Abstract
We aimed to evaluate the physicochemical properties and starch gelatinization of an Iranian corn grain (single crass 702) processed using different thermal processing methods including 1) grinding (G, 2mm), 2) super-conditioned pelleting (SCP; moisture 20%, retention time 6 min and conditioning temperature 95°C), 3) extruding (EX; moisture 20%, temperature of melting zone 75°C and die zone 125°C, screw speed 75 rpm and time 150s) and 4) puffing (PUF; puffing temperature 200°C, hot air velocity 25 m/s, feed rate 100 g/m). The particle size of the samples was measured through sieves. Apparent density and chemical composition were measured based on AOAC methods. Starch gelatinization was determined in accordance with the enzymatic procedure. Data were analyzed by GLM procedure of SAS (P< 0.05) using a completely randomized design with 4 replications for every treatment. Apparent density in G and SCP corn were similar but greater than EX and PUF corns (0.85 and 0.77 via 0.29 and 0.06 (kg/L), respectively). The PUF corn showed the most geometric mean particle size (10.55 mm) and followed by EX (8.68 mm), SCP (3.55 mm) and G (1.60 mm). The DM, OM, CP, EE, NDF and NFC % were not significantly (P > 0.05) affected by different processing methods. Starch content in thermal processing methods of SCP, EX and PUF (73.27, 73.22 and 73.20 % of DM, respectively) was greater (P = 0.04) than the G corn (72.23 % of DM). The highest (P < 0.01) starch gelatinization was provided by the PUF (26.85 %), followed by the EX, SCP and G processes (22.95, 16.45 and 4.68 %, respectively). Obtained results imply that super-conditioned pelleting process as a new processing method despite of greater apparent density provided more starch gelatinization similar to extruded and puffed corn, thus it can increase the efficacy of starch utilization in corn grain.