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Extracting useful proteins from beer-brewing leftovers

| By Gerald Ondrey

Brewers’ spent grain (BSG) is the most significant byproduct of the beer-brewing industry, making up 85% of the total waste. Globally, about 36.4 million ton/yr of spent grain are produced. This spent grain is typically discarded after its primary use in brewing beer. While some efforts are made to repurpose BSG in applications, such as animal feed, biofuel production or composting, a substantial portion still ends up in landfills, generating greenhouse gases, such as methane and CO2.

After exploring new uses for the BSG proteins, researchers from Nanyang Technological University, Singapore’s (NTU Singapore; www.ntu.edu.sg) Food Science and Technology (FST) program have developed a method that extracts over 80% of the available protein in BSG. The researchers say their protein-extraction method could help reduce waste, and the extracted proteins could be used to enrich diets and even for cosmetic applications.

The extraction method, described in a recent issue of Innovative Food Science and Emerging Technologies, is called microwave-assisted, three-phase partitioning (MATPP). The BSG is first fermented with a food-grade fungus, Rhizopus oligosporus. The fermented BSG is dried and ground into a powder, then blended with water and strained through a cloth to form a crude BSG extract (CBE). After microwave treatment, the CBE is saturated with ammonium sulfate, then t-butanol is added. This mixture is then vortexed, allowed to settle and finally centrifuged to form three phases. The upper (organic) and lower aqueous phases are removed, leaving the solid intermediate layer, which is collected and lyophilized. One kilogram of BSG yields 200 g of protein.

The researchers note that BSG proteins are safe for human consumption and of high quality, making them suitable for direct use in supplements and for enhancing the protein content of plant-based foods. The proteins were also found to be rich in antioxidants, which could not only protect human skin from pollutants, but could also extend the shelf life of cosmetics, such as body lotions and moisturizers.

The NTU FST team will be in discussion with Heineken Asia Pacific to scale up their protein-extraction method, and plans to collaborate with several food-and-beverage and cosmetic companies to further implement their technology, with an eye towards commercialization.