Mechanisms of Food Additives, Treatments, and Preservation Technology 317
conditions of blanching. Losses of nutrients can be reduced, for example, by the use
of microwave blanching (Ramesh et al., 2002).^ Exudation is undesirable in the case
of nutrients but it can be beneficial for reduction of toxic constituents; for example,
water blanching can reduce nitrate content from 339 mg/kg in raw carrots to 165
mg/kg after the washing and blanching process (95°C)^ (Selman, 2000). Blanching
treatment also reduces microbial contamination. The microorganisms on the surface
of produce are rinsed out or inactivated by heat. The reduction rate depends on the
conditions of the process and the properties of the microorganisms.
10.2.2.2.3 Prevention of Texture Softening by Dipping
Slicing, cutting, or shredding usually results in losses of firmness of fruit or vegetable
tissues due to enzymatic pectinolysis and other changes in damaged cells and
adjacent layers. Softening is mainly caused by changes in pectins. Calcium salts are
used to decrease softening in a number of minimally processed fruits and vegetables.
The ions infiltrate the tissue and bind to the cell wall and middle lamellae^ (Glenn
and Poovaiah, 1990). Calcium ions interact with pectin polymers to form a cross-
linked polymer network that increases the mechanical strength of the tissues. A
dipping solution of calcium salts is relatively common in the processing of pome
fruits. Dipping in a solution of 0.1 up to 1% CaCl 2 is used (Soliva and Martin-
Belloso, 2003). Calcium salts can also be added to the wash water or to brine. This
is frequently used for vegetables such as pickled peppers and cucumbers. The direct
addition of CaCl 2 can affect taste because of the bitter taste of calcium chloride. For
this reason, the use of nonchloride salts of calcium, such as phosphates and lactates,
is common^ (Kyzlink, 1990). When dipping is used as an antisoftening treatment, it
is usually combined with other treatments: dipping solutions usually have added
antibrowning agents, preservatives, or disinfectants.
10.2.3 PROTECTION AGAINST MICROBIAL SPOILAGE
To explain the mechanisms of various preservation treatments of fruits and vegetables
the following general rule can be used: R = microbe count and virulence/resistance
of the environment. The intensity of food spoilage (R) is proportional to the count
of microorganisms present on or in the food products and to the virulence of the
microflora (ability to survive and grow) and it is inversely proportional to the
resistance of the environment. The preservation methods should reduce or eliminate
the microbial contamination (disinfection, cleaning, removing the microorganisms
from the food products; killing the microorganisms or reducing their virulence to
render them harmless) or increase the resistance of the environment (hurdle princi-
ple) (Kyzlink, 1990; Leistner, 1995; Bibek, 1996).
10.2.3.1 Removal of Microorganisms from Food Products
10.2.3.1.1 Washing and Cleaning
Raw fruits and vegetables covered with soil, mud, or sand should be carefully cleaned
before processing. A second wash is usually done after peeling or cutting^ (Laurila
and Ahvenainen, 2002). Any washing removes microorganisms and also tissue fluids
containing sugars, organic acids, and other nutrients liberated from the damaged