Slađana Rakita

Determination of free sulphydryl groups in wheat gluten under the influence of different time and temperature of incubation: Method validation

The aim of the present study was to determine the characteristics of an analytical method for determination of free sulphydryl (SH) groups of wheat gluten performed with previous gluten incubation for variable times (45, 90 and 135min) at variable temperatures (30 and 37°C), in order to determine its fitness-for-purpose. It was observed that the increase in temperature and gluten incubation time caused the increase in the amount of free SH groups, with more dynamic changes at 37°C. The method characteristics identified as relevant were: linearity, limit of detection, limit of quantification, precision (repeatability and reproducibility) and measurement uncertainty, which were checked within the validation protocol, while the method performance was monitored by X- and R-control charts. Identified method characteristics demonstrated its acceptable fitness-for-purpose, when assay included previous gluten incubation at 30°C. Although the method repeatability at 37°C was acceptable, the corresponding reproducibility did not meet the performance criterion on the basis of HORRAT value (HORRAT<2).

Content of free amino groups during postharvest wheat and flour maturation in relation to gluten quality

The objective of this study was to monitor the changes in the content of free amino groups during postharvest wheat and flour maturation. The content of free amino groups of wheat flour was analysed immediately after wheat harvest, after 50 days of wheat storage and after 14 days of flour storage varying by wet gluten samples incubation temperatures and incubation times (0, 90 or 135 min at 30°C and after that 180 min at 37°C). The results were observed in relation to wheat-bug damaged kernels content, gluten index values, proteolytic activity and electrophoretic properties of gliadins and glutenins. The content of free amino groups increased during postharvest wheat and flour maturation periods. Proteolytic activity values were the highest 50 days after the wheat storage. The electrophoretic determination indicated a macromolecular redistribution of the gluten proteins from the moment of the wheat harvest until the moment of flour stabilisation.

Changes in the rheological properties of wheat dough during short‐term storage of wheat

BACKGROUND The aim of the present study was to investigate the ability of the small- and large-deformation fundamental rheological tests to monitor the changes during short-term post-harvest storage of wheat. RESULTS At the end of wheat storage period, wet gluten quantity decreased, while gluten index increased in comparison to those of freshly harvested samples. The rheological properties of dough changed over the pre-defined period of storage in terms of becoming more elastic and less extensible in comparison to that of freshly harvested wheat. Visco-elastic properties of weaker flour samples changed more markedly during storage than those of stronger flours, indicating that the intensity of dough rheological changes during wheat storage might be dependent on gluten quality and were the characteristic of wheat variety. CONCLUSION It was shown that small deformation dynamic oscillation and large deformation creep-recovery tests can be successfully employed to monitor the changes in flour quality during wheat storage and that required storage period after wheat harvesting has to be defined according to wheat variety initial rheological properties and its gluten quality.

Predicting rheological behavior and baking quality of wheat flour using a GlutoPeak test

The purpose of this research was to gain an insight into the ability of the GlutoPeak instrument to predict flour functionality for bread making, as well as to determine which of the GlutoPeak parameters show the best potential in predicting dough rheological behavior and baking performance. Obtained results showed that GlutoPeak parameters correlated better with the indices of extensional rheological tests which consider constant dough hydration than with those which were performed at constant dough consistency. The GlutoPeak test showed that it is suitable for discriminating wheat varieties of good quality from those of poor quality, while the most discriminating index was maximum torque (MT). Moreover, MT value of 50 BU and aggregation energy value of 1,300 GPU were set as limits of wheat flour quality. The backward stepwise regression analysis revealed that a high-level prediction of indices which are highly affected by protein content (gluten content, flour water absorption, and dough tenacity) was achieved by using the GlutoPeak indices. Concerning bread quality, a moderate prediction of specific loaf volume and an intense level prediction of breadcrumb textural properties were accomplished by using the GlutoPeak parameters. The presented results indicated that the application of this quick test in wheat transformation chain for the assessment of baking quality would be useful. PRACTICAL APPLICATIONS Baking test is considered as the most reliable method for assessing wheat-baking quality. However, baking test requires trained stuff, time, and large sample amount. These disadvantages have led to a growing demand to develop new rapid tests which would enable prediction of baked product quality with a limited flour size. Therefore, we tested the possibility of using a GlutoPeak tester to predict loaf volume and breadcrumb textural properties. Discrimination of wheat varieties according to quality with a restricted flour amount was also examined. Furthermore, we proposed the limit values of GlutoPeak parameters which would be highly beneficial for millers and bakers when determine suitability of flour for end-use.

Fatty Acid Composition and β-Carotene Content in Egg Yolk of Laying Hens Fed with Linseed, Paprika and Marigold

Summary Eggs enriched with n-3 fatty acids and natural pigments are desirable in human food chain due to numerous benefits for health. In this study, we investigated the effects of inclusion of co-extruded linseed and sunflower meal into laying hens’ diet and replacement of synthesized pigment with paprika and marigold flower as sources of natural pigments. Four hundred 18–wk-old Bovan laying hens divided in two groups (control and experiment) were fed for 12 weeks. Fatty acids and β-carotene were monitored every fourth week and successively analyzed. Significantly (p<0.05) increased content of α-linolenic acid in egg yolk in the experimental group in comparison to the control group was observed with addition of linseed, paprika and marigold in laying hens’ nutrition. Nearly the same tendency was observed in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content. Supplementation of the co-extruded linseed and sunflower meal into laying hens’ diet demonstrated significantly (p<0.05) lower n-6/n-3 FA ratio in experimental group compared to control group. The obtained results showed that the synthetic pigment added to laying hens’ diet provided better pigmentation of egg yolks after one and two months of the feeding trial than paprika and marigold flower. The concentration of β-carotene in egg yolks increased in experimental group after three months of the treatment, and that was the first time that concentrations of β-carotene did not significantly (p < 0.05) differ among control and experimental group, which shows that paprika and marigold flower as sources of natural pigments can successfully replace synthetic pigment. We shall continue research in this field with other supplemented mixtures, as there are indices for other potential feed enhancements among oily seeds and herbs.