Fire Through Water

With the summer heat come the pleasures of nicely grilled hot dog crowned with a generous helping of mustard. Mustard’s world goes far beyond the near-fluorescent yellow goo from the traditional squeeze bottle.

The condiment comes initially from a flowery plant part of the Brassica family, along with cauliflower, cabbage, Brussels sprout, rapeseed and broccoli. Production of mustard can be traced as far back as the Antiquity, when Roman macerated crushed mustard seeds in grapes mash – the must, to get mustum ardens; the ardent must. The idea is likely to have been borrowed from the Gallic tribes producing their own version in the now celebrated city of Dijon. Their condiment has always been widely popular across Europe, being for a long time the only spice available to a commoner’s meal.

When it comes to mustard, water feeds its fire rather than extinguish it. To prepare the condiment, the seeds of the mustard plant are macerated in water often along with vinegar or, more rarely, alcohol. The longer they soak, the hotter the mustard will be.

The heat of mustard comes from an enzyme called myrosinase. They are an integral part of the defense system of the Brassica family. The enzyme is kept isolated in the when the plant is damaged, the freed myrosinase hydrolases the glycosides bond of certain glucosinate, producing a series of pungent compounds. When the enzyme is realeased, it thus needs the water to do its work. The intricate myrosinase chemistry (nicknamed the “mustard oil bomb”) is assumed to serve as an herbivore- repellent in Brassica. In black mustard seeds, allyl isothiocyanate is produced from sinigrin, giving mustard its spice. White seeds give a milder, sweeter mustard as they contain a different glucosinate, sinalbin. If the seeds are heated before being mixed in a dish (as in many Indian recipes), the result will be a milder mustardy taste. Allyl isothiocyanate also can be degraded by heat: if you cook with mustard oil and wish to purge its aggressive taste, heat is until it stars smoking.

Unconcerned by mustard? Show some pride: 90% of modern mustard seeds production comes from Canada. Saskatchewan spearheads the market, weighing in for half the country’s production. Skeptics, feel free to ask confirmation to the Saskatchewan mustard development commission – yes, there is such a thing; http://www.saskmustard.ca...

Live by the truffle code

Molecular biologists have explored the brave new worlds of the human genome, various animal models, a plethora of pathogenic organisms, crops and plants. Even the platypus saw his nucleic secrets revealed to the world. European researchers have now added one more genome organism to the databases; fruity, aromatic and expensive, princes of the fungi and diamonds of the kitchen: the black truffle.

For centuries, gourmands considered the truffle a delicacy, searching among oak roots where the symbiotic fungi hid. At first, they used truffle hogs, boars attracted by the truffle's aroma, until trufficulture was developed in the 19^th century. The last ice age nearly wiped out truffles completely, except for two species: Tuber magnatum, the white truffle in one in a warm pocket of northern Italy and, in the region of Piedmont, southern France, Tuber melanosporum, the Black truffle. Today, you might pay close to 500$ for one black truffle.

The market for truffles justifies the research effort by European agricultural agencies: wines, cheeses, crops, the cultures of food want to optimize and preserve their natural treasures. The genome of the black truffle will not help only contribute to its culture, but also to curb smuggling and counterfeiting and has a genuine fundamental biological value. It is only the second genome from a symbiotic fungi uncovered. Its comparison with the previously sequenced Laccaria bicolor genome demonstrated many genetic mechanisms behind symbiosis. First rule of the symbiotic fungi: Travel light. The truffle's genome contains very little similar gene pairs for a genome of its size (125 Mb), starting from a Pezizomycotina ancestor with a compact genome, the organism evolved by loosing little genes, but gaining highly specialized ones. This brings us to the second rule of symbiotic fungi: Milk them dry. Many of the genes the truffle developed encode membrane transporters. The diamonds of the kitchen knows how to cannibalize their host for everything they got. To preserve their ecological edge, the truffle got their third rule: Shuffle the cards. Their gene is highly heterogeneously distributed between areas of transposable elements. These flexible areas facilitated genetic rearrangements of the truffle’s ancestor genome during the last Ice Age, separating then from other ascomycetes, but allowing some populations to survive.

Of course, the genome of the black truffle revealed an array of enzymes involved in sulphides biosynthesis, giving the visually unappetizing mushroom its status of delicacy. One of the most important of these, 2,4-dithiapentane caused uproar in the gastronomic circles in February 2008. In a much-publicized article in the New York Times, chef Daniel Patterson revealed that truffle oil was not made by infusing truffles in olive oil like most cook assumed, but by spiking the oil with pure 2,4-dithiapentane. Many shunned this “artificial” condiment. After all, if 2,4-dithiapentane comes is extracted from a truffle, it is NOT a chemical… right?

Further reading :

Martin F et al. (2010) Périgord black truffle genome uncovers evolutionary origins and mechanisms of symbiosis. Nature. 464(7291):1033-8.

Sushi fans down to their gut

It is only a personal opinion, but I think the Japanese are cool. From technology to arts, they scoured the world for the best ideas, import them… and made them even better. They have the same attitude toward their table. From South-Asia, they adapted the sour, dishes of fermented fish in rice to their own taste to create the sushi has we know and love it. A recent paper showed that not only did they become expert at preparing them; they are adept at eating them.

Hehemann et al. first discovered a new type of glycoside hydrolase in Zobellia galactinovorans.

Algae comports unique sulphated polysaccharides and marine bacteria have evolved a biochemical toolkit of their own to digest them. The enzyme the French group noticed is able to able to cleave L6S saccharide links, particular to porphyran, a polysaccharide rich in Porphyra algae. Where b-agarases present a Tyr residue, the b-porphyranases comport variable, smaller amino acids, opening a positively charged binding pocket for the SO4^- moiety.

When the group searched the databases for amino acid signature specific to b-porphyranase, they retrieved them in only one type of organism apart of marine Bacteroidetes: B. plebeius, a gut Bacteroides. Moreover, b-porphyranases are only observed in Bacteroides from Japanese gut microflora, not in North American microflora. The high homology (35%-55%) of sequence between the genes from marine and gut bacteria indicates the Japanese bugs got their hydrolase by horizontal gene transfer.

Algae, especially of the Porphyra genre (on which Z. galactinovorans thrives) are a staple of Japanese cuisine. Nori comes to mind immediately: Porphyra is grown in marine farms, and processed in sheets, which are used as a condiment on noodles... and to prepare sushi. Bacteroides in Japaneses’ guts has thus been in contact with their porphyran-digesting cousin and inherited the gene that would help them make the most of the Japanese diet.

Further reading :

Hehemann JH, Correc G, Barbeyron T, Helbert W, Czjzek M, Michel G. (2010) Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota. Nature 464, 908-912