Saccharomyces cerevisiae KA01 was isolated from palm wine obtained from a local brewer in Songkhla province, Thailand. Mannoproteins with emulsification properties were extracted from the cell walls of S. cerevisiae KA01 cultivated in YM medium by autoclaving in a pH 7.0 citrate buffer for 60 min with a yield of 0.32 g/g wet cells. The mannoprotein extract obtained was evaluated for its chemical and physical stability to establish its potential use as a natural emulsifier in processed foods. The mannoprotein extract exhibited emulsion with the vegetable oils tested and showed emulsion activity of 65% towards palm oil as oil-in-water with a critical emulsifier concentration of 20 g/l. The mannoprotein extract had similar emulsifying properties to the commonly used food emulsifiers gum arabic and lecithin. Palm oil-in-water emulsions were stabilized over a broad range of conditions from pH 5 to 8 with up to 3% (w/v) sodium chloride and up to 0.1% (w/v) CaCl2 and MgCl2 in the aqueous phase. Temperature did not affect the emulsion activity of the mannoprotein extract. Preliminary trials showed that mannoproteins from S. cerevisiae KA01 had potential for use in salad dressing.

It is generally known that both chemical substances and many kinds of microorganism can be used to produce surfactants or surface-active compounds. Surfactants derived from microorganisms are called biosurfactants, or bio-surface active compounds. Recently, biosurfactants have become more interesting because of their advantages, such as less toxicity and more degradability, which cannot be found in traditional surfactants. Biosurfactant production faces some problems, such as a high cost of production. In the medical field, biosurfactants are attractive, because the products from biosurfactants can be used effectively in small amounts. This can compensate for the high cost of production. In addition, there have been many great discoveries of biosurfactants in the medical field.

Mannoprotein from spent yeast obtained from Thai traditional liquor distillation was extracted by autoclaving in a neutral citrate buffer for 30 min. The yield of mannoprotein was 0.27 g/g wet cells. The mannoprotein obtained was evaluated for chemical and physical stability to establish its potential use as a natural emulsifier in processed foods. The extracted mannoprotein exhibited emulsion of 60.23% toward palm oil as oil‐in‐water and had a critical emulsifier concentration of 20 g/l. The composition of the mannoprotein was 96% carbohydrate and 4% protein. The emulsion activity of the mannoprotein was similar to those of commercial emulsifiers (lecithin and gum arabic). The emulsion activity of mannoprotein towards palm oil was stable over a broad range of pH (3–12), NaCl concentrations of 0–3% (w/v), CaCl2 and MgCl2 concentrations of 0–0.1% (w/v). Temperature did not affect the emulsion activity of mannoprotein. Mannoprotein from spent yeast could be developed as a source of bioemulsifier for use in the food industry. PRACTICAL APPLICATIONS Mannoprotein from spent yeast obtained from Thai traditional liquor distillation is considered to have an activity similar to the commercial emulsifiers, lecithin and gum arabic. It could be developed as a source of bioemulsifier for use in the food industry. The production of the bioemulsifier would be economically advantageous as the process converts a low‐value waste into a high‐value product.

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