The knowledge developed in this work can be used as a base for the development of soy/dairy products with unique textural properties and a healthy image. These results advance the understanding of the intermolecular interactions between two important classes of food proteins, facilitating the design of new foods or ingredients. The results of this work are also expected to have a significant economic impact, by helping the local and national food industry develop products that are not currently on the market.
impact statement issue
The proven health benefits of high-protein, low-fat foods have increased the demand for such products by today's health-conscious consumers. Consumption of soy foods is continuously gaining popularity in the U.S., mostly because of their healthy image. Yet, soy consumption in the U.S. is relatively limited, and most Americans are rather unlikely to adopt soy-only products as a main component of their diet. One way to introduce soy proteins into the American diet is to integrate them into products that are both healthy and highly acceptable, such as dairy products. Blends of milk proteins and soy proteins represent an attractive combination for the modern food industry, since they combine a healthy image and complementary functional properties. The few attempts that have been made in this direction were not very successful because of the unacceptable sensory properties of the resulting products. A good understanding of the interactions between milk and soy proteins and of the factors that influence them is expected to facilitate the development of products and / or ingredients of unique texture and functionality.
impact statement response
This phase of the project focused on elucidating the occurrence and nature of heat-induced interactions between casein and soy proteins. Native micellar casein and soy protein powders were used to prepare both individual and mixed protein solutions. The protein solutions were heat treated for 15 min, both under denaturing and non-denaturing conditions for the soy proteins (40C, 60C and 95C), cooled to 25C and their rheological properties determined. The nature of intermolecular interactions was assessed with a differential solubilization method. Both covalent bonds (prevalent) and physical interactions were identified in the mixtures, especially at higher temperatures, which explains the significant increase in heat treated mixtures' yield stress. The results of the study suggest that the covalent bonding induced by the high temperature treatments occurred mostly between soy proteins. From a rheological point of view, the semi-dilute mixtures proved to be the most interesting, since heat treatments largely impacted the flow properties, covering a range of behaviors from a non-Newtonian "physical gel" (below 70C) to a Newtonian fluid (above 80C).
impact statement summary
Combining milk and soy proteins could result in mixtures of unique functionality and health properties. This phase of the project focused on elucidating the occurrence and nature of heat-induced interactions between casein and soy proteins. Casein and soy protein powders were used to prepare both individual and mixed protein solutions. The protein solutions were heat treated, both under denaturing and non-denaturing conditions, and their rheological properties determined. The nature of intermolecular interactions was assessed with a differential solubilization method. Both covalent bonds (prevalent) and physical interactions were identified in the mixtures, especially at higher temperatures. From a rheological point of view, the semi-dilute mixtures were the most interesting. Heat treatments largely impacted the flow properties, which ranged from a non-Newtonian "physical gel" (below 70C) to a Newtonian fluid (above 80C). This complex rheological behavior could be useful in designing food products or ingredients of desired texture and functionality.
