Spectrophotometric assay of hydroxylated by-products in penicillin V fermentations and its application in screening of mutant penicillin producer strains on agar media.

A fast and sensitive spectrophotometric method has been developed to measure the level of hydroxylated by-products (p-hydroxyphenoxyacetic acid and p-hydroxypenicillin V) in penicillin V fermentations. The method is based on a color reaction of the above-mentioned phenolic by-products with nitrous acid, yielding yellow nitroso derivatives. Both the nitroso derivative of p-hydroxyphenoxyacetic acid and that of p-hydroxypenicillin V have an absorption peak at 450 nm in alkaline solution with a molar absorption of 4.00 x 10(3) M-1cm-1 for both compounds. No fermentation medium components were found to interfere considerably with the assay. On the basis of the color reaction, an agar prescreen method has been developed for isolation of nonhydroxylating Penicillium chrysogenum strains in strain-improvement programs.