Fate of maize DNA during steeping, wet-milling, and processing

The fate of DNA during steeping, wet-milling, and subsequent processing of maize was examined using a sensitive polymerase chain reaction (PCR-based) detection system. The system used specific amplification of maize DNA seque nces by primers generated toward plant nuclear- and chloroplast-encoded gen es. The PCR method facilitated analysis of DNA content in food products, wh ich is an important issue in use of genetically modified organisms. In a co nventional laboratory wet-milling countercurrent steep system, DNA was dete cted in maize kernels throughout the process but was not found in steepwate r. After kernels were wet-milled, DNA was detected in the starch, germ, coa rse fiber, and wet gluten fractions but not in the fine fiber fraction. Whe n dried by heating at 135 degrees C for 2 hr, DNA was degraded to undetecta ble levels in the wet-milled gluten fraction and hydrated kernels. DNA was not detected in feed pellets, starch, dextrose, sorbitol, or high-fructose maize syrup made from industrial wet-milled samples. Although DNA could be detected in laboratory wet-milled fractions, some degree of degradation occ urred after extended exposure to steepwater. Countercurrent steepwater samp les from the later stages of the steeping process were able to degrade DNA. The level of DNA degradation appeared to correspond to the presence of sul fur dioxide and may represent a physiochemical rather than an enzyme-mediat ed process. Our results indicate that some steps in the steeping and wet-mi lling process can degrade maize genomic and plastid DNA.