Fungal treatment to enhance the nutritional value of canola meal for animal feed

Abstract

Canola or rapeseed meal is an agricultural co-product of the canola oil production industry. Recycling canola meal as livestock feed and subsequently integrating it into the human food supply chain is essential for enhancing environmental sustainability and economic efficiency. Despite canola meal being a valuable source of high-quality protein, vitamins, and essential minerals, its utilization for monogastric animals has been hindered by the presence of antinutrients and fiber. Microbial bioconversion offers a promising solution, enabling the degradation of antinutrients and fiber, increasing the protein content and key amino acids, and improving dry matter digestibility.In this study, food-grade Pleurotus ostreatus was inoculated on canola meal to degrade antinutritional factors (fiber, phenols, and glucosinolates) while providing additional digestible amino acids. The optimum cultivation conditions for P. ostreatus were at 65% moisture content and 8 days of fermentation. Illumination before spore germination and agitation during cell cultivation could negatively affect fungal protein production. With the bioconversion using P. ostreatus, the protein content of the fermented canola meal increased by 19.2%; meanwhile, the glucosinolates, sinapine, and phytate content of the meal decreased by 96.7%, 95.5%, and 55.0%, respectively. The total lipid content of the fermented samples decreased as this fungus is lipolytic rather than lipogenic. Furthermore, the applied treatment did not have any adverse effects on the in vitro digestibility of dry matter (DM) in the fermented meal. The obtained data demonstrate the feasibility of the P. ostreatus fermented canola meal to be applied as an economical, high-quality supplement in the monogastric livestock industry. While substantial improvements were achieved in various feed qualities, dry matter digestibility remained unchanged. Mechanical fractionation has demonstrated the capability to isolate fractions of canola meal with higher digestibility, but it has also yielded fractions with lower digestibility and reduced protein and amino acid content compared to the original meal. Additionally, mechanical fractionation does not effectively separate antinutrients. Our research aims to further enhance the quality of the superior fractions, especially by targeting the degradation of antinutrients. Furthermore, we explore the potential for improvement in the less desirable fractions, which would provide significant added benefits. In the next step, mechanical fractionation and solid-state fungal fermentation were conducted to improve the nutrient profile and reduce the antinutrient content of canola meal. Mechanical processing, including milling, sieving, and air classification, was used to fractionate canola meal and redistribute its components in different fractions. Then, these fractions were inoculated for fungal fermentation. The results showed that 12-day solid-state fermentation with Pleurotus ostreatus increased the protein content in all fractions by 11-18%, decreased sinapine, glucosinolates, and phytate up to 99.8%, 98.8% and 75.8%, respectively, and increased the in vitro digestibility of selective fractions. Overall, Pleurotus ostreatus-based solid-state fermentation has the potential to be an effective treatment to improve the nutritional profile of canola meal.