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

Application potential of cold neutron radiography in plant science research

Though comprehensive knowledge of water status and water flow are important prerequisites for plant in many aspects of modern plant science truly non-destructive methods for the in-situ study of water transport are rare. Advanced imaging methods such as Magnetic Resonance Imaging (MRI) or Cold Neutron Radiography (CNR) may be applied to fill this gap. In CNR strong interaction of cold neutrons with hydrogen provides a high contrast even for small amounts of water. The combination of CNR with the low-contrast tracer D2O allows the direct visualisation of water flow and the calculation of water flow rates in plants with a high resolution at the tissue level. Here, we give a general introduction into this method, describe their latest developments, report about studies applying neutron radiography in plant science and provide most recent results of our experiments in this field

Rapid Fusarium head blight detection on winter wheat ears using chlorophyll fluorescence imaging

Fusarium infection on wheat is a widespread thread for humans' and animals' nutrition as these fungi are known to produce the highly dangerous mycotoxin deoxynivaleol (DON). Besides this, Fusarium also induces head blight, a disease resulting in huge economic losses due to shrivelled and low mass or dead kerneIs. Early disease detection could help to reduce yield losses and health threads from DON contamination. The potential of chlorophyll fluorescence imaging (CFI) to yield these aims was investigated in laboratory experiments applying a FluorCam 700MF commercial CFI system. Healthy (control) plants as well as plants artificially infected with Fusarium culmorum were rated visually according to the stage of development and the degree of disease. Subsequently, a chlorophyll fluorescence image analysis of the potential maximum photochemical efficiency (Fv/Fm) was applied to determine the degree and the distribution of the damage of the ears. Between the sixth and eleventh day after artificial inoculation photosynthetic activity of single damaged kernels of diseased ears dropped to zero.Although this only marginally affected the average maximum photochemical efficiency of entire ears, the infection led to a significant increase in the statistical distribution of Fv/Fm in the images. Pixelwise integration of Fv/Fm-values (from low to high) of the fluorescence images allowed a differentiation, in steps of 10%, between ears of different degree of disease of 10% on in the BBCH stage 75. Lowest level of disease detection by CFI corresponded to a visually rated degree of disease of at least 5%. However, the possibility to distinguish between diseased and healthy ears became highly limited with incipient ripening of kerneIs and concomitant chlorophyll degradation at growth stage 81.Abbreviations: CFI - chlorophyll fluorescence imaging, dai - days after inoculation, DON - deoxynivalenol, Fo - basic fluorescence emission of a dark-adapted plant, Fm - maximal fluorescence emission of a dark-adapted plant, Fv = Fm - Fo - variable fluorescence measured on dark-adapted plant, Fv/Fm - maximum fluorescence yield of PS II (photosynthetic efficiency), PS II - Photosystem I

Effects of temperature and water relations on carrots and radish tuber texture

Tissue firmness and stiffness are functions of tissue and cell wall structure, water status and temperature, and their interactions. This investigation elaborates the physiological basics of temperature and water status effects on firmness of fresh intact carrots and radish tubers. The results can add to a better understanding of the mechanical properties at least of these succulent plant storage organs. Water potential of intact carrot roots and radish tubers was measured with a pressure bomb, firmness was determined as the force necessary to cut the entire tuber perpendicularly to the length axis with a microtome knife adapted to a universal testing machine, and osmotic potential psychrometrically in expressed tissue sap. Hence, volume averaged pressure potential or turgor could be calculated from water potential and osmotic potential data. Water potential and turgor were positively correlated with cutting force in both species. Beyond wilting, the variation of cutting force with declining water potential was less pronounced. In carrot but not in radish tubers, cutting force and turgor were higher at lower tissue temperature (ca 10degreesC compared to ca 20degreesC). On the other hand, temperature did not influence the relationship between water status and texture in radish. In contrast, tuber development led to an increase in cutting force. From the presented results it seems obvious that the temperature effect on cutting force in carrots is mediated by affecting cell wall properties and not water status

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

Changes of water status, elastic properties and blackspot incidence during storage of potato tubers

The blackspot bruise susceptibility of potato tubers after mechanical load may change during prolonged storage. Both an increase and a decrease of the occurrence probability of this defect with storage duration have been reported. Increasing blackspot susceptibility has often been related to declining tissue turgor and/or increasing tuber water losses. In the presented study the relationship between elastic properties, water status and blackspot incidence of potato tubers, and its variation during 8 month of storage has been investigated. Tubers of' the cultivars 'Afra' and 'Milva' differing in their starch content were stored at 4-5°C in boxes in a practical storage room and in a climate chamber at 4-5°C and 97-100% relative humidity. In spite of a pronounced, mainly water loss-related mass reduction ('Afra': 3.1%, 'Milva': 2.7%) during 5 1/2 months in high humidity storage the tuber turgor remained almost stable or even increased under both storage conditions. This turgor maintenance which guarantees vitaliy of the cells despite the observed water losses may result from elastic adjustment as indicated by a strongly increasing intrinsic volumetric elastic modulus of the inner tuber tissue. The apparent quasi-static modulus of elasticity and the dynamic stiftness of the intact whole tubers from practical storage decreased for both varieties. The blackspot susceptibility of both varieties was subject to strong ftuctuations during the duration of storage and no clear relation to any of the measured parameters for water status and elastic properties was identified. In contrast to the general notion blackspot susceptibility was not higher for 'Afra' than for 'Milva' despite the higher starch content of the former