ORIGINAL PAPER Tredwell Lukondeh Æ Nicholas J. Ashbolt Peter L. Rogers Evaluation of Kluyveromyces marxianus FII 510700 grown on a lactose-based medium as a source of a natural bioemulsifier Received: 14 April 2003 / Accepted: 7 November 2003 / Published online: 19 December 2003 Ó Society for Industrial Microbiology 2003 Abstract Mannoprotein with emulsification properties was extracted from the cell walls of Kluyveromyces marxianus grown on a lactose-based medium by auto- claving cells in a citrate buffer at pH 7.The purified product was evaluated for chemical and physical sta- bility to establish its potential use as a natural emulsifier in processed foods. The yield of purified bioemulsifier from this strain of K. marxianus was 4–7% of the ori- ginal dry cell weight. The purified product, at a con- centration of 12 g l )1 , formed emulsions that were stable for 3 months when subjected to a range of pH (3–11) and NaCl concentrations (2–50 g l )1 ). The composition of this mannoprotein was 90% carbohydrate (mannan) and 4–6% protein. These values are similar to manno- protein extracted from cells of Saccharomyces cerevisiae, which is the traditional source. Consequently K. marxianus cultivated on a low-cost lactose-based med- ium such as whey, a lactose-rich clean waste of the dairy industry, could be developed as a source of bioemulsifier for use in the food industry. Keywords Bioemulsifier Æ Extraction Æ K. marxianus Æ Mannoprotein Æ Yeast Introduction In recent years there has been increasing interest in the isolation and identification of new microbial emulsifiers and surfactants [3, 8, 12, 38, 39, 45, 48] that might have application in the oil [7, 10] pharmaceutical [34, 41, 52, 53], mining [14], food [11, 15, 50] and other industries [31, 47]. The majority of microbial emulsifiers have been reported in bacteria [25, 27, 29, 30,35, 36, 38, 42]. However, a large number of emulsifiers from bacterial sources are not suitable for use in foods due to the pathogenic nature of the producer organisms [50]. Recently a filamentous fungus was reported to pro- duce an agent containing a polysaccharide-protein complex capable of stabilising oil in water emulsions [45]. Yeasts on the other hand, have been used exten- sively for the production of emulsifiers. Bioemulsifier- producing strains include Candida petrophilum [32], C. tropicalis [37], Torulopsis petrophilum [23], C. lipoly- tica [18,19] and C. bombicola [13]. However, emulsifying agents from these sources are produced only in the presence of water-immiscible substrates, such as alkanes and oils, which appear to facilitate the necessary metabolism [17] and these water-immiscible substrates pose a challenge in the isolation of the produced bio- emulsifier, requiring enzyme digestion, foam fraction- ation and repeated extraction with solutions of chloroform-methanol. Furthermore, the emulsifier yields obtained at the end of these elaborate protocols are low, hence commercial development of bioemulsifi- ers from these yeast strains is unattractive [17]. Since, due to consumer demand, natural emulsifiers are becoming increasingly important in the food industry over synthetic emulsifying agents, which are suffering diminishing popularity due to high production costs and potential human health hazards, the quest to find reliable sources of these natural emulsifiers has intensified [51]. Consequently, strains of Saccharomyces produced by low-cost biotechnology methods using water-soluble substrates, as well as spent brewerÕs yeast from the wine and brewing industries, have become important sources from which bioemulsifiers are extracted [9, 51]. These sources offer the advantages of low cost and high volume of yeast biomass, which translates into high bioemulsifier yields in comparison with synthetic sources [9, 51]. J Ind Microbiol Biotechnol (2003) 30: 715–720 DOI 10.1007/s10295-003-0105-6 T. Lukondeh (&) Æ N. J. Ashbolt School of Civil and Environmental Engineering, The University of New South Wales, 2052 Sydney, Australia E-mail: t.lukondeh@unsw.edu.au Tel.: +61-2-93855214 Fax: +61-2-93138624 P. L. Rogers School of Biotechnology and Biomolecular Sciences, The University of New South Wales, 2052 Sydney, Australia Downloaded from https://academic.oup.com/jimb/article/30/12/715/5992214 by guest on 23 March 2023