Different microorganisms for bio-processing of lentil hulls, in view of their use as food ingredient

Lentil hulls (LH) are by-products from handling of lentils, amounting at 20-30% of the total quantity of lentils subjected to dehulling. Although mainly used in animal feeding, they could be exploited as ingredients for food/dietary supplements, because of their content in proteins, lipids, vitamins, minerals, phenolics, and, above all, dietary fibre. However, LH contain antinutritional factors (ANF), such as phytate, saponins, tannins, and inhibitors of digestive enzymes. Since previous research showed that microorganisms could decrease the concentration of some ANF, during the OnFoods project, we aimed to investigate bioprocessing of LH using lactic acid bacteria (LAB), or fungi (either unicellular or filamentous). Lactiplantibacillus plantarum LPLDL, Lactococcus lactis VMO01, Lacticaseibacillus casei BGP 93, Lacticaseibacillus rhamnosus LR 4PD (all provided by Sacco Srl), Furfurilactobacillus rossiae LV-S3, and five Pediococcus acidilactici strains (all isolated from lentil hulls that had been provided by Terre di Altamura Srl) were singly inoculated, at cell density ranging from 6 to 7 log CFU/g, in a mixture (1:4) of lentil hulls (ground to a particle size of about 500 μm) and water (both previously autoclaved, separately). Fermentation was run at 30-37 °C for 48 h. Yeasts (Debaryomyces hansenii DSM 70238, Geotrichum candidum DSM 13629, Wickerhamomyces anomalus DSM 6766) and filamentous fungi (Penicillium roqueforti D1, P. roqueforti ITEM 9579, Rhyzopus oryzae ITEM 18876, belonging to Microbial ISPA-CNR Collection) were inoculated, at 7 log CFU/g, in an autoclaved mixture of LH and water. Solid state fermentation was run at 25-30 °C for 120 h. Overall, LAB increased by 1 to 2 log cycles during fermentation, decreasing pH to 4-5.4. L. plantarum LPLDL showed the best growth and acidification performances. All the fungal strains increased their cell density and marked proteolysis was found in LH bioprocessed by filamentous fungi. Levels of ANF were variously affected, depending on the microorganism used.