Degradation of lignocellulosic matrix of oilseed cakes by solid‐state fermentation: fungi screening for enzymes production and antioxidants release

Abstract

BACKGROUND: Vegetable oils are yearly produced in large amounts generating solid by-products, the oilseed cake (OC). OCs are lignocellulosic materials that have been used for animal feed with some limitations due to high fibre content from the plant cell walls. Biotechnological processes can help to overcome these limitations and contribute to up-grading such by-products, enhancing their nutritional value as feed ingredients.RESULTS: All fungal species were able to decrease neutral detergent fibre and acid detergent fibre in all by-products. Additionally, relevant enzymes were produced by the three fungi studied resulting in an improved antioxidant capacity of all fermented OCs. Aspergillus niger led to the highest activity of cellulase (109 U g −1 ), xylanase (692 U g −1 ) and protease (157 U g −1 ) per dry OC matter and to the recovery of an extract rich in antioxidants, with the highest scavenging potential of free radicals and superoxide anion, iron chelation ability and reducing power. Rhyzopus oryzae produced the highest activity of ⊎-glucosidase (503 U g −1 ) and led to the highest liberation of total phenolic content (TPC). Principal components analysis showed that extracts with high antioxidant potential were obtained in solid-state fermentation (SSF) with high enzymatic activity. A positive correlation was established between the action of ⊎-glucosidase and TPC.CONCLUSION: Within the same bioprocess it was possible to improve the nutritional value of OCs and to obtain relevant bioactive compounds such as lignocellulosic enzymes and phenolic compounds with antioxidant potential, resulting in a significant improvement of already valuable by-products with commercial interest for animal feed.

Potential of Red, Green and Brown Seaweeds as Substrates for Solid State Fermentation to Increase Their Nutritional Value and to Produce Enzymes

“…According to Fernandes et al [ 17 ], the SSF of unwashed U. rigida with A. ibericus led to a higher total polysaccharide reduction, along with higher cellulase and xylanase production. The same correlation between polysaccharide reduction and enzyme production was also observed using other substrates in SSF, such as brewer’s spent grain [ 63 ], or soybean and rapeseed cakes [ 56 ].…”

“…Carbon (C), nitrogen (N), and the C/N ratio are essential factors for SSF since the C supplies the energy necessary for the microorganisms’ growth and metabolism, while the N stimulates fungal conidiation [ 56 ]. In this study, the carbon and nitrogen contents of the seaweeds ranged between 21.7–38.1% and 3.03–5.27%, respectively, while the C/N ratios varied between 5.86 ( Gracilaria sp.)…”

“…On the other hand, a decrease in the crude protein during the SSF with both fungi was observed for Gracilaria sp. Sousa et al [ 56 ] also observed a protein reduction after SSF of sunflower, rapeseed, and soybean cakes with Rhyzopus oryzae and A. ibericus , concluding that these fungi may use the available N to support their growth, since no N supplementation was carried out.…”

Enzymes and microorganisms jointly promote the fermentation of rapeseed cake

“…At the same time, the utilization of linseed oil as a supplement to the fermentation was positive for fungal growth and the production of protein ( 5 ). During solid-state fermentation, adding mixed fungi such as Rhyzopus oryzae , Aspergillus ibericus , and Aspergillus niger can obtain more cellulase and xylanase, which can improve bioactive compounds, so as to improve the nutritional value of rapeseed cake and improve animal feed by-products ( 6 ).…”

Biotechnological valorization of oilseed cakes: Substrate optimization by simplex centroid mixture design and scale‐up to tray bioreactor

“…The protein content of sunflower cake (SFC), rapeseed cake (RSC) and soybean cake (SBC) accounts for 14-46% (w/w) of dry weight while fiber varies between 5 and 37%. 9,10 Additionally, OC have residual concentrations of phenolic compounds ranging from 3 to 12 g kg −1 with antioxidant properties allowing them to act as radical scavengers, chelators, or reduction agents. 9 The employment of these OC in low-cost and environmental impact technologies such as bioprocessing allows the valorization of this biomass, contributing to the improvement of vegetable oil production chains.…”