Acoustic characterisation of pH dependant reversible micellar casein aggregation

Protein of yak milk residue: Structure, functionality, and the effects on the quality of non-fat yogurt

The purpose of this study was to compare the structural and functional of protein from yak milk residue, which collected from different elevations (MRP1 and MRP2) in Tibet, as well as their potential for enhancing the quality of non-fat yogurt. The results showed that MRP1 exhibited higher levels of β-sheet, turbidity, particle size, and gel properties. MRP2 had better flexibility, emulsification, foaming, water/oil absorption capacity. The addition of MRP1 (3%) could improve texture and sensory properties of yogurt. Although MRP2 yogurt had higher hardness, gumminess, chewiness and water holding capacity, poor mouthfeel. Rheological test showed that MRPs yogurt exhibited typical gel-like and shear-thinning behavior. Moreover, the fortification of non-fat yogurts with MRP1 brought the formation of larger protein clusters with a more tightly knit network of smaller pores. These results indicate that MRP1 can be used as a fat substitute to improve the quality of non-fat yogurt.

Role of Clay Substrate Molecular Interactions in Some Dairy Technology Applications

The use of clay materials in dairy technology requires a multidisciplinary approach that allows correlating clay efficiency in the targeted application to its interactions with milk components. For profitability reasons, natural clays and clay minerals can be used as low-cost and harmless food-compatible materials for improving key processes such as fermentation and coagulation. Under chemical stability conditions, clay materials can act as adsorbents, since anionic clay minerals such as hydrotalcite already showed effectiveness in the continuous removal of lactic acid via in situ anion exchange during fermentation and ex situ regeneration by ozone. Raw and modified bentonites and smectites have also been used as adsorbents in aflatoxin retention and as acidic species in milk acidification and coagulation. Aflatoxins and organophilic milk components, particularly non-charged caseins around their isoelectric points, are expected to display high affinity towards high silica regions on the clay surface. Here, clay interactions with milk components are key factors that govern adsorption and surface physicochemical processes. Knowledge about these interactions and changes in clay behavior according to the pH and chemical composition of the liquid media and, more importantly, clay chemical stability is an essential requirement for understanding process improvements in dairy technology, both upstream and downstream of milk production. The present paper provides a comprehensive review with deep analysis and synthesis of the main findings of studies in this area. This may be greatly useful for mastering milk processing efficiency and envisaging new prospects in dairy technology.

Reversible modulation of protocell volume via collective response of functional protein in its membrane

Volume change plays an important role in biological cells to regulate their internal microenvironment. To adapt to the rapid variation of the surface area during the volume change, the lipid membrane is dynamically modulated via membrane folding invagination, or spontaneous uptake or release of lipid molecules under osmotic pressure. Here, we demonstrate an alternative approach to design a functional protocellular system capable of dynamically adjusting its volume and intracellular microenvironment in response to the alteration of pH. By assembling and subsequently cross-linking pH-responsive caseinate at the water-oil interface, the caseinate-based protocell with more than ten thousand caseinate units in its membrane was established and showed a reversible volume and pore size change to pH variation due to the collective response of the caseinate in the membrane, which could be used to control the spatial distribution of proto-organelle by regulating of the viscosity inside the protocell.

Application of high-resolution ultrasonic spectroscopy for detection of the plasmin activity toward β-casein

High-resolution ultrasonic spectroscopy (HR-US) was applied for precise detection of plasmin activity towards β-casein in buffer at pH 7.8 and 37 °C. The evolution of ultrasonic velocity and ultrasonic attenuation measured at 15.5 MHz is related to the concentration of peptide bonds hydrolyzed and loss of β-casein aggregates, respectively. The ultrasonic assay presents sensitive and direct activity-based quantification of plasmin levels in milk. The variation in plasmin concentration between HR-US and ELISA method owed to the differing detection principles. The real-time ultrasonic profiles of hydrolysis were utilized to describe the kinetic aspect of plasmin activity. The non-linear activity curve was fitted with classic and inverse Michaelis-Menten type models. Within 1-8.6 mg·mL^-1 β-casein, the V_max and K_M obtained were (6.30 ± 2.21) × 10^-5 mol.kg^-1·min^-1 and 10.33 ± 3.50 mg·mL^-1, respectively. The maximum peptide bond cleaved was 5-6 (2.7% degree of hydrolysis) achieved at 1 mg·mL^-1 β-casein.