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

Effects of saline irrigation on growth, physiology and quality of Mesembryanthemum crystallinum L., a rare vegetable crop.

World wide increased desertification due to recent global changes enhances the need of irrigation, which, in turn, provokes the risk of soil salinization. Furthermore, limited fresh water resources may increasingly constrain the use of low quality irrigation water. Hence, intensified use of halotolerant crop plants will be necessary, even in Europe.Commercial use of halophytes as fresh food is limited. Several facultative halophytic members of Aizoaceae are nowadays used as special crop plants. A rare leafy vegetable species is the common ice plant Mesembryanthemum crystallinum, a Crassulacean acid metabolism (CAM) species, which is mostly cultivated in India, California, Australia, and New Zealand. It is also known in Europe as a quickly cooked tender vegetable. With their succulent, mellow, slightly salty tasting leaves and young shoots, M. crystallinum is getting interesting as delicious cool flavored salad greens during recent years. However, it is a perishable product and thus, shelf live is short. On the other hand, CAM capacity of M. crystallinum can be largely enhanced by saline irrigation. Increased CAM potentially reduces water and carbon losses.In this project we studied whether moderate salt treatment affects physiology, growth and yield of this rare crop plant. Furthermore, we investigated whether such treatment that enhances the irreversible C3 to CAM shift in young leaves of this CAM species, potentially prolongs shelf live. Results showed that moderate salt treatment did not negatively influence growth, yield and sensory quality. When in CAM, leaves showed reduced transpiration water losses and CAM also reduced carbon losses during storage

Addressing potential sources of variation in several non-destructive techniques for measuring firmness in apples

Measurements of firmness have traditionally been carried out according to the Magness Taylor (MT) procedure; using a texture analyser or penetrometer in reference texture tests. Non-destructive tests like the acoustic impulse response of acoustic firmness sensors (AFSs), a low-mass impact firmness sensor Sinclair International (SIQ-FT) and impact test (Lateral Impact – UPM) have also been used to measure texture and firmness. The objectives of this study were to evaluate the influence of different sources of variation in these three non-destructive tests and to evaluate their respective capabilities of discriminating between fruit maturity at two different harvest dates, turgidity before and after dehydration treatment and ripening after different storage periods. According to our results, fruit studied an unexpected AFS trend with turgidity. Contact measurements (Lateral Impact – UPM and SIQ-FT) appeared highly sensitive to changes in turgidity, but were less able to follow changes in ripening caused by storage period. Contact measurements were suitable for detecting differences between fruits from different harvest dates and showed higher correlation coefficients with reference texture tests than acoustic measurements. The Lateral Impact – UPM test proved better at separating fruits according to turgidity than the SIQ-FT instrumen

Effects of pulsed electric field on the viscoelastic properties of potato tissue

We have investigated whether transient permeabilization caused by the application of pulsed electric field would give rise to transient changes in the potato tissue viscoelastic properties. Potato tissue was subjected to nominal field strengths (E) ranging from 30 to 500 V/cm, with a single rectangular pulse of 10−5, 10−4, or 10−3 s. The changes on the viscoelastic properties of potato tissue during pulsed electric fields (PEF) were monitored through small amplitude oscillatory dynamic rheological measurements. The elastic (G′) and viscous moduli (G″) were measured every 30 s after the delivery of the pulse and the loss tangent change (tan-δ) was calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Results show a drastic increase of tan-δ in the first 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by pulsing conditions and is independent of the total permeabilization achieved by the pulse. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of tan-δ to values similar to those before pulsation strongly suggests recovery of cell membrane properties and turgor, pointing at reversible permeabilization of the cells. A slight increase of stiffness traduced by a negative change of tan-δ after application of certain PEF conditions may also give an indication of events occurring on cell wall structure due to stress responses. This study set the basis for further investigations on the complex cell stress physiology involving both cell membrane functional properties and cell wall structure that would influence tissue physical properties upon PEF application.Fundação para a Ciência e a Tecnologia (FCT

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