The study, published in Food Chemistry, found that chemical modification of glutelin – the second most abundant fraction in barley storage proteins – by removing an amide group from the chemical structure (a process called deamidation) produced superior ingredient for use as an emulsifier in foods.
“Results indicate that deamidated glutelin can exert a strong emulsifying effect […] In this way, undesirable property changes resulting from excessive deamidation can be avoided thereby facilitating broader applications of deamidated barley glutelin as an emulsifying ingredient in food and non-food applications,” said the researchers, led by Lingyun Chen, assistant professor in the department of agricultural, food and nutritional science at the University of Alberta, Canada.
Barley is the fourth most widely cultivated cereal in the world after wheat, rice and corn.
Barley grown in popularity as a part of the human diet after recent health claims made about its beta-glucan component. The soluble fibre is known to reduce both blood cholesterol and the glycemic index.
Many techniques have been developed to isolate beta-glucan from barley grains, for use as healthful ingredients in food products. However the remaining fractions are a good source of proteins, starch and lipids – Barley grain has been found to contain between 8 and 13 per cent protein, depending on the variety.
“These compounds are awaiting research to develop their full value,” said the authors.
However, many proteins have been found to have poor solubility, which strongly limits their applications in foods and beverages.
“Development of strategies to improve barley protein solubility in water is essential to expand their usages for human consumption because protein generally has to be in a solution or in a fine suspension to exert other desired functionalities,” said Chen her and colleagues.
They noted that the removal of an amide functional group (deamidation) is one of the most popular ways to alter cereal protein structures and properties – by converting the glutamine (Gln) to glutamic acid (Glu). This leads to increased electrostatic repulsion among protein chains, which can interfere with protein aggregation and improve protein solubility.
Previous work has revealed that appropriate control of the deamidation degree is crucial to achieving better functionalities.
Glutelin is the second most abundant fraction in barley storage proteins (35-45% of the total storage protein). It has demonstrated excellent emulsifying properties, as it ahs a structural profile which enables it to adsorb to dispersed oil droplets quickly.
Deamidation was found to improve barley glutelin solubility and emulsifying properties.
Chen and her co-workers reported barley glutelin underwent a rapid break down (hydrolysis) and unfolding at the initial stage of deamidation.
They added that this rapid hydrolysis and unfolding, led to “remarkably improved glutelin solubility at both acidic and neutral pHs.”
“The deamidated glutelin formed soluble aggregates with very high molecular weight … These aggregates stabilized the emulsions at a broad range of deamidation levels,” said the authors.
The deamidated glutelin also demonstrated a strong tendency to form soluble clusters (aggregates) of large molecular weight. These aggregates were found to play a major role in stabilizing emulsions at a broad range of deamidation levels (between 2.2 snd 43 per cent deamidation).
The authors noted that such findings may mean that undesirable property changes resulting from excessive deamidation can be avoided, “leading to wider applications of deamidated barley glutelin as an emulsifying ingredient in food and non-food applications.”
Source: Food Chemistry
Published online ahead of print, doi: 10.1016/j.foodchem.2011.04.009
“Effects of deamidation on aggregation and emulsifying properties of barley glutelin”
Authors: J. Zhao, Z. Tian, L. Chen