Sustainable valorization of lignocellulosic corn husks via solid-state fermentation: enhanced recovery of phenolic compounds and organic acids

Corn husks (CHs), a major residues of corn production, is generated in large quantities worldwide and represents a promising substrate for biowaste valorization. This study investigated the potential of CHs as a source of phenolic compounds and organic acids through solid-state fermentation (SsF) using Aspergillus niger ATCC 6275 over ten days. Thus, chemical composition was assessed using AOAC protocols, sugar metabolism and organic acid production via HPLC-RID, phenolic profiling by HPLC-DAD-ESI-MS, and antioxidant potential through ABTS, DPPH, FRAP, and CUPRAC methods. Although CHs displayed low levels of minerals, proteins, and lipids, it was rich in carbohydrates (84.48 ± 0.29 g/100 g fw). Throughout SsF, simple sugars were rapidly utilized, coinciding with an increase in organic acids, notably oxalic (35.43 mg/g dw) and citric acids (8.46 mg/g dw). Phenolic profiling revealed the presence of various phenolic acids, including caffeic and ferulic acids, along with quinic acid esters. Notably, SsF led to a marked increase in specific phenolic acids, with caffeic acid reaching 337.60 ± 16.88 µg/g by day six, and 3-caffeoylquinic, 5-caffeoylquinic, and 4-feruloylquinic acids increasing to 390.73 ± 19.54, 429.07 ± 21.45, and 556.00 ± 27.80 µg/g, respectively, by day nine. Several glycosylated flavones, such as maysin, were initially detected but were fully metabolised by day ten, accompanied by a concomitant increase in free aglycones, including methoxyluteolin. Additionally, antioxidant capacity significantly improved during fermentation. These findings underscore the potential of CHs as a low-cost, lignocellulosic substrate for generating value-added products, including organic acids and phenol-rich nutraceuticals, through controlled SsF processes.