Vorkommen und verteilung von staphylokokken und mikrokokken in sojaextraktionsschroten

Gram-positive, catalase-positive cocci were isolated from spoiled and unspoiled soybean oil meal. Of 129 isolates, 123 were allotted to the staphylococci and only four were identified as Micrococcus varians. S. xylosus dominated among the staphylococci accounting for 95% of these organisms. The strains identified as S. cohnii, S. saprophyticus and Staphylococcus sp., as well as M. varians, were found in spoiled material only. It was assumed that infection of the material had taken place during storage, as staphylococci and micrococci were neither present in the soybean nor in the freshly produced soybean oil meal.

Contamination with these microorganisms was rather high, as viable counts of 10⁴ to 10⁷/g were ascertained in 70% of the unspoiled stored soybean oil meal. In contrast, the typical residual bacterial flora (bacilli and Gram-positive rod bacteria) surpassed values of 10⁴/g in only a few cases.

The successful colonization of soybean oil meal with staphylococci, particularly S. xylosus, may be explained by the growth of these facultative anareobic organisms at a rather low water activity and by their capability to utilize proteins and lipids. Staphylococci isolated from soybean oil meal exhibit lipase and protease activity more frequently than do corresponding isolates from human and animal skin.

A comparison of strains from spoiled and unspoiled oil meal revealed that in general a higher percentage of isolates from heated material can grow at a higher temperature (up to 42°C) and evidence proteolytic activity. The colony counts of spoiled soybean oil meal is usually higher (39% of the samples ≧ 10⁷/g) than that of unspoiled meal (2% of the samples). Lower colony counts found in spoiled samples (36% contain 10³–10⁵/g) may be due to overheating the material.