Treatment of spent grains by hydrothermal cleavage to purify dietary fibers

Technical Session 21: Spent Grains Session
Julia Steiner, TU München, Freising, Germany
Co-author(s): Martin Zarnkow and Thomas Becker, TU München, Freising, Germany

ABSTRACT: Seventy-five percent of all organic residues originating from brewing are spent grains, which constitute the most important and energy-rich by-product from the brewing process. Refining spent grains rich in beneficial ingredients is of great interest for valuable preservation of human nutrition. Although they are a remnant, they still contain high-quality dietary fibers (i.e., arabinoxylan and beta-glucan), which are difficult to utilize due to their structure and the preceding process steps. Therefore, the use of hydrothermal cleavage was investigated, and possible fields of application for beverage technology have been developed. It was the purpose of this study to break down the complex insoluble polysaccharides to educe and transfer the cleavage products to a soluble state in order to add them to new beverages as an ingredient with health beneficial attributes. With regard to an increase in health consciousness and the shift in consumption habits toward soft drinks, the brewing industry faces new opportunities and challenges. Based on the current trend, beverages rich in dietary fiber have emerged. These successful innovations receive distinctive appreciation and sustained acceptance by consumers. In particular, beta-glucan offers a comprehensive potential for functional beverages, due to its origin in natural raw materials and its scientifically proven positive and health-promoting effects. This paper presents an innovative way to produce novel fiber-based drinks using lactic acid fermentation. Dietary fibers are purified using hydrothermal cleavage, and subsequently the hydrolysates are fermented by selected strains. The resulting fermentation products are mixed with different beverages and carbonated, resulting in well-balanced refreshment. Laboratory-scale trials have been carried out to select the best process parameters in order to gain maximum dietary fiber content. The evaluation of the novel utilization technology is based on analytical attributes measured using HPLC. To ensure the hydrothermal reaction conditions and to determine the influence of temperature and residence time, the cleavage process was conducted at temperatures ranging from 170 to 230°C and varying residence times. Consequential rising decomposition products such as hydroxymethylfurfural and furfural, which may not exceed certain concentrations due to possible health risks, are undesired. By contrast, a preferably high proportion of arabinoxylan and beta-glucan is definitely desired. Suitable approaches to and treatment intensities for an improved yield of dietary fibers and a low yield of undesired substances (under the critical limit) are shown in this research. Particular attention is directed toward functional ingredients, with a focus on beta-glucan, which was shown to be stable in the produced beverages. With an adequate concentration of beta-glucan, specific application examples could be offered as a reward for functional food with an additional benefit by the EFSA and FDA.

Julia Steiner was born in 1984 in Munich, Germany. In 2009 she graduated from the Technische Universität München as with a Dipl.-Ing. degree in technology and biotechnology of food. Since 2010 she has been working as a Ph.D. student at the Institute of Brewing and Beverage Technology in Weihenstephan, TU München. Julia is investigating complex spent grain components, pursuing the aim to preserve this brewery by-product, which is valuable for human nutrition. The intent of this research project is the transfer of insoluble dietary fiber fractions into a soluble state in order to add them to novel beverages as an ingredient with health benefits.