No Lions And Witches—The Pantry Leads To Chemistry

When I’m in the kitchen, it’s hard to keep my mind off pure substances, even if I’m just getting items from the pantry. I picked up some MAGIC baking powder, looked at the label and wondered why sodium bicarbonate(baking soda) is the last ingredient, meaning there’s less of it than anything else in the container. The pantry door once again became like the wardrobe in C.S. Lewis’ novel, but instead of carrying me into a fantasy world of lions and witches, it brought me into the more interesting realm of chemistry.

Unless there’s an acidic ingredient like lemon in baked goods, there won’t be anything to neutralize baking soda(NaHCO3) to produce the needed carbon dioxide. So MAGIC also has an acidulant, in this case monocalcium phosphate (Ca(H2PO4)2), which has more aliases than a rap star–the IUPAC name being the best: calcium dihydrogenphosphate.

But why provide more acidulant than baking soda? The dihydrogen phosphate ion (H2PO4) ion reacts with baking soda’s hydrogen carbonate ion(HCO3) in a one to one ratio.

H2PO4+ HCO3–> HPO42-+ H2O + CO2

Dissociating to provide two moles of H2PO4 , a mole of Ca(H2PO4)2  reacts with a pair of baking soda moles. But doubling the latter’s molar mass of 84 still amounts to less than the acidulant’s molar mass of 234 grams per mole, so for every gram of baking soda, you need more Ca(H2PO4)2, 1.39 to be exact.  Finally, the primary ingredient is corn starch, which may also have the role of acting as a filler to accommodate teaspoon measurements but is definitely there to absorb moisture. Otherwise there would some reaction in the packaging stage or on the shelves, leading to a premature release of carbon dioxide.

Another surprise is the presence of calcium chloride(CaCl2) in most canned tomatoes. People from the Food Network believe the additive leads to lumpier sauces, and they advise cooks not to use tomatoes from cans. But one of the 3 brands in our pantry, Italpasta, is free of calcium chloride. What’s more interesting is the strong industrial link between the ubiquitous calcium chloride and baking soda and soda ash(Na2CO3), a connection that is however vanishing, thanks to the less costly means of producing soda ash directly from the mineral trona

(Na3CO3HCO3.2H2O).

Exactly 150 years ago, in 1867,  using a method he had developed a few years earlier, the Belgian chemist Ernest Solway founded a company in order to produce sodium carbonate(soda ash).

The compound is used mostly in glass-making to lower the melting point of silica, but it finds its way into many other consumer products. The method, which only consumes table salt and limestone, is brilliant in that it creates little waste. It reuses two intermediate products, carbon dioxide(CO2) and ammonia(NH3), and creates not only soda ash but our firming agent for tomatoes.

The overall reaction, as is often the case in both natural and industrial processes, is very deceiving:

2 NaCl(aq) + CaCO3(s) –> Na2CO3(s) + CaCl2(aq) .

It’s as if you would bring in the groceries, place them on the counter, walk away from the kitchen during the preparation of the meal, return just in time when the cooked meal is on the table and conclude:

                                                       groceries  –> lasagna.

You would not be acknowledging any of the cooking process. Calcium carbonate is sparingly soluble at neutral pH’s. Adding a sodium chloride solution to it would yield insignificant amounts of products. But the Solway method begins by treating brine with NH3 gas to generate ammonium chloride(NH4Cl). In Solway towers, carbon dioxide is then injected to yield baking soda. Next heat is used to drive off carbon dioxide from the baking soda to yield soda ash and regenerating CO2, which is used again in the towers.The ammonium chloride meanwhile reacts with limewater(Ca(OH)2), releasing ammonia gas that is kept to re-initiate the cycle. The alkaline solution is produced by cooking calcium carbonate, which releases lime and which creates more carbon dioxide for the in-between reaction. Our calcium chloride is the byproduct of the step that releases ammonia.

If an industry is only interested in making calcium chloride it can also rely on the direct action of 36% HCl (hydrochloric acid) on calcium carbonate. The reaction is 2 HCl + CaCO3 –> CaCl2 + H2O + CO2, and the recovered carbon dioxide is used to make soft drinks. A cheaper method that however produces a less pure product relies on the purification of natural brine water. First magnesium ions are precipitated out with the addition of limewater.The water is slowly evaporated which forces out sodium chloride solid, leaving behind the more soluble calcium chloride.

The greater solubility of CaCl2 is part of the reason it is a valuable additive to street salt to melt ice in colder climates. Although CaCl2 is about three times as expensive as NaCl, its calcium ion does not harm plants like sodium ion does, and it melts ice at much lower temperatures than rock salt(NaCl)’s -10 oC limit. The reason why calcium chloride is a firming agent for tomatoes is one of the reasons it makes regular salt more effective at melting ice.

It’s because CaCl2 is hygroscopic–it easily attracts and holds on to water.

Compared to table salt, calcium chloride tastes much saltier, but it cannot be used as a substitute. Ca2+ plays an important role in cell signalling, and cells are sensitive to high levels of the ion. Not surprisingly the lethal dose that will kill 50% of mice is only 1940 mg CaCl2 /kg of body weight as opposed to 4000 mg/kg for table salt. But the concentrations of calcium chloride in canned tomatoes is nowhere near toxic levels. It’s not only approved in the United States but in Europe, which is usually more strict with additives.
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Blood Pressure Linked To Gut Bacteria, Bread Preservative & Nasal Receptors

That biology’s four themes— unity, diversity, continuity and interaction— are constantly at play is obvious in a good paper published last month by Jennifer Pluznick and fourteen other lead researchers throughout the United States and France.

Background Information

Propionate (or propanate) is the anion resulting from the split-up of propanoic acid. It’s used as a mold-inhibitor in bread and also found in sweat and milk. It’s one example of a group of 2 to 5-carbon fatty acids known as short chain fatty acids (SCFAs) that bacteria create when breaking down complex carbohydrates and sometimes protein. Also relevant is that SCFAs are found in the colon where they are absorbed into the blood stream.

In a similar way that opioid receptors are found in both the nervous and digestive systems, the type of olfactory receptors that bind to detectable molecules in the nose are also found in kidneys, smooth vessel cells and nerves. One specific renal olfactory-type receptor(Olfr78) in mice binds to the SCFAs acetate and propionate. Olfr78’s human equivalent, OR51E2, behaves similarly towards the two ions, at least in test tube studies that used SFCA-concentrations comparable to those found in our blood plasma.

Evidence That SCFA Receptors Control Blood Pressure in Mice

a) one receptor’s location
Using the reverse transcriptase-polymerase chain reaction, RNA made from the Olfr78 gene was detected in mice kidneys. Other experiments revealed that the gene was expressed in a specific part of the kidney where renin is released. Renin helps regulate body fluids and blood pressure. The diagram reveals the precise location: the juxtaglomelurular arteriole(JGA).

Source of diagram: (http://renalfellow.blogspot.ca/2008/10/review-juxtaglomerular-apparatus.html)

b) bonding of propionate to kidney olfactory receptor leads to renin release
Using fluorescent quinacrine, investigators labeled renin-releasing arteriole granules in solutions made with JGA glomeruli from wild strained mice. As they added propionate, the fluorescence decreased, suggesting that the short chain fatty acid which interacted with Olfr78 increased the secretion of renin. But solutions made from tissue of mice who lacked the Olfr78 receptor were unaffected.

c) live-mice experiments: second olfactory receptor also contributes to control of blood pressure  
When Olfr78-less mice were fed a diet rich in polysaccharides (which led to high plasma levels of propionate), there was not enough renin produced.  Meanwhile, a different olfactory receptor, Gpr41 (a G protein-coupled receptor found in the renal and iliac arteries and in the aorta), bonded to propionate and lowered blood pressure. This happened because without the presence of pressure-raising Olfr78, Gpr41’s action could not be counterbalanced.

To verify that the gut bacteria were indeed the source of propionate, mice were treated with a cocktail of 3 antibiotics for three weeks. This had no effect on the blood pressure of mice possessing the Olfr78 gene. In light of the fact that activated Gpr41 and Olfr78 have opposing effects on blood pressure, this makes sense. Without propionate, neither receptor could play its role. But for antibiotic-treated mice who were without Olfr78, blood pressure actually increased. It’s not as contradictory as it seems on the surface. In the presence of propionate, Gpr41 was acting “alone” in Olfr78-less mice. After taking away the ligand (propionate) for Gpr41, blood pressure rose relative to whatever homeostasis existed previously.

Sources:
SCFAs: The Enigma of Weak Electrolyte Transport in the Colon http://physiologyonline.physiology.org/content/14/2/58.full
Olfactory receptor responding to gut microbiota-derived signals plays a role in renin secretion and blood pressure regulation