New study of pine nuts leaves mystery of 'pine mouth' unsolved

Ali Reza Fardin-Kia, Sara M. Handy and Jeanne I. Rader note that more than 20,000 tons of pine nuts are produced each year worldwide. "Pine mouth," first reported in Belgium in 2000, is a bitter metallic taste that develops within one to two days of eating pine nuts and can last from one to two weeks. In 2009, the French Food Safety Administration reported a possible link between "pine mouth" and consumption of nuts of Pinus armandii, a pine species whose nuts are not traditionally eaten by humans. Researchers have identified certain fatty acids whose levels vary among pine species, making them a potentially useful tool for telling different species apart. To determine the source of pine nuts sold in the U.S., the first such effort, they measured the ratio of these compounds to the overall amount of fatty acids in the nuts.

Using fatty acid composition and a fatty acid diagnostic index (DI) along with DNA analysis, they found that most pine nuts sold in the U.S. are mixtures of nuts from different pine species, including Pinus armandii. They report that combining the fatty acid DI and DNA analysis is a useful way to determine which samples of pine nuts are mixtures of nuts from several species, but that this information itself may not definitively predict which pine nuts may cause "pine mouth." Its cause remains a mystery.

More information: Characterization of Pine Nuts in the U.S. Market, Including Those Associated with “Pine Mouth”, by GC-FID, J. Agric. Food Chem., 2012, 60 (10), pp 2701–2711. DOI: 10.1021/jf205188m

Abstract
Taste disturbances following consumption of pine nuts, referred to as “pine mouth”, have been reported by consumers in the United States and Europe. Nuts of Pinus armandii have been associated with pine mouth, and a diagnostic index (DI) measuring the content of ?5-unsaturated fatty acids relative to that of their fatty acid precursors has been proposed for identifying nuts from this species. A 100 m SLB-IL 111 GC column was used to improve fatty acid separations, and 45 pine nut samples were analyzed, including pine mouth-associated samples. This study examined the use of a DI for the identification of mixtures of pine nut species and showed the limitation of morphological characteristics for species identification. DI values for many commercial samples did not match those of known reference species, indicating that the majority of pine nuts collected in the U.S. market, including those associated with pine mouth, are mixtures of nuts from different Pinus species.

Provided by American Chemical Society (news : web)

Why do dew drops do what they do on leaves?

In the study, Martin E. R. Shanahan observes that drops of water have a preference for exactly where they collect on leaves as their surfaces cool in the morning and afternoon. Those droplets, which condense from water vapor — moisture — in the air, collect randomly across the surfaces of flat leaves. However, dew drops tend to accumulate at the tips of spindly leaves, even if that means defying gravity by moving upwards. He explains that an inherent "unwillingness" or "lack of necessity" of water drops to move on a dry surface governs their positioning on flat leaves, causing them to stay where they form. Dew's tendency to head to the end of finely pointed leaves, however, sent Shanahan looking for a different explanation.

The answer is based on the fundamental principle of free energy, that everything in nature seeks the lowest possible energy state. Shanahan modeled two types of dew drops on a theoretical (simplified) cone-shaped leaf: a thin, cylindrical sheath of water and a spherical drop centered on the cone's axis. In both cases, he found that the drop lowered its energy by moving toward the point of the leaf.

More information: On the Behavior of Dew Drops, Langmuir, 2011, 27 (24), pp 14919–14922. DOI: 10.1021/la203316k

Abstract
It may be observed that, when dew drops form, although they may be positioned randomly on flat leaves, they tend to accumulate at the pointed ends of thin, slightly conical growths. We discuss here the basic physics leading to this phenomenon.

Provided by American Chemical Society (news : web)

Colorful leaves: New chlorophyll decomposition product found in Norway maple

 Autumn is right around the corner in the northern hemisphere and the leaves are beginning to change color. The cause of this wonderful display of reds, yellows, and oranges is the decomposition of the compound that makes leaves green: chlorophyll.

Bernhard Kräutler and a team at the University of Innsbruck (Austria) have now published a report in the journal Angewandte Chemie about the discovery of a previously unknown chlorophyll decomposition product in the leaves of Norway maples. The different spatial arrangement of its atoms is indicative of a different decomposition pathway than those of other deciduous trees.

During the summer months, green leaves carry out photosynthesis: chlorophyll converts sunlight into chemical energy. In the fall, deciduous trees reabsorb critical nutrients, such as nitrogen and minerals, from their leaves. This releases the chlorophyll from the proteins that normally bind it. However, chlorophyll is phototoxic in this free from, and can damage the tree when exposed to light. It must therefore be “detoxified” by decomposition.

“Essential pieces of the puzzle of this biological phenomenon have been solved only within the last two decades,” reports Kräutler. Various colorless tetrapyrroles, molecules with a framework of four nitrogen-containing five-membered carbon rings, accumulate in the dying leaves of higher plants, and have been classified as decomposition products of chlorophyll. These are called “nonfluorescent” chlorophyll catabolytes (NCCs). Says Kräutler, “ they are considered to be the final breakdown products of a well-controlled, “linear” and widely common decomposition pathway.” This premise is beginning to get a little shaky.

Kräutler and his co-workers have studied the decomposition of chlorophyll in the Norway maple, a tree native to Eurasia. “We found none of the typical breakdown products in yellow-green or yellow Norway maple leaves,” says Kräuter. “Instead, the main product we found was a dioxobilane, which resembles a chlorophyll breakdown product found in barley leaves.”

However, there are small but important differences in the spatial arrangements of the atoms relative to each other. There is no plausible decomposition pathway that starts with the NCCs and leads to this new decomposition product. “There is clearly a chlorophyll breakdown pathway occurring in Norway maple leaves that differs from those previously known.”

The structure of this newly discovered dioxobilane is reminiscent of bile pigments, which are products of the breakdown of heme, and thus are important constituents of mammalian metabolisms as well as acting as light sensors in plants. “This supports the idea that chlorophyll breakdown is not only a detoxification process; the resulting decomposition products can also play a physiological role,” states Kräuter. “Chlorophyll breakdown products can act as antioxidants in the peel of ripening fruits, making the fruits less perishable. What role they play in leaves is not yet clear.”

More information: A Dioxobilane as Product of a Divergent Path of Chlorophyll Breakdown in Norway Maple, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.201103934

Provided by Wiley (news : web)