**4. Conclusion**

and retain higher levels after 3 months of frozen storage compared to untreated samples [58]. Both UV light and thermal stress created by PL induce the production of phenolic compounds through increased activity of phenylalanine ammonia lyase (PAL). However, increasing the duration of treatment (20–30 s) leads to over dosage of thermal stress producing severe damages

Plasma is a quasi-neutral gas state, considered the *"fourth"* state of matter, and composed of a mixture of partially ionized gas molecules, ions, atoms and free electrons in their fundamental or excited state with an overall net neutral charge [59]. Plasma can be generated by using several types of energies to excite molecules. In the food industry, the general approach of producing plasma is to subject atmospheric air to an electric or electromagnetic field of constant or alternating amplitude, to induce electron collisions and generation of the ionized species [60]. The dielectric barrier discharge (DBD) and the plasma jet (see **Figure 5**) [59] are two common design types used to breakdown gas in a stationary electric field between electrodes to create the ionizing effect. The term cold plasma (CP) is considered a nonthermal technique

) in the plasma (*Te*

of CP is at ambient temperature without raising the temperature of the surrounding medium. Under Atmospheric cold plasma (ACP), several reactive oxygen species (ROS); as well as reactive nitrogen species (RNS) are formed with high lethal effects, capable of inactivating a wide range of microorganisms [62]. The nonthermal nature of CP technology, coupled with its high antimicrobial effects, has provided an alternative treatment for the decontamination of fruits

Misra et al. studied the effects of ACP on fresh strawberries and demonstrated significant reductions of 2.4 and 3.3 log cycles for mesophiles and surface yeast and mold respectively, with minimal impact to color and firmness between treated and control samples [63]. This is in agreement with other studies conducted on whole cherry tomatoes where CP did not induce metabolic changes that adversely affect critical quality parameters of color, firmness, pH and weight loss [61, 64]. Studies conducted by Tappi et al. on the effect of CP on fresh-cut apples and melon had variable changes on texture. Whilst apples showed a significant loss in *"crunchiness"* in texture, melons exhibited no significant differences in the cut fruit [65, 66]. However,

**Figure 5.** Schematic diagram of (A) dielectric barrier discharge; and (B) plasma jet system. Adapted from Pankaj et al. [59].

 *> > Tg*

) is much higher than the temperature of the

) [61]. Thus the overall temperature

to plant tissue, discoloration of the fruit skin and loss in bioactive content.

from the fact that the temperature of electrons (*Te*

200 Phytochemicals - Source of Antioxidants and Role in Disease Prevention

and vegetables whilst minimizing deleterious quality impacts.

ions, neutrals and global gas (*Tg*

**3.5. Cold plasma (CP)**

The recent global rise in consumer health awareness has prompted some food producers to utilize nonchemical preservation treatments to maintain and enhance the integrity of food products. Enhancing the competitiveness of the food industry requires technological innovation for improving quality, nutritious and safe ready to eat foods. Some studies have shown that unlike traditional thermal processing, nonthermal alternatives such as pulsed electric field (PEF), pulsed light (PL), ultra sound (US), high pressure processing (HPP) and cold plasma (CP) techniques have the ability to preserve and in some cases elicit increased phytochemical content of some fruits and vegetables. Such novel food preservation technologies have shown promising evidence in producing foods capable of reducing noncommunicable diseases with benefits to both domestic and export markets. In summary, the review has focused on both the application and impact of nonthermal technologies on the bioavailability of phytochemicals in fruits and vegetables which can positively impact the Food and Beverage industry.
