4.1. Agri-Food Residues: Handling and Characterization

Cheese whey, crab headshells, residual soy cake, and brewer’s spent yeast (BSY) were the substrates used for fermentation assays. Residues were obtained from Canadian agri-food enterprises (Quebec). Cheese whey was conserved at −20 °C until its use. The crab headshells were rinsed with distilled water, dried at 60 °C for 48 h (Thermo Herathern Fisher oven, OMS180, USA), and submitted to a grinding mill (Fritsch Universal Cutting Mill 19.5720/021704, Germany) to obtain particles with sizes from 1 to 2 mm. These particles were milled with a pestle and mortar into fine powder. The residual soy cake was dried at 60 °C for 48 h (Thermo Herathern Fisher oven, OMS180) and milled with a pestle and mortar into fine powder. The BSY was conserved at −20 °C until being used for fermentation assays.

The residues were characterized to determine the content of total nitrogen (Kjeldahl analyzer, Foss, Kjeltec 8200, Denmark), total solids, ashes [37], total protein (Lowry’s method), and cations (inductively coupled plasma–optical emission spectroscopy, ICP-OES OPTIMA 4300 DV, Australia). For cheese whey and BSY, the pH (Fisher Scientific benchtop pH meter, Accumet AB250, Singapore), content of COD (HACH kit and spectrophotometer, Canada), and dissolved organic carbon (TOC-L analyzer, Shimadzu, Canada) were determined according to standard methods [37].