Colonna, Emma (2015) Agronomic factors and quality of vegetable crops. [Tesi di dottorato]

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Abstract

Quality has a product- and a consumer-dependent dimension in which the relationship between objective and subjective aspects represents the core of the economic importance of quality. Globe artichoke, strawberry and baby leaf vegetables were selected as the experimental crops due to their high importance on national and international markets. For instance, in Italy 46,954 and 6,000 ha are produced annually for globe artichoke and strawberry, respectively. Besides Italy is the European leader in leafy vegetables, with about 3000 ha produced annually under protected cultivation and destined to fresh-cut products such as wild rocket, leaf lettuce, lamb's lettuce, spinach, and swiss chard. Most aspects of food quality perception by consumers are based on experience or credence characteristics, associating local and traditional produce with high-quality and healthy products. The food quality perception leds to an increasing demand for organic products, partially due to the general thought that organic foods are healthier and more nutritive than conventionally produced products; even if scientific evidence is still insufficient to confirm or reject this assumption. Recently, consumers' and producers' interest is based on the evolution of the life styles and food style. Particularly, the increasing application of products with high content of services is determining a progressive increase of leafy vegetable destined to fresh-cut products. Epidemiological studies support the increasing attention of consumers to the nutritional quality of fruits and vegetables with elevated health-promoting properties due to the presence of an array of secondary metabolites, collectively called phytochemicals. The quantity and quality of phytochemicals may be affected by diverse biotic and abiotic stresses, the development stage of the produce, plant genotype, growing season and harvest time, field location and soil quality, available nutrients, light, temperature, irrigation, chemical fertilizers and conventional/organic management. Within this context, particular attention is given to sustainable agriculture and low environmental impact with elevated crop production rich in phytonutrients. Arbuscular mycorrhizal (AM) fungi have been shown not only to improve plant nutrition and reduced chemical inputs, but also to induce changes in plant secondary metabolism. Beneficial impact of AM fungi on plant mineral and secondary metabolite contents depends not only by AM fungal species or isolates, but also by plant genotype and fertilization. Farming practices as conventional and organic management are as important as genetic variation in determining various components in a crop. Desirable and undesirable compounds in plants are affected by sunlight integral and other factors such as temperature, light intensity, photoperiod and carbon dioxide concentration. The genetic background, nitrate supply, harvesting time and light intensity during the growing season are predominant factors for nitrate content. Based on this preliminary information, the influence of agronomic, genotypic and environmental factors on nutritional/nutraceutical profile of vegetable crops was performed. The agronomic factor was evaluated showing the effect of arbuscular mycorrhizal inoculation and field locations on mineral composition, antioxidant activity, phenolic acids and sesquiterpene lactones (SLs) content of globe artichoke. The agronomic and genotypic factors were evaluated showing the effect of farming system and cold storage on quality attributes in strawberry (Fragaria × ananassa Duch.) cultivars Sabrina and Ventana. The genotypic and environmental factors were evaluated showing the nutritional characterization of selected baby leaf vegetables destined to fresh-cut products belonging to the families of Chenopodiaceae (red chard, spinach, swiss chard), Asteraceae (chicory, green and red lettuce), Brassicaceae (mizuna, rocket, tatsoi), Valerianaceae (Lamb's lettuce), and the variation in visual appearance, proteins content, minerals content, antioxidant activity, ascorbic acid and total phenols content of the selected leafy vegetables in relation to the light intensity (low and high Photosynthetically Active Radiation, PAR) at time of harvest. Analysis of the obtained data on artichoke's experiment revealed significant variations among field locations for the agronomic and nutraceutical parameters. Mycorrhizal treatments did not significantly affect the mineral content of the crop. The activation of plant secondary metabolism in response to AM fungi resulted in increases of the content of individual molecules, with a general but not significant positive influence due to the synergistic effect of Glomus spp and mycorrhizal helper bacteria. The portional division of the plant and head parts showed the highest SLs content in the leaves and the highest total phenols content in the edible part, without univocal result if related to inoculation. The data obtained for the strawberry cultivars' experiment showed that the organic 'Sabrina' strawberry had a higher soluble solids content while the organic 'Ventana' had a higher hydrophilic antioxidant activity. An opposite trend was observed on total phenols and ellagic acid for 'Ventana' and 'Sabrina', respectively. Organic farming did not increase the reducing sugars and ascorbic acid contents in both cultivars compared to conventional management farming. The higher nutritional value in terms of hydrophilic and lipophylic antioxidant activities in 'Ventana' and the higher ellagic acid content in 'Sabrina' indicated that the choice of cultivar for a specific farming system is essential since it may affect quality attributes of strawberry fruit. The nutritional/nutraceutical characterization of ten leafy vegetable destined to fresh-cut products rewards the Brassicaceae family and leafy vegetables harvested at low in comparison to high PAR, except for total phenols content in chicory, green lettuce, lamb's lettuce, mizuna, red chard, and red lettuce. All factors considered in this study have influence on nutritional/nutraceutical quality. From the objective point of view, considering also the nutraceutical properties, quality is not determinable in univocal way.

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