Effects of UV pre-treatments on frozen vegetables quality

Vegetables play a particularly important role in human diet and their stabilization after harvesting and during sub-sequent storage is critical. Among several long-term preservation processes, freezing is widely recognized as a proven and efficient method for vegetables. Most vegetables require a short heat treatment (blanching) prior to freezing to reduce microbiota and inactivate enzymes responsible for deteriorative reactions. However, detrimental effects occur during this process, such as alterations of plant tissues and consequent texture changes, solubilisation of nutrients in the blanching medium, thermal degradation of nutrients, weight loss and color changes, resulting in quality losses. Therefore, a rigorous balance between enzyme inactivation (correlated to degradation) and minimization of quality losses must be achieved in order to produce the highest final quality of frozen product. The increasing consumers demand for high-quality food standards, have stimulated research on alternative and/or mild processing technologies that extend shelf-life without the detrimental effects caused by severe heating. From an industrial perspective, thermal processes are extremely energy consuming and have high environmental impact. Non-thermal processes, or their combination with less severe heat treatments applied before low-temperature storage, are emergent challenges with potential applications in the food industry. The application of ultraviolet irradiation is an example of such processes. Ultraviolet radiation (UV) occupies a wide band in the non-ionizing region of the electromagnetic spectrum, with a wavelength between 100 and 400 nm. Application of UV-C radiation in the germicidal range (240-260 nm) as a non-thermal food processing technology, by pulses or continuously to food right after thermal processing of frozen vegetables, may improve the process' quality by reducing heat. It is generally claimed that the main parameters influencing sensory and quality changes on food are the dose of UV radiation applied (measured in intensity of flux in J/m2), treatment time, and the distance between the UV source and product. UV-C pre-treatments present a high potential to retain the vegetable quality after freezing process and storage.