Short communication: Changes in fluorescence intensity induced by soybean soluble polysaccharide–milk protein interactions during acidification

Abstract

Interactions between stabilizer and milk protein are believed to influence the stabilizing behavior of the milk system. We investigated changes in fluorescence intensity induced by interactions of soybean soluble polysaccharide (SSPS) and milk protein (Mp) during acidification. The fluorescence intensity (If) of Mp increased as pH decreased from 6.8 to 5.2. Compared with Mp alone, If of SSPS-Mp mixtures increased as the pH decreased from 6.8 to 5.2. We found that the If of the SSPS-Mp mixture decreased in a pH range from 5.2 to 3.6, which indicated a change in the polarity microenvironment around the Trp residues. We also found that the maximum emission wavelength (λmax) shifted from 337 to 330nm as pH decreased from 6.8 to 3.6, in further support of SSPS interacting with the polar portion of Mp during acidification. Furthermore, an excited monomeric molecule (pyrene exciplex) was found as a ground-state pyrene formed and a broad band was shown at about 450nm. The intensity ratio of the first peak to the third peak (I1:I3) of Mp increased slightly, and the ratio of intensity of pyrene exciplex to monomer (Ie:Im) decreased because pyrene molecules were located in a less hydrophobic microenvironment during acidification. However, the ratio of I1:I3 decreased clearly at pH below 5.6 and the ratio of Ie:Im showed the opposite trend in the SSPS-Mp mixture. Changes in intrinsic and exogenous fluorescence intensity confirmed that interactions of SSPS and Mp could change the polarity of the microenvironment and that SSPS probably interacted with the polar portion of Mp. These results could give insight into the behavior of stabilizers in acid milk products.

Structural Transitions of Alpha-Amylase Treated with Pulsed Electric Fields: Effect of Coexisting Carrageenan

“…This indicates that the tryptophan residues of α-amylase are moving to a less polar environment after binding with λ-carrageenan. The degree of quenching of the α-amylase/λ-carrageenan 10:1 mixture was the largest, suggesting they had a strong binding interaction [ 31 ]. After the second PEF cycle, the fluorescence intensity of α-amylase alone decreased dramatically, and the quenching rate reached more than 60%.…”

Effects of Molecular Weight and Degree of Esterification of Soluble Soybean Polysaccharide on the Stability of Casein under Acidic Conditions

“…In contrast to HMP, it is suggested that SSPS prevents aggregation of casein mainly by the steric repulsion, and the electrostatic repulsion is auxiliary [3,28]. The electrostatic interaction between SSPS and casein plays a major role in the formation of complexes [30].…”