During food processing or storage, milk proteins can react with reducing sugars via the Maillard reaction (glycation), which may alter their techno-functional properties. The aim of this study was to investigate the relationship between molecular changes of casein occurring during different stages of the Maillard reaction and its acid-induced gelling properties. Therefore, sodium caseinate was heated in a dry state at 60 °C in the presence of lactose and analyzed for structural modifications by determining Amadori compounds (glycoconjugation) indirectly as furosine, the total lysine modification, and the extent of protein cross-linking. For techno-functional characterization, acid-induced gels were prepared by the addition of glucono-δ-lactone and evaluated by measuring pH kinetics during gel formation, gel strength, and water holding capacity. The time to reach pH 4.6 during the gelation process was significantly delayed with increasing extent of the Maillard reaction. Glycation with lactose also led to a significant increase in gel strength and water holding capacity. The increase in gel stability was rather independent from the amount of sugars covalently bound to the proteins during the early phase of the Maillard reaction but strongly correlated to the degree of protein polymerization. Small-and medium-sized casein oligomers, formed during advanced stages of the Maillard reaction, contributed considerably to the formation of stronger gels with higher water holding capacity, whereas a sharp increase in the relative amount of the polymer fraction observed during prolonged crosslinking processes caused a spontaneous destabilization of the gel network. Knowledge about structure−function relationships on a molecular level can provide useful information to control food texture by raw material quality.

The influence of covalent protein modifications resulting from the Maillard reaction (glycation) of casein and lactose on the noncovalent association behavior of the protein was studied. Nonenzymatic cross-linking with methylglyoxal (MGO) and glutaraldehyde (GTA) as well as enzymatic cross-linking with microbial transglutaminase (mTG) was investigated in comparison. Molar mass, particle size, and conformational characteristics of nonmicellar casein associates as well as the extent of intraparticle protein cross-linking were examined utilizing size-exclusion chromatography (SEC) combined with UV detection and static and dynamic light scattering. Cross-linking resulted in the stabilization of a certain fraction of casein associates, with particle sizes of approximately 30 nm in radius of gyration (R g), and promoted an incorporation of further casein molecules into those particles, yielding molar masses (M w) of 1.0–1.2 × 106 g/mol. When caseins were additionally conjugated with lactose during the early Maillard reaction, a further growth of the associates up to approximately 50 nm in R g with a M w of 2.1 × 106 g/mol was observed. Furthermore, glycation reactions induced a transition from slightly elongated, random-coil structures toward more anisotropic conformations. Associates consisting of caseins cross-linked with GTA appeared to preserve the original particle conformation.

Casein gels consist of a fractal organized network of aggregated casein particles. The gel texture thereby depends on the structure, the spatial distribution, and the interaction forces of the network’s elementary building blocks. The aim of this study was to explore the technofunctional consequences of a possible specificity of Maillard reaction-induced cross-linking reactions on casein with respect to texture and microstructure of acid gels. Therefore, sodium caseinate glycated with lactose in the dry state (60 °C, a w 0.5) was compared with casein samples cross-linked with methylglyoxal, with glutaraldehyde, or via microbial transglutaminase, respectively, at similar levels of protein cross-linking as confirmed by size-exclusion chromatography under denaturing conditions. Casein gels prepared by acidification with glucono-δ-lactone were characterized concerning pH kinetics during gelation, mechanical texture properties under large deformation, and water-holding capacity, while viscometric properties of casein suspensions were obtained prior to gelation. The gel microstructure was captured by confocal laser scanning microscopy and evaluated by means of image texture analysis. All protein cross-linking reactions studied led to an enhanced gel strength which was accompanied by an increased interconnectivity of the gel network and a decrease in apparent pore sizes. Gels with more densely packed strands, as was the case for enzymatically modified casein, exhibited pronounced mechanical stability. The spontaneous destabilization of the gel network upon prolonged glycation reactions, which was not obviously displayed by microstructural features but connected to an increased viscosity and pronounced pseudoplastic flow of the unacidified suspension, suggests a limitation of particle rearrangements and the weakening of interparticle protein–protein interactions by additional structure attributes formed during the early Maillard reaction (glycoconjugation).

Silica‐based composite particles are complex catalyst materials that are widely used in petrochemistry. The preparation of particles that are well defined in form, composition, and chemical and rheological behavior by spray drying of suspensions remains an important industrial challenge. Here, zeolite HY, kaolin, and the cheap binder water glass are used. Experimental and model regimes of slurry peptization are analyzed based on their pH value, zeta potential, and mixing speed to control the process. The results show a pseudoplastic behavior of the silica slurries for zeta potential below 20 mV, which is explained by surface charge, hydroxyls, and pH‐dependent coagulation. Thus, a quick acidification of the slurry, additional mechanic shear, and subsequent pH control during spray drying enable control of peptization kinetics.

Insekten werden in zahlreichen Kulturkreisen der Welt als traditionelle Lebensmittel zubereitet und verzehrt. In den letzten Jahren ist das wissenschaftliche und wirtschaftliche Interesse an Insekten, v.a. als alternative Proteinquelle für die humane Ernährung auch in Europa enorm gewachsen. Die Proteinisolate einiger Käferlarven-, Schaben-und Heuschreckenarten zeigen neben ihren guten ernährungsphysiologischen Eigenschaften ein ebenso vielversprechendes Schäumungs-, Emulgier-oder Gelierverhalten [1-3], und bieten damit Potential für den Einsatz als technofunktionelle Lebensmittelinhaltsstoffe. Inwieweit diese funktionellen Eigenschaften auf einzelne, spezifische Proteine der Insekten zurückzuführen sind, ist bislang nicht bekannt. In dieser Studie sollte eine Strategie zur Extraktion und Fraktionierung der Proteine des Mehlwurms (Tenebrio molitor) und der Schwarzen Soldatenfliegenlarve (Hermetia illucens) auf Basis ihrer Ionenstärke-abhängigen Löslichkeit getestet und die isolierten Fraktionen hinsichtlich ihrer Emulgiereigenschaften charakterisiert werden. Gefriergetrocknete, entfettete Insektenmehle wurden nach einem Fraktionierschema für tierisches Muskelprotein [4] aufgetrennt und die Proteine anschließend nach tryptischem Verdau mittels LC-MS/TOF identifiziert. Zur technofunktionellen Charakterisierung wurden die fraktionierten Proteinisolate zur Herstellung von O/W-Emulsionen eingesetzt und diese mithilfe von Trübungsmessungen sowie der Auswertung lichtmikroskopischer Aufnahmen hinsichtlich ihrer Emulgieraktivität und -stabilität bewertet. In den Fraktionen konnten Zellproteine, sowie myofibrilläre und Stromaproteine beider Insekten nachgewiesen werden. Trotz des hohen Anteils an Muskelgewebe der Insektenlarven sowie der strukturellen Analogien zu anderen tierischen Muskelproteinen zeigten sich deutliche Unterschiede im Proteinmuster sowie der Proteinausbeute verglichen zu fraktioniertem Schweinefleisch. Art-und fraktionsspezifische Unterschiede waren ebenfalls anhand der Emulgieraktivität ableitbar. Die Erkenntnisse schaffen eine erste Basis zum Verständnis grundlegender Struktur-Wirkungsbeziehungen im Hinblick auf das Potential spezifischer Insektenproteine für technofunktionelle Anwendungen.