Ann Schenk

Using survival analysis to investigate the effect of UV-C and heat treatment on storage rot of strawberry and sweet cherry.

Ultraviolet light and heat treatment are proposed as alternative techniques for the use of chemicals to reduce the development of the spoilage fungi Botrytis cinerea and Monilinia fructigena on strawberry and sweet cherry, respectively, during storage. In order to investigate the effect of both physical techniques on microbial inactivation and on fruit quality, inoculated berries were subjected to different temperatures (40-48 degrees C) and UV-C doses (0.05-1.50 J/cm2). For each condition, 20 berries were used. After the treatment, fungal growth, visual damage (holes, stains) and fruit firmness were evaluated during a period of 10 days. The experimental data were analysed statistically using survival analysis techniques. Fungal growth on strawberries was significantly retarded using UV-C doses of 0.05 J/cm2 and higher. The same treatment had no significant effect when applied to cherries. The highest doses (1.00 and 1.50 J/cm2) had a negative effect on the calyx of the strawberry, causing browning and drying of the leaves. No beneficial effect of a low temperature treatment (40-48 degrees C) on the shelf life of strawberries was observed, but fungal development on cherries was retarded at temperatures of 45 and 48 degrees C. These temperatures caused severe damage on strawberries (soft stains, holes, decreased firmness), but had no influence on the quality of sweet cherries.

Genotype effects on internal gas gradients in apple fruit

A permeation-diffusion-reaction model was applied to study gas exchange of apple fruit (Kanzi, Jonagold, and Braeburn) as effected by morphology and respiratory metabolism. The gas exchange properties and respiration parameters of the fruit organ tissues were measured. The actual internal tissue geometry of the fruit was reconstructed from digital fruit images and the model was solved over this geometry using the finite element method. The model was validated based on measurements of internal gas concentrations and the gas flux of the fruit to its environment. Both measurements and an in silico study revealed that gradients of metabolic gases exist in apple fruit, depending on diffusion properties and respiration of the different cultivars. Macroscale simulation confirmed that Jonagold has large potential for controlled atmosphere (CA) storage while low diffusion properties of cortex tissue in Braeburn indicated a risk of storage disorder development. Kanzi had less O(2) anoxia at CA storage compared with Braeburn.

Apple mealiness detection using fluorescence and self-organising maps

The chlorophyll fluorescence kinetics of ‘Jonagold’ and ‘Cox’ apples, stored under different conditions to induce mealiness, were measured. Three different storage conditions were considered causing three mealiness levels: not mealy, moderately and strongly mealy. Also destructive measurements of the texture (firmness, hardness, juice content and soluble solids content) were done. Classification into different mealiness levels based on the fluorescence measurements was more performant than a classification based on the destructive measurements. To estimate the mealiness level in a non-destructive way from the fluorescence features, a number of different classifiers were constructed. Quadratic discriminants and supervised and unsupervised neural networks were tested and compared. The self-organising map gives promising results when compared with the multi-layer perceptrons and quadratic discriminant analysis. The different advantages of the constructed classifiers suggest that fluorescence can be used in an automatic sorting line to assess certain types of mealiness.

Evaluation and optimization of high-throughput enzymatic assays for fast l-ascorbic acid quantification in fruit and vegetables.

In this paper, we compare and evaluate the applicability of three UV-VIS absorbance based assays for high-throughput quantification of ascorbic acid in horticultural products. All the methods involve the use of a common enzyme (ascorbate oxidase) in combination with a different indicator molecule. The three methods were retrieved from literature: a direct oxidase-method, an OPDA coupled oxidase-method and a PMS-method, which is commercially available. The analysis in high-throughput context involved the analysis in microplates in combination with the use of an automated liquid handling system. We checked (i) the performance factors of the selected methods on standard solutions, (ii) the applicability of the defined methods in high-throughput context, and, (iii) the accuracy of the methods on real samples using HPLC as a reference technique. The OPDA-method was found to be the most appropriate method for the quantification of ascorbic acid in high-throughput context with a linear range between 7.0 and 950 mgL(-1) and excellent correlation parameters (slopes close to 1, intercepts close to 0, R(2)>0.91) with the reference technique when real samples were analyzed. Finally, this method was optimized for assay cost and assay time. Hereto the enzymatic reaction was mathematically described using a model for enzyme kinetics, which was then used to calculate the optimal concentrations of ascorbate oxidase and OPDA. As a result of the modeling the amount of enzyme in the assay could be reduced with a factor 2.5 without affecting significantly the reaction time. In a last step the optimal concentrations were used for a successful validation with the HPLC-reference technique.

Modelling fruit characteristics during apple maturation: A stochastic approach

At present, mathematical models to predict the change of fruit quality attributes during apple maturation are deterministic and do not take into account the large natural variability of fruit quality attributes during the growing season. In this work a stochastic system approach was developed to describe the quality evolution of fruit. The basic dynamics of fruit quality evolution was represented by means of a stochastic system, in which the initial conditions and the model parameters were specified as random variables together with their probability density functions. A fundamental approach from stochastic systems theory was used to compute the propagation of the probability density functions of fruit quality attributes, which requires the numerical solution of the Fokker–Planck equation.

CA research - the interactive game of applied and fundamental science.

The quality of fruit and vegetables is essential to the Flemish horticultural sector. It is therefore important to produce, store and commercialize these products in ideal conditions. The non-profit organisation Flanders Centre of Postharvest Technology (VCBT) has been established in 1997 as a collaborative project between the Association of Belgian Fruit and Vegetable Auctions and the Catholic University of Leuven (KU Leuven). Its mission is to perform applied research and provide technological advice and extension services related to CA storage technology and quality of fruit and vegetables to producers and co-operatives. The VCBT closely collaborates with the division BIOSYST-MeBioS of K.U. Leuven which carries out fundamental research related to CA storage and quality of horticultural produce. As both groups are tightly interrelated a fertile environment is created to, on one hand, signal practical problems to subject them to fundamental research and, on the other hand, guide the practical implementation of scientifically derived solutions. This contribution will provide an overview of the work done over the last 10 years, taking internal browning in pear as a case study. This contribution will emphasize the fruitful interactions between an experimental station and a university research group, highlighting the various fundamental and applied approaches taken. Starting from the classical search for optimal CA conditions various paths have been followed ranging from physiological and physics studies to targeted metabolomic and full proteomic studies with a major role for various modelling approaches. Through all these approaches we have come to an improved fundamental understanding while at the same time practical solutions could be provided to the industry.

Fluorescence Based Quality Sorting of Apples Using Self-Organizing Maps

Abstract The chlorophyll fluorescence kinetics of ‘Jonagold’ and ‘Cox’ apples, stored under different conditions to induce mealiness, were measured. Three different storage conditions were considered, causing 3 mealiness levels: not mealy, moderately and strongly mealy. Also destructive measurements of the firmness and texture (compression, juiciness and shear) were done. Classification into the different meatiness levels based on the fluorescence measurements was superior to a classification based on the destructive measurements. To estimate the mealiness level in a non-destructive way from the fluorescence features, a number of different classifiers was constructed. Quadratic discriminants and supervised and unsupervised neural networks were tested and compared. The SOM in general outperforms the other methods. The different advantages ofthe constructed classifiers suggest that fluorescence can be used in an automatic sorting line to assess the mealiness, and the senescence in general, and eventually to predict the time a certain quality level can be guaranteed to the consumers under certain conditions