Curious Cook in the New York Times: Chemical signals that boost basil flavor

In today's Curious Cook column I write about the elusive flavor advantage of organic foods, and about a simple treatment that can increase the flavorfulness of basil and quite possibly other herbs and vegetables.


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P. Maeder et al., Wheat quality in organic and conventional farming: results of a 21 year field experiment. J. Science of Food and Agriculture, 2007, 87, 1826-35. http://dx.doi.org/10.1002/jsfa.2866


H.-J. Kim et al. Effect of chitosan on the biological properties of sweet basil (Ocimum basilicum L.). J. Agriculture and Food Chemistry 2005, 53, 3696-3701. http://dx.doi.org/10.1021/jf0480804

Rice: Old and new flavors; cooking; parboiled

A last installment (for the time being) of rice news.

Old and new Japanese As I've mentioned, Japan generally prefers their rice as fresh as possible; new-harvest rice is prized. Japanese scientists looked at the flavor changes that take place during aging, and found some pretty significant changes. The acidity of the grain increases, probably because oils are broken down into free fatty acids--the same molecules that also cause a firmer, dryer texture. This effect can be minimized if the rice is washed before cooking. The sucrose sugar in the grain is broken down into a mixture of glucose and fructose, which is slightly sweeter, and which is faster to undergo browning reactions and discolor if the grains dry out slightly at the end of cooking. And the mouth-filling umami sensation, caused by natural monosodium glutamate and ribonucleotides, declines with time. So for real rice connoissseurs, people who eat it every day and notice the nuances of its flavor and texture, it makes sense to buy rice labelled "new harvest" and use it quickly.


Cooking water and times From France and Switzerland, a study of the basic cooking properties of different milled rice types. The scientists looked at how much water the rices absorbed, how long they took to cook, and what might account for the differences.

They found that the kernel size and shape are what determine cooking times: not surprisingly, the thicker the longer. (There are three dimensions to a rice kernel: the length; the height, from back to belly; and the thickness through the sides). They found that both short- and long-grain rices absorbed about the same amount of water to give an al dente texture, with 95% of the grain starch soft and gelated; the workable ratio was 2.55 parts water to 1 of rice by weight, giving a grain that's about 75% water, 25% solids (dry rice is about 10% water). Short-grain rices were somewhat better at a ratio of 2.0, and long-grain at 3.0. The usual cooking instructions on packages and in books call for more water, probably to compensate for losses to steam that escapes around the edges of the lid.

The cooking experiments were done in Volvic mineral water with 0.35% salt, about a tenth the concentration of seawater. The rice was added to the boiling water and cooked just until all the rice starch had gelated. The cooking times ranged from 9.5 to 15.4 minutes. Smaller grains generally took less time to cook. But there were deviations from this rule, and they probably have to do with the effects of aging on rice, which slow the penetration of water into the grain and then into the starch granules. The scientists also looked at the microstructure of the grains, and suspect that the rice cell walls and their carbohydrates are arrayed differently in different varieties and may influence water penetration during cooking.

The takehome lesson from this paper is that long- and short-grained rices take about the same amount of water to develop a fully cooked texture, but cooking times vary by 50% or more, and there's no way to predict that. Longer cooking times may require more water to replenish the steam losses during prolonged cooking.


Parboiled rice: color and flavor From Belgium, a study of the qualities of parboiled rice, which is soaked, steamed, and dried before the bran is removed. (Normally the brain is milled away first, and the rice packaged raw.) Parboiling allows some of the bran nutrients to penetrate into the grain; and it results in a firmer rice that doesn't get as soft or leak sticky starch as much as standard rice, so the cooked grains are more tolerant to overcooking and remain separate and loose. They have their own distinctive flavor, with overtones of vanilla and nuttiness that come from the cooking and drying processes. Parboiling goes back thousands of years in India and is also used to manufacture packaged rices.

The Belgian scientists looked at the the typical yellowish color and the flavor of parboiled rice. They found that despite the high water content and moderate temperature, the rice bran underwent browning reactions. The soaking step encouraged rice enzymes to release reactive reducing sugars, and the steam heat encourages them to combine with amino acids from the proteins, generating brown pigments and toasty flavors. Both the native bran pigments and the browning-reaction products diffused into the rice gain during steaming and drying, giving it both it yellowish color and added flavor.

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Tran, T.U. et al. Detection in changes in taste of japonica and indica brown and milled rice during storage . . . . J Agric. Food Chem. 2005, 53, 1108-18.

Vidal, V. et al. Cooking behavior of rice in relation to kernel physicochemical and structural properties. J Agric. Food Chem. 2006, 54, 336-46.

Lamberts, L. et al., Impact of browning reactions and brand pigments on color of parboiled rice. J Agric. Food Chem. 2006, 54, 9924-29.

Rice: Red and brown

Rice news continued.

Red rice: I've enjoyed this exotic premium rice from Bhutan for years without realizing that in much of the rest of the world, the U.S. included, it's a troublesome weed. According to a recent report from the USDA National Rice Research Center at Stuttgart, Arkansas, some red rices are strains of the same Oryza sativa that gives us ordinary brown and white rices, while others are sister species. They're undesirable in ordinary rice fields because they "shatter," or drop their grains when they're mature, instead of retaining them so that they can be harvested; and their red outer bran layer adheres more tightly to the grains, which are often broken in the milling process.

But red rice has long been cultivated as a staple crop and cooked with its bran intact in Bhutan, parts of China and India, and elsewhere in Asia. Recently it has become popular in Japan for its high content of antioxidant phenolic compounds. The red pigments in the bran are water-soluble anthocyanins that are bonded to some of the rice bran proteins. The qualities of the weedy U.S. strains vary, but most red rices had higher protein contents than ordinary rices. Maybe the weed is on its way to the mainstream.

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Patindol, J. et al. Comparison of physicochemical properties and starch structure of red rice and cultivated rice. J. Agric. Food Chem. 2006, 54, 2712-18.

Rice: Scented and un-, old and new

Last week I wrote in the New York Times about the distinctive aroma of Himalayan basmati and Thai jasmine rices and the chemical that contributes it. I've collected several other interesting studies of rice over the last few months. They come from labs all over the world: not surprisingly Japan and Korea and Thailand, but also France, Switzerland, Italy, Belgium--and Arkansas. Here's some of their news; more tomorrow.


Rice Flavor: From Thailand, a study of the basmati/jasmine flavor molecule, 2-acetyl-1-pyrroline, 2AP for short, notes that 2AP is produced through the whole of the rice plant except for the roots. It's also found at very high levels in pandanus leaf, or screwpine (Pandanus amaryllifolius), an Asian herb that's often used to impart that same aroma to cooked dishes of various kinds. And in "bread flowers," flowers of Vallaris glabra, a tropical shrub, which form part of the traditional wedding potpourri in Malaysia. The Thai researchers found that the unmilled, brown fragrant rice had several times as much 2AP as it did after milling into white rice. And aged Indian basmatis had half the 2AP as fresh Thai jasmine. So you can get more intense basmati aroma from the brown rice and from newly harvested rice.


Rice texture: Interestingly, in the Himalayan region where basmati rice is produced, the people prefer their rice aged for several months--which apparently means that they lose some of the flavor for which basmati is prized. By contrast, Japanese consumers prize newly harvested rice, and don't like the cooking qualities of old rice. India and Pakistan prefer the grains to remain separate and firm, while Japan prefers them somewhat sticky and soft. As any rice sits for months, in the warehouse or in the kitchen cabinet, its cooked texture gets progressively firmer and less sticky.

These changes are probably the result of a number of factors, including the breakdown of grain oils into free fatty acids, which form very stable, hard complexes with starch molecules. A Japanese team looked at what happens to rice during storage, and found that normally dissolvable proteins at the rice surface become oxidized and undissolvable. They were able to reverse the increased firmness and decreased stickiness of the cooked texture by adding a chemical reducing agent, sodium sulfite, to the cooking water (to reverse the oxidation), or by abrading away the surface of the aged grain.

So apparently as a rice grain sits in storage, the surface proteins become oxidized, bond to each other, and form a thin skin on the grain, which limits water penetration into the grain, and limits the starch leakage outward that causes stickiness. That's at least part of the cause of the firmer cooked texture in aged rice.

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Sriseadka, T. et al. Rapid method for quantitative analysis of the aroma impact compound, 2-AP, in fragrant rice . . . . J. Agric. Food Chem. 2006, 54, 8183-89.

Ohno, T. and N. Ohisa. Studies on textural and chemical changes in aged rice grains. Food Sci. Technol. Research 2005, 11, 385-89.

Curious Cook in the New York Times: Of mice and wine, and rice

In today's dining section I write about the surprising connection between an obnoxious off-flavor in wines and the prized flavor of aromatic rices.

Check back in a couple of days for more news about rice.

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Snowdon, E. et al. Mousy off-flavor: A review. J. Agric. Food Chem. 2006, 54, 6465-74. http://dx.doi.org/10.1021/jf0528613

Acrylamide: an update

Acrylamide is the industrially useful but toxic chemical that reared its ugly head among our potato chips and fries in 2002, when Swedish food chemists first thought to look for it in foods. Acrylamide is known to cause cancer and other illnesses in animals, and nerve damage in humans. It's suspected to be a human carcinogen as well. Acrylamide concentrations in drinking water are regulated by the Environmental Protection Agency, and the Swedish chemists found food levels hundreds of times higher than the EPA limit.

Since 2002, we've learned a lot about acrylamide in food. It's formed in both food manufacturing and in our kitchens during the heating of carbohydrate-rich foods (potatoes, grains and their products) at temperatures high enough to cause browning and the development of the desirable flavors typical of browned foods (above about 250 degrees F, 120 degrees C). It arises from the reaction of a particular amino acid, asparagine (the major amino acid in potatoes), with glucose and other sugars. Among the foods that contribute most to our daily intake of acrylamide are french fries and potato chips, breakfast cereals, cookies, and coffee. Breads, toast, pies and cakes, and corn snacks are also significant sources. Recently acrylamide was even detected in Japanese green teas, which contain asparagine and are finished by roasting at 250-280 degrees F, 120-140 degrees C.

Food chemists are coming up with a lot of new information about acrylamide levels in foods and ways to minimize them. Here are some recent findings.

A study from Donald Mottram and colleagues at the University of Reading shows that the addition of a little citric acid and the amino acid glycine reduces the acrylamide levels on cooked potatoes without reducing flavor.

Mottram and others have also found that the asparagine content of wheat flours, and their tendency to form acrylamide, depend strongly on the wheat variety, growing conditions, and farming methods. Inadequate sulfur nutrition can increase acrylamide production by a factor of 5. Less refined flours with more of the outer protein-rich aleurone layer produce more acrylamide, as do flours made from sprouted wheat.

Felix Escher and colleagues at the ETH in Zurich have found that during the last stage of potato frying, when the moisture content of the potato falls below 20%, the energy required for acrylamide production increases, while flavor production continues unaffected. This means that acrylamide levels can be minimized by lowering the oil temperature toward the end of the frying process.

What we don't yet know about acrylamide is the actual risk that it poses in our current diet. That bottom-line question is under active investigation by scientists in several countries. The fact that coffee consumption isn't associated with a higher cancer risk suggests to me that other protective factors in food compensate for its presence. But until we know for sure, it's prudent to go easy on fries and packaged snacks.

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Mizukami, Y., et al. Analysis of acrylamide in green tea . . . . J. Agric. Food Chem. 2006, 54, 7370-77.

Low, M.Y. et al. Effect of citric acid and glycine addition on acrylamide and flavor in a potato model system. J. Agric. Food Chem. 2006, 54, 5976-83.

Muttucumaru, N. et al. Formation of high levels of acrylamide during the processing of flour derived from sulfate-deprived wheat. J. Agric. Food Chem. 2006, 54, 8951-55.

Claus, A. et al. Influence of agronomic factors and extraction rate on the acrylamide contents in yeast-leavened breads. J. Agric. Food Chem. 2006, 54, 8968-76.

Amrein, T.M. et al. Influence of thermal processing conditions on acrylamide generation and browning in a potato model system. J. Agric. Food Chem. 2006, 54, 5910-16.