Rapid Detection of Microbial Contaminants in Fruit Juice by Enzyme-linked Immunosorbent Assay

We examined immunological methods for the detection of microbial contaminants in fruit juice. Polyclonal antibodies against native yeast of 7 species, including Candida, Cryptococcus, Rhodotorula and Saccharomyces, and the monoclonal antibody against native C. intermedia, which was named mAb44 (IgG2a subclass), were prepared for use as probes in enzyme-linked immunosorbent assay (ELISA). These antibodies reacted with yeast cell-surface antigens that are thought to consist of protein moieties. The cross-reactivities between the antibodies and yeast antigens of 12 species were investigated by immunofluorescence and immunoblotting methods. C. intermedia polyclonal antibody showed extensive cross-reactivities with yeast antigens of 11 species. ELISA was carried out using C. intermedia polyclonal antibody and mAb44. Yeast cells (104-107) suspended per 100μl of fruit juice or PBS could be quantitatively measured using polyclonal antibody, although quantitative values were not obtained in the case of mAb44. When more than 103 per 100μl yeast cells were present, they were detectable by using mAb44 as well as polyclonal antibody. These results show that ELISA is a valuable method to detect microbial contaminants in fruit juice.