22 Biochemistry of Fruit Processing 525juice.) Pectinase used in apple juice processing is
extracted from the fungus Aspergillus niger. Pec-
tinase developed for apple mash pretreatment acts
mainly on the cell wall, breaking the structure and
freeing the juice. Also, the viscosity of the juice is
lowered, and it can emerge more easily from the
mash. The high content of pectin esterase (PE) in the
mash causes the formation of deesterified pectin
fragments, which have a low water-binding capacity
and reduce the slipperiness of the mash. These pec-
tins consist of chains of galacturonic acid joined by
alpha-glycoside linkage. In addition, polymers of
xylose, galactose, and arabinose (hemicelluloses)
form a link with the cellulose. The entire system
forms a gel that retains the juice in the mash. The
extraction is easier, even if the pectins are partially
broken by pectin esterase. The pomace acts like a
pressing aid, when used with mash predraining. The
application of enzyme treatment can increase the
press throughput by 30–40% and the juice yield by
over 20%. Mash pretreatment also increases the flux
rate of ultrafiltered apple juice by up to 50%.
An important by-product of apple juice industry
is pectin, so overtreatment of mash with pectinolytic
enzymes could render the pomace unsuitable for the
production of pectin. Inactivation of the enzyme
after reaching the appropriate level of pectin degra-
dation is therefore an important step in the produc-
tion of apple juice. Also, residual pectic enzymes in
apple juice concentrate could cause setup problems,
for example, when concentrate is used for making
apple jelly.
One recent development in apple juice extraction
is the process of liquefaction. Liquefaction is a pro-
cess of completely breaking down the mash by using
an enzyme preparation, temperature, and time com-
bination. The liquefied juice is extracted from the
residual solid by the use of decanter centrifuges and
rotary vacuum filters. It is a common practice, with
the addition of cellulose enzyme to the mash, to
further degrade the cellulose to soluble solids, in-
creasing the juice Brix by nearly 5°. Commercially
available enzyme preparations contain more than
120 substrate-specific enzyme components.
Another popular extraction method is the counter-
current extraction method, developed in South Af-
rica and refined in Europe in the 1970s. The princi-
ple of the system is as follows: the mash is heated,
predrained, and counter-washed with water and re-
cycled hot juice. A 90–95% recovery is possible
when the throughput is about 3 tons/hour. The main
disadvantage of the system is the lower soluble
solids content of the juice obtained (6–8 versus 11–
12 from other methods). Juice yield from different
types of extraction varies from 75 to 95% and de-
pends on many factors, including the cultivar and
maturity of the fruit, the type of extraction, the
equipment and press aids, the time, the temperature,
the addition of enzyme to the apple mash, and the
concentration of the added enzyme.Enzyme ApplicationsEnzyme applications in apple juice processing fol-
low extraction, especially when producing a clari-
fied type of juice. The main objective is to remove
the suspended particles from the juice (Smock and
Neubert 1950). The soluble pectin in the juice has
colloidal properties and inhibits the separation of the
undissolved cloud particles from the clear juice.
Pectinase hydrolyzes the pectin molecule so it can
no longer hold juice. The treatment dosage of pecti-
nase depends on the enzyme strength and varies
from one manufacturer to another. A typical “3X”
enzyme dosage is about 100 mL/4000 L of raw
juice. Depectinization is important for viscosity
reduction and the formation of galacturonic acid
groups that help flocculate the suspended matter.
This material, if not removed, binds to the filters,
reduces production, and can result in haze formation
in the final product. There are two methods of en-
zyme treatment commonly used in the juice indus-
try: (1) hot treatment, where the enzymes are added
to 54°C juice, mixed, and held for 1–2 hours; and (2)
cold treatment, where the enzymes are added to the
juice at reduced temperature (20°C) and held for 6–
8 hours. The complete breakdown of the pectin is
monitored by means of an acidified alcohol test.
Five milliliters of juice are added to 15 mL of HCl-
acidified ethyl alcohol. Pectin is present if a gel
develops in 3–5 minutes after mixing the juice with
the ethanol solution. The absence of gel formation
means the juice depectination is complete. In the
cloud of the postprocessed juice, other polymers
such as starch and arabinans can be present; there-
fore, the clear juice is treated with alpha-amylase
and hemicellulase enzymes, in order to partially or
completely degrade the polymers. Gelatin can be
used to remove fragmented pectin chains and tan-
nins from the juice. Best results are obtained when