Formation of ethyl acetate from whey by Kluyveromyces marxianus on a pilot scale

Whey arising in huge amounts during milk processing is a valuable renewable resource in the field of White Biotechnology. Kluyveromyces marxianus is able to convert whey-borne lactose into ethyl acetate, an environmentally friendly solvent. Formation of ethyl acetate as a bulk product is triggered by iron (Fe). K. marxianus DSM 5422 was cultivated aerobically in whey-borne medium originally containing 40 μg/L Fe, supplemented with 1, 3 or 10 mg/L Fe in the pre-culture, using an 1 L or 70 L stirred reactor. The highest Fe content in the pre-culture promoted yeast growth in the main culture causing a high sugar consumption for growth and dissatisfactory formation of ethyl acetate, while the lowest Fe content limited yeast growth and promoted ester synthesis but slowed down the process. An intermediate Fe dose (ca. 0.5 μg Fe/g sugar) lastly represented a compromise between some yeast growth, a quite high yield of ethyl acetate and an acceptable duration of the process. The mass of ethyl acetate related to the sugar consumed amounted to 0.113, 0.265 and 0.239 g/g in the three processes corresponding to 21.9%, 51.4% and 46.3% of the theoretically maximum yield. The performance on a pilot scale was somewhat higher than on lab scale.