Genetic modification of the yeast results in mutants that produce lower levels of unsaturated fatty acids and a higher level of saturated fatty acids, thereby producing a more cocoa butter-like composition.
inform November 2008, Vol. 19 (11) 763 Annual Meeting Oleaginous yeast—a potential source of renewable oil This article is based on a presentation given by Sam Beattie at the Hot Topic Symposium, “Honoring 50 Years of Lipid Research by Earl Hammond: Modifying Lipids to Improve Food and Fuel,” 99th AOCS Annual Meeting & Expo, Seattle, Washington, USA, May 20, 2008. Sam Beattie and Earl Hammond Oleaginous fungi are yeasts and molds that are able to accumulate over 20% of their biomass as lipid, usually tria- cylglycerols (single cell oil, SCO). Since their discovery in the late 1800s, a dozen or so molds and yeasts (Table 1 and Fig. 1) with the ability to grow fat when grown on simple carbon sources have been described. possibly the first yeast observed to contain oil was the common fermentative yeast Saccha- romyces cereviseae, which produces Earl Hammond (left) and Sam Beattie. relatively little oil. Proposed and actual uses for SCO include as alternatives to vegetable oils source of oils. They made a number of key lation in some organisms. Once the noncar- for human consumption, in production of observations about growth requirements of bon nutrient has become limiting, the yeast specialty oils or fats, and as alternatives oleaginous yeast. Lindner and coworkers shift to synthesizing oil from the carbon to petroleum-based fuels. These uses are showed that oleaginous fermentations re- source of the medium. An example of the somewhat dependent on an inexpensive quired a medium with a good source of fer- growth, substrate utilization, and lipid ac- and abundant yeast feedstock. Currently, mentable carbohydrate, a limiting nutrient, cumulation is shown in Figure 2. the major use of oleaginous fungi is in the and adequate oxygenation. They also expe- In the 1970s, Nancy Moon and Earl production of specialty fatty acids such as rienced many of the difficulties of achiev- Hammond isolated the oleaginous yeast arachidonic or docosahexaenoic acids by ing oxygenation in fermentations, which Candida curvata, since renamed Crypto- molds in the Mortierella genus. remains one of the greatest economic costs coccus curvatus, from a floor drain in the Paul Lindner discovered the oleagi- of oleaginous fermentations today. Iowa State University Dairy Plant. This nous yeast now known as Metschnikowia One general feature of lipid accumula- yeast is able to grow on whey permeate, pulcherrima in 1899. and over the years, tion by oleaginous yeast is that it is a two- a high-carbon (lactose) low-nitrogen me- yeasts with higher oil content have been phase process. A growth phase in nutrition- dium, to a fat content of 60% and a cell discovered and are listed in Table 1. Lind- ally complete medium is followed by a de density of about 15 grams dry yeast/liter ner is best known for his work in Germany novo lipid accumulation phase that begins of medium. The fatty acid composition re- during World War I. Central Europe was once a key nutrient other than carbon be- sembles that of palm oil, and about 95% cut off from oil imports, and he and co- comes limiting. Most often, nitrogen is the of the chemical oxygen demand (COD) workers investigated sing
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