Effect of pH on heat-induced interactions in high-protein milk dispersions and application of fluorescence spectroscopy in characterizing these changes

Abstract

This study investigated casein-whey protein interactions in high-protein milk dispersions (5% protein wt/ wt) during heating at 90°C for 1.5 to 7.5 min at 3 different pH of 6.5, 6.8, and 7.0, using both conventional methods (gel electrophoresis, physicochemical properties) and fluorescence spectroscopy. Conventional methods confirmed the presence of milk protein aggregates during heating, similar to skim milk. These methods were able to help in understanding the denaturation and aggregation of milk proteins as a function of heat treatment. However, the results from the conventional methods were greatly affected by batch-to-batch variations and, therefore, differentiation could be drawn only in nonheated samples and samples heated for a longer duration. The front-face fluorescence spectroscopy was found to be a useful tool that provided additional information to conventional methods and helped in understanding differences between nonheated, low-, and high-heated samples, along with the type of sample used (derived from liquid or powder milk protein concentrates). At all pH values, tryptophan maxima in nonheated samples derived from powdered milk protein concentrates presented a blue shift in comparison to samples derived from liquid milk protein concentrates, and tryptophan maxima in heated samples presented a red shift. With the heating of the sample, Maillard emission and excitation spectra also showed increases in the peak intensities from 408 to 432 and 260 to 290 nm, respectively. As the level of denaturation increased with heating, a marked differentiation can be seen in the principal component analysis plots of tryptophan, Maillard emission, and excitation spectra, indicating that the front-face fluorescence technique has a potential to monitor and classify samples according to milk protein interactions as a function of pH and heat exposure. Overall, it can be said that the pattern of protein-protein interactions in high-protein dispersions was similar to the observation reported in skim milk systems, and fluorescence spectroscopy with chemometrics can be used as a rapid, nondestructive, and complementary method to conventional methods for following heat-induced changes.

Influence of High-Protein Food on Physical Function of Athletes

“…Singh Amamcharla thinks that physical fitness refers to the athlete's special training and competition load, maximizing the mobilization of all organ systems of the organism, overcoming fatigue, and completing the functional ability of special physical fitness and competition with high quality [12]. It is also proposed that basketball is not only a skill-based project but also a speed-strength, confrontational physical-skill-based project with high physical fitness requirements.…”

Synchronous Front-Face Fluorescence Spectra: A Review of Milk Fluorophores

“…Its fluorescent spectrum is well characterized and widely used to assess milk. Just to cite a few examples: it has been observed that tryptophan spectra could be used to distinguish between different levels of heat treatment [ 6 , 7 ], to identify the geographical origin of milk [ 5 , 33 ], to differentiate between homogenized and non-homogenized milk [ 9 ], to check milk authenticity [ 58 ], to investigate protein interactions [ 59 ] and to predict storage time in infant milk formula [ 17 ].…”

The Influence of Sodium Hexametaphosphate Chain Length on the Physicochemical Properties of High-Milk Protein Dispersions

“…Dynamic light scattering (DelsaMax PRO, Beckman, Germany) with DelsaMax ASSIST was used in measuring the mean particle size and zeta potential for heated and unheated high-protein dispersions following the method described by Singh et al [10]. Samples were diluted to 1:100 with distilled water and slowly injected into the flow cell using a syringe.…”