Effects of B-glucan fractions from barley on structure, texture, sensory characteristics and nutritional value of processed cereal foods

Abstract

Much attention has been given recently to improving the nutritional value of foods. Notably, cereal foods have been negatively affected with the popularity of "nutritional" diets, such as the Atkins diet. These diets have linked carbohydrate consumption to obesity and as such, require the individual to reduce dietary intake of carbohydrates in order to optimise weight loss. However, grains are a good source of complex carbohydrates, of which ß-glucans are one. These complex carbohydrates have been linked to a reduction in coronary heart disease, reduction in cholesterol and a possible control of blood glucose levels.

A major technical problem exists in both extracting these ß-glucans from cereal materials, and applying them into cereal food systems. The current project examined the potential health claims associated with ß-glucan inclusion into food systems and reviewed the available research regarding such issues, as well as examining the economic possibilities of ß-glucan extraction and inclusion. The review clearly illustrated substantial data indicating the potential nutritional benefit of ß-glucans in human foods. It also indicated that the potential bottleneck of such a use of these ingredients was in developing reliable and relatively inexpensive extraction processes.

Different extraction processes were analysed in terms of their effects on ß-glucan yield, processing characteristics and cost effectiveness. This showed that the physical characteristics (potential processing behaviours) of ß-glucans were dependent on the extraction process used. Although water extracted ß-glucans provided a cost-effective way of extraction, combination of amylase purification of the isolates (to remove excess starch) produced a higher ß-glucan return in terms of yield, and also the physical chemical properties of these isolates were more consistent and useful in terms of application to the food industry. Barley ß-glucan fractions from water extracted barley flours were used in the production of bread samples. The results indicate that high levels of ß-glucan (above 5%) may have negative effects on processability (loaf volume and crumb structure), which would again have negative effects on the sensorial properties of the breads.

However lower level inclusions had no significant effects in bread structure. From a nutritional point of view, inclusion of ß-glucan fractions had a beneficial effect in reducing the rate of starch breakdown during in vitro digestion, and hence in reducing sugar release. This appeared to be because the ß-glucan may inhibit (or reduce) the degree of starch gelatinisation. Such a reduction in reducing sugar release shows a great potential for the use of such additives in improving the nutritional quality of cereal foods. In a separate experiment, a commercially available form of ß-glucan (Glucogel) was obtained from the supplier and similar processing and nutritional analysis performed. Similar results were obtained for this commercial sample, indicating that commercial processing of such glucan fractions is a possibility.

Further research on pasta products showed a similar trend with regards to the inclusion of purified ß-glucans being of nutritional benefit to the potential consumer. Research was also conducted on the possibility of increasing the ß-glucan composition of breads and pastas by using barley flour as opposed to ß-glucan extracts. However the research illustrated that the use of barley flour, at high enough levels to obtain a significant amount of ß-glucan in the food product, had major negative effects on bread and pasta quality, As such, the use of ß-glucan extracts are the most process friendly way to incorporate ß-glucan material into cereal foods.

The results illustrate the possible use of ß-glucan extracts from UK-grown barley, in the human food system. Barley ß-glucan inclusions can significantly improve the nutritional quality of breads and pasta without significantly affecting the textural, physical and sensory characteristics of such foods. As such there is a possible novel ingredient market which could be explored for the use of high ß-glucan barley varieties in being a source of such food ingredients.