Características de calidad de fresas cultivadas en sistema sin sueloestudio metabolómico preliminar

Resumo

The direct relationship between the quality of strawberry and its metabolites content determines the need to study its chemical composition using analytical methodology that allows accurate identification and quantification and reproducible of the largest number of compounds related to organoleptic, nutritional and nutraceutical properties. The economic importance of strawberries in Huelva and the competitiveness in the sector makes necessary the development of new production methods based on manipulating natural resources (light, water and nutrients) for improving plant resistance, productivity, quality and nutraceuticals properties. In this sense, soilless culture seems a promising alternative to increase sustainability and competitiveness of strawberry cultivation. Also, the introduction of early varieties that enable off-season production is another challenge posed by the sector. Fruit quality, including nutritional and nutraceutical properties, is influenced by the variety, cultural practices, climate and the region of production as well as the sampling time, degree of maturity and biotic and abiotic stressors. Therefore, many variables can affect significantly the dietetic values of fruit. Numerous studies have explained the relationship between fruit quality and these factors. For these reasons in this doctoral thesis it has been studied and analyzed several varieties of strawberries grown in soilless system in different agronomic conditions, and conventional system in order to evaluate the effect of these agricultural and environmental conditions on the quality of strawberry. The results of this memory have been structured in three chapters. The first one provides a more thorough knowledge of organic and inorganic composition of strawberries for assessing the effect of production methods on fruit quality. For this proposal, two groups of samples were used: The samples representing group I consisted of six varieties, i.e.Camarosa, Candonga, Chiflón, BG 269, Tamar and Diamante cultivated in a soilless system using coconut fiber as substrate. Fruit of five varieties cultivated using conventional practices, i.e. Camarosa, Candonga, Medina, Marina and Ventana, represented group II. In order to evaluate the quality of the strawberry some chemical parameters (soluble solids, sugars, organic acids and mineral elements) were determined in strawberries of several cultivars. In addition, differences between strawberries cultivated in soilless systems versus the conventional crop system were also investigated applying multivariate statistical techniques. The analyses were carried out using liquid chromatography (HPLC-DAD-RID) for determination of sugars and organic acids, and mineral contents were determined by inductively coupled plasma optical emission spectrometry (ICP- OES). Differences among cultivars were observed based on the mineral composition and glucose and fructose concentrations in both cultivation systems. However, no significant differences between cultivars were detected in sourness. Tamar and Camarosa were the sweetest cultivars among those grown in soilless and soil system, respectively. Both varieties also had the highest total sugars/total acids ratio. The comparison between strawberries cultivated in soil and soilless systems also revealed significant differences in the mineral composition, content of sugars and related parameters. In the second chapter the influence of environmental factors, seasonal and genetic factors on nutritional and nutraceutical quality of strawberry fruits are evaluated. Also it will allow to correlate them with changes in concentration of primary (sugars and organic acids) and secondary (phenolic compounds) metabolites and their bioactivity (antioxidant activity). The study of metabolites was performed in three strawberry varieties grown in soilless system under different agronomic conditions. The study of metabolites was performed in three strawberry varieties grown in soilless system under different agronomic conditions (detailed in experimental part of chapter II). The three varieties were chosen basing on their sensitivity to environmental conditions: Palomar (very sensitive), Festival (sensitive), and Camarosa (resistant). Throughout the campaign, three samplings were performed: December (extra-early production), January (early production), and March (early production). The analyses were carried out using liquid chromatography (HPLC-DAD) and UV-vis spectrophotometry. The results showed that variety Festival was the sweetest genotype and also had the highest total sugars/total acids ratio, whereas Camarosa was richest in anthocyanins. Considering the harvest time, it has been observed that the strawberry harvested in January and March (early production) had higher quality. Fruits harvested in January were richer in phenolic compounds whereas fruits harvested in March were richer in taste-related compounds (sugars and organic acids). In the third chapter, an untargeted metabolomic strategy was used to characterize the primary metabolome of different strawberry cultivars and to study metabolite alterations in response to different crop conditions and environmental stress. For this purpose, it were analyzed three varieties of strawberries with different sensitivity to environmental factors (Camarosa, Festival and Palomar) grown in soilless systems, and using various agronomic conditions: three levels of electrical conductivity (EC = 1, 2, and 3 dS/m), two different types of coverage (covered or uncovered) and Three types of substrates (coconut fiber, perlite and rock wool). Primary metabolites were profiled by gas chromatography mass spectrometry (GC-MS). The results showed significant alterations in primary metabolites between the three strawberry cultivars studied in this work, including sugars (fructose, glucose), organic acids (malic acid, citric acid) and amino acids (alanine, threonine, aspartic acid), among others.