January 21, 2016—By 2020, the global demand for protein ingredients is expected to reach 4.6 million tons and generate revenues of nearly $30 billion. But proteins can be problematic ingredients, and by using modified protein ingredients, a finished product’s performance can be positively impacted, said Baraem (Pam) Ismail, Ph.D., Associate Professor, Department of Food Science and Nutrition, University of Minnesota, in her presentation “Better Protein Ingredients via Controlled Maillard Reactions,” given at the 2015 Protein Trends & Technologies Seminar.
A common solution to several formulation challenges is to use protein hydrolysates, which can enhance digestibility, improve functionality, reduced allergenicity and and enhance bioactivity. Ismail explained this and more in her presentation titled “Considerations in Protein Ingredient Use: The Impact of Processing and Molecular Interactions.”
However, when proteins are hydrolyzed, they partially unfold, exposing groups that also can cause aggregation. That is, some peptides are actually aggregate promoters and will interact with other proteins, to create peptide-peptide interactions, and with carbohydrates to participate in undesirable Maillard reactions.
Aggregation is caused by both intrinsic factors, such as the source and structure of the protein, and extrinsic factors, such as heat, acid and protein concentration in the food system. Maillard reaction is an interaction of protein with carbohydrate, and its progression to advanced stages results in protein polymerization and reduced overall quality and shelflife. “One promising approach to limit aggregation is controlled Maillard-induced glycation, which involves covalent bonding of a protein and a sugar molecule,” said Ismail.
Research has shown one way to eliminate Maillard reaction-induced polymerization in nutrition bars formulated with whey protein isolate (WPI) is to substitute sorbitol for HFCS, a reducing sugar. This formula adjustment hinders Maillard browning reactions and the formation of high-molecular weight polymers.
Ismail discussed a study that looked at soy protein isolate (SPI) and soy protein hydrolysate (SPH) that were stored at high-water activity. The researchers monitored the change in free amine groups over time. The results showed a faster rate of aggregation in the SPH because of the release of higher levels of free amine groups that would participate in the Maillard reaction.
Solubility in beverages is a challenge when formulating with higher protein levels. Whey protein denatures between 60-70°C, causing the protein to unfold and expose hydrophobic residues and SH groups. These residues react and result in polymerization between proteins/peptides.
As the polymer grows, the protein falls out of solution. At the protein’s isoelectric point, solubility will be very poor. Fruity beverages formulated with whey protein are typically formulated to a pH below 3.5 to achieve clarity. Being good buffers, the presence of proteins necessitates addition of a considerable amount of acid to reach the desired pH. An excess amount of acid, however, can result in a finished beverage that is sour and astringent. These beverages are typically formulated to less than 4% protein, but 4.2% protein is required in order to make an “excellent source of protein” claim. One study using a partially glycoated whey protein achieved good solubility at concentrations between 5-7% protein.
Whey protein contains an “EF loop:” a three-dimensional structure that functions as a gate to hydrophobic residues. At the protein’s isoelectric point, the gate opens, exposing the hydrophobic groups, and polymerization results. However, it is possible to change protein functionality through glycation at specific sites, preventing the EF loop from opening.
By carefully controlling the Maillard reaction, an ingredient manufacturer can stop the reaction at a specific point, before the protein is completely glycated and before progression into undesired advanced stages. Advantages of this partial glycation are: increased net negative charge on proteins; increased surface hydrophilicity; reduced denaturation rate; reduced disulfide interchanges; and increased steric hindrance due to bulky polysaccharides. The net effect is enhanced stability and reduced protein/peptide interactions.
Food formulators should get as much information as possible from their protein supplier. By understanding how a protein was processed (and possibly modified), they can more accurately predict the sweet spot of optimal protein level with good product stability.
Baraem (Pam) Ismail, Ph.D., Associate Professor, Department of Food Science and Nutrition, University of Minnesota, bismailm@umn.edu, +1.612.625.0147
The summary above is an excerpt from the “2015 Protein Trends & Technology Magazine: Formulating with Proteins.”
