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Friday, October 23, 2009

Milk and Microbes Part 1

I've noticed a rise recently in debates and articles exhorting the benefits of consuming unpasteurized or "raw" milk, some from the perspective of flavor, but most alleging nutritive and immunological benefits. There are some merits to these arguments - aged cheeses prepared from raw milk has a different character than those prepared from pasteurized milk, and as a fermented product, the point of initial pasteurization is mostly moot. Moreover, the draconian enforcement of pasteurization laws, initially meant to protect the public health, is stepping into the territory of small farmers transacting with private consumers - people who are aware of the risks, and are consenting to undertake them. It's not wise, but the debate there is about government stepping into areas between consenting adults.

I do, however, take issue where scientific merit is taken, and twisted in the name of propaganda for the raw milk movement. Take for example, this recent blog posting from a Orchard Chronicles about a "Campaign for Raw Milk", despite a noble intent to espouse healthier living, is rife with scientific inaccuracies. I'll try to clear up a few of them:

1. rBST is not a fake hormone. It is, in fact, molecularly identical to the bovine somatotropin. The recombinant part simply means that it used recombinant DNA technology to mass produce it so it can be cheaply made. I reserve judgment on whether or not rBST treatment of cows for
improved milk production is wise.

2. Modern farmers do use prophylactic antibiotics to ward off early infections, but it does not "disinfect" milk, nor keep it from being contaminated. The issue with heavy use of antibiotics center more along accelerating the evolution of antibiotic resistance through horizontal gene transfer among bacteria - and raw milk consumption has nothing to do with that.

3. Phosphate in milk is not destroyed by the transient heating involved with pasteurization. In fact, the presence of free phosphate is deleterious to retention of calcium, as the formation of calcium phosphate as an insoluble salt happens, and it precipitates out. The papers citing problems with this involve heat labile compounds in milk that keep phosphate away from calcium to prevent this precipitation. And not because humans can't absorb the calcium (after all, the acid environment in the stomach will release free calcium from the salt), rather, it's because the salting out can clog up harvesting and processing tubes.

Mind you, the papers being cited here are published in the 1920s and 1930s - I have found no more recent publications backing them up, and pasteurization practices have changed since. Also, in many of these early milk nutrition studies that involve mouse models, the assumption in the experiment is that milk is the sole nutritive source. Most studies indicate that nutritive loss during pasteurization is at most minor (mostly to heat labile vitamins) that are easily made up in a varied human diet.

4. Perhaps the most problematic issue in this posting is the poor understanding of microbiological terms, and a direct misinterpretation of the sources behind them.

4a. Coliform is a generic term referring to the shape of bacteria - in this case, short rod shaped cells. Coliform bacteria are both benign, and pathogenic, and I have found no peer reviewed published evidence of "cultured coliforms" being used to treat Staphylococcus infections. In fact, since 15% of human fecal bacteria are coliform, water and food safety assays look for a coliform count as a rough measure of fecal contamination.

4b. Milk as it emerges from the teat is sterile - all bacteria found in it are present by way of contamination. The problem with contamination is that it is difficult to control, either in kind or amount, which is the problem with distinguishing between so called beneficial or pathogenic bacteria. But there is no argument that before pasteurization, milk borne diseases were a major public health hazard.

4c. Lactose is the primary sugar (disaccharide) in milk. Human infants produce the enzyme lactase in the intestinal lining to digest milk, but as most mammals mature, they lose this enzyme. Some humans, however, by quirk of evolution, retain lactase to adulthood, while others do not. The inability to digest lactose unassisted is thus diagnosed as lactose intolerance - even though it's really the ability to digest lactose that is the odd thing out. But it is a beautiful example of how natural selection acting on variations in the species results in propagation of traits (in this case, the incorporation of harvested milk as an adult food source).

4d. Lactobacilli are a general term for spore forming bacteria that can use lactose as a primary carbon source, and converting it to lactic acid. They are important in fermentation of things from kimchi to sourdough, but in this case - fermented milk products like yogurt and cheese. They do not assist humans in digesting fresh milk. When you convert milk to these other milk products, then yes, their actions will cause the lactose content to drop (but the acidity to rise). Fresh milk does not have appreciable levels of benign lactobacilli to have an impact on lactose digestion. Milk can be treated with lactase early on to produce lactose-free milk. But to hold it that long, pasteurization is advisable.

---> to be continued --->...Who was Weston A. Price?

1 comment:

  1. On point 4d, I'll just add:

    There's very little microbial activity in the stomach. Most bacteria go into survival mode ast hey pass through the stomach, and primarily metabolize in the small and large intestines. Indeed, the primary symptoms of lactose intolerance are due to bacteria in the small and large intestines metabolizing lactose that didn't get broken down in the stomach by our own enzymes. That said, any natural lactobacilli in the milk that might survive long enough to metabolize it in your gut would be contributing to the symptoms of lactose intolerance. The only way they would help is if they actually broke down the lactose in the milk prior to ingestion, thus curdling the milk. So, unless you're drinking chunky milk, it's gonna give you lactose intolerance issues.

    In an interesting irony, the ads currently showing in your google ad area are for the "Raw Milk Conspiracy - Find out why you should never drink pasteurized milk."