In the past K. Beullens has collaborated on articles with S. Vermeir and E. Róth. One of their most recent publications is Evaluation and optimization of high-throughput enzymatic assays for fast l-ascorbic acid quantification in fruit and vegetables. Which was published in journal Analytica Chimica Acta.

More information about K. Beullens research including statistics on their citations can be found on their Copernicus Academic profile page.

K. Beullens's Articles: (3)

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

AbstractIn 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 mg L−1 and excellent correlation parameters (slopes close to 1, intercepts close to 0, R2 > 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.

Sex differentiation, changes in length, weight and eye size before and after metamorphosis of European eel (Anguilla anguilla L.) maintained in captivity

AbstractMigrating European eel (Anguilla anguilla L.) glass eels were collected annually in the Garonne Basin (France) during 1987–1989 and subsequently raised under freshwater conditions. In 1990 and 1991 sex differentiation, gonadal development, length/weight and eye size were studied in relation to metamorphosis from yellow to silver eel stage. Differentiation from intersexual gonads to testes took place after 2 years and was synchronized with metamorphosis. Differentiated ovaries, however, were already present in 2 + yellow eels indicating that expression of female gonadal sex was not synchronized with metamorphosis.Body length and eye size were used to assess the ontogenetic stage of individual fish. The majority of female yellow eel and male and female silver eel of the experimental fish could be identified using these external morphological characteristics. Intersexual yellow eel could not be identified with this method. Intersexual and female yellow eel reached the silver stage at ages of 2–3 and 3–4 years and at body weight ranges of 78–410 and 309–830 g, respectively, implying that metamorphosis in captivity took place at earlier ages and at heavier body weights than in nature. Metamorphosis with respect to enlargement of eyes up to the size of mature silver eels occurred in the hatchery population without hormonal intervention. The testes of silver eels contained spermatogonia in mitotic arrest and the ovaries had oocytes, which were blocked in late prophase of meiosis.Body length and eye size were not suitable characteristics to assess sexual maturity in hatchery raised silver eel. Males and females continued to eat and grow after they became silvery whereas gonadal development gradually stopped. The relationship between age, length/weight, feed intake and metamorphosis (including integumental colour change, enlargement of eyes, degeneration of the alimentary tract, gonadal growth/maturation) as well as the role of gonadotropins are discussed.

Postharvest quality of integrated and organically produced apple fruit

AbstractApple cv. ‘Jonagold’ fruit were picked in three different regions of Belgium. In each region one organic and one integrated orchard with identical climatic and soil characteristics was sampled. Fruit were stored in air and under CA conditions (1% O2, 2.5% CO2) at 1 °C for 6 months. The acoustic stiffness, firmness, soluble solids contents, acid and sugar contents, and the aroma profile were measured. Quality parameters were analysed right after harvest and storage. At both times an additional shelf-life experiment was carried out to simulate the conditions in the commercial chain.The quality attributes of apples coming from different regions and different production systems did not differ significantly, neither at harvest nor after storage. There was a considerable softening during storage in air and shelf-life, but not under CA conditions. Immediately after harvest, high malic acid, quinic acid and sucrose contents were observed, while glucose and citric acid contents were higher after storage. The aroma profile changed during shelf-life, except for apples stored in air, which even immediately after storage already had an aroma profile comparable to that after shelf-life. The volatile responsible for the typical apple aroma (2-methylbutyl acetate) had the highest relative abundance after CA storage and subsequent shelf-life, followed by apples immediately after CA storage. The effect of storage conditions on the quality of the apples was in general much larger than that of the possible effects of the production system. Aroma profiles of air-stored and CA-apple converge during shelf-life conditions.

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