Rice being explored as a 'clean label' thickener

Naturally occurring polyphenols and proteins from pigmented waxy rice may help starch ingredients improve texture without any chemical modification, according to Ya-Jane Wang, professor of carbohydrate chemistry at University of Arkansas.

Chemically modified starch is a common thickener in soups and other foods. Without modification, starch breaks down during high-temperature and high-shear food processing and no longer functions properly as a thickening agent.

As consumers express concerns over chemically modified ingredients, Wang is looking at alternatives. With the help of a $400,000 U.S. Department of Agriculture National Institute of Food and Agriculture grant awarded in 2023, Wang is exploring how to use polyphenols and proteins naturally present in pigmented waxy rice as a natural starch strengthener.

Polyphenols are a micronutrient that naturally occur in plants. She used pigmented waxy rice because the presence of polyphenols in the rice and the polyphenol–protein interaction that arises. ‘Waxy’ rice is also known as ‘sticky’ or ‘sweet’ rice due to its low level of amylose, one of the ingredients that make up starch. Higher levels of amylose cause the rice to separate and become fluffy, whereas lower levels of amylose produce higher viscosities. Polyphenol–protein interactions naturally present in the pigmented rice aid in retaining a food’s viscosity, or thickness, during the cooking process.

Annegret Jannasch, left, and Ya-Jane Wang, professor of carbohydrate chemistry, are looking at the components of pigmented waxy rice to serve as a ‘clean label’ starch strengthener. (Photo by Ariel Romero, courtesy of University of Arkansas System Division of Agriculture under CC BY-SA)

“We propose that pigmented waxy rice can function like chemically modified starches but without the use of chemicals, so it will be a clean label ingredient,” Wang said.

‘Clean label’ is not a scientific term, but the food industry, academics and consumers define the phenomenon as choosing foods with easy-to-recognise ingredients and no artificial ingredients or synthetic chemicals, according to the Institute of Food Technologists.

Consumer perception

In recent years, consumers have raised concerns about ingredients used in food production, Wang noted. Some consumers aim to consume only minimally processed food.

The idea of minimal processing varies from person to person, Wang said. Some consumers prefer wheat flour, but others might consider wheat flour too processed and consume whole wheat flour instead.

Wang’s research may alleviate consumer concerns related to modified starch.

Many foods contain modified starch, which is chemically altered to improve processing and storage stability, Wang said. Starches function as thickening agents to improve the texture and consistency of food products.

The inspiration for this project came from Wang’s recent research that explored the possibility of using the interactions among polyphenols, protein and starch in pigmented waxy rice to increase satiation, the feeling of fullness. In that original project, Wang found that the pigmented waxy rice’s unique interactions between polyphenols and proteins allow starch to swell more in an acidic condition that simulates gastric environments.

“Starch, when it swells, is like a balloon — it becomes bigger and bigger,” Wang said. During food processing “the temperature, the shear, the high acidity will completely break down the balloon. You want the balloon to swell more — that is how you create the viscosity — but you don’t want it to swell too much. The polyphenol–protein interactions help to maintain the starch structure so it will stay at that stage.

“That is why you can use starch to thicken any soup because the starch can swell more than 10 times its volume, but once it gets to that stage, it becomes very fragile,” she said.

Outside of consumer perception, Wang said that applying this pigmented waxy rice, as opposed to using modified starch, could provide additional environmental and health benefits.

With any chemical modification comes a residue, Wang said, so using a naturally occurring starch with these properties eliminates that concern. Polyphenols are present in many berries and vegetables, and a high amount of polyphenols are known to have antioxidant, anti-inflammatory and antidiabetic properties.

A three-phase approach

The research will take place in three phases. Wang and her team have finished the first phase, which evaluated pigmented waxy rice samples and their contents and compositions of proteins, starch and polyphenols. A research article, titled ‘Elucidating the effect of polyphenol-protein interactions on rheological properties of purple waxy rice’, was published in the Journal of Cereal Science this month.

Jannasch with a dish of pigmented waxy rice. Image credit: University of Arkansas System Division of Agriculture photo by Ariel Romero.

The next phase will determine the nature of the polyphenol–protein interactions in pigmented waxy rice. Interactions between polyphenols and proteins involve chemical bonds linking two molecules, and it is important because a strong bond helps maintain granule integrity under high shear, temperature and acidic conditions, Wang said.

Finally, the researchers will apply thermal processing conditions to alter the extent of polyphenol–protein interactions so the resulting products will produce a wide range of viscosities for different applications.

“We really want to see the possibility of commercialising the resulting technology,” Wang said. “We want to see if any companies are interested and work with them.”

Companies using this to make cereals, pudding or pasta is something that Wang hopes to see.

Wang will share an update on this research at the USDA-NIFA project director meeting in Amherst, Massachusetts, on 17–18 June.

​To learn more about the University of Arkansas Division of Agriculture research, visit aaes.uada.edu.

This is a modified version of a news item published by University of Arkansas System Division of Agriculture under CC by SA

Top image credit: iStock.com/Professor25