Research Article Cheese whey as a renewable substrate for microbial lipid and biomass production by Zygomycetes Three Zygomycetes, Mortierella isabellina, Thamnidium elegans and Mucor sp., were tested for their ability of producing biomass and lipid-containing g-linolenic acid (GLA) during their cultivation on cheese whey. M. isabellina consumed all of the available lactose and a significant amount of the available protein. On the contrary, the two other fungi seemed incapable of consuming lactose after protein exhaustion. In the second series of experiments, for M. isabellina a supplementary quantity of lactose was added into the medium in order to increase the C/N ratio and hence to increase the production of fat. In the case of T. elegans and Mucor sp., a supplementary quantity of ammonium sulfate was added in order to favor the consumption of lactose and the production of biomass. Indeed, enhancement of lipid production was observed for M. isabellina and biomass production for T. elegans and Mucor sp.. Fatty acid analysis of the microbial lipid showed a composition that presented non-negligible changes in relation with the age of the culture and the C/N molar ratio of the medium. Further analysis of the fat showed that the quantity of neutral lipids was the more abundant. The fatty acid composition of neutral lipids resembled to that of total lipids. Phospholipids were the more unsaturated fraction for Mucor sp. and M. isabellina. GLA was synthesized in all trials but its concentration presented differences related with the utilized strains and the fermentation time. Growth of M. isabellina on lactose- supplemented whey resulted in a maximum GLA production of 301 mg/L. Keywords: g-Linolenic acid / Biomass / Single-cell oil / Whey / Zygomycetes Received: March 25, 2010; revised: June 3, 2010; accepted: June 15, 2010 DOI: 10.1002/elsc.201000063 1 Introduction Cheese whey is the liquid residue that remains after milk has been curdled and strained during cheese-making process [1]. Typically, cheese whey is composed of 92–95%w/w water and 5–8% w/w dry matter, of which around 10–20% are proteins (Prts), 60–80% are lactose (Lac) and the rest are minerals, vitamins, fat, lactic acid and trace elements [1, 2]. The chemical composition of whey differs according to the types of cheese produced and especially from the kind of milk used for cheese production [1]. Cheese whey, being the major by- product of the dairy industry, is produced in very high and constantly increasing quantities [3] and in most of the cases is disposed-off, representing a loss of milk constituents of excellent nutritional value and causing major environmental pollution, due to its high organic load that makes treatment cost prohibitive [2]. For instance, the 5-day biochemical oxygen demand (BOD) value of whey ranges from 35 to 60 g of oxygen per liter of whey, which represents an important Afroditi-Nectaria Vamvakaki 1,2 Ioannis Kandarakis 2à Stelios Kaminarides 2 Michael Komaitis 3 Seraphim Papanikolaou 1 1 Laboratory of Food Microbiology and Biotechnology, Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece 2 Laboratory of Dairy Science and Technology, Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece 3 Laboratory of Food Chemistry and Analysis, Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece à Professor Ioannis Kandarakis sadly passed away on January 7 2010, at only 63 years old. The authors dedicate this manuscript to his memory. Abbreviations: GLA, g-linolenic acid; G1S, glycolipids plus sphin- golipids; Lac, lactose; NL, neutral lipids; P , phospholipids; Prt, protein; PUFA, poly-unsaturated fatty acid; SCO, single-cell oil; SCP , single-cell protein; TAG, triacylglycerol; Correspondence: Dr. Seraphin Papanikolaou (spapanik@aua.gr), Assistant Professor in Food Bioprocesses, Laboratory of Food Micro- biology and Biotechnology, Department of Food Science and Tech- nology, Agricultural University of Athens, Athens, Greece. & 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.els-journal.com 348 Eng. Life Sci. 2010, 10, No. 4, 348–360