Hydrothermal and β-glucanase effects on the nutritional and physical properties of starch in normal and waxy hull-less barley

Cereals having a waxy (high amylopectin) starch type may offer advantages for animal feed associated with heat processing characteristics and/or starch digestibility. Nutritional and physical characteristics of starch were evaluated in hull-less barley cultivars having a normal or waxy starch type (228 and 55 g kg(-1) amylose, respectively). Broiler chicks (192) were fed one of eight diets in a 2 x 2 x 2 factorial arrangement from 3 to 21 days of age. The dietary factors included: (1) normal or waxy starch type barley; (2) pelleted (75 degrees C, 160 g kg(-1) total moisture) or meal form; and (3) with or without addition of beta-glucanase. The pelleted diets were reground to remove any physical aspect of feeding pellets. There were no differences in body weight gain (BWG), feed intake (FI), feed-to-gain ratio (F/G) or intestinal starch digestibility due to starch type, nor were treatment interactions significant (p > 0.05), Feeding waxy starch barley resulted in higher digests viscosity than normal starch barley, which was attributed to its higher beta-glucan content. Fecal digestibility of waxy starch was 10% higher (p < 0.05) than that of normal starch. Pelleting did not affect BWG, Fl, or F/G,but reduced (p < 0.05)digesta viscosity by 45% and increased starch digestibility by 17% in non-enzyme supplemented diets. beta-Glucanase addition improved BWG, FI, F/G, and starch digestibility (p < 0.01), and eliminated the high digesta viscosity otherwise associated with feeding the waxy starch diets in meal form. Starch characteristics during heating were examined with 11 hull-less barley samples (5 waxy and 6 normal starch types) using a Brabender Viscoamylograph. Waxy starch hull-less barley exhibited peak viscosity approximate to 10 degrees C lower than did normal starch, exhibited a higher peak viscosity, paste instability and a lower cold-paste viscosity (negative set-back). Waxy barley may offer advantages in feed processing associated with lower gelatinization temperature, as indicated by superior pellet hardness in a model pelleting system over a range of added moisture levels and temperatures. The waxy trait did not compromise chick performance when diets were supplemented with beta-glucanase. (C) 1999 Elsevier Science B.V. All rights reserved.