Alternative source of proteins for animal feed: A byproducts preservation and circular economy approach

Throughout the world, animal protein producers are seeking alternatives to support their efforts towards a more sustainable feed-to-food chain. For animal feed production, by-products can provide a cost-effective and reliable source of valuable nutrients. However, high moisture content makes these materials sensitive to decomposition and nutrient spoilage by microbes. Treating by-products with Selko Yeast Inhibition solutions for protein extraction is an innovative approach that supports a more circular economy…

Andrea Lopez
Global Product Manager
Selko

By-products from the food and beverage industry are increasingly popular and inexpensive sources of protein, sugars, and fibre compared to the conventional raw materials used in animal feed. Conventional ingredients can fluctuate in price and availability due to weather conditions affecting crop quality and yield. As global demand for animal feed continues to grow, reliance on crops like soybeans, corn and other conventional feed sources leads to environmental challenges, including deforestation, and water and land depletion.

Throughout the world, animal protein producers are seeking alternatives to support their efforts towards a more sustainable feed-to-food chain. For animal feed production, by-products can provide a cost-effective and reliable source of valuable nutrients. However, high moisture content makes these materials sensitive to decomposition and nutrient spoilage by microbes. Within hours of production, by-products can significantly deteriorate. To protect that nutritional content, they require a combination of effective on-site treatments that inhibit microbial proliferation, such as drying, ensiling or fermentation. Though effective, these treatments can add expense and increase energy consumption and processing. Since these by-products can be considered waste streams by food and beverage producers the objective is to remove these materials at a low cost. Offering a solution that is more cost-effective and easier to apply – while significantly increasing the shelf-life and maintaining dry matter and nutritional value – provides a key to overcome these challenges.

Both brewers’ spent grain (BSG) and dried distillers’ grains with solubles (DDGS) – which provide a protein concentration of 16%–22% – are commonly used for animal feed. But they also contain high levels of moisture, which allows for the fast proliferation of mould and yeast when the feed ingredients have not been properly managed or stored. Specific organic acid blends, including Revalet, Selko-SVG, Selko-BE+, and Selko-RSD decreases the pH of by-products. This acidification inhibits microbial growth, specifically yeasts, moulds and spoilage bacteria, thereby preventing protein degradation and helping retain amino acid profiles, crucial for the nutritional quality of animal feed.

Animal feed producers may incorporate the complete byproduct or extract the protein component depending on their nutritional needs or by-product quality. Regardless of intended use, BSG and DDGS are treated at the production site or at trader facilities. If only the protein component is desired, then the protein extraction process begins. That process may include drying the BSG for efficacy before particle size reduction using mechanical grinders, like hammer or roller mills, occurs. The BSG is mixed with water to adjust the pH to a base level of 9-11, at which point proteins become soluble. As moulds and yeasts can survive in a basic environment, the initial acidification step before processing is vital to prevent the degradation of the extracted proteins.

Once the pH is raised using mild alkali, the mixture is stirred for 1-2 hours to allow protein solubilization. Then the slurry is centrifuged or filtered to separate the solid or residual fibre from the liquid containing the solubilized protein. The solubilized protein is then dried to a powder that can be easily stored and incorporated into animal feed.

The protein extract can be mixed with other nutritional components like vitamins or minerals depending on the feed requirements of the specific target species. The protein concentrate is typically pelletized into animal feed to ensure uniform distribution and ease of consumption.

Other high moisture by-product streams rich in protein are whey (a by-product of cheese making), brewer’s spent yeast (a by-product of beer brewing) and wet corn gluten feed. These by-products are also prone to microbial spoilage and protein degradation if not properly preserved. In unpreserved whey and spent yeast, microbial activity can lead to protein hydrolysis, resulting in the breakdown of proteins into smaller peptides and amino acids, which could reduce their nutritional value and digestibility for animals. Whey typically has a pH around 6.0-6., while brewer’s yeast may have neutral pH at around 7. Acidification to a pH of 3.5-4.5 creates unsuitable conditions for microbial growth while still being safe for proteins. To optimise the extraction of protein for animal feed, Selko Yeast Inhibition organic acids blends are often used to stabilise and preserve these by-products prior to extraction.

BREWER’S SPENT YEAST PROTEIN EXTRACTION
Live yeast cells that are used for alcohol production have a thick cell wall, so physical, mechanical, or enzymatic disruption is often required to break the cells and release proteins. These steps may include heating, centrifuging or treatment with specialised enzymes, but some extraction methods are more expensive than others. The industry’s preferred method is direct steam application or heating live yeast to 80°C, which can produce protein degradation. Selko Revalet offers a cheaper solution for yeast inactivation and protein preservation and avoids damaging heat treatments and additional energy consumption. In a research trial comparing the protein content found in brewery spent yeast that was untreated, heat treated or treated with a blend of organic acids, the acidified content maintained 6.48% protein content – almost the initial 6.6% content – for 7 days, while the heat-treated product fell to 3.8% during that period (Figure 1). However, Selko Revalet not only inactivates live yeast cells, once the cell is destroyed, proteins are released in yeast extract and will remain in the same concentration. Additionally, adding the organic acid blend prevents microbial proliferation during transportation and storage of the yeast extract.

Figure 1. Brewery spent yeast treated with Revalet Super (RS) and Heat (HT). A decreased protein content is noticed when yeast is treated with heat from 6.0% to 4.60% with moisture content of 80%. Revalet reduce protein loses vs heat treatment.

When an enzymatic treatment is added to create cell disruption and provide proper preservation of the yeast extract, it also helps maintain the proteins for solubilization using the process as described earlier in this article. Since the yeast has been preserved with Revalet the proteins are more likely to remain intact, which improves the efficiency of the extraction process.

IN CONCLUSION
The treatment of high-moisture by-products with Selko Yeast Inhibition solutions plays a crucial role in preventing microbial proliferation and preserving the integrity of proteins for subsequent extraction. Lowering the pH of these by-products creates an environment that inhibits the growth of bacteria, moulds and yeasts. By controlling microbial spoilage, these solutions prevent the breakdown of proteins by microbial enzymes, ensuring that the proteins remain intact for efficient extraction and use in animal feed. Once stabilised, the protein extraction process can proceed with minimal degradation, leading to higher protein yields and improved quality. These proteins can then be incorporated into animal feed formulations, providing a nutritionally rich, affordable, and sustainable alternative to conventional feed ingredients.

Treating by-products with Selko Yeast Inhibition solutions for protein extraction is an innovative approach that supports a more circular economy by making waste products valuable in their own right and preserves natural resources. It transforms what was once considered waste into a valuable feed ingredient, contributing to more sustainable, efficient, and eco-friendly animal production systems.

How organic acids attack: Mode of action explained

Specific blends of buffered and non-buffered organic acids prevent spoilage by inhibiting microbial growth. By lowering the pH and creating a hostile environment for spoilage organisms, these acids help to preserve the proteins present in liquid byproducts. Organic acids have been found to attack unwanted microbial organisms, like bacteria, in several ways including by damaging the cellular walls of these organisms, creating energy competition, increasing the permeability of cell walls, raising intracellular osmotic pressure, and inhibiting biomolecule synthesis. For example, these acids can enter the cell of an unwanted microbe and dissociate to generate acid ions and protons (H+), which alters the internal pH. The cell becomes more acidic, causing it to waste its energy actively expelling protons. Similarly, the collection of acid ions increases intracellular osmotic pressure and dealing with that pressure interrupts normal cell growth and the function of its metabolism. Direct antimicrobial action of organic acids in their undissociated form can penetrate microbial cell membrane and disrupt metabolic processes, leading to microorganism death. Ultimately these effects lead to increased cell death for the unwanted microbes. As the harmful microbes perish, they can no longer break down proteins and cause formation of unwanted metabolites, like toxins or ammonia, which reduce protein quality. Furthermore, organic acids ensure the proteins stay intact by preventing microbial proteases – enzymes that break down proteins – from being produced by bacteria or moulds. This collection of modes of action helps prevent the decomposition of proteins, preserves amino acid profiles, and maintains nutrient suitability for extraction and use in animal feed.

About Andrea Lopez
Andrea Lopez is Selko’s Global Product Manager for Yeast Control and Food2Feed program. She is a dynamic professional with a background in biotechnology and a wealth of experience in sustainable practices within the food and feed industry. Her work experience has been dedicated to implementing sustainable solutions that optimize the utilization of by-products as alternative protein and nutrients sources, replacing common raw materials used in animal feed.

Currently, Lopez serves in a pivotal role focusing on the application of organic acids for nutritional preservation and microbial control in high moist by-products. As an integral member of the team, she spearheads initiatives aimed at harnessing the potential of organic acids to enhance the nutritional quality and safety of these by-products when used on animals. Her dedication to addressing environmental concerns while promoting nutritional preservation underscores her commitment to shaping a more sustainable future for the feed and food industry.

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