Page 30 - FoodFocusThailand No.197 August 2022

SPECIAL FOCUS

A Chemical-free Sanitizing Technology

for Fruits and Vegetables

Microorganisms can contaminate fruits and vegetables from any number of sources – fertilizers, irrigation water,
the use of pesticides, and bacteria from animals can all impact the cleanliness of fresh produce. Therefore,
fruits and vegetables must be thoroughly and suitably washed to reduce the health risks from bacteria, such
as E.coli or other chemicals that cause sickness.

For several decades, chlorine has been used to wash fresh fruits and How to use plasma in many industrial fields
vegetables to kill microorganisms and remove pesticides. Even today, chlorine There are two types of plasma: hot plasma (thermal) and cold
is heavily relied upon for sanitation purposes – but it does have its plasma (non-thermal). Hot plasma is mostly used in cutting and
disadvantages. Its limited effect in destroying microorganisms on the surface welding metal. Cold plasma, on the other hand, has some
of fresh produce means that high dosages of chlorine are often used, properties that could be used in the food and agricultural industries,
sometimes with limited added benefit and often leaving a residue on the such as sanitizing the raw materials, preserving food, or removing
produce to be consumed by customers. pesticides and fungicides from fresh fruits and vegetables, as well
Even though the use of chlorine at high levels when processing fresh as acting as a nitrogen fertilizer for plants when mixed with
produce is still permitted, there are many reasons why food manufacturers water.
should look for alternative products and processes for cleaning and
disinfection. Reasons to avoid using chlorine include the health concerns What is the process of plasma washing?
around the safety of fresh produce due to the carcinogenic by-products of This technology employs electricity to oxidize some water and air,
chlorine use as well as the increasing environmental concern about the chlorine resulting in a free radical particle known as plasma-activated water
levels in discharged waters. (PAW). It can be used as a bacterial disinfection reagent or react
Fortunately, there are many new ways to sanitize fresh fruits and with pesticides and fungicides to change its structure in mass
vegetables without using chlorine, like disinfecting them with ultrasound production. This is suitable for industrial use due to its low operation
technology or plasma. cost compared with other technologies such as chlorination,
ozonation, and electrochemical processes; and it also cleans
What is plasma? without changing the product characteristics. In this process, the
Plasma is defined as a state of matter predominantly comprised of ions and main chemical components that affect bacteria are reactive oxygen
electrons. An ion is formed when an atom or molecule gains or loses electrons, species (ROS) and reactive nitrogen species (RNS), together
yielding an overall charge (either positive or negative). The presence of called reactive oxygen and nitrogen species (RONS). The RONS
charged ions means that a plasma is highly electrically conductive and consists of the hydroxyl radical (•OH), hydrogen peroxide (H O ),
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responds strongly to magnetic and electric fields. Its behavior is most the superoxide radical (•O −), oxygen (O ), and the nitric oxide
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comparable to that of a gas, as the plasma has no defined volume but instead radical (•NO). These species damage the DNA inside of bacteria.
assumes the volume of the container it is in. Despite all of the constituent Therefore, cross-contamination is reduced.
particles being charged, the plasma itself typically has no overall charge. This technology is aimed at the minimally processed fresh
produce industry, specifically looking to replace or reduce the use
of aggressive chemicals in water used while washing and chilling
fresh produce in tubs to mitigate the negative impacts. It can also
be used in conjunction with emerging cultivation technologies,
such as vertical farming, hydroponics, aquaponics, etc., to prevent
cross-contamination, but regular washing is still required.
There was a study to test the pH value, electrical conductivity
(EC) value, oxidation–reduction potential (ORP) value, and •OH
and H O concentrations generated by PAW, which could play a
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significant role in the antimicrobial mechanism. It was also claimed
that this approach could replace chlorine sanitization to eliminate
bacteria in the relevant industries. Moreover, this study used the
desirability function approach (DFA) to analyze the relationship
between variable factors and responses of PAW towards bacteria
reduction.
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In Thailand, researchers from Chiang Mai University invented
the plasma fruit and vegetable cleaning technology to replace the
use of harsh chemicals in the fresh produce industry and add more
safety to the cleaning process by leaving no foodborne bacteria,
pesticides, or fungicides on the product. Besides, this plasma
sanitizing process does not create a new problem for consumers,
and it could be combined with other technologies, such as
ultrasound, to make a better solution for bacteria and chemical
cross-contamination.

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