Comparison of commercial allergen ELISA kits for egg detection in food matrices.

Consumption of low levels of egg already can evoke harmful physiological responses in humans in those allergic to eggs. By detection of egg in food products, using Egg ELISA kits to determine its unintended presence, food producers can respond to avoid potential safety or quality risks of their products. Selection of an ELISA kit fit for the issue at hand is challenging due to, amongst others, lack of information on assay performances with specified matrices. In this study, performances of seven commercial egg ELISA kits are compared for nine different relevant matrices: cookie, chocolate, pasta, dressing, stock cube, wine, vegetable drink and milk, ice cream and meat/meat replacers. The presence of egg was unified for all ELISA kits to mg total egg protein kg-1 food product. In every matrix, kit performances for recovery, intra- and interassay were compared, and also processing is accounted for by determination of egg in incurred samples. All seven kits were able to detect egg qualitatively at the VITAL3 ED01 level of 0.2 mg total egg protein and the corresponding relevant portion size for each matrix. For quantitative results, each ELISA kit showed an increase in detected egg concentration with increased egg levels and performed within the set criteria for recovery for the cookie, chocolate, stock cube and wine. For pasta, vegetable drink and milk, ice cream, and salad dressing, recovery of egg was within the set criteria for at least 4 ELISA kits. Most challenging matrices were meat/meat replacers, showing high matrix effects which could not be explained by the possible egg presence in the cognate blank. Only one ELISA kit was able to recover egg within the set criteria for the meat/meat replacer matrix. Results enable food industry to choose for ELISA kits suitable for egg detection in the matrix of interest.

Tailor-made fructan synthesis in plants: a review.

Fructan, a fructose polymer, is produced by many bacteria and plants. Fructan is used as carbohydrate reserve, and in bacteria also as protective outside layer. Chicory is a commercial fructan producing crop. The disadvantage of this crop is its fructan breakdown before harvest. Studies using genetically modification showed that fructan biosynthesis is difficult to steer in chicory. Alternatives for production of tailor-made fructan, fructan with a desired polymer length and linkage type, are originally non-fructan-accumulating plants expressing introduced fructosyltransferase genes. The usage of bacterial fructosyltransferases hindered plant performance, whereas plant-derived fructan genes can successfully be used for this purpose. The polymer length distribution and the yield are dependent on the origin of the fructan genes and the availability of sucrose in the host. Limitations seen in chicory for the production of tailor-made fructan are lacking in putative new platform crops like sugar beet and sugarcane and rice.

Sink filling, inulin metabolizing enzymes and carbohydrate status in field grown chicory (Cichorium intybus L.).

Inulin is a fructose-based polymer that is isolated from chicory (Cichorium intybus L.) taproots. The degree of polymerization (DP) determines its application and hence the value of the crop. The DP is highly dependent on the field conditions and harvest time. Therefore, the present study was carried out with the objective to understand the regulation of inulin metabolism and the process that determines the chain length and inulin yield throughout the whole growing season. Metabolic aspects of inulin production and degradation in chicory were monitored in the field and under controlled conditions. The following characteristics were determined in taproots: concentrations of glucose, fructose and sucrose, the inulin mean polymer length (mDP), yield, gene expression and activity of enzymes involved in inulin metabolism. Inulin synthesis, catalyzed by sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99) (1-SST) and fructan:fructan 1-fructosyltransferase (EC 2.4.1.100) (1-FFT), started at the onset of taproot development. Inulin yield as a function of time followed a sigmoid curve reaching a maximum in November. Inulin reached a maximum mDP of about 15 in September, than gradually decreased. Based on the changes observed in the pattern of inulin accumulation, we defined three different phases in the growing season and analyzed product formation, enzyme activity and gene expression in these defined periods. The results were validated by performing experiments under controlled conditions in climate rooms. Our results show that the decrease in 1-SST that starts in June is not regulated by day length and temperature. From mid-September onwards, the mean degree of polymerization (mDP) decreased gradually although inulin yield still increased. The decrease in mDP combined with increased yield results from fructan exohydrolase activity, induced by low temperature, and the back transfer activity of 1-FFT. Overall, this study provides background information on how to improve inulin yield and quality in chicory.

Increased production of nutriments by genetically engineered crops.

Plants are the basis of human nutrition and have been selected and improved to assure this purpose. Nowadays, new technologies such as genetic engineering and genomics approaches allow further improvement of plants. We describe here three examples for which these techniques have been employed. We introduced the first enzyme involved in fructan synthesis, the sucrose sucrose fructosyltransferase (isolated from Jerusalem artichoke), into sugar beet. The transgenic sugar beet showed a dramatic change in the nature of the accumulated sugar, 90% of the sucrose being converted into fructan. The use of transgenic sugar beet for the production and isolation of fructans will result in a more efficient plant production system of fructans and should promote their use in human food. The second example shows how the over-expression of the key enzyme of flavonoid biosynthesis could increase anti-oxidant levels in tomato. Introduction of a highly expressed chalcone isomerase led to a seventyfold increase of the amount of quercetin glucoside, which is a strong anti-oxidant in tomato. We were also able to modify the essential amino acid content of potato in order to increase its nutritional value. The introduction of a feedback insensitive bacterial gene involved in biosynthesis of aspartate family amino acids led to a sixfold increase of the lysine content. Because the use of a bacterial gene could appear to be controversial, we also introduced a mutated form of the plant key enzyme of lysine biosynthesis (dihydrodipicolinate synthase) in potato. This modification led to a 15 times increase of the lysine content of potato. This increase of the essential amino acid lysine influences the nutritional value of potato, which normally has low levels of several essential amino acids. These three examples show how the metabolism of primary constituents of the plant cell such as sugar or amino acids, but also of secondary metabolites such as flavonoids, can be modified by genetic engineering. Producing fructan, a soluble fiber, increasing the level of flavonoids, an antioxidant, in tomato or increasing the level of essential amino acids in potato are all clear examples of plant genetic modifications with possible positive effects on human nutrition.