TiFN research identifies new enzymes that break-down resistant starch

2 February 2017 - What has a very long tail and degrades starch granules through pore formation? Two enzymes, identified by TiFN’s PhD fellow Vincent Valk, acting and looking very different to other members of the amylase family. The microbiologist describes them in his thesis; defended on 27 January 2017 at Groningen University. His work continues TiFN’s long tradition of supporting the food industry in product development.

The amylases, named MaAmyA and AmyB, are produced by Microbacterium aureum B8.A. This microorganism was isolated from sludge obtained from a wastewater treatment plant of a potato-starch processing factory. “The two enzymes work together, efficiently degrading resistant-starch granules”, says Valk. “They are extremely long, over twice the size of the amylase found in saliva. Moreover, they completely degrade starch granules through pore formation, whereas amylases in the human gastrointestinal tract are unable to fully degrade such granules.”

Low-calorie products
The findings will provide leads for diverse product development. “Using starch granules produced by enzymes could enhance the development of low-calorie bread”, Valk illustrates. The use of granules with pores might also facilitate cost reduction, due to their increased flavouring-holding capacity. By using them to partly break-down resistant starch into sugars, one could create an extra sweet taste without adding extra sugars.

Apart from the new enzymes, Valk’s work - part of TiFN’s Slow Starch project - also provided new insights into the breakdown of resistant starch in the gastrointestinal tract. “We have found a novel carbohydrate-binding domain (CBM74) in the enzyme MaAmyA”, he explains.  “Detailed analysis revealed that this domain was mainly found in large complex amylases, which are produced by bacteria present in the microbiota of the large intestine.” The findings indicate that CBM74 plays an important role in the fermentation of resistant starch in the large intestine.

The enzymes are produced by, for example, Ruminoccoccus bromii and Bifidobacterium adolescentis; microorganisms that, according to earlier research, appear to be almost absent in people with obesity. “This could explain why these people are often incapable of fermenting resistant starch in their intestines”, says Valk. The outcomes underline the importance of creating a beneficial environment for the microbiota, and provide leads for targeted development of pre- and probiotics.

Creating desirable new products
Valk looks back appreciatively at his TiFN time. “It was fascinating to see the hoops food manufacturers must jump through to get health claims approved, or how they to communicate a higher product price to the consumer”, he says. “Margins are small, especially in carbohydrate-rich products like bread, potatoes and pasta. You really need to demonstrate added value in order to justify increasing prices. I hope our enzyme discoveries will help manufacturers to create useful and desirable new products.”