BLBS102-c28 BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm Printer Name: Yet to Come
28 Biochemistry of Fruit Processing 563Washing and sortingDisintegratorJuice extractionEnzyme treatmentFiltrationEvaporationStandardizationStorageRaw appleFigure 28.4.Apple juice and concentrate flow chart.other methods). Juice yield from different types of extraction
varies from 75% to 95%, and depends on many factors includ-
ing the cultivar and maturity of the fruit, the type of extraction,
the equipment and press aids, the time, temperature, and the
addition and concentration of the enzyme to the apple mash
(Fig. 28.4).Enzyme ApplicationsEnzyme applications in the apple juice processing follow the
extraction, especially when producing a clarified 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 hy-
drolyzes the pectin molecule so it can no longer hold juice. The
treatment dosage of pectinase depends on the enzyme strength
and varies from one manufacturer to another. A typical ‘3X’
enzyme dosage is about 100 mL per 4000 liters of raw juice.
Depectinization is important for the viscosity reduction and the
formation of galacturonic acid groups that helps flocculate thesuspended matter. This material, if not removed, binds to the fil-
ters, reduces the production, and can result in a haze formation
in the final product. There are two methods of enzyme treatment
commonly used in the juice industry including (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 postpro-
cessed juice, other polymers such as starch, and arabinans can
be present and therefore, the clear juice is treated with alpha-
amylase and hemicellulase enzymes, in order to partially or
completely degrade them. Gelatin can be used to remove frag-
mented pectin chains and tannins from the juice. Best results
are obtained when hydrating 1% gelatin in warm 60◦C water.
Gelatin can be added in combination with the enzyme treatment,
bentonite, or by adding midway through the enzyme treatment
period. The positively charged gelatin facilitates the removal of
the negatively charged suspended colloidal material from the
juice. Bentonite can be added in the range of 1.25–2.5 kg of re-
hydrated bentonite per 4000 L of juice. Bentonite is also added to
increase the efficiency of settling, protein removal, and preven-
tion of cloudiness caused by metal ions. For cloudy and natural
apple juice, enzymes are usually not used. The enzyme-treated,
refined, and settled apple juice is then pumped from the settled
material (lees) and further clarified by filtration.
The filtration of apple juice is done with or without a filter
aid. The major types of filters are pressure leaf, rotary vacuum,
frame, belt, and Millipore filters. To obtain the desired product
color and clarity, most juice manufacturers use a filter medium
or filter aid in the filtration process. The filter media include
diatomaceous earth, paper pulp pads, cloth pads or socks, and
ceramic membranes to name a few. The filter aid helps to pre-
vent the blinding of the filters and increase throughput. As the
fruit matures, more filter aid will be required. Several types of
filter aids are available, in which the most commonly used is
diatomaceous earth or cellulose-type materials. Additional juice
can be recovered from the tank bottoms or “lees” by centrifuga-
tion or filtration. This recovered juice can be added to the raw
juice before filtration.
Diatomaceous earth, or kieselguhr, is a form of hydrated silica.
It has also been called fossil silica or infusorial earth. Diatoma-
ceous earth is made up of the skeletal remains of prehistoric
diatoms that were single-cell plant life and is related to the algae
that grow in the lakes and oceans. Diatomaceous earth filtration
is a three-step operation: (1) first, a firm thin protective precoat
layer of filter aid, usually of cellulose, is built up on the filter
septum (which is usually a fine wire screen, synthetic cloth,
or felt); (2) the use of the correct amount of a diatomite body
feed or admix (about 4.54 kg per 3000 cm^2 of filter screen);
and (3) the separation of the spent filter cake from the septum
prior to the next filter cycle. Prior to the filtration, centrifugation
may be used to remove high-molecular weight suspended solids.