In vitro evaluation of the effects of steam-flaking conditions on starch availability of barley grain

Abstract

Objective: The objective was to determine how steam-flaking conditions affect starch availability of barley grain. Materials and Methods: Five independent sources of barley were used in a 3 × 3 + 1 factorial with the main effects of steam-conditioning duration (5, 20, or 35 min) and flaking density [targeting 0.43 (HFD), 0.34 (MFD), and 0.25 (LFD) kg/L] compared with samples that were not processed (control). Samples were analyzed for 7-h in vitro digestibility, amyloglucosidase reactive soluble starch (AGR), and 6-h amylase reactive insoluble starch (ARIS). Insoluble reactive starch, digestive insoluble starch, and predicted ruminal starch digestion (PRSD) were calculated. Results and Discussion: Flaking densities were 0.47 ± 0.031 kg/L (HFD), 0.37 ± 0.021 kg/L (MFD), and 0.32 ± 0.010 kg/L (LFD). The control barley had less AGR, ARIS, insoluble reactive starch, and PRSD (P < 0.01) but greater digestive insoluble starch (P < 0.01) relative to flaked barley. Extending conditioning duration tended to increase AGR (P = 0.06) but did not affect PRSD or 7-h in vitro digestibility. Reducing flaking density increased AGR (P < 0.01; 9.26, 12.75, 21.41% for HFD, MFD, and LFD, respectively), ARIS (P < 0.01; 51.15, 57.26, 61.52%, respectively), PRSD (P < 0.01; 95.89, 97.32, 99.20%, respectively), and 7-h starch digestibility (P < 0.01; 86.3, 83.8, 78.9%, respectively). Implications and Applications: Relative to the nonprocessed barley grain, steam-conditioning increased starch reactivity, but steam-conditioning durations greater than 5 min had minimal additive effects. Decreasing the flaking density of barley grain increased starch reactivity.