarified and filtered before
pasteurization and bottling. Natural juice is a juice
that comes from the press. Up to 2% of ascorbic acid
can be added before pasteurization and bottling in
order to preserve the color. Crushed apple juice is
produced by passing coarsely ground apples through
a pulper and a juice extraction device before pas-
teurization.
Juice concentrates can be of two types: (1) frozen,
when the Brix is about 42°, or (2) regular (commer-
cial) concentrate, with a Brix of 70° or more. Re-
gardless of the type of apple product that is to be pro-
duced, the quality of the apple juice is directly related
to the quality of the raw material used in its produc-
tion. Only sound ripe fruits should be used in the pro-
cessing of apple juice. Windfalls, apples that are fall-
en and picked from the ground, should not be used for
the juice due to the risk of contamination by path-
ogens such asE. coliO157:H7,Cryptosporidium par-
vum,Penicillium expansium(producing the myco-
toxin patulin) and also the risk of pronounced musty
or earthy off-flavor in the juice. Overmature apples
are very difficult to process, whereas immature apples
give a starchy and astringent juice with poor flavor.
The processing of apple juice starts with washing
and sorting of the fruit in order to remove soil and
other foreign material as well as decayed fruits. Any
damaged or decayed fruit should be removed or
trimmed in order to keep down the level of patulin in
the finished juice. Patulin is an indicator that tells if
the juice was produced from windfalls or spoiled
apples. The acceptable level of patulin in most coun-
tries is less than 50 ppb. Patulin is carcinogenic and
teratogenic. Various methods are currently used to
reduce the levels of patulin in apple juice, namely,
charcoal treatment, chemical preservation (with sul-
fur dioxide), gamma irradiation, fermentation, and
trimming of fungus-infected apples. A recent study
shows that pressing followed by centrifugation re-
sulted in an average toxin reduction of 89%. Total
toxin reduction using filtration, enzyme treatment,
and fining was 70, 73, and 77%, respectively, in the
finished juice (Bissessur et al. 2001). Patulin reduc-
tion was due to the binding of the toxin to solid sub-
strates such as the filter cake, pellet, and sediment.
Prior to pressing, apples are ground using disinte-
grators, hammers, or grating mills. The effectiveness
of the pressing operation depends on the maturity
level of the fruits, as more mature fruits are often
difficult to press. A wide range of presses are used in
juice extraction including hydraulic, pneumatic, and
screw/basket types. The vertical hydraulic press is a
batch-type press that requires no press aid. Its main
disadvantage is that the press is labor intensive and
produces juice with low solids content. Hydraulic
presses are the oldest type of press and are still used
worldwide. The newer versions are automated and
require press aids such as up to 1–2% paper pulp,
rice hulls, or both in order to reduce spillage and
increase juice channel in the mash.
Although the apple mash has many natural
enzymes, enzymatic mash treatment has been devel-
oped to improve the pressability of the mash and,
therefore, the throughput and yield. Pectinolytic
enzyme products contain the primary types of pecti-
nases, pectin methylesterase (PME), polygalactur-
onase (PG), pectin lyase, and pectin transeliminase
(PTE). PME deesterifies methylated carboxylic acid
moieties of pectin, liberating methanol from the side
chain, after which PG can hydrolyze the long pectin
chains (Fig. 22.3). From 80 to 120 mL of enzyme
per ton is added to the apple mash in order to break
down the cell structure. (High molecular weight
constituents of cell walls, like protopectin, are insol-
uble, and they inhibit the extraction of the juice from
the fruit and keep solid particles suspended in the