Fifty four hydocolloids from natural sources (Table 1) were measured for contaminant microorganisms by the classical agar plate assay and the ATP bioluminescence assay. The agar plate assay revealed that most of these are contaminated with bacteria within the range of 10 to 1,900 counts (as the general bacterial count) per g of the sample (Table 2). Especially, all or some of guar gum, traganthgum, carrageenan, rocastbean gum, gellan gum and xanthan gum gave more than 500 counts per g. All the three pectins tested gave no such count. Some samples were contaminated with funji. Especially, karaya gum 1-2 gave 420 counts of funji per g. Yeast, Escherichia coli and Staphylococcus aureus were not detected at all. All the samples gave a significant luminescence on the ATP bioluminescence assay (Table 3), which shows that these contained ATP. The radiation efficiency with authentic ATP added to the reaction mixture as the internal standard varied remarkably depending on the kind of the samples used (Table 3). A statistical caluculation on 25 samples giving more than 50% of the efficiency indicated a significant correlation between the bacterial count on the agar plate assay and the ATP content obtained from the ATP bioluminescence assay (Table 4, Figs. 1 and 2).
