Enzymes key to improving plant-protein stability, study finds

'Oat is a unique cereal due to its relatively high protein content and distinct protein composition compared to other cereals,' write the authors.  © iStock/Skorpion1

Plant protein uptake is still being hampered by poor solubility and limited functionality, but the right kind of enzymes can boost stability and foaming properties, say Finnish researchers.

Using the enzymes transglutaminase (derived from the bacteria Streptomyces mobaraensis) and Tyrosinase (from the fungus Trichoderma reesei), the researchers wanted to see the impact on colloidal stability and foaming properties of protein isolate from oats and faba beans (also commonly known as fava beans or broad beans).

“­The colloidal stability and foaming properties of oat protein suspension were improved by transglutaminase treatment,” write the scientists from Finland's VTT research centre. “The increased colloidal stability was likely due to improved electrostatic stability and intra-particle crosslinking causing stability against dissociation/re-association in oat protein particles.

“The colloidal stability of oat protein isolate was drastically improved with transglutaminase treatment. This could be exploited when developing protein-based foams that need long shelf-life at cold storage before use.”

They found that the foaming properties of faba protein isolate, however, decreased with increasing enzyme dosage.

Streptomyces mobaraensis is a spore forming bacterium species used in the food industry to produce transglutaminase – also known as ‘meat glue’ for its binding properties. Transglutaminase, a texturiser for meat and fish products, can come from plant- and animal-based sources.

By treating the isolates with the protein crosslinking enzymes, they found that transglutaminase increased the absolute zeta-potential values and reduced the particle size of oat protein particles.

Tyrosinase, on the other hand, had limited crosslinking ability on both oat and faba beans, and greatly reduced the solubility of oat protein despite limited crosslinking. Tyrosinase did not have effect on zeta-potential or colloidal stability of either protein, but it impaired foaming properties of both.

The crosslinking enzymes studied caused significantly different end product functionality, presumably due to the different mechanism of action,” write the authors.

"Structuring the plant proteins by enzymatic crosslinking is an attractive option due to mild reaction conditions needed and the specificity of the enzymes. Enzymatic crosslinking has been studied in modifying textural and structural properties in protein-based food matrices such as, emulsions and foams."

Rapeseed protein 

Previously, researchers at the same institute in Finland looked into using a variety of enzymatic preparations - pectinase, xylanase and cellulase - to extract useful protein from rapeseed press cakes, a 34-million-tonne, global industrial by-product.

Depending on the extraction process used, they found that certain rapeseed proteins, which have a good nutritional profile thanks to high levels of amino acids, could act as effective emulsifiers with foaming properties. 

Source: Food Chemistry

“Structuring colloidal oat and faba bean protein particles via enzymatic modification”

Published online ahead of print, 15 September 2017, doi.org/10.1016/j.foodchem.2017.03.114

Authors: Outi Nivala, Outi E. Mäkinen, Kristiina Kruus et al. 

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