Effects of UV-C radiation on minimally processed lettuce and apple: a review

Abstract

The increasing demand for nutritive, ready-to-eat foods has prompted the minimally processed (MP) fruits and vegetables market. However, these foods have short shelf-live, marked by their rapid deterioration. Ultraviolet-C (UV-C) radiation is a clean, low-cost and non-thermal technique that can be an alternative to commonly used sanitizers. However, this conservation method has a limited application in this branch of industry due to its low penetration in foods. The objective of this review was to evaluate the germicidal effect of UV-C radiation on minimally processed lettuce and apple, the possible damage to physical and sensorial properties, as well as the factors involved in this technique. A log reduction from 1 to 2 log CFU/g of the natural microflora of these vegetables can be easily achieved at moderate doses, for diverse groups of spoilage microorganisms. A higher reduction level above 4 log CFU/g of inoculated pathogens was accomplished, when higher doses were applied. For MP lettuce, its irregular surface is considered a limiting factor due to contact attenuation between radiation and microorganisms. This limitation can be overcome by changing process parameters, such as distance from the emitting source and exposing both sides of the lettuce. The color of the leaves was better preserved with the use of UV-C radiation at moderate doses. Undesired alterations in MP apple, such as intense weight loss and pronounced browning were associated to severe cell damage at higher doses. By exposing the fruit for a shorter time, these alterations could be prevented. In general, there was good acceptability of MP lettuce and apple treated with UV-C. The vegetable type and its topography had an important influence on the efficiency of the technique. It was not possible to suggest an adequate dosage for each vegetable seeing that there are few availabe studies that differ between each other in terms of the vegetable variety, the way treatments were conducted and the exposed dose.

Keywords:  Minimal processing; Dose; Microorganisms; Germicidal effect; Color; Shelf life