Abstract
Proteins are frequently used as emulsifiers and stabilizers. In this work, two proteins with different isoelectric points were used: lactoferrin and ovalbumin. Solutions containing different proteins ratios, with different pH values, were stored for 7 days at 25 °C to analyze the system stability. Systems containing 3% w/v lactoferrin remained stable at all pH values studied, while systems containing 1% w/v ovalbumin remained stable only at a high pH value (8.0). Emulsions containing a mixture of proteins remained stable at a pH between the isoelectric points of the two proteins, which was attributed to an electrostatic bond because of the opposite charges of proteins at this pH. During the analysis of rheological properties, it was possible to observe a non-Newtonian behavior of the emulsions, using the models of Carreau and Cross to describe the pseudoplastic behavior of suspensions. This study provides important information for the use of functional ingredients.
Highlights
Proteins are widely used as emulsifiers in foods
Lactoferrin (Lf) is a glycoprotein obtained from milk, with a molecular weight of 80 kDa and an isoelectric point close to 8.0; its main feature is the ability of each molecule to bind to two iron ions[8]
Studies of emulsion stability using lactoferrin have shown that the protein has a great stabilizer capacity[10,11,12]
Summary
Proteins are widely used as emulsifiers in foods. For this reason, the proteins have been widely studied to better understand the mechanisms involved in the stabilization of emulsion systems. Emulsions emulsified and/or stabilized with proteins are highly sensitive to stresses such as pH, ionic strength, and temperature[5,6,7]. Ovalbumin (OVA), the most abundant egg protein, is widely used in the food industry due to its ability to form gels with other polymers. It has a molecular weight of 42 kDa, is negatively charged at a neutral pH, and has an isoelectric point of approximately 4.8[13]. Niu et al.[15] studied the stability of emulsion w/o by complexes formed between egg albumin and arabic gum under stress conditions as changes in pH, ionic strength and heating, observing stability in acid pH conditions, in the absence of salt ions and upon heating, while in a second study, Niu et al.[16] studied the stability of emulsion w/o using the same complex, showing improved physical and oxidative stability in the ratio 1: 2 and, through the rheology, noted that this proportion provide systems more viscous with higher storage modulus
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