Fungal fermentation inducing improved nutritional qualities associated with altered secondary protein structure of soybean meal determined by FTIR spectroscopy

Abstract

Abstract A FTIR spectro-chemometric measurement was first-ever made available to monitor chemical and molecular structural changes during the fungal fermentation of soybean meal. The samples of soybean meal were fermented for 72 hr using single Aspergillus ficuum or combined Aspergillus ficuum + Aspergillus niger inoculants. Nutrient contents determined by chemical methods on three independent sub-samples taken at 24 hr intervals were predicted by a method of FTIR. Furthermore, secondary protein components were quantified by FTIR spectra deconvolution method. Fungal fermentation caused enriched soybean meal with protein and organic acids with lowered dietary fibre, tannin, phytic acid and urease contents, while there was increased trypsin inhibitors. The chemometric model excellently predicted the nutrient contents with high accuracy (99% recovery rate) and precision (R2 = 0.98), except for the crude ash and total carbohydrate. Fermented soybean meal has a re-organised secondary protein structure: a complete degradation of α-helix component caused to an increased β-sheet (6%), β-turn (15%) and random coil component (100%). It is recommended that infrared spectroscopic monitoring of fermentation process can replace the chemical methods due to its low cost and robustness.