Influence of growth phase and zeolite clinoptilolite on the concentration of sphingoid bases in Saccharomyces uvarum brewer's yeast

Sphingolipids having a long-chain sphingoid base backbone are primarily located in the yeast's plasma membrane. They are found in various types of foods, and although they are not essential food ingredients, they play an important role as bioactive molecules in preventing certain human diseases. Today, due to its high nutritional value, brewer's yeast is increasingly being used in the food and pharmaceutical industry. The aim of this study was to evaluate the potential of S. uvarum, a by-product of the brewing industry, as an economically feasible source of sphingolipids. For that purpose, the growth phase dependence on sphingolipid production in S. uvarum as well as the effect of zeolite addition to the growth medium was investigated. The experiments were designed to explore the dependence of growth phase on sphingolipids metabolism, by comparing initial (starter) culture of brewer's yeast (laboratory propagated, designated as zero yeast generation, serving here as control), and surplus brewer's yeast (a residue produced after 5 successive beer fermentations), by-product of beer fermentation, with and without the addition of zeolite. HPLC analysis of individual molecular species of sphingoid bases obtained by acid hydrolysis of complex sphingolipids from S. uvarum yeast produced the following results: about 65% of total sphingoid bases represents C18 phytosphingosine, about 32% represents unknown long-chain base, and about 1.5-2% represents C18 DL-erythro-sphinganine. In the case of C18 phytosphingosine, production was about 11.5-fold higher during exponential phase compared with the other growth phases. For C18 DL-erythro-sphinganine, production was highest during the lag and acceleration phase of growth. In most cases, zeolite addition (1%) to the growth medium resulted in an increase up to 2.5-fold in the sphingoid bases level.