23 Biochemistry of Vegetable Processing 545300 mm 407 mm cans to 10 minutes for 603 mm
700 mm cans. Exhaust is also done by mechani-
cal vacuum closing machines (Lopez 1987, Gould
1992).
Processing
The processing time of canned tomato depends on
many factors including the pH of the canned tomato,
the major spoilage microorganisms of concern, the
size of the can, and the type of retort (sterilizer).
Organisms of concern in canned tomatoes are C.
pasteurianumand C. butyricum, as well as Bacillus
coagulans (B. thermoacidurans).Spores of butyric
acid anaerobes are destroyed at 93.3°C for 10 min-
utes when the pH is higher than 4.3, and after 5 min-
utes when the pH is between 4 and 4.3. Canned
tomatoes can be processed with a rotary sterilizer,
with a conventional stationary retort, or in an open
nonagitating cooker. In general, the processing time
is longer if the cooling is done by air instead of with
water. For a rotary sterilizer the processing time at
100°C for a can of 307 mm 409 mm may be
reduced to 9 minutes or less if air cooled, and to 13
minutes or less if water cooled. For the same size of
can at 100°C an open nonagitating cooker or a con-
ventional retort would require a processing time of
35–55 minutes. The can center temperature should
reach 82°C when air cooled, and 90°C when water
cooled (Lopez 1987). The retort time depends on the
size of the can, the fill weight, and the initial temper-
ature of the canned product.
TOMATOJUICEPROCESSING
Processing
Tomato juice is defined as the unconcentrated, pas-
teurized liquid containing a substantial portion of
fine tomato pulp extracted from good quality, ripe,
whole tomatoes from which all stems and unneces-
sary portions have been removed by any method that
does not increase the water content; it may contain
salt and a sweetening ingredient in dry form (Cana-
dian Food and Drugs Act). Only high quality toma-
toes should be used for juice production. Tomatoes
are an important source of vitamins A and C and an-
tioxidants such as lycopene. In tomato and tomato
products, color serves as a measure of total quality.
Consumers notice color first, and their observation
often supplements preconceived ideas about other
quality attributes such as aroma and flavor. Color in
tomato is due to carotenoids, a class of isoprenoid
compounds varying from yellow to red color. Most
carotenoids are tetraterpenes (C 40 ), derived from
two C 20 isoprene units (geranylgeranyl pyrophos-
phate). The most isolated and quantified carotenoids
in tomato and tomato products include lycopene,
lycope-5-6-diol, -carotene, -carotene, -carotene,
-carotene, lutein, xanthophylls (carotenol), neuro-
sporene, phytoene, and phytofluene. Lycopene is the
major carotenoid of tomato and comprises about
83% of the total pigments present in the ripe fruit
(Thakur et al. 1996). Therefore the levels of lyco-
pene are very important in determining the quality
of processed tomato products. It not only determines
the color of tomato products, but also provides anti-
oxidant properties to them. Lycopene is considered
as a preventive agent against coronary heart disease
and cancers (Gerster 1991, Clinton 1998). The flow-
chart for making tomato juice is as follows: fresh
tomatoes →washing →sorting and trimming →
comminution →extraction →deaeration →homog-
enization →salting and acidification →thermal
processing →tomato juice.Comminution Comminution is a process of chop-
ping or crushing tomatoes into small particles prior
to extraction. The comminuted tomatoes are subject-
ed to either cold break or hot break processing. The
cold break processing produces tomato juice with a
more natural color, fresh flavor, and higher vitamin
C content than does the hot break process. The hot
break process, on the other hand, produces tomato
juice with higher consistency and less tendency to
separate, but with a cooked flavor. During the cold
break process, the comminuted tomato is heated be-
low 65°C (to introduce rapid enzyme inactivation)
and held at room temperature for a short time (a few
seconds to many minutes) prior to extraction. In the
hot break process, the tomatoes are rapidly heated to
above 82°C, immediately following comminution,
in order to inactivate pectin esterase and enhance
pectin extraction. Hot break process can be done
either in a rotary heat exchanger or in a rotary coil
tank. The latter not only inactivates the enzymes fast
enough to retain most of the serum viscosity, but
also deaerates the juice. Low pH inhibits pectic en-
zymes and enhances the extraction of macromole-
cules such as pectin. Therefore, the addition of citric