Pasteurization-assisted solid-state bioconversion of Caragana korshinskii residues by Irpex lacteus n6

In the arid and semi-arid landscapes of northern China, a hardy shrub known as Caragana korshinskii plays a vital role in holding the soil together and restoring fragile ecosystems. This plant, a member of the legume family, thrives where few others can, resisting drought and cold while its deep roots anchor the earth against wind erosion. However, as these shrublands mature, the plants become woody and tough, accumulating a thick layer of pruning waste each year. While millions of tons of this material are produced annually, most is simply burned or left to rot, representing a lost opportunity. The challenge lies in the plant's structure: its fibers are locked away in a rigid, lignin-rich matrix that makes it difficult for animals to digest. To turn this tough residue into useful animal feed, scientists look to nature's own recyclers: fungi. Certain fungi, particularly white-rot species, possess a unique ability to secrete enzymes that break down lignin, the glue holding plant fibers together, effectively unlocking the nutrients trapped inside. This biological process offers a gentler, more sustainable alternative to the harsh chemical treatments often used in industry, potentially transforming a waste product into a valuable resource for livestock.

Researchers at Inner Mongolia Agricultural University set out to find the perfect fungal partner for this specific task. They collected eleven different wild strains of a fungus called Irpex lacteus from the very habitats where the shrubs grow. The goal was to identify which of these native strains could best colonize the tough shrub residue and break it down efficiently. The team first tested how quickly each strain could spread across a bed of shredded shrub material. While all the strains grew, two of them, labeled n4 and n6, expanded the fastest, covering the test surface in just one week. To understand why, the scientists examined the enzymes these fungi produced. They used simple color-changing tests to see how well the fungi could attack different parts of the plant. One test measured the ability to oxidize a substance similar to lignin, while another checked for the ability to dissolve cellulose, the main structural fiber in plants. The results showed that while some strains were good at one thing and others at another, strain n6 stood out as the most versatile. It produced the highest levels of the specific enzymes needed to dismantle both the lignin glue and the cellulose fibers, making it the strongest candidate for further study.

With the best strain identified, the researchers then focused on how to grow it most effectively. They tested various conditions to see what helped the fungus thrive, experimenting with different temperatures, acidity levels, and food sources. They found that the fungus grew best at a warm temperature of 30 degrees Celsius in a slightly acidic environment. When it came to food, the fungus preferred maltose, a type of sugar, and peptone, a nutrient derived from proteins, as its primary diet. To prepare enough of this fungus to treat large amounts of shrub waste, the team also needed a way to grow it quickly on a grain-based medium. They tested five different grains—buckwheat, sorghum, maize, millet, and wheat—to see which would support the fastest growth. Buckwheat proved to be the clear winner, allowing the fungus to spread more rapidly and densely than on any of the other grains. This discovery provided a practical method for producing the necessary amount of fungal starter culture for the main experiment.

The final phase of the study involved putting the fungus to work on the actual shrub residue. The researchers prepared the shredded plant material in two different ways to see which method worked best. One group of samples was sterilized using high-pressure steam, a standard method that kills all other microorganisms but requires significant energy. The other group was pasteurized, a milder heat treatment that reduces competing microbes without completely sterilizing the material. Both groups were then inoculated with the buckwheat-grown I. lacteus n6 strain and left to ferment for 56 days. The results were striking. The samples treated with the milder pasteurization method and then inoculated with the fungus showed the most dramatic improvements. Compared to the untreated, pasteurized control, the fermented material saw its fiber content drop significantly. The amount of neutral detergent fiber, which represents the total indigestible cell wall, decreased by nearly 17 percent. The acid detergent fiber, a measure of the even tougher, less digestible parts, also fell by about 16.5 percent. Most impressively, the acid detergent lignin, the stubborn component that makes the plant so hard to eat, was reduced by almost 50 percent.

Beyond just breaking down the tough fibers, the process also improved the nutritional value of the feed. The amount of crude protein in the treated material rose from about 8 percent to over 12 percent, while the water-soluble carbohydrates, which provide quick energy for animals, increased more than fivefold. These changes suggest that the fungus not only softened the plant structure but also added its own biomass to the mix, enriching the final product. The study demonstrated that using a locally sourced fungus combined with a simple pasteurization step is a viable way to upgrade this abundant shrub waste. While the research confirms that the material becomes more digestible and nutritious, the authors note that further testing is needed to see how well animals actually eat and utilize this new feed. Nevertheless, the work provides a solid foundation for turning a massive, underused waste stream into a potential solution for sustainable livestock production in the region.