A A C C   2 0 0 0   A n n u a l   M e e t i n g

Hamburger buns and wheat tortillas are two commonly produced baked products processed under different conditions which have different shelf life characteristics (5 days vs. 3 weeks, respectively). The objective of this study was to determine the thermal characteristics of starch as it relates to retrogradation and the shelf life of these two products. Starch crystallinity during processing and storage of hamburger buns and wheat flour tortillas was monitored using Differential Scanning Calorimetry (DSC). Samples were collected periodically over 8 days and stabilized by extracting with methanol and drying at 50°C. A small amount (0.1 kJ/g) of native starch crystallinity was retained after baking and during storage of hamburger buns, whereas in tortillas, native starch crystallinity was not detectable after baking for 15 sec. More amylose-lipid complexed in hamburger buns (1.3 kJ/g) compared to tortillas (0.5 kJ/g). Amylopectin retrogradation was detectable in hamburger buns following 24 hr of storage, whereas it was detectable after just 5 hr in tortillas. Hamburger buns had 40% of the enthalpy of tortillas at 24 and 194 hr storage (0.8 vs 2.1 kJ/g at 194 hr, respectively). The lower amylopectin retrogradation in hamburger buns may be the result of more dispersion of starch during gelatinization, since hamburger buns are processed under harsher processing conditions (470°C for 7 min vs. 370°C for 0.5 min for tortillas). Therefore, the ability of amylopectin to retrograde during storage is not a good measure of staling, rather, it is probably a measure of starch dispersion during processing.