Os pigmentos castanhos produzidos por Yarrowia lipolytica e a sua relacao com o acastanhamento de queijos. Estudos bioquimicos e tecnologicos

This work was aimed to study cheese browning. A small group of yeast strains isolated from various Portuguese traditional cheeses with browning problems was found to be able to produce brown pigments from tyrosine. Several yeast strains were screened for their ability to produce brown pigments from tyrosine. It was observed that this activity is almost exclusive of Yarrowia lipolytica, and thus, a differential medium was developed for the rapid identification of this species, based on this characteristic. The catabolic pathway of tyrosine in Y, lipolytica was found to be distinct from the usual pathway in yeasts, as it was suggested by the identification of p-hydroxyphenylacetic acid, p-hydroxyphenethyl alcohol, and homo gentisic acid as aromatic intermediates of the process. It was also demonstrated that pigments results from the accumulation and subsequent auto-oxidation and polymerization of homo gentisic acid in the culture medium. Several technological trials were performed using Camembert cheese in order to study the influence of Y. lipolytic in cheese browning. Under the tested conditions, Mn"2"+ and Penicillium candidum were the main factors responsible for cheese browning. It was further demonstrated, for the first time, that P. candidum is able to produce brown pigments from tyrosineAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga