RESUMEN
This research reveals the underlying mechanisms that make high-intensity ultrasound an effective tool to reduce the viscosity of micellar casein concentrates and to enhance the solubility of the respective powders. Micellar casein concentrates (MCC) gained great importance in the production of valuable food products with high protein content, but the processing properties of the reconstituted solutions are deficient. Even though several presumptions were established, the reasons why ultrasound is able to reduce the product viscosity and what limitations occur when using sonication technology are still not clear yet. Our study aims to investigate those reasons by combining analyses of viscosity measurements, particle size distributions, solubility, and hydration. The data presented demonstrate that undissolved, highly hydrated particles play an important role in micellar casein concentrates showing a high viscosity. We conclude on the high voluminosity of those particles, since improved solubility and decreased viscosity are accompanying effects. The determined voluminosities of those particles are 35-40% higher than for colloidal dissolved micelles. Hence, the viscosity reduction of up to 50% can be only obtained by sonicating micellar casein concentrates derived from powder reconstitution, whereas ultrasonication of freshly prepared membrane-filtrated MCC does not reduce viscosity.
RESUMEN
Casein hydrolysates are important additives to foods for elderly and sports nutrition. However, due to the enzymatic generation of so-called bitter peptides, their application is limited. Therefore, the procedure needs to be optimized in order to restrict their occurrence. For this, extensive sensory evaluations are necessary. By combining two separation techniques using comprehensive two-dimensional liquid chromatography, we present a novel method for estimating the bitter taste of hydrolysate samples on the basis of their elution pattern. Using a size exclusion column in the first and a reversed phase column in the second dimension allows for a detailed sample evaluation regarding peptide size and relative hydrophobicity. The results obtained for different casein hydrolysates were correlated with the sensory evaluation. We found that hydrolysates with increasing bitterness contain a higher amount of peptides of high hydrophobicity and a molecular weight less than 6.5 kDa.