Abstract
The present study evaluated the effect of feed particle size, thermal processing different levels of fat inclusion and of moisture addition on the amount of gelatinized starch in a corn-soybean broiler diet. The different processing factors were combined in a 2 x 4 x 4 x 2 factorial arrangement in a three randomized block design consisting of three production series: two particle sizes (coarse: 1041 microns and medium: 743 microns), four fat inclusion levels at the mixer (15, 25, 35, and 45 g/kg of feed), four moisture addition levels in the conditioner (0, 7, 14, and 21g/kg of feed), and two thermal processing treatments (conditioning-pelleting or conditioning-expanding-pelleting) which resulted in 64 different processed feeds. For the determination of the amount of gelatinized starch one feed sample was collected per treatment in each of three production series, totaling three replicates/treatment. Data were transformed using a variation of Box-Cox transformation in order to fit normal distribution (p>0.05). Adding moisture up to 21g/kg of feed in the conditioner linearly increased the amount of gelatinized starch (p<0.05). The conditioner-expander-pelleting treatment of the diets (at 110°C) increased (p<0.05) the degree of starch gelatinization from 32.0 to 35.3 % compared with the conditioner-pelleting treatment (at 80-82°C). The gelatinized starch content increased from 30.2 to 37.2% in the feed (p<0.05) as the particle size increased from medium to coarse. Fat inclusion had a quadratic effect (p<0.05) on starch gelatinization. The degree of starch gelatinization was significantly reduced with fat inclusion levels higher than 35 g/kg of diet. The factors evaluated in this study resulted in interactions and significant effects on degree of starch gelatinization.
Highlights
Starch is stored in plants as granules
When the starch granule is submitted to heat, moisture, and shear force during feed expansion and or conditioning a phenomenon known as starch gelatinization may occur
Based on the enzymatic assay employed in this enough to achieve the ideal ratio for complete starch study, it was observed that 22.7% of the total starch gelatinization, results in a more favorable water:starch feed content (502.0 +/- 24.4 g starch/kg of feed) was ratio for starch granule hydration, swelling, and already gelatinized in the mash feed before thermal rupture
Summary
Starch is stored in plants as granules. The starch granule is a structure composed by crystalline and amorphous regions and, due to the lower order of cristallinity, the gelatinization occurs first in the amorphous region than in the crystalline region (Lund & Lorenz, 1984). Gelatinization is an irreversible process: water diffuses into the starch granule, hydrogen bonds are disrupted, the granule swells and loses shape, and amylose begins to leach (Holm et al, 1988; Lund & Lorenz, 1984; Moritz et al, 2005; Coral et al, 2009). White et al (2008) reported that the changes in the optical properties of starch can be monitored by the disappearance of ‘Maltese crosses’ and the disappearance of A-type diffraction patterns in the X-ray diffractograms when wheat granules are submitted to extrusion. The temperature at which starch loses its crystallinity and the material
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