Screening of antioxidant properties of the apple juice using the front-face synchronous fluorescence and chemometrics

Fluorescence spectroscopy is gaining increasing attention in food analysis due to its higher sensitivity and selectivity as compared to other spectroscopic techniques. Synchronous scanning fluorescence technique is particularly useful in studies of multi-fluorophoric food samples, providing a further improvement of selectivity by reduction in the spectral overlapping and suppressing light-scattering interferences. Presently, we study the feasibility of the prediction of the total phenolics, flavonoids, and antioxidant capacity using front-face synchronous fluorescence spectra of apple juices. Commercial apple juices from different product ranges were studied. Principal component analysis (PCA) applied to the unfolded synchronous fluorescence spectra was used to compare the fluorescence of the entire sample set. The regression analysis was performed using partial least squares (PLS1 and PLS2) methods on the unfolded total synchronous and on the single-offset synchronous fluorescence spectra. The best calibration models for all of the studied parameters were obtained using the PLS1 method for the single-offset synchronous spectra. The models for the prediction of the total flavonoid content had the best performance; the optimal model was obtained for the analysis of the synchronous fluorescence spectra at Delta lambda = 110 nm (R (2) = 0.870, residual predictive deviation (RPD) = 2.7). The optimal calibration models for the prediction of the total phenolic content (Delta lambda = 80 nm, R (2) = 0.766, RPD = 2.0) and the total antioxidant capacity (Delta lambda = 70 nm, R (2) = 0.787, RPD = 2.1) had only an approximate predictive ability. These results demonstrate that synchronous fluorescence could be a useful tool in fast semi-quantitative screening for the antioxidant properties of the apple juices.info:eu-repo/semantics/publishedVersio

Evaluation of 2 unstructured mathematical-models for the Penicillin-G fed-batch fermentation

The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuss (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product. It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes

Analysis of apple (Malus domestica Borkh.) wax by means of chromatographic techniques and confocal microscopy

The wax of three economically important Belgian apple cultivars, 'Jonagold', 'Jonagored' and 'Elstar', was analysed chemically and structurally before and after 4 and 8 months of optimal ultra low oxygen (ULO) storage and during shelf life. Macroscopically and microscopically the surface properties of 'Elstar' were clearly different from the two other cultivars. These properties changed similarly for all cultivars during storage and shelf life. Chromatographic patterns of the three cultivars were dominated by the carbohydrate fraction with nonacosane (C29) as the major component. Again 'Elstar' differed in composition compared to 'Jonagold' and 'Jonagored'. For the non-destructive structural analysis confocal microscopy was used, and this led to the development of a new technique for the determination of the wax layer thickness. This technique was compared with the chemical technique known for determination of wax layer thickness. With the confocal technique 'Elstar', 'Jonagold' and 'Jonagored' could be significantly (p=0.05) discriminated based on wax-layer thickness, showing values of 4.14 mum, 2.58 mum and 3.41 mum, respectively

Prediction of postharvest water loss across the cuticle of apple (Malus domestica Borkh.) by means of finite element modelling

The cuticle of apple basically consists of a cutin and wax layer in parallel, each with different structures and diffusion properties. In order to obtain an accurate description of moisture transport through this cuticular membrane, a complex finite element model was developed. Model geometries of cracks and lenticels were based on confocal laser scanning microscopy (CLSM) images of the cuticle. In all geometries separate diffusion coefficients were attributed to the different surface layers. These diffusion properties were experimentally determined by means of a gravimetrical set-up. In a first series of simulations with the developed model, actual diffusion coefficients were obtained for cutin, tissue and wax. These actual diffusion coefficients differed from the experimentally determined apparent coefficients by taking into account the specific contribution of cuticular features such as cracks, open and closed lenticels. Next, the 'actual' diffusion coefficients were used in the model to predict moisture loss during long-term storage. After six months the predicted moisture loss was 4.1% for 'Elstar' and 3.5% for 'Jonagold', which accorded well to the data retained from practice. In addition, the model was evaluated in three case studies to describe the effect of different surface structures, relative humidity and blocked lenticels on moisture loss of fruit in long-term storage

Modeling of ethylene biosynthesis during ripening and CA storage of 'Jonagold' apples

Simulation models can make the determination of optimal storage conditions for new cultivars of Malus domestica less expensive and less time consuming. On top of this, modeling creates the opportunity to apply batch dependent conditions. Two experiments were set up to develop a model to describe ethylene production during the ripening and storage of 'Jonagold' apples. Fruit were harvested at different dates around the optimal harvest date to obtain different ethylene production rates at different ripeness stages. Apples harvested at the three most extreme harvest dates were used for the storage experiment (CA conditions, 1% O-2, 3% CO2) and either treated or not treated with Smartfresh (TM), a commercially applied ethylene inhibitor. The ethylene production rate was determined by gas chromatography and S-adenosyl-L-methionine (SAM) concentrations were measured with capillary electrophoresis. During fruit ripening and during the storage of untreated fruit, an increase in ethylene production rate was noticed. SAM concentrations on the other hand were not influenced significantly during the 4 weeks period around optimal harvest time

Ethylene metabolism in 'Jonagold' apple during CA storage and shelf life : a modeling approach

To be able to preserve climacteric fruit like Malus domestica for a long time suppression and control of the ripening process is crucial. Based on measurements of metabolites and enzymes of ethylene biosynthesis and taking into account the underlying pathway, a kinetic model to predict and simulate ethylene metabolism during storage and shelf life of Jonagold apple was developed. Data was gathered during ripening, storage and shelf life experiments. The obtained model explains 80% of the data