Objectives of my research were 1) to understand effects of drying temperature and storage of corn kernels at an elevated humidity on starch structure and functions, and 2) to develop a method to produce cassava-based feed that resembles a commercially available corn-based feed product. Corn kernels with 32.5% moisture (db) dried at higher temperatures (80yC or 120/80yC) had higher starch digestibility than that dried at a low temperature (37yC). Starch isolated from the corn kernels dried at the higher temperatures had higher gelatinization temperature and lower gelatinization enthalpy-changes than that from corn kernels dried at the lower temperature because of partial starch gelatinization. The partially-gelatinized starch exhibited loss of Maltese-cross of the starch granules when viewed under a polarized-light microscope. The starch digestibilities of the dried-corn samples decreased after storage at 37yC and 93% relative humidity (RH) for 3 and 6 days.Effects of storing dried corn kernels at 27yC and 85-90% (RH), resembling a tropical climate, for up to 6 months on starch structure and functions were investigated. Freshly-harvested corn samples (B816, 27.8% moisture, db) were sun-dried (SD) at 35yC or machine dried (MD) at 80yC. Storage of the dried corn kernels decreased starch digestibilities and peak viscosities of the ground corn samples. The rate of enzymatic hydrolysis of starch isolated from the sun-dried corn increased with storage, whereas that from machine-dried corn decreased with storage. Peak viscosity and gelatinization enthalpy-changes of starches isolated from both sun-dried and machine-dried corn decreased but the gelatinization temperature, pasting temperature, and percentage crystallinity of the starches increased after storing the corn. Numbers of damaged starch granules and starch granules with pinholes increased and the molecular weights of starch and long branch-chains of amylopectin decreased with storage time of corn. The starch isolated from sun-dried corn (35yC, SD) after storage suffered greater levels of endogenous and/or microbial enzymatic hydrolysis than that from machine-dried counterpart (80yC, MD) after the same period of storage.Cassava-based feed with slower starch digestive rate, resembling corn-based feed and improved nutritional values, was produced by blending cassava flour (CA) with other ingredients, including dietary oils (palm oil, soybean oil, and corn oil), Distiller\u27s Dry Grains with Soluble (DDGS), or defatted-soybean meal (SBM), followed by a heat-moisture treatment (HMT). Blending dietary oils (6%, v/w) or DDGS (10%, 20%, 30%, w/w) with cassava flour followed by HMT at 100yC for 1h substantially reduced the starch digestion rate of the processed cassava flour. Dietary oils with larger proportions of unsaturated fatty acids had greater impacts on reducing the starch digestive rate of cassava flour. HMT conditions, such as heating temperature and initial moisture content of the blends, were evaluated. Cassava flour-DDGS blends had a lower starch digestive rate than cassava flour-SBM blends at equivalent protein levels.
展开▼
