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* old and bologna study programme


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Nadja Sadar, 2013, dissertation

Abstract: Colour and taste are important attributes of apple fruit quality that is generated during the fruit-growing period. Despite a plethora of studies dealing with this topic, the detailed information on how quality is generated is, however, still lacking. This is because traditionally, the obtained agro-morphological and biochemical data are analysed with empirical models using mean values of large samples, without taking the effects of biological variation into account, thus completely masking the spatio-temporal physiological mechanisms. To really understand quality, its generation during fruit growth needs to be monitored and modelled. When knowledge exists on the type and kinetics of the processes involved, the variation in properties can be described and taken into account by using so-called fundamental models, built on theoretical considerations. To understand the behaviour and the variation of colour and taste compounds, within or between individual fruits, and to assess their importance throughout the food supply chain, it is therefore important to understand the dynamics of these compounds during growth. The study consisted of (1) a preliminary experiment, aiming to determine the suitability of the semi-destructive biopsy sampling technique for in-vivo monitoring of certain metabolites during apple fruit development on a tree, (2) an experiment on spatial distribution, and (3) an experiment on temporal distribution of metabolites and colour in developing individual apple fruit. The experiment on spatial distribution was conducted to determine the effect of location on the accumulation of the individual quality components within apple fruit, and the parallel temporal experiment was conducted to monitor the dynamics and mechanisms of these components in apple fruit during on the tree development. Diameter and standard maturity indices of fruit flesh firmness, soluble solids content, starch degradation index, titratable acidity, and Streif maturity index were also determined, to obtain relations between individual quality components. Colour descriptors (L*, a* b*), individual sugars (fructose, sucrose, glucose), sorbitol, and individual organic acids (malic, citric, shikimic, fumaric) were monitored from 40 and 54 days before to 16 and 32 days after the optimum maturity for long term storage on individual apples of cv. ‘Gala’ and cv. ‘Pinova’. Data were analysed with classic empirical statistics as well as with non-linear indexed regression, based on process oriented models, which included biological variation between apples of the same batch. Frequently probelation and quantile regression were applied. The results of the preliminary experiment confirmed that the novel biopsy sampling technique is suitable for in-vivo monitoring of the spatio-temporal distribution of colour and individual taste components during on-tree apple fruit development. In the results from the experiment on spatial distribution, a sinusoidal distribution over locations at 70° above the fruit equator was observed for all the monitored quality components. Descriptor a* was highest at the blush, and b* and L* at the shaded side of the fruit. Citric acid preferentially accumulated at the shaded side of the fruit, whereas fructose in cv. ‘Gala’ tended to accumulate at the blush. Other metabolites were more or less equally distributed within fruit. The results of longitudinal monitoring reveal a sigmoidal increase of a*, an exponential increase of diameter and sugars, and an exponential decrease of organic acids over time. In both cultivars, large variations were observed between individual fruit for all the monitored quality components. When analysed with non-linear indexed regression, based on process-oriented models, and after the probelation combined with quantile regression, the explained parts of the majority of the monitored quality components were well above 90 %. The mechanism of colour development was the same for both cultivars. The biological shift factor for all metabolites and colour had roughly the same value within cultiv
Keywords: apple fruit, colour, models, organic acids, spatio-temporal monitoring, sugars
Published: 19.12.2013; Views: 2246; Downloads: 239
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