Food Biochemistry and Food Processing (2 edition)

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29 Biochemistry of Vegetable Processing 581

C

p

Quantity of adsorbed

compounds

Concentration

(A) Horizontal (B) Vertical

Adsorption state of polymers

(C) Stichlike

Figure 29.3.Isotherm of adsorption of polymers; polymer adsorption states.

The rapid growth of fast-food restaurants in the 1980s en-

couraged the development and use of fresh-cut products. As

the demand for products increased, new technology and prod-

uct innovation were developed to help make fresh-cut produce,

one of the fastest growing segments of the food industry. It is

estimated that in the US fresh-cut produce market, up to 8%

of all produce is sold in retail grocery outlets and 20% sold in

the food service industry. It is expected to continue growing in

size and popularity as more products are introduced and con-

sumers change their buying habits. In the first quarter of 2006,

the sale of fresh cut produce in the United States accounted

for $1.3 billion, with major sales (∼80%) coming from vegeta-

bles. In 2007, the fresh cut produce market was estimated at

$15.9 billion in the United States (www.agecon.ucdavis.edu).

Freshly prepared ready to eat salads, now with cut tomatoes,

will have a shelf life of up to 14 days utilizing unique Modified

Atmosphere Packaging technology.

Processing

The major operations in processing of MPR produce in-

clude Sorting/Sizing/Grading, Cleaning/washing/disinfection,

Centrifugation, and Packaging and Distribution. For certain veg-

etables such as eggplant, the peeling operation follows the sort-

ing operation that results in a size reduction, and mixing, packag-

ing and distribution. Washing of vegetables for minimal process-

ing, uses a significant amount of water (5–10 L/kg) to achieve

a reduction in the bacterial load. The main pathogen of concern

in this type of products isListeria monocytogenes. The water

temperature of about 4◦C is recommended. The safety of the

product is best secured through disinfection with chlorine at a

concentration of about 100 mg/L. Two forms of chlorine are

commonly used: gaseous chlorine, which is 100% active chlo-

rine, and calcium or sodium hypochlorites. The latter is most

popular in MPR industry.

Centrifugation is one of the major operations in MPR process-

ing. The purpose is to dry the vegetables rapidly. The efficacy

of the centrifugation depends on the speed and time of rotation

of the centrifuge. Certain antioxidants such as ascorbic acid and

citric acid at a concentration of about 300 ppm in the wash solu-

tion would enhance the quality of the products. The processing

techniques employed usually wound the tissue and may cause

the liberation of “wound ethylene” that can activate deteriorative

reactions within the tissue. Vegetables of high quality may also

have a good complement of the antioxidants (vitamins C and

E, reduced glutathione) and the antioxidant enzyme system that

comprise the enzymes such as superoxide dismutase, catalase,

peroxidase, ascorbate peroxidase, and so on. An active pentose

phosphate pathway is required for the supply of reduced nicoti-

namide adenine dinucleotide phosphate-reduced form for the

efficient functioning of the antioxidant enzyme system. Mem-

brane phospholipid degradation mediated by phospholipase D,

is activated in response to wounding the tissue. Damage to the

tissue during processing can cause the leakage of ions such as

Ca^2 +and H+which can activate phospholipase D. Naturally

occurring phospholipase D inhibitors such as hexanal can be

used to reduce the activity of phospholipase D in processed

tissues and enhance their shelf life and quality (Paliyath et al.