How Arabinoxylans Modify Gluten and Starch Related Wheat Flour Characteristics

The positive nutritional impact of dietary fibres (DF) gives growing interest to their role in the formation of wheat product quality. Although we are getting closer to characterize the effect of DF on the end use quality, the roles of individual components are not well described yet. Arabinoxylans (AX) are the main compounds of wheat DF, therefore getting more knowledge about its behaviour in wheat based food systems, like dough or end products, could be useful from both theoretical and practical points of view. The aim of this study was to investigate the impact of the AX content on wheat flour quality using a dough model system provided by blends of flour and AX isolate. Rapid Visco Analyser (RVA) and recently developed micro Zeleny test were used for characterization of mixtures. We found that although Zeleny values are basically related to protein-dependent quality, the addition of AX isolate has major impact on the sedimentation volume of flour. In the RVA studies we demonstrated that AX has influence not only on the viscosity values but also on the rate of viscosity change. The effect of AX addition was compared to that of starch addition and was corrected by the rate of dilution. The model system and the experimental method applied here can be suitable to separate the individual effects of non-starchy carbohydrates

INVESTIGATION OF SOME FUNCTIONAL AND NUTRITIVE PROPERTIES OF CEREAL GERM PROTEINS

Proteins, protein concentrates and isolates were prepared frolll wheat, rye, barley, rice and maize germs. after defatting with hexane or supercritical carbon dioxide, by alkaline extraction (NaOH, pH=10) and acid precipitation (0.1 mol/l HCI). The chemical composition, amino acid composition and functional properties (emulsifying properties, foam activity and stability, water , and oil absorption, solubility) were determined. The digestibility and biological value of protein preparations were also calculated. Protein isolates had a high protein content (75.8 - 94.3%). The oil content was low, except in maize germ protein isolates, obtained after defatting with supercritical carbon dioxide. High digestibility (83 - 90%) and moderate biological value (63 - 7,5 FAO/WHO index) was characteristic of all isolates. Methionine and cysteine were the limiting amino acids. Ivlaize germ protein isolates showed the best functional properties, being comparable with those of soy protein isolates. Other germ protein isolates also had acceptable properties. No significant. differences were observed bet ween the functional properties of isolates prepared after defatting with hexane or supercritical carbon dioxide, except the foaming properties. The latter were adversely affected by supercritical fluid extraction

Identification of key effects causing weak performance of allergen analysis in processed food matrices

The weaker performance of generally used analytical methods for allergen analysis in processed foods can be connected to protein denaturation. To understand the nature of protein denaturation processes, experimental but realistic model matrices (corn starch based mixture, hydrated dough, and heat treated cookies) were developed that contain a defined amount of milk, egg, soy, and wheat proteins individually or in combination. The protein subunit composition was investigated in every processing phase, i.e. after mixing, dough formation, and baking. SDS-PAGE measurements were carried out to monitor the protein distribution of sample food matrices in non-reducing and reducing gels. The results clearly show that the highly decreased protein solubility is caused by denaturation, aggregation, or complex formation, which are the most significant factors in poorer analytical performances. Solubility can only partly be improved with the application of reducing agents or surfactants, and the rate of improvement is depending on the proteins and the matrices

Celiac disease-specific prolamin peptide content of wheat relatives and wild species determined by ELISA assays and bioinformatics analyses

Enzyme-linked immunosorbent assays (ELISAs) are widely used to determine gluten contamination in gluten-free and low gluten food samples. ELISA assays developed using monoclonal antibodies against known toxic peptides have an advantage in the identification of toxic prolamin content in protein extracts of different food samples, as well as raw materials. R5 and G12 monoclonal antibodies specific for two known toxic peptides used in commercially available gluten ELISA assays were applied to test toxic peptide contents in wheat relatives and wild wheat species with different genome composition and complexity. Although the R5 peptide content showed some correlation with ploidy levels in Triticum species, there was a high variance among Aegilops species. Some of the analysed diploid Aegilops species showed extremely high R5 peptide contents. Based on the bioinformatics analyses, the R5 peptide was present in most of the sulphur rich prolamins in all the analysed species, whereas the G12 epitope was exclusively present in alpha gliadins. High variation was detected in the position and frequency of epitopes in sequences originating from the same species, thus highlighting the importance of genotypic variation within species. Identification of new prolamin alleles of wheat relatives and wild wheat species is of great importance in order to find germplasm for special end-use quality purposes as well as development of food with reduced toxicity

Determination of acetone in cow’s raw milk by flow injection and gas chromatographic methods

An automatic flow injection (FIA) and two possible reference gas chromatographic (liquid and headspace sampling GC) methods including appropriate sample preparation were developed and validated for determination of acetone in milk. The methods were tested by preserved raw milk samples. The FIA results were compared with data obtained by GC determinations. It was found that FIA procedure is suitable for rapid automated measurement of acetone in the range of 0-5 mmol l-1 in milk, therefore it is a promising analytical method for ketosis monitoring in dairy farms

Investigation of the effects of sample preparation on gluten quantitation in rye and barley flours

Proper gluten quantitation is essential for providing safe gluten-free food for patients living with celiac disease (CD). However, gluten quantitation faces several challenges: the lack of a reference method and certified reference materials, the variability of methods and the effects of genetic and environmental factors on gluten. Among all these challenges our research group focuses on gluten reference material development. Gluten content is determined by enzyme linked immunosorbent assay (ELISA) methods to obtain comparable data for the selection of cultivars used in our reference material development efforts. As ELISA methods are developed for determining low gluten concentrations, application for these special research purposes requires a 10,000-fold dilution. The formerly performed process was a post-extraction liquid dilution that proved to be sufficient for wheat samples. However, gluten contents of rye and barley samples were found to be overestimated by ELISA methods. One of the suggested reasons is the structural and solubility changes of gluten proteins during the dilution process. Therefore, our present study focuses on the comparison of the original dilution method and a revised version using solid-phase dilution in a gluten-free matrix

Application of Micro Z-arm dough mixer in wheat research - Effect of protein addition on mixing properties of wheat dough

A Micro Z-arm mixer has been developed which needs only four grams of flour per test. The new instrument is suitable for screening new wheat cultivars in the early phase of selection on the basis of dough mixing properties. The micro-scale instrument can also be viewed as a valuable research tool for investigation of the structure/function relationships in flour and the effects of different ingredients and additives on rheological parameters. The effects of protein addition on mixing properties of wheat dough were studied. Alkali-soluble isolates and Osborne protein fractions extracted from wheat, corn-, rice germs and amaranth seeds were used as protein additives. Dough development time, maximum resistance of dough and resistance breakdown was calculated from recorded mixing curves. Results showed that the micro-scale equipment is sensitive enough for detection of the effect of less than 40 mg of protein addition on mixing parameters. The effects of additions depend on the type of proteins added to the wheat flour and the parameters calculated from the mixing curves