Chemical composition and porcine in vitro digestibility of corn whole stillage pretreated with heat at various temperatures and times

A study was conducted to identify optimal conditions (time and temperature) for heat pre-treatment of corn whole stillage (WS). Six samples of WS from different sources were divided into 13 sub-samples to give a total of 78 sub-samples. Thirteen treatments were applied to 13 sub-samples from each source (1 sub-sample/treatment). The treatments were untreated WS, and WS that was pre-treated (70 psi) for 10, 20, or 30 min and at 100, 120, 140, or 160 °C in a 3 × 4 factorial treatment arrangement. Sub-samples were subjected to in vitro digestion with porcine pepsin and pancreatin, followed by in vitro fermentation for 72 h. Accumulated gas production was recorded and modeled to estimate kinetics of gas production. Heat pretreatment of WS at ≥ 120 °C decreased (P < 0.05) its total dietary fiber (TDF) and chemically available lysine content by approximately 10 and 19 %, respectively; and increased (P < 0.05) total furans (TF) content from 0.50 to approximately 154 mg/kg. Pretreatment time and temperature interacted on TDF and TF content in WS, such that an increase in pretreatment time had no effect on TDF and TF content in WS when pretreated at 100, 120, or 140°C, but reduced (P < 0.05) TDF content and increased (P < 0.05) TF content in WS when pretreated at 160°C. Pretreatment time and temperature interacted (P < 0.05) on chemically available lysine content of WS, such that an increase in pretreatment time unaffected chemically available lysine content when the WS was pretreated at 100 or 120 °C, but reduced (P < 0.05) chemically available lysine content when the WS was pretreated at 140 or 160 °C. Pre-treatment time and temperature did not interact on in vitro disappearance of dry matter (IVD-DM), and total gas production. The coefficient of IVD-DM for untreated WS was 0.734. An increase in pre-treatment temperature from 0 to 160 °C resulted in linear increase (P < 0.05) in coefficient of IVD-DM by 13 %, and of total gas production by 16 %. Response surface analysis indicated that maximum coefficient of IVD-DM and total gas production resulted from longer pretreatment times (20–30 min) and highest pretreatment temperature, whereas maximum chemically available lysine content resulted from pretreatment at 100 °C for 20 min. In conclusion, the optimal conditions for pretreatment of WS for production of distillers dried grains with solubles of improved digestibility and fermentability by pigs were temperature of 140–160 °C, and duration of approximately 20 min.