Short communication: Ground corn steeped in citric acid modulates in vitro gas production kinetics, fermentation patterns and dry matter digestibility

Abstract This study investigated the effect of citric acid (CA) concentration and steeping time (ST) treatment of ground corn on ruminally resistant starch (RRS) contents and subsequent effects on starch resistance to rumen degradation using batch culture technique. It was hypothesized that CA concentration and ST are keys affecting the RRS in CA treated ground corn. The experiment was 3 × 3 factorial arrangement using three CA solutions combined with three ST. Ground corn (2 mm) was steeped in an equal quantity (i.e., in a ratio of 1:1, w/v) of tap water alone (Ctr), of 5 (Low) or 10 g/L (High) CA solution for 12, 24 or 48 h. Chemical composition of CA treated corn was measured, and gas production (GP), volatile fatty acids (VFA), NH 3 -N and dry matter (DM) disappearance (DMD) were determined at 6 and 24 h of incubation. Inocula were obtained from three ruminally cannulated beef heifers fed a diet consisting of 300 g/kg barley silage, 670 g/kg dry rolled barley and 30 g/kg vitamin and mineral supplement (DM basis). No CA × ST interaction was detected. Citric acid treated corn had greater (P 0.05) RRS than Ctr, with no differences between Low and High CA treatments; the content of RRS was greater (P 0.05) at 48 h ST than 12 or 24 h. At 24 h of incubation, CA treated corn had lower (P 0.05) asymptotic cumulative GP, GP rate, DMD, total VFA and NH 3 -N concentrations than did Ctr. Rate of GP, DMD and NH 3 -N concentration were highest (P 0.01) with 12 h, intermediate with 24 h and lowest with 48 h ST at 24 h of incubation. Total VFA concentration was also higher (P  4 and CO 2 decreased (P 0.05) either by CA treatment or with increasing ST. These results indicated that CA treated ground corn increased RRS content, altered fermentation pattern for more acetate production and decreased ruminal DMD in batch culture. Use of CA to treat corn grain can be an effective processing to reduce ruminal corn starch digestion, and thus potentially alleviate risk of rumen acidosis.