# Applications of Pulsed Light Decontamination Technology in Food Processing: An Overview
## 5 Role of Pulsed Light Technology in Food Safety
### Microbial Decontamination in Food Products  
PL activity is different for solids and liquid food products. Solid foods absorb the PL and there is an exponential decay of light intensity as light goes on being absorbed as a function of the depth of food and its absorption coefficient. The extent to which PL penetrates the food products is termed its penetration depth, which has been defined as the distance where the light fluence rate is reduced to 37% (1/e; e = 2.7128) of its initial value [14]. There are some other convention state penetration depths where light intensity is reduced to 10% of surface incident intensity. The penetration depth is defined as such because the reduction of light intensity to such a lower percentage is unable to carry out any inactivation beyond that depth. [PERSON] et al. [120] reported that lower absorption coefficient, and higher absorption and transmission coefficients increase the penetration of PL. [PERSON] and [PERSON] [86] demonstrated a penetration depth of 2.3 mm in Vienna sausages by the PL for a fluence of 9.4 J/cm\({}^{2}\) at 50.8 mm sample distance from lamp and achieving a 1.39 log reduction in _L. innocua_. [PERSON] et al. [121] reported penetration of PL up to 10 mm depth in whey protein gels. [PERSON] and [PERSON] [64] obtained penetration depth of 41.7 and 15.9 mm for apple juice and cider respectively at fluences of 8.8 and 11.7 J/cm\({}^{2}\) and 50.8 mm sample distance from lamp. They also reported greater reductions of _E. coli_ of more than 7 and 5.5 for apple juice and cider respectively. In another study, coconut water of depth 5 mm was successfully treated by PL at fluence level of 19.2 J/cm\({}^{2}\) and lamp distance of 50 mm [113]. Considering almost the same light intensity at the surface of any substrate, this indicates that PL has greater penetration in liquid foods than solid foods, with a steeper decay in light intensity in the solid foods. Since in the case of solid foods products, the light does not penetrate well, PL application is mostly limited to surface inactivation and these are superficially decontaminated [38]. For, its superficial inactivation characteristics, PL would be effective for totally smooth products, where microorganisms would be totally exposed to light flashes. However, surfaces of solid foods are especially not smooth. Minute surface cracks and crevices could possibly shelter microorganisms, where light would not reach. Therefore, the entire superficial area of the foods has to be flashed so as to achieve the total decontamination of its surface despite surface unevenness, which makes the process very complex [16]. Several researches have been done on surface-treatment of fruits for microbial reductions. The possibility of PL to decontaminate the surfaces of fruits like strawberries and raspberries was demonstrated by [PERSON] and [PERSON] [28], with insignificant damage of fruits being reported. They treated raspberry surfaces using fluence of 72 J/cm\({}^{2}\) and obtained _E. coli_ 0157:H7 and Salmonella reduction by 3.9 and 3.4 logs, respectively. Similarly, in strawberries, they obtained _E. coli_ 0157:H7 and Salmonella reduction by 3.3 and 4.3 logs respectively at 64.8 J/cm\({}^{2}\). However, very high fluence values were used. Marine and poultry products have also been treated efficiently by PL. Successful decontamination of surfaces was demonstrated for shrimp and fish [122]. Listeria on shrimp surface were reduced by 1-3 logs using 4-8 flashes of 1-2 J/cm\({}^{2}\) PL. Whereas fish treated with 3 PL flashes at intensity of 10 J/cm\({}^{2}\) gave reduction of about 2 logs of surface psychrotrophic bacteria. [PERSON] et al. [123] treated chicken surface with high-power PL of 1000 pulses and dose 5.4 J/cm\({}^{2}\) and reduced _S._ Typhimurium and _L. monocytogenes_ by 2-2.4 logs and total aerobic mesophiles by 2 logs. Eggshells have also shown to be successfully decontaminated using light pulses.