Wednesday, August 26, 2015

Inadvertently edible tiny food-based animals

Bacteria and fungi are basically everywhere, so it's not much of a surprise to find them in food. Heck, unless they're Salmonella or have managed to multiply to the point of being visible or stinking things up, we usually don't care. Moving up a bit on the size scale, there are a couple of tiny animals inhabiting foods we eat. These include itty bitty worms living in artisanal vinegars and mites residing upon classy European cheeses.

The vinegar eelworm (Turbatrix aceti) is a resilient microbe-eating nematode (roundworm) naturally found on decaying fruits and subsequently in vinegar made from them. Vinegar is an aqueous solution of acetic acid produced by microorganisms. If you can ferment it to make booze (e.g. fruit, grains, honey), you can further ferment it to make vinegar. The former is carried out by yeasts (sugars -> ethanol), while the latter is done by acetic acid bacteria (ethanol -> acetic acid). T. aceti is able to survive the low pH of a vinegar and feed on the bacteria responsible for making it. With the exception of certain 'natural' products (often apple cider vinegar), vinegar sold at the grocery store is usually filtered and treated with heat (pasteurized) to remove the worms prior to it being sold. They tend to squick people out for some reason.

Apple cider undergoing a journey to vinegar (Source)

Nematodes are one of the most common phyla of animals, and can be grouped into parasitic and free-living species. The latter group, to which T. aceti belongs (it's harmless to people), tend to be smaller. Getting all precise like, our vinegar-residing protagonist is 1-2 mm long and 50-80 μm in diameter. This is sufficiently large that swarms of the worm infesting a flask of vinegar are readily visible to the naked eye if you hold it up to a light source.

T. aceti makes good eating for fish and crustacean larvae, many of which require live food to meet their nutritional requirements. In particular, the worm is able to synthesize omega-3 fatty acids, which apparently are pretty good for you. Due to its nutritional fortitude and easy cultivation, T. aceti has been used by aquarium keepers for decades and more recently has been investigated as a suitable live food for use in aquaculture. Unlike most roundworms, it's able to swim. This is pretty useful if you want to feed the worms to fish, since they will swim throughout the water column instead of clumping at the bottom of a tank. This encourages fish to eat the worm, as they are attracted to its swimming motion. Other non-swimming nematodes used as fish food have be actively suspended into the water column (via aeration or moving water) and so require a more complicated feeding setup.

T. aceti has also been employed by researchers to study aging and its association with DNA damage and the capacity to repair this damage. It has been used for this purpose because it's relatively easy to grow, usually only lives about a month, and most of its cells don't divide during its lifespan (it apparently grows by enlarging its cells, not by making more of them).

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Switching gears from nematodes to arthropods, several species of mite are essential to the production of weird European cheeses. For hundreds of years now, these tiny creatures have been intentionally added to the surface of a cheese block to assist with its ripening. They eat into the cheese, creating a distinctive textured rind, and their bodies, poop, eggs, and moulted skin collectively form a fine brown to grey dust that apparently confers the cheese with a nutty and fruity flavour. The mites also release digestive juices capable of percolating into the cheese, further altering its composition and flavour.

The very hard French cheese (and cantaloupe lookalike) Mimolette is produced using Acarus siro mites, which otherwise are considered a pest of stored grains and flour. The flesh of this cheese has a characteristic orange colour due to the addition of annatto, a carotenoid-rich substance produced from the seeds of the South American achiote tree.

Milbenkäse, a sour German cheese, is produced using Tyrolichus casei mites, and dates back to the Middle Ages. The mites are often permitted to eat the heck out of the cheese, resulting in a sad powdery lump of deliciousness.

Many mites died to bring us this cheese (Source)

While it ripens, cheese is often stored above 4°C and at greater than 60% relative humidity, conditions which are amenable to mite growth. While the cheeses mentioned above are produced by encouraging mite activity, many other cheeses are negatively impacted by mite infestation. For example, the Spanish blue cheese Cabrales is eaten by the mite Acarus farris. If conditions are right, this mite can cause the loss of a quarter of the final product by weight.


References

Berenbaum M. 2007. A mite unappetizing. American Entomologist 53(3):132-133. [Full text]

Brüggemann J. 2012. Nematodes as live food in larviculture – A review. Journal of the World Aquaculture Society 43(6):739-763.

Buck BH, Brüggemann J, Hundt M, Bischoff AA, Grote B, Strieben S, Hagen W. 2015. Improving nematode culture techniques and their effects on amino acid profile with considerations on production costs. Journal of Applied Ichthyology 31(1):1-9.

Marcellino OSB, Benson DR. 2013. The good, the bad, and the ugly: Tales of mold-ripened cheese. Microbiology Spectrum, 1(1). [Full text]

Melnyk JP, Smith A, Scott-Dupree C, Marcone MF, Hill A. 2010. Identification of cheese mite species inoculated on Mimolette and Milbenkase cheese through cryogenic scanning electron microscopy. Journal of Dairy Science 93(8):3461-3468.

Targovnik HS, Locher SE, Hariharan PV. 1985. Age associated alteration in DNA damage and repair capacity in Turbatrix aceti exposed to ionizing radiation. International Journal of Radiation Biology 47(3):255-260.

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