Agriculture Reference
In-Depth Information
Factors That Infl uence Antimicrobial Activity in Produce Washing
Washing Conditions
Antimicrobial Concentration
The effi cacy of a produce wash operation is primarily determined by the concentration
of the antimicrobial. High concentrations typically result in high antibacterial activity
when pH, temperature, and organic content are held constant, but it may also damage
produce tissue. The impact of the antimicrobial on the environment at high concentra-
tions is another factor that has to be taken into consideration. Each antimicrobial and
produce combination has an optimal concentration with which the quality degradation
of the produce will be minimal. Additionally, there are regulatory limitations on the
level of chemical agents that are allowed for use on specifi c food products, and each
country has its own regulatory body. In the United States, the Food and Drug
Administration (FDA) and the Environmental Protection Agency (EPA) regulate the
level of the antimicrobial agents that is allowed for use on fruits and vegetables. It is
also important to maintain a consistent effective concentration of antimicrobial during
the course of washing.
Time
In an industrial produce wash, a two-stage strategy is normally used, fi rst to remove
debris and soil in stage one, followed by stage two, where reducing the microbial load
is the main target. The time used in each stage can range from 30 sec to 1 or 2 min and
will be determined by throughput, produce type, harvest location and time, and other
pertinent factors. Generally, an increase in washing time will result in an increased
removal of bacteria. However, extending washing time is not always effective in a
produce wash. In a washing study using a laboratory fl ow - through wash system, Wang
and others (2007) reported a fast
E. coli
O157:H7 population reduction in the fi rst
2-3 min of washing cantaloupe and fresh-cut apples with aqueous peroxyacetic acid
(POAA). Prolonging the washing beyond 3 min, however, did not induce signifi cantly
more reduction in the microbial population. This dual-phase microbial inactivation
where a fast microbial count reduction in the fi rst few minutes of washing is followed
by a slow reduction region was also documented by Wang and others (2006) in a
produce wash test with chlorine, electrolyzed water, and POAA. In produce washing
operations, washing in the slow reduction stage is ineffective and should be avoided.
Temperature
An increase in the temperature of an antimicrobial solution generally produces an
increase in bactericidal activity. However, to minimize degradation of the produce
quality, especially during storage, currently the produce industry employs a low-
temperature wash practice. Normally the entire supply chain, including washing in
the plant is maintained at 4 °C. In addition, because the maximum solubility of chlorine
in water occurs at about 4 °C, this cooler water temperature is more effective in retain-
ing its antimicrobial activity. However, in order to establish a temperature difference
that minimizes product uptake of wash water (which may introduce microorganisms
into the produce), ideally the temperature of the wash water should be at least 10 °C
higher than that of the fruits or vegetables (Beuchat 1998).
