Rye Bread Defects: Analysis of Composition and Further Influence Factors as Determinants of Dry-Baking.

For decades, the evaluation of rye milling products have been aimed at detecting raw material defects that are linked to excessive enzyme activity. Those defects were indirectly characterized by the rheological methods of the dough or the final products. However, such methods do not sufficiently reflect the baking properties of all rye flours present on the market. A further problem is the continuing climate change, which affects compound composition in rye. So far, these bread defects can only be corrected by process engineering (e.g., extended dough resting). Therefore, it is necessary to characterize the main determinants of the quality defects prior to the baking process in order to predict baking quality and not waste raw material, energy, and time. In this study, it was found that the water accessibility of starch for gelatinization and its partial inhibition by certain components play a major role in baking quality. Specifically, high amounts of insoluble nonstarch-polysaccharides (NSPSs) and a hindered denaturation of proteins seem to be an indication and reason for poor baking quality. However, traditional quantitative analysis of the ingredients and properties of the rye milling products (e.g., falling number, protein content, amylographic data) does not allow any reliable conclusions about rye flour suitability for use as bread rye. It can be concluded that more complex compositional aspects (e.g., complexation of compounds) need to be characterized for future quality control of rye.

Glycemic index and microstructure analysis of a newly developed fiber enriched cookie.

A diet with a high glycemic index (GI) is associated with an elevated risk for obesity or type 2 diabetes. We investigated the GI of a newly-developed fiber enriched cookie and characterized the microstructure of ingredients used. In a study with 26 non-diabetic healthy volunteers it was shown that the fiber enriched cookie has a GI of 58.9 in relation to white bread as reference. Using a conversion factor of 1.4, the GI of the fiber enriched cookie in relation to a glucose-solution is 42.0 and can be classified as a low-GI food. Postprandial insulin concentration was significantly lower after consumption of fiber enriched cookies compared to white bread. Glucose release after in vitro digestion was significantly lower from fiber enriched cookies compared to other cookies tested. In addition to its high percentage of fiber, the cookies' low GI can be attributed to the limited gelatinization potential of the starch granules found in the ingredients used. Using confocal laser scanning microscopy it is shown that starch granule surface area of whole grain barley flour, spelt flour and oat flakes bears cluster-shaped protein-NSPS complexes that preferentially absorb water in conditions of water shortage and thereby prevent starch gelatinization.

High hydrostatic pressure/temperature modeling of frankfurter batters.

The impact of high pressure/temperature treatment on structure modification and functional sensory properties of frankfurter batter was investigated. The degree of solubilization of meat proteins, particularly of myosin, was identified as a key process with significant effect on the batter's structural properties. The maximal solubilization level was at 200 MPa/40 °C IT for all formulations which was found to be treatment time dependent. The impact of the pressurizing gradient - PG=40 MPa/s and PG=2.5 MPa/s was investigated and estimated to have a significant effect on the protein network and functional properties, respectively. These were improved at low PG (2.5 MPa/s) as a phenomenon of secondary network formation parallel to the main matrix. Batter secondary-structure characteristics were found to be ionic-strength dependent. According to SDS-PAGE analysis, the major role in the solubilization, aggregation and gelation processes occurring in the aqueous phase was due to the myosin S-1 and S-2, N-terminal, C-terminals, the MLC and actin during the high pressure/temperature treatment.

Influencing emulsifying properties of egg yolk by enzymatic modification with phospholipase D. Part 2: structural changes of egg yolk due to incubation.

The effects of a direct incubation of egg yolk (EY) by phospholipase D (PLD) with respect to EY structure and interface properties of oil-in-water (o/w)-emulsions prepared with this EY were investigated. PLD incubation of EY mainly converts phosphatidylcholine into phosphatidic acid (PA). EY structures were characterised using circular dichroism and scanning electron microscopy. Composition (protein and phospholipid contents), charge, and appearance of interfaces in EY stabilised o/w-emulsions were described, too. The improved emulsifying activity of EY after PLD incubation could be attributed both to a higher interface activity of the PA itself and to modified interactions of protein and phospholipids in EY. PA possesses a negative charge resulting in droplet interfaces with higher charge. This effect increased repulsion forces between droplets compared to application of EY without PLD incubation. A higher portion of alpha-helix structures could be detected in the PLD-incubated EY enabling a higher flexibility of proteins on droplet surfaces. Additionally, a better preservation of EY protein structures during heat treatment due to the presence of PA enabled a higher thermal stability of such emulsions.

Influencing emulsifying properties of egg yolk by enzymatic modification by phospholipase D from Streptomyces chromofuscus Part 1: technological properties of incubated egg yolk.

Impact of a direct incubation of egg yolk with phospholipase D (PLD) from Streptomyces chromofuscus was investigated with respect to its effect on rheological and emulsifying properties. Egg yolk has been shown to be a suitable substrate for incubation with PLD after a slight dilution with water (70/30, w/w). A considerable increase of egg yolk viscosity during incubation was observed correlating with formation of phosphatidic acid due to enzymatic activity. Emulsions prepared with such an incubated egg yolk showed a higher viscosity, in particular at high egg yolk concentration. Especially in the case of lower concentrations, smaller droplets indicating better emulsifying activities were detected in emulsions prepared with the incubated egg yolk compared to the application of untreated egg yolk. Stability after heat treatment of the emulsions could be significantly improved by the application of egg yolk incubated with PLD.

Preparation and characterization of multilayer coated microdroplets: droplet deformation simultaneously probed by atomic force spectroscopy and optical detection.

We report the preparation and characterization of multilayer coated droplets in an emulsion. Stability and control of mass transport across the interface are the key issues for such coated microdroplets. Shelf life of cosmetic, pharmaceutical, and food formulations can be improved by increasing stability. Moreover, such emulsions have potential applications in drug delivery and storage. A primary oil-in-water emulsion with caseinate as an emulsifier was prepared. On the basis of attractive electrostatic interactions, polyelectrolytes with opposite charges were added layer by layer. The oil droplets (particle size around 10 microm) were successively coated with casein, pectin, whey proteins, pectin, whey proteins, and pectin. Laser diffraction spectroscopy, particle charge measurements, and confocal laser scanning microscopy were applied to characterize the multilayer droplets. The complementary results indicate that the inner layers merge and the packing density of the interface increases. AFM-induced mechanical compression of single oil droplets coated with casein and pectin is monitored by an inverted optical microscope, and simultaneously AFM force curves are recorded. Thus, the deformation of the droplet is reflected by its lateral expansion and the force curve. Force volume imaging is applied to probe the lateral distribution of mechanical properties of the droplet.