Impact of postharvest UV-C and ozone treatments on microbiological properties of white asparagus (Asparagus officinalis L.)

To meet the increasing demand for safe and high quality fresh white asparagus and the recent food safety regulations, optimization of postharvest handling, processing and storage is essential. Modern sanitation techniques relying on physical methods and/or Generally Recognized As Safe (GRAS) compounds are desired for reducing microbiological spoilage. To evaluate the effects of aqueous ozone and UV-C on the microbial load of spears, samples were UV-C irradiated (254 nm, 1 kJ m-2) and/or washed with ozonated water (approx. 3 ppm or 4.5 ppm at 10 °C), and analyzed at three times during a four day storage. Also, the potential effects of initial natural microbial loads, and precondition of the spears in terms of water and sugar contents on the responsiveness of asparagus to these treatments were determined in detail over four growing seasons. The initial microbial loads (mould and yeasts, and aerobic mesophilic total bacterial counts) of white asparagus spears varied considerably during the different harvest seasons of this four-year study. This variability could not be explained by the variance of climatic conditions nor by the respective water and sugar content. Furthermore, there was never a clear cut relation of the initial microbial load and the growth of pathogens during four-day storage at 20 °C in nearly water vapour saturated atmosphere. Neither washing the spears with ozonated water (3 or 4.5 ppm) nor treating them with UV-C radiation (1 kJ m-2) systematically and significantly affected their microbial loads during storage. In addition, the assumption that a combination of both treatments could synergistically improve the effect of each treatment could not be verified during this long-term study. In conclusion, microbial load and pathogen development in asparagus spears are highly persistent and, thus, to meet hygienic requirements further investigations will be necessary

Impact of postharvest UV-C and ozone treatment on textural properties of white asparagus (Asparagus officinalis L.)*

Optimization of postharvest treatments and storage requirements to reduce microbiological spoilage is essential for the food supply chain of asparagus. In this context, Generally Recognized As Safe (GRAS) treatments such as UV-irradiation and washing with ozonated water gain more and more importance. Information on UV-C and ozone as postharvest treatment for quality assurance of white asparagus is scanty. In the present study, asparagus spears were harvested and exposed to the above mentioned treatments and their combination. The infl uence of both postharvest treatments on biomechanical and biochemical textural related cell wall metabolism was investigated. UV-C-irradiation and washing with ozonated water resulted in a slight reduced respiration in white asparagus spears, but increase in spear tissue toughness. Total cell wall compounds were only tendentiously reduced after 4 days of shelf-life at 20 °C by application of aqueous ozone and UV-C. However, the dosages used in this experiment were relatively low and, hence, did not have pronounced effects. Furthermore, the possible mechanism of UV-C and ozone mediated changes in textural related enzyme activities of white asparagus spears have to be investigated in more detail

Postharvest treatments of fresh produce

Postharvest technologies have allowed horticultural industries to meet the global demands of local and large-scale production and intercontinental distribution of fresh produce that have high nutritional and sensory quality. Harvested products are metabolically active, undergoing ripening and senescence processes that must be controlled to prolong postharvest quality. Inadequate management of these processes can result in major losses in nutritional and quality attributes, outbreaks of foodborne pathogens and financial loss for all players along the supply chain, from growers to consumers. Optimal postharvest treatments for fresh produce seek to slow down physiological processes of senescence and maturation, reduce/inhibit development of physiological disorders and minimize the risk of microbial growth and contamination. In addition to basic postharvest technologies of temperature management, an array of others have been developed including various physical (heat, irradiation and edible coatings), chemical (antimicrobials, antioxidants and anti-browning) and gaseous treatments. This article examines the current status on postharvest treatments of fresh produce and emerging technologies, such as plasma and ozone, that can be used to maintain quality, reduce losses and waste of fresh produce. It also highlights further research needed to increase our understanding of the dynamic response of fresh produce to various postharvest treatments