Nikos Tzortzakis

Postharvest ozone application for the preservation of fruits and vegetables

ABSTRACT Vegetables and fruits have been recognized as a healthy and nutritive value food, with both a noticeable rise in consumption nowadays and greater frequency of foodborne illnesses associated with fresh produce. Current sanitation disinfectants fail to adequately control common spoilage microorganisms as well as potential harmful human pathogens. Alternative and effective disinfectants are being sought, with ozone being a viable alternative to traditional disinfectants. Despite the considerable commercial interest that ozone has attracted, several contradictions regarding the ozone efficiency are often found in the literature and further research is still needed to explore its potential application in the food industry as sanitizer.

Effects of substrate and salinity in hydroponically grown Cichorium spinosum

The present work, examined the effect of salinity (5, 40 and 120 mmol L-1 NaCl) in the growth and the quality of hydroponic culture of stamnagathi (Cichorium spinosum L.). Plants were developed in perlite, pumice, rockwool and sand respectively. High salinity decreased leaf number, leaf size and plant biomass in plants grown in perlite, pumice and sand. Reduced plant biomass also observed in plant grown in rockwool, although an increased number of leaves were produced. Leaf area reduced in plants grown in rockwool and sand under 120 mmol L-1 NaCl. Low salinity maintained almost similar status as the control treatments. Symptoms of tip burn appeared in 120 mmol L-1 NaCl treated stamnagathi for perlite and pumice. No differences observed in leaf chlorophyll content, leaf fluorescence and in symptoms of discoloration. When the perlite was used as substrate, salinity increased total phenols and decreased protein content. Finally, the low concentration of salinity improved some plant quality parameters as recorded by panelists, following organoleptic test. Thus, stamnagathi proved to successfully tolerate low salinity concentration in hydroponically grown plants.

Origanum dictamnus Oil Vapour Suppresses the Development of Grey Mould in Eggplant Fruit In Vitro

Grey mould rot (Botrytis cinerea) development in vitro or in eggplant (Solanum melongena L.) fruit was evaluated after treatment with dittany (Origanum dictamnus L.) oil (DIT) and storage at 12°C and 95% relative humidity during or following exposure to the volatiles. DIT volatiles used in different concentration (0-50-100-250 μL/L) and times of exposure (up to 120 h) examined the effects on pathogen development as well as fruit quality parameters. In vitro, fungal colony growth was inhibited with the application of DIT oil (during or after exposure) and/or time of application. Continuous exposure to oils reduced conidial germination and production with fungistatic effects observed in 250 μL/L. In vivo, fungal lesion growth and conidial production reduced in DIT-treated fruits. Interesting, in fruits preexposed to volatiles before fungal inoculation, DIT application induced fruit resistance against the pathogen, by reduced lesion growth and conidial production. Conidial viability reduced in >100 μL/L DIT oil. Fruits exposed to essential oil did not affect fruit quality related attributes in general, while skin lightness (L value) increased in 50 and 100 μL/L DIT oil. The results of the current study indicated that dittany volatiles may be considered as an alternative food preservative, eliminating disease spread in the storage/transit atmospheres.

Substitution of peat with municipal solid waste compost in watermelon seedling production combined with fertigation

Interest in reusing organic residues as substrate medium in nurseries has increased worldwide as peat availability has been reduced over time. In this study, the effect of fertigation and/or a partial substitution of peat with municipal solid waste compost (MSWC) on the emergence, growth, and nutrition of watermelon (Citrullus lanatus L.) seedlings were tested. The MSWC extracts (MSWC:water at 10-1 and 10-2 dilutions) maintained seedling germination. Under nursery conditions, six media prepared from commercial peat and MSWC were further assessed in conjunction with nutrient application as basic fertilizer (BF) or hydro fertilizer (HF). Adding MSWC to the substrate inhibited seed emergence and mean germination time, whereas fertigation maintained seed emergence in 15% MSWC but decreased in 45% MSWC. Adding 45% MSWC reduced seedling height, leaf number, and fresh weight. The HF increased fresh weight (up to 44%) and growth in seedlings cultivated in 15% MSWC. Leaf photosynthetic rate and stomatal conductance increased (up to 2.6-fold) in MSWC-based (< 45% MSWC) substrates, but no differences were observed in chlorophyll a, chlorophyll b, total carotenoid content, and leaf fluorescence. The HF reduced chlorophyll a and total carotenoids, but increased chlorophyll b content. The K, N, and Na content increased (ranging from 2- to 5-fold) when adding MSWC, whereas P content did not differ. Fertigation benefits seedling nutritive status. Low content (15% to 30%) of MSWC may act as an alternative substitute for peat with more positive effects if minerals are provided through HF.

Chemical characterization of biochar and assessment of the nutrient dynamics by means of preliminary plant growth tests

Biochar can be produced from several organic sources with varying nutrients and metal concentrations. Four commercial grade biochars were evaluated as peat substitute. Biochars were characterised for plant nutrients and for biological stability. The results showed that there were negligible quantities of N and P and generally high levels of K and high biological stability. When these materials were mixed with peat at 10, 25 and 50% and nutrients were added to bring them to the same level of nutrients as in fertilized peat, it was found that biochar mixtures considerably reduced the levels of calcium chloride/DTPA (CAT) extractable N (including nitrate), P, and electrical conductivity- greater extent with higher rates of biochar addition except for K. The pH and K levels were increased with biochar addition. The drop in EC has important implications regarding the use of other materials used to dilute peat, for example, composted green waste, the rate of dilution is limited due to high EC and biochar addition gives the potential for higher peat dilution of these materials. Nitrate and phosphorus are very vulnerable to leaching of these nutrients in the environment in peat substrates and the binding of these by biochar has implication for leaching and nutrient application strategy. Root development using Cress test and tomato plant height and biomass using containers, were in some cases better than peat indicating that biochar could be used to dilute peat e.g. for seedling production where root development and rapid growth are very important. Application of biochars resulted in a marked reduction of N (and P) in the plant. There were significant correlation between CAT extractable N and P and corresponding plant concentration, indicating the standard growing media test, CAT, would be suitable for assessing the nutrient status of peat biochar mixes.

Optimization of potassium fertilization/nutrition for growth, physiological development, essential oil composition and antioxidant activity of Lavandula angustifolia Mill

Lavandula angustifolia (Mill.) is a medicinal plant of great importance with a variety of applications in perfume and pharmaceutical industries or landscaping, but only limited information is available about its response to potassium supplementation. This experiment was conducted in order to determine the effects of potassium (K: 275-300-325-350-375 mg L-1) levels on the morphological and biochemical characteristics of lavender grown hydroponically. Results showed that K levels affected plant growth, mainly the root development while no differences were found for leaf chlorophyll content and stomatal conductance. Essential oil yield increased in the 300 mg L-1 in comparison to 275 or 325-375 mg L-1 of K application. The middle ranged K levels (300-325-350 mg L-1) enhanced leaf content in total phenols, flavonoids and antioxidant activity (DPPH, FRAP). Lipid peroxidation content (MDA) employed as damage index, was lower in the 325 mg L-1 of K treatment. No differences were observed in antioxidant enzymes (SOD, CAT, APX) activity and H2O2 content among K applications. The main constituents of leaves essential oil (1,8-cineole, borneol, camphor, α-terpineol, myrtenal) and mineral accumulation were affected by K treatments. Lavender grown in 300 mg L-1 of K was appropriate for the essential oil uses/production while the 325 mg L-1 of K were more appropriate for lavender cultivation for fresh and dry matter uses.

Ozone: A Powerful Tool for the Fresh Produce Preservation

The consumption of vegetables and fruits has risen noticeably during recent decades, leading to a greater frequency of foodborne illnesses associated with fresh produce. Traditional disinfectants, including chlorinated compounds, fail to adequately control common spoilage microorganisms as well as potential harmful human pathogens. Safe, effective alternatives to halogenated disinfectants are required to reduce spoilage losses, improve food safety, and gain consumer approval. Research and commercial applications have established that ozone (O3) may provide a viable alternative to traditional disinfectants, with some additional benefits documented. This technology has attracted considerable commercial interest, especially because ozone does not leave any residues on the treated produce and it is also accepted by many organic grower organizations. However, several contradictions regarding the efficacy of this technology are often found in the literature and further research is still needed. Different findings could be attributed to a great variability of the research work conditions (ozone generation and application methods, O3 exposure time and concentration, packed produce). Indeed, ozone enrichment induces fruit resistance and suppresses fungal growth-spores production, enhances fruit quality, and may alter gene and protein expression. Each commodity needs to be optimized for the specific ozone application. Consequently, it would be possible to improve its potential as a sanitizer in the food industry.

Effects of Ascophyllum nodosum seaweed extracts on lettuce growth, physiology and fresh-cut salad storage under potassium deficiency: Effects of Ascophyllum nodosum seaweed extracts on lettuce growth

BACKGROUND Potassium (K) deficiency in leafy vegetables such as lettuce is a major concern regarding quality. Seaweed (SW) extracts, as biostimulants, are biodegradable materials and have become increasingly popular as they are reported to enhance crop growth and yield. RESULTS In order to overcome K deficiencies (i.e. 375 vs 125 mg L-1 ), alternative foliar applications with extracts of Ascophyllum nodosum SW or K were examined using lettuce plants which were grown hydroponically. Potassium deficiency (at 125 mg L-1 ) reduced plant biomass, photosynthetic rate, leaf stomatal conductance, lettuce potassium content and tissue antioxidant capacity as compared with the higher K level (375 mg L-1 ). Application of SW increased the relative growth of lettuce in the low-K treatment. The K level and/or SW application altered the plants enzyme protective activity (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD) against oxidative stress and hydrogen peroxide (H2 O2 ) production. Spray applications of SW mitigated the effects of K deficiency on indicators of enzyme activity and plant damage, back to levels of high K content (375 mg L-1 ). The high K level, but also SW application, increased the antioxidant activity of the processed lettuce before storage. Foliar application of the SW extract increased the quality of cut lettuce grown in 125 mg L-1 K conditions by reducing the rate of respiration and increasing consumer preference. CONCLUSION The SW application could alter the detrimental effects of K deficiency during lettuce growth and storage of processed products.

Physiological and Biochemical Responses of Lavandula angustifolia to Salinity Under Mineral Foliar Application

Saline water has been proposed as a solution to partially cover plant water demands due to scarcity of irrigation water in hot arid areas. Lavender (Lavandula angustifolia Mill.) plants were grown hydroponically under salinity (0–25–50–100 mM NaCl). The overcome of salinity stress was examined by K, Zn, and Si foliar application for the plant physiological and biochemical characteristics. The present study indicated that high (100 mM NaCl) salinity decreased plant growth, content of phenolics and antioxidant status and essential oil (EO) yield, while low-moderate salinity levels maintained the volatile oil profile in lavender. The integrated foliar application of K and Zn lighten the presumable detrimental effects of salinity in terms of fresh biomass, antioxidant capacity, and EO yield. Moderate salinity stress along with balanced concentration of K though foliar application changed the primary metabolites pathways in favor of major volatile oil constituents biosynthesis and therefore lavender plant has the potential for cultivation under prevalent semi-saline conditions. Zn and Si application, had lesser effects on the content of EO constituents, even though altered salinity induced changings. Our results have demonstrated that lavender growth/development and EO production may be affected by saline levels, whereas mechanisms for alteration of induced stress are of great significance considering the importance of the oil composition, as well.