Brewer’s spent grain can become nutritious food

Environment and sustainability 2. aug 2021 2 min Professor, Group Leader Solange I. Mussatto Written by Morten Busch

Brewing beer requires malting large amounts of barley, wheat or rye to add flavour. The by-product, brewer’s spent grain, accounts for up to 85% of the total residue from brewing and has traditionally been discarded. Now researchers have found out how the high protein content of the spent grains can be used as for both people and animals. The process does not even involve any environmentally harmful chemicals – only clean water.

Beer drinkers leave about 39 million tonnes of brewer’s spent grain (BSG) in their wake each year. Although BSG is packed with both sugar and protein, it often just gets discarded. The grain residue is wet and sweet after the brewing process and therefore attracts microorganisms. The sugar can be extracted from the BSG, but extracting the protein has been a greater challenge. Now researchers have found a simple and highly effective way to do this.

“We have tried various pretreatment strategies including alkaline, acid and enzymatic. They are effective but resource-intensive, non-specific and not environmentally sustainable. Now we instead tried hydrothermal treatment, using just water and heat, and we can extract 65% of the protein. In addition, the process improves the quality of the protein extracted. Since this grain has a very high protein content, the hydrothermal process has considerable potential. The large volume of protein can be used either in animal feed or for fitness products for people,” explains Solange I. Mussatto, Professor and Group Leader, Department of Biotechnology and Biomedicine, Technical University of Denmark, Kongens Lyngby.

Wet and rich in protein

A growing global population combined with emerging economies in low- and middle-income countries and urbanisation have increased the demand for protein. Currently available resources for protein are mainly food crops such as wheat, soybean and maize. However, the current traditional production capacity will not be able to meet the growing anticipated demand for protein-rich foods and products.

“An alternative to cultivating more land with traditional resources is to recover protein from biomass such as agricultural wastes and by-products from industrial processes. A challenge for processing these types of resources is to develop technologies that can cost-effectively and sustainably extract protein from biomass with high yields. We have therefore focused on using BSG to obtain protein,” says Solange I. Mussatto.

Depending on the type of grain mixture, BSG contains 18–30% protein and is the most abundant sidestream from brewing, accounting for 85% of all brewing residue and 20 kg of wet weight per 100 litres of beer produced. This enormous amount of protein is often discarded, mostly because BSG has a very short shelf life since it is wet and rich in protein and sugars and therefore susceptible to attack by bacteria and fungi.

“Our goal was not just to find the method that maximises the extraction yield. Acid or enzymatic treatments can recover about 90% of the protein but using acid comes at a high environmental cost in terms of pollution and energy consumption, while using enzymes is not a cheap option. Conversely, a hydrothermal pretreatment process achieved lower yields but is a clean, precise and specific method,” explains Solange I. Mussatto.

Higher than many other types

Hydrothermal vents are small cracks in the Earth’s surface through which scalding water flows – often associated with volcanic activity. Hydrothermal processes in the laboratory are not as dramatic. The wet spent grain is mixed with water and heated to 60°C in a closed container, creating the necessary pressure to extract the proteins.

“In contrast to acid treatment, almost all the extract is protein, and not a single chemical is used, so this is clearly preferable to the acidic process. Although hydrothermal pretreatment achieves protein extraction of 64–66% versus 90% for acid treatment at 120°C for 1 hour, the hydrothermal process clearly has environmental benefits,” says Solange I. Mussatto.

The researchers think that even more can be gained from the hydrothermal pretreatment process by adjusting the temperature, but since the protein content in BSG is so much higher than in many other types of residue such as agricultural wastes and by-products of industrial processes, the potential for protein extraction is enormous despite non-optimised process conditions.

“Extraction processes for protein from this type of biomass can recover a great deal of protein to meet the growing future demand. It can enrich animal feed to increase the protein content of meat, be added directly to food products in low-income countries or become a raw material for fitness products such as protein bars. In any case, this will reduce the amount of land that needs to be cultivated, which benefits the environment,” concludes Solange I. Mussatto.

Evaluation of different pretreatment strategies for protein extraction from brewer’s spent grains” has been published in Industrial Crops and Products. All authors are affiliated with the Biomass Conversion and Bioprocess Technology group, Technical University of Denmark.

The Biomass Conversion and Bioprocess Technology (BCBT) group is a leading research group at the Technical University of Denmark, dedicated to develop...

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