NICE, France _ Years ago, the Pacific fishing fleet returned toPuget Sound with a cargo of salmon in its holds. Salmon with adifference: Their flesh was white, not pink.
Evidently, some ecological aberration had temporarily bleached theocean plankton and krill, which normally supply the fish with theirreddish carotenoid pigment. Dismay and disaster confronted the fishcanneries: Who would buy white salmon?
Until a resourceful advertising man saved the day _ and the market.He came up with a label: "PACIFIC SILVER SALMON: GuaranteedNot to Turn Pink in the Can."
A somewhat similar problem currently confronts the world's salmonindustry, which raises 30 percent of its catch in fish hatcheries, ratherthan the open ocean. Trouble is that the fish grown in pens are a palecopy of their deeper pink, wild-type, ocean-going cousins. Animals(humans included) can't grow their own carotenoids.
Deepening Salmon's Saleable Hue Comes High
So the aquaculture industry feeds its farm-grown salmon that samecarotenoid pigment, astaxanthin, which it obtains from chemicalsynthesis. This practice comes at a horrendous cost. The syntheticdietary dye carries a price tag of around $2,500 per kilogram,representing 15 percent of total feed expense.
Also, "the introduction of artificial food pigments into the humanfood-chain is frowned upon, particularly by the Food and DrugAdministration in America." This regulatory understatementappeared on one of the 1,041 posters presented at the EuropeanCongress here last week. Its title: "Yeasts as Source of the RedPigment Astaxanthin for Farmed Salmon."
Its author is David Harvey, a doctoral candidate in the chemicalengineering and processing department of Glasgow's StrathclydeUniversity. The yeast from which he is extracting astaxanthin isPhaffia rhodozyma. In nature, it oozes from broad-leafed trees inJapan, Alaska and Siberia.
P. rhodozyma secretes astaxanthin all right, but in modest quantities.Wild strains of the yeast assay at 0.4 milligrams of carotenoid pergram of dry yeast. As Harvey told BioWorld Today, "A lot ofcompanies are interested in the subject, because it's a high-value-added product."
He noted that Hoffmann-La Roche of Basel, Switzerland, has amonopoly on the synthetic pigment, and that among the many visitorsto his poster was a Roche representative. Another was from Pernod-Ricard Research Center in Paris, which is mutating the yeast for itswine-aroma-enhancing properties.
At Mid-Point, Stronger Tint, Warmer Temperature
Harvey has determined that P. rhodozyma grows best at 30 C."which," he said, "nobody else has yet found." So far, all otherinvestigators are hung up on an awkward 22 C. He added: "I'm inmid-stage of my research, which is my doctoral dissertation. Myinitial objective is to find optimal fermentation conditions of the wildstrain, while at the same time developing mutants."
Harvey has so far generated some 50 mutant strains of the yeast,using antimycin A as a mutagen. "Now I've pinpointed these down totwo first-generation strains, which give a stronger color on solidmedia than the wild strain. The next stage," he said, "will be to raisesecond-generation variants, hopefully marked by further performanceprogression."
While Harvey has to focus on fermentation kinetics until he finisheshis thesis. He intends to turn then toward Phaffia's genetics andmicrobiology. "Most of the visitors to my poster," he said, "aremainly interested in the genetics of microorganisms."
He also pointed out that P. rhodozyma's pink pigment is an anti-oxidant, which "makes it especially interesting in America, wherepeople are very keen on not using free-radical food additives." n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.