Improvement of solubility and of emulsifying properties of milk proteins at acid pHs by esterification

Abstract

Three milk proteins (beta-lactoglobulin, alpha-lactalbumin and beta-casein) were esterified to different extents with methanol, ethanol and propanol, then their solubility was studied in the pH-range of 3-10. Their emulsifying properties were also checked in the pH-range of 3-7 by measuring the oil-droplet size using laser light scattering. Solubility of all esterified proteins was improved in the acidic pH range (3-6). The magnitude of improvement was depending on the extent of esterification, the nature of the grafted ester group and the nature of the modified protein. Emulsifying activity and stability of esterified milk proteins in the acidic pH range of 3-5 were generally higher compared to the corresponding native proteins. This improvement was associated with the degree of solubility, the degree of esterification, the type of ester group grafted and the nature of the used protein. The highest emulsifying activity improvement was observed for methyl ester derivatives at pH 5 where the native proteins have poor emulsifying properties.

Comparative Evaluation of Antimicrobial Activity and Functional Properties of Native and Esterified Legume Proteins

“…Increasing pH more than 7 reduced the solubility and gave a minimum value (12 %) at pH 8. These data are in good agreement with Sitohy et al, (2001b) who recorded that solubility of β-lacto globulin esters depends on the degree of esterification as well as on the nature of the grafted ester groups. The conformation of the esterified protein might play an important role on the solubility of the protein.…”

“…Similar results were obtained by (Sitohy and Osman 2010) who stated that the antibacterial activity observed with the tested proteins is mostly due to the positive charges condensed on protein molecules through the process of esterification and these positively charged modified proteins may have a direct inhibitory action on the bacterial growth. Esterification blocks free carboxyl groups rising, thus the net positive charge and rendering more basic the modified protein (Halpin and Richardson, 1985;Sitohy et al, 2001aSitohy et al, , 2001b. In general, increasing the positive charge on the protein and peptide molecules enhances their antimicrobial, and more specifically, antibacterial effects.…”

“…Esterification is an important and easy tool for the proteins modification. Esterification blocks free carboxyl groups thus raising the net positive charge and rendering more basic the modified protein (Halpin andRichardson, 1985 andSitohy et al, 2001b). Generally, increasing the positive charge on the protein and peptide molecules enhances their antibacterial effects.…”

Antimicrobial activity of native and esterified legume proteins against Gram-negative and Gram-positive bacteria

“…Esterification is an important and easy tool for the modification of proteins. Esterification blocks free carboxyl groups thus elevating the net positive charge and rendering more basic the modified protein (Halpin & Richardson, 1985;Sitohy, Chobert, & Haertlé, 2001b). In general, increasing the positive charge on the protein and peptide molecules enhances their antimicrobial, and more specifically, antibacterial effects.…”

Maillard glycation of β-lactoglobulin induces conformation changes

“…BLG has been modified by several methods [23] as phosphorylation [24], esterification [25,26], alkylation [27], and amidation [28] in order to improve its functional and physicochemical properties. Functional properties of BLG can also be improved by glycation [29,30], which occurs naturally in food products during heating and storage [31].…”