In food science an emulsion is a temporary stable mixture of two immiscible liquids, the most basic example being oil and water. In food product development we’re often tasked with creating products that require long-term, stable emulsions in many product categories. From soups and sauces, to ready-to-drink (RTD) beverages, processed meats, vinaigrettes, dairy drinks and bakery products emulsions exist all over. One particular food ingredient, milk proteins, are actually well-known for their ability to help stabilize emulsions and this particular property will be discussed throughout this whitepaper.
Milk proteins are nutritionally complete proteins that contain both major protein molecules casein and whey, typically in the same ratio that exists naturally in fluid milk. They are typically available in concentrates known as Milk Protein Concentrates (MPC) or Milk Protein Isolate (MPI) and can range from protein content as low as 42% and up to 90% or more. Used throughout the food industry, MPC and MPI are not only versatile, but also highly functional proteins, especially when looking at their emulsification properties. As milk itself is by definition an emulsion, it’s only natural that the concentrated proteins, which are responsible for the emulsion, would lend themselves to other emulsions.
When working with spray dried MPC or MPI (MPC/I), in order to maximize functional properties the protein must first be fully hydrated and solubilized. Since MPC/I solubility decreases over time it’s important that product be as fresh as possible and properly stored; storage at ambient temperatures and lowest possible humidity are considered optimal. Since solubility is considered a critical property for manufacturers it’s important to note that in order to solubilize spray dried MPC/I it takes time, and is directly related to the water temperature and agitation. When solubilizing, use water that is between 320C and 600C is ideal and takes a minimum of 30 – 40 minutes; some experts prefer longer holds like 6 – 12 hours (under refrigerated condition).
Looking deeper into understanding why MPC/I have great emulsification properties one needs to look at the protein aggregates – the larger the aggregate, especially casein, the better at stabilizing the emulsion. In studies published in The Journal of Food Science it was noted that MPC85 was the most stable when compared to alternative dairy proteins such as sodium caseinate (for emulsion). The study authors hypothesize this is in part due to the aggregate in MPC85 too large to cause flocculation. The same group of researchers later came to understand that the dispersion of aggregated proteins in dissociating buffer improved the emulsification strength.
When formulating with higher protein MPC/I there are some important developmental tips to consider:
- Ensure the protein is properly dispersed and hydrated
- When hydrating the protein leave other ingredients that compete with the protein out of the mix until the protein has finished hydrating
- Adding a monovalent salt such as sodium or potassium chloride can enhance protein solubility
- Shear can be applied for better reconstitution; industry standard is a tri-blender or vortex mixer
- Most formulations will require a pH adjustment, especially beverages, this should not occur until the protein has been fully hydrated
- Homogenization is typically recommended for those solutions over 10% protein, and most especially prior to processing under UHT or retort conditions