Study unravels effects of processing on food microstructure

By Nathan Gray

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Related tags: Starch

The digestibility of foods like pasta – made up of starch in a protein matrix – may depend on the processing method, says new research that shows the importance of mixing on a finished product.

According to a new study published in LWT - Food Science and Technology​, processed starch-protein foods “can exhibit a variety of microstructures”​, which may lead to different mechanical properties and starch digestibility. However they said that a relationship between these parameters “is yet to be resolved.”

“It has been observed that conditions during the development of a dough (e.g., mixing or shearing rates) yield different gluten microstructures, consequently different rheological properties of dough, but the relationship between this microstructure and the bioaccessibility of starch has received little attention so far,”​ explained the authors, led by Javier Parada from the Department of Chemical and Bioprocess Engineering, Pontificia Universidad Católica de Chile, Chile.

“The study shows the importance of mixing and other process factors on the microstructure of foods containing starch dispersed in a protein matrix, hence, on their physical and nutritional properties,”​ they added.

Starch structure

Parada and colleagues explained that different starchy foods (for example pasta and baked foods) elicit different glycemic responses. They explained that several factors have influence on how starch is digested, and therefore its glycemic response, adding that “one of these factors is the food microstructure.”

“Basically, some starchy foods are composites of starch entrapped in a three-dimensional matrix of proteins or other biopolymeric material (such as fiber) … For example, it is argued that when starch is entrapped in a protein matrix, as in the compact structure of cooked pasta, this microstructure as well as the physical state of starch … may explain the differences in the in vivo and in vitro enzymatic susceptibility of starch,”​ said the researchers.

They said that whilst native starch granules are “hardly attacked by amylases”​, when gelatinized, they become digestible.

“In fact, starch granules may be present in some foods with different degrees of gelatinization which modulates the extent of the digestion of the starch,”​ explained Parada and co-workers.

Furthermore, the type of matrix may affect the degree of gelatinization of starch, and thus affect the digestion process.

“The capability of gluten to influence the bioaccessibility of starch depends on the matrix that is formed and the degree of interaction with starch,”​ said the authors.

Study details

The new research examined the effect of three processing factors (extent of mixing, cooking temperature and cooking time) on the microstructure of a model dough system consisting of potato starch, wheat gluten and water, and the in vitro​ digestibility of starch in the matrix as well as the relationship between microstructure and starch digestibility.

Parada and colleagues observed that the extent of mixing of the dough determined the structure, which in turn, explained differences in in vitro ​digestibility of the cooked products.

They said found that higher degrees of mixing promoted a higher disruption of the gluten matrix by starch, “hence the matrix would be weaker to external forces, and then the accessibility of digestive enzymeswould be higher.”

“A higher level of mixing of the model dough resulted in starch granules more uniformly dispersed in the gluten matrix, a softer cooked product that was ruptured at a lower strain and stress, and more rapidly available glucose after in vitro enzymatic analysis, suggesting a weaker matrix where enzyme accessibility to starch was facilitated,”​ reported the authors.

They added that the degree of gelatinization, and mechanical properties, of cooked products were also affected by cooking temperature and time, however the in vitro ​digestibility of starch was only affected by cooking temperature.

Source: LWT - Food Science and Technology
Published online ahead of print, doi: 10.1016/j.lwt.2011.03.012
“Microstructure, mechanical properties, and starch digestibility of a cooked dough made with potato starch and wheat gluten”
Authors: J. Parada, J.M. Aguilera

Related topics: Science

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