Abstract
The nutrient digestibility and feeding value of rapeseed meal (RSM) for non-ruminant animals is poor due to the presence of anti-nutritional substances such as glucosinolate, phytic acid, crude fiber etc. In the present study, a solid state fermentation (SSF) using Aspergillus niger was carried out with the purpose of improving the nutritional quality of RSM. The chemical composition and physicochemical properties of RSM before and after fermentation were compared. To further understand possible mechanism of solid state fermentation, the composition of extracellular enzymes secreted by Aspergillus niger during fermentation was analysed using two-dimentional difference gel electrophoresis (2D-DIGE) combined with matrix assisted laser desorption ionization—time of flight—mass spectrometer (MALDI-TOF-MS). Results of the present study indicated that SSF had significant effects on chemical composition of RSM. The fermented rapeseed meal (FRSM) contained more crude protein (CP) and amino acid (AA) (except His) than unfermented RSM. Notably, the small peptide in FRSM was 2.26 time larger than that in unfermented RSM. Concentrations of anti-nutritional substrates in FRSM including neutral detergent fiber (NDF), glucosinolates, isothiocyanate, oxazolidithione, and phytic acid declined (P < 0.05) by 13.47, 43.07, 55.64, 44.68 and 86.09%, respectively, compared with unfermented RSM. A. niger fermentation disrupted the surface structure, changed macromolecular organic compounds, and reduced the protein molecular weights of RSM substrate. Total proteins of raw RSM and FRSM were separated and 51 protein spots were selected for mass spectrometry according to 2D-DIGE map. In identified proteins, there were 15 extracellular hydrolases secreted by A. niger including glucoamylase, acid protease, beta-glucanase, arabinofuranosidase, xylanase, and phytase. Some antioxidant related enzymes also were identified. These findings suggested that A. niger is able to secrete many extracellular degradation enzymes (especially lignocellulosic hydrolyzing enzymes, acid proteases and phytase) during fermentation of RSM, thus altering chemical composition and physicochemical properties of RSM.
Highlights
Rapeseed is the world’s third largest source of vegetable oil
The crude fat was lower for fermented rapeseed meal (FRSM) than that for unfermented Rapeseed meal (RSM)
Small amounts of starch granules was observed in raw RSM, after 3 d fermentation, starch granules was disappeared in FRSM
Summary
Rapeseed meal (RSM) is the byproduct of oil extraction from seeds and is mainly composed of proteins, lignocellulosic fiber and minerals [1]. The nutrient digestibility and feeding value of RSM for non-ruminant animals is poor due to the presence of anti-nutritional substances such as glucosinolate, phytic acid, crude fiber etc. Glucosinolates are hydrolyzed by myrosinase enzyme present in the rapeseed or animal gastrointestinal tract to release a range of products including isothiocyanate, thiocyanate and nitrile. These degradation products impair palatability, affect liver and kidney functions, and interfere with iodine availability [4]. RSM contains relatively high levels of fiber which may accelerate the digesta passage rate and result in reduced time for digestion and reduced nutrient utilization [3]
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