Curious Cook

Curious Cook in the New York Times: Organic produce and yak cheese

In today's Curious Cook column I write about nutritional claims made for organic fruits and vegetables and for yak cheese made in Nepal.

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 Benbrook, C. et al. New Evidence Confirms the Nutritional Superiority of Plant-based Organic Foods. The Organic Center, March 2008.

http://www.organic-center.org/science.nutri.php?action=view&report_id=126

 

Or-Rashid, M.M. et al. Fatty acid composition of yak (Bos grunniens) cheese including conjugated linoleic acid and trans-18:1 fatty acids. J. Agricultural and Food Chemistry 2008, 56: 1654-60. http://dx.doi.org/10.1021/jf0725225

 

In the dark: olive oil, milk, butter, and beer

In my last post I mentioned that olive oil is best stored in the dark. The same is true for milk and butter and beer. It's turning out that all these foods are sensitive to light for similar reasons.

Grass-Fed Beef vs. Farmed Salmon

My post last August about the weak claim of grass-fed beef to healthful quantities of omega-3 fatty acids has drawn a skeptical response from Robert Buxbaum, who found a contrary view in Michael Pollan's important new book, The Omnivore's Dilemma. I'd like to dissect the discussion a bit, because I think it's a cautionary example of how easily speculations about food and nutrition can stray from the facts, become accepted as fact themselves, and end up being unintentionally misleading.

Good Fats In Grass-Fed Beef?

My friend Daniel Patterson, the chef and owner of Coi in San Francisco, recently told me that some of his meat suppliers have been promoting grass-fed beef as a good source of healthful omega-3 fatty acids, both the linolenic acid found in walnuts and canola oil, and the very long chain fatty acids characteristic of fish oils. Beef, the archetype of foods laden with cholesterol-raising saturated fats, as a health food? I took a fresh look at the numbers.

Sure enough, grass-fed beef has substantially more omega-3 fatty acids than conventional beef raised on grain or a combination of grain and other concentrated nutrients. This makes sense: green grass doesn’t have much fat or oil, but its membranes are rich in linolenic acid. When the grass is cut and turned into hay, the linolenic acid tends to be oxidized and converted into other molecules, so hay is a poorer source, and grains contain little or no linolenic acid.

Once it gets into cattle, the grass linolenic acid meets several fates. Much of it is hydrogenated by microbes in the animal’s rumen, and turned into more saturated, less valuable fatty acids. Some of it enters intact into the circulation, and ends up being deposited in both muscle and milk. And a small portion of it is converted by the cattle tissues into the longer-chain fatty acids found in abundance in fish.

So is grass-fed beef a meaningful source of omega-3s? No. An entire grass-fed beefsteak contains hundredths of a gram of long-chain omega-3s, and less than a quarter of a gram of linolenic acid. You can get the same quantities from a couple of walnut pieces and a few grams—a very small bite—of salmon or oyster. Beef is wonderful stuff, and grass-fed beef is especially lean and flavorful, but it’s still beef. 

Dannenberger, D. et al., J. Agric. Food Chem. 2004, 52 (21) 6607

Hold that watermelon

With the exception of fruits in the process of ripening, most produce deteriorates once it has been harvested, and benefits from being cooled down to refrigerator temperature, where its metabolism is slowed down. Thanks to Penelope Perkins-Veazie and Julie K. Collins at the USDA lab in Lane, Oklahoma, we now know that watermelon is a big exception. The red color of watermelons comes from lycopene, the valuable antioxidant relative of carotene that also colors red tomatoes. The USDA scientists found that watermelons held for two weeks at room temperature continue to produce lycopene and so deepen in color, and end up with from 10 to 40% more pigment than freshly harvested melons. Conversely, refrigerated melons lose lycopene and tend to develop areas where the cells are damaged and leaky. (The watermelon plant came originally from hot, arid regions of Africa, and its fruits just don't do well in the cold.) So it's actually a good thing to let watermelons sit out after harvest, and chill them only just before eating.

I haven't been able to find out how the watermelon stores its lycopene, but it appears to be in a form that's more available to the human body than the lycopene in raw tomatoes. Other studies show that fresh-frozen watermelon juice is a good source, roughly equivalent to canned tomato juice.

Perkins-Veazie, P. and J.K. Collins, J. Agric. Food Chem. 2006, 54 (16) 5868

Carotene pigments in mango and carrot

Mangoes and carrots are beautiful to look at because they contain rich deposits of carotene pigments. The carotenes come in many different variations, and range in color from yellow to deep orange. Beta carotene in particular is a valuable nutrient because it's an antioxidant, and because our bodies can convert it into vitamin A, which has important roles in our eyes and in other tissues. So we can count on orange-colored fruits and vegetables to be especially good for us. But often we don't get as much of their goodness as we might think.