23 Biochemistry of Vegetable Processing 551Odumeru et al. (1997, 1999) defined ready-to-use
vegetables as fresh-cut, packaged vegetables requir-
ing minimal or no processing prior to consumption.
It is generally accepted that MPR F&V are products
that contain live tissues or tissues that have been only
slightly modified from the fresh condition and are
fresh-like in character and quality.
The rapid growth of fast-food restaurants in
the 1980s encouraged the development and use of
fresh-cut products. As the demand for these prod-
ucts increased, new technology and product inno-
vation were developed that helped make fresh-cut
produce one of the fastest growing segments of
the food industry. It is estimated that in the United
States fresh-cut produce market, up to 8% of all pro-
duce is sold in retail grocery outlets and 20% in the
food service industry. This market is expected to
continue growing in size and popularity as more
products are introduced and consumers change their
buying habits. In the United States over the next
5 years, fresh-cut produce sales are expected to
reach $19 billion, compared with $5 billion in 1994.
Freshly prepared, ready-to-eat salads, now with cut
tomatoes, will have a shelf life of up to 14 days uti-
lizing unique modified atmosphere packaging tech-
nology.
Consumption
In the United States, consumption of fresh vegeta-
bles (excluding potatoes) has increased from 60 kg
in 1986 to 72 kg in 2003. In 2003 the most consumed
fresh vegetable was head lettuce at 12 kg, followed
by onions at 9 kg, and fresh tomatoes at 8 kg. In the
same year, the consumption of processed tomatoes
per capita was 35 kg and processed sweet corn 9.5
kg. In Canada, the consumption of fresh vegetables
(excluding potatoes) has been increasing steadily,
reaching 70.2 kg/capita in 1997 from 41 kg/capita in
- Also in 1997, the consumption of fresh vegeta-
bles had declined 2.4% from the amount of fresh veg-
etables consumed in 1996 (71.9 kg/capita). Lettuce
(16%) is the most consumed fresh vegetable, fol-
lowed by onions (12.1%), carrots (12.0%), tomatoes
(11.6%), and cabbage (8.1%). Brussels sprouts,
parsnips, asparagus, beets, and peas each represent
less than 1.0% of Canadian fresh vegetable diet. On a
per capita basis, Canada has one of the highest con-
sumption rates of fresh vegetables in the world.
Frozen vegetable consumption has declined 3.4% to
5.6 kg/capita, while canned vegetables and vegetable
juices have increased 2.4% to 12.9 kg/capita for the
same period. Vegetable purchases by consumers rep-
resent 6.6% of total food expenditures, virtually
unchanged in the past 10 years.ProcessingThe major operations in processing MPR produce are
sorting, sizing, and grading; cleaning, washing, and
disinfection; centrifugation; and packaging and dis-
tribution. For certain vegetables such as eggplant, the
peeling operation follows the sorting operation, and
then there is a size reduction, mixing whenever neces-
sary, packaging, and distribution. Washing of vegeta-
bles for minimal processing is done with a lot of water
(5–10 L/kg) in order to reduce the bacterial load. The
main pathogen of concern in this type of product
isListeria monocytogenes. A water temperature of
about 4°C is recommended. The safety of the product
is best secured through disinfection with chlorine in
the concentration of about 100 mg/L. Two forms
of chlorine are commonly used: gaseous chlorine,
which is 100% active chlorine, and calcium or sodi-
um hypochlorites. Calcium and sodium hypochlo-
rites are most popular in MPR F&V industry.
Centrifugation is one of the major operations in
MPR processing. The purpose is to dry the vegeta-
bles rapidly. The efficacy of the centrifugation de-
pends on the speed and time of rotation of the cen-
trifuge. Certain antioxidants such as ascorbic acid
and citric acid, at a concentration of about 300 ppm
in the wash solution, would enhance the quality of
the products. The processing techniques employed
usually wound the tissue and may cause the libera-
tion of “wound ethylene,” which can activate deteri-
orative reactions within the tissue. Vegetables of
high quality may also have a good complement of
the antioxidants (vitamins C and E, reduced glu-
tathione) and the antioxidant enzyme system that
comprises enzymes such as superoxide dismutase,
catalase, peroxidase, and ascorbate peroxidase. An
active pentose phosphate pathway is required for
the supply of reduced nicotinamide adenine dinu-
cleotide phosphate (NADPH) for the efficient func-
tioning of the antioxidant enzyme system.
Membrane phospholipid degradation mediated by
phospholipase D is activated in response to wound-
ing. Damage to the tissue during processing can
cause the leakage of ions such as Ca^2 and H,