INTERMITTENT MILLING AND DYNAMIC STEEPING PROCESS FOR CORN STARCH RECOVERY

A procedure that reduces diffusional limitations by periodically milli ng the corn to reduce particle size and stirring the ground mash in th e presence of sulfur dioxide (SO2) and lactic acid was developed. The process, called intermittent milling and dynamic steeping (IMDS), incl udes three main stages: initial soaking (a short-time immersion in wat er) of whole kernels, initial cracking of the partially hydrated kerne ls, and dynamic steeping with interspersed milling. This study evaluat ed the three stages of the process separately, evaluating the effect o f variables on each stage of the process. Corn fractions yield (germ, fiber, gluten, starch) were used to decide the best conditions for the soaking and steeping stages, and germ damage was used to determine th e best kernel cracking method. Starch, gluten, and germ yields were no t affected by soak temperatures (52-68 degrees C) or soak time (1-3 hr ). A temperature of 60 degrees C was chosen for soaking because it inc reased the rate of kernel hydration without gelatinizing starch, which happens at higher temperatures. A 2-hr soak time was preferred becaus e there was less fiber in the germ fraction and less germ damage was o bserved. Although there were no advantage to using SO2 or lactic acid in the soak water, the presence of these compounds during dynamic stee ping enhanced starch yield. The starch yield for 3 hr of dynamic steep ing was not statistically different from the starch yield for a 7.5-hr dynamic steep. The Bauer mill was preferred over the use of a roller mill or a commercial grade Waring blender for kernel cracking. The IMD S process produced, on an average, 1 percentage point more starch than the conventional 36-hr steeping process. Total steep or kernel prepar ation time was reduced from 24-40 hr for conventional wet-milling to 5 hr for the IMDS process.