Microbiological and biochemical characterization of the steeping phase of the corn wet milling proces

The steeping phase of the corn wet milling industry represents the most variable step of the process. Although the industry has been in existence since the 1880's, the environment of steeping and the major bacterial participant, the homolactic steep lactobacilli, remain poorly characterized. To achieve a greater understanding of steeping and the lactobacilli involved, steep water samples from seven mid-west steep series were collected and key biochemical variables measured. Twenty-nine homolactic and five heterolactic isolates of Lactobacillus were isolated during 13 samplings of the seven steep series. These isolates were characterized and compared with Lactobacillus rhamnosus ATCC 15820, a Lactobacillus isolated by Kuznetsov in the late 1950's from a Russian steep series.;The homolactic steep lactobacilli shared common carbohydrate utilization patterns, these patterns restricted to carbohydrates found in corn. Likewise, they required soluble corn components for luxurious growth. Their maximal growth temperatures matched the upper temperature limits of industrial steeping. The lactic acid product was either a mixture of isomers or predominantly L(+) lactic acid. Steep lactobacilli were highly resistant to the inhibitory effects of bisulfite, requiring an average of 0.073% bisulfite for inhibition. Although the isolates were nearly identical physiologically, separate strains of steep lactobacilli could be identified by restriction endonuclease digestion of the DNA with either NotI or SmaI and separation of the fragments by pulsed field gel electrophoresis. Separate strains had varying ability to promote the release of starch from the corn kernel, beyond the effects of the lactic acid produced by these organisms.;The homolactic steep lactobacilli were found to be highly specialized to grow in the steep environment and on corn as a substrate. Additionally, they were metabolically and genetically distinct from Lactobacillus rhamnosus ATCC 15280 and the heterolactic lactobacillus isolates from steep water.* ftn*Originally published in DAI Vol. 57, No. 5. Reprinted here with corrected author name.