2.2.2 Solid-state fermentation
The HE and CP canola meals (200 g
of each) were fermented with A. niger NRRL 334 and A.
oryzae NRRL 5590 spore suspensions. Both spore suspensions were
standardized to a spore concentration of 107 colony
forming units (CFU) to apply on per gram of meal and used as the starter
culture for fermentation as described by Croat et al. (2016;
2017) and Shi et al. (2015). The canola meal, spore suspension, and
deionized water were mixed at speed 5 for 3 min using a commercial stand
mixer (Pro 600, KitchenAid, Benton Harbor, MI, USA) before being spread
out thinly (<1.5 cm) and evenly onto a stainless-steel sheet
pan. The fermentation was performed at a 50% (w/w) moisture content at
30℃ over a 72-h period in an Isotemp incubator (Fisher Scientific, Model
650D, Waltham, MA, USA). Mill-Q water was added based on the weight loss
each day to maintain the 50% (w/v) moisture content. Samples
(~50 g) were collected on random spots from each batch
at the time of initial inoculation
(0), 24, 48, and 72 h, freeze-dried (Benchtop Pro 8L ZL-105, SP
Scientific, Warminster, PA, USA) and saved for later analyses. All the
meals were frozen at –20°C to terminate the fermentation until further
freeze-drying. The dried powders were stored at 4℃ until used in
testing.