BLBS102-c29 BLBS102-Simpson March 21, 2012 13:27 Trim: 276mm X 219mm Printer Name: Yet to Come
29 Biochemistry of Vegetable Processing 577C, and antioxidants 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 pre-
conceived 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 2 C-20 isoprene units
(Geranylgeranyl pyrophosphate). The most isolated and quan-
tified carotenoids in tomato and tomato products include ly-
copene, lycope-5–6-diol,α-carotene,β-carotene,γ-carotene,
δ-carotene, lutein, xanthophylls (carotenol), neurosporene, phy-
toene, 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
lycopene are very important in determining the quality of pro-
cessed tomato products. Not only does it determine the color of
tomato products, but also provides antioxidant properties to it.
Lycopene is considered as a preventive agent against coronary
heart disease and cancers (Gerster 1991, Clinton 1998). The
flowchart for making tomato juice is as follows: Fresh toma-
toes→Washing→Sorting and Trimming→Comminution→
Extraction→Deaeration→Homogenization→Salting and
Acidification→Thermal Processing→Tomato juice.ComminutionComminution is a process of chopping or crushing tomatoes into
small particles prior to extraction. The comminuted tomatoes are
subjected to either cold-break or to hot-break processing. The
cold-break processing produces tomato juice with a more natural
color, fresh flavor, and higher vitamin C content than does hot-
break process. The hot-break process on the other hand, produces
tomato juice with higher consistency, lesser tendency to separate,
but with a cooked flavor. During the cold-break process, the
comminuted tomato is heated below 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
pectinesterase 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 enzymes and enhances the extraction of
macromolecules such as pectin. Therefore, the addition of citric
acid to the juice during comminution improves the consistency
of the juice (Miers et al. 1970, Becker et al. 1972).ExtractionExtraction is a process of separating the seeds and skins from
the juice. There are two types of extractors: screw type and
paddle type. The screw-type presses tomatoes between a screw
and a screen with about 0.5–0.8 mm (Lopez 1987). Paddle-type
extractors beat the tomato against screens. The extraction yields
3% of seeds and skins and 97% juice. Procedures that target alower yield of 70–80% result in a better quality juice and a high
quality residue for other purposes.DeaerationThe deaeration process improves color, flavor, and ascorbic acid
content of the juice. It is done immediately after the extraction
by a vacuum deaerator. Removal of oxygen inhibits oxidative
processes.HomogenizationA stable juice is one in which the solid and liquid phases do not
separate during storage for a long period of time. The ability of
a juice to separate depends on many factors including the serum
viscosity, the gross viscosity, the pH of the medium, the size and
shape of the suspended solids and so on. Homogenization is a
process of forcing the juice through narrow orifices at a pressure
of 6.9–9.7 MPa and a temperature of about 65◦C to break up the
suspended particles to a fine consistency (Lopez 1987).SaltingSodium chloride is sometimes added to the juice at a rate of
0.5–1.25% by weight in order to improve the taste of the tomato
juice. Citric acid is added to improve the color, flavor, and taste.
In addition, citric acid inhibits polyphenoloxidase by removing
the bound copper from the enzyme, reducing browning reactions
and improving color.Quality Attributes of Tomato and Processed ProductsThe major quality attribute of ripe tomato is its red color, which is
due to the lycopene content of the fruit. Other important physic-
ochemical parameters, which determine the quality of tomato
are Brix, acidity, pH, vitamin C, ash, dry matter, firmness, fruit
weight, and flavor volatiles. For processed tomato product, the
required quality attributes are precipitate weight ratio, serum vis-
cosity, total viscosity (Brookfield), and lycopene content of the
product. Several quality attributes of tomato and tomato prod-
ucts can be improved by genetic modification of tomatoes (Oke
et al. 2003). These comparisons were made between fruits ob-
tained from untransformed and genetically transformed tomato
plants carrying an antisense phospholipase D cDNA, and juice
prepared from these fruits. The levels and activity of phospholi-
pase D, the key enzyme involved in membrane lipid degradation,
were considerably reduced by antisense transformation. These
changes potentially resulted in increased membrane stability and
function that also improved several quality parameters. The fla-
vor profiles of blended antisense tomato fruits were different
from the controls, being enriched in volatile aldehydes such as
pentenal and hexenal. Increased membrane stability in trans-
genic fruits potentially resulted in lowered degradation of unsat-
urated fatty acids such as linoleic and linolenic acids and may
have contributed to increased substrate availability for lipoxyge-
nase pathway enzymes (lipoxygenase, hydroperoxide lyase, and
so on) during blending with an increased evolution of volatile