What's really in that luscious chocolate aroma?

The mouth-watering aroma of roasted cocoa beans — key ingredient for chocolate — emerges from substances that individually smell like potato chips, cooked meat, peaches, raw beef fat, cooked cabbage, human sweat, earth, cucumber, honey and an improbable palate of other distinctly un-cocoa-like aromas.

That's among the discoveries emerging from an effort to identify the essential aroma and taste ingredients in the world's favorite treat, described here today at the 242nd National Meeting & Exposition of the American Chemical Society (ACS). The research, which chronicles flavor substances from processing of cocoa beans to melting in the mouth, could lead to a new genre of "designer chocolates" with never-before-experienced tastes and aromas, according to Peter Schieberle, Ph.D.

"To develop better chocolate, you need to know the chemistry behind the aroma and taste substances in cocoa and other ingredients," said Schieberle. A pioneer in revealing those secrets, Schieberle received the 2011 ACS Award for the Advancement of Application of Agricultural and Food Chemistry at the meeting. "That understanding must begin with the flavor substances in the raw cocoa bean, extend through all the processing steps and continue as the consumer eats the chocolate.

"When you put chocolate in your mouth, a chemical reaction happens," explained Schieberle. "Some people just bite and swallow chocolate. If you do that, the reaction doesn't have time to happen, and you lose a lot of flavor."

Chocolate is made from cacao (or cocoa) beans, the seeds of cacao trees. Raw cocoa beans have an intense, bitter taste and must be processed to bring out their characteristic flavor. Processing starts with fermentation, in which the moist seeds sit for days in baskets covered with banana leaves while yeasts and bacteria grow on the beans and alter their nature. The beans are dried in the sun and then roasted. Much of the chocolate used in baking, ice cream and hot cocoa undergoes "Dutch processing," which gives it a milder taste. Worldwide, about 3 million tons of cocoa are produced each year.

Cocoa production developed over the years by trial and error, not by scientific analysis, so the substances that give chocolate its subtle flavors were largely unknown, said Schieberle. He is a professor at the Institute for Food Chemistry at the Technical University of Munich, Germany. Over the past 20 years, his team has uncovered many secrets of chocolate's allure.

The distinctive chocolate flavor evolves throughout its production. Odorless, tasteless "precursors" form during fermentation, and these precursors react during roasting to form taste and aroma compounds. The flavors of chocolate and other foods come not just from taste buds in the mouth, Schieberle noted. Odor receptors in the nose play an important role in the perception of aroma. Schieberle and colleagues identified various substances present in cocoa for aromas that bind to human odor receptors in the nose. They mimicked the overall chocolate flavor in so-called "recombinates" containing those ingredients, and taste testers couldn't tell the difference when they sampled some of those concoctions. Individually, those substances had aromas of potato chips, peaches, cooked meat and other un-chocolatey foods.

"To make a very good cocoa aroma, you need only 25 of the nearly 600 volatile compounds present in the beans," said Schieberle. "We call this type of large-scale sensory study 'sensomics.'" Sensomics involves compiling a profile of the key chemical players responsible for giving specific foods their distinctive taste and aroma.

Because no individual compound was identified bearing the typical aroma of cocoa, the researchers had to pick apart individual aromas and put them back together for taste testers to experience. This is a crucial step toward determining how aroma substances work together to stimulate human odor and taste receptors to finally generate the overall perception of chocolate in the brain.

Some of Schieberle's research also uncovered a way to improve the taste of chocolate. The group found that by adding a little bit of sugar to the cocoa before Dutch processing, the chocolate becomes even milder and more velvety due to the formation of previously unknown taste components.

Schieberle's data could help manufacturers control and improve the flavor of cocoa products by assessing these key components in their mixtures.

Provided by American Chemical Society (news : web)

Discovery could create retinas from 'Jell-O'

Researchers at the University of Toronto have developed a new method for creating 3D hydrogel scaffolds that will aid in the development of new tissue and organs grown in a lab.

The discovery is outlined in the latest issue of Nature Materials. Watch a video below.

Hydrogels, a “Jell-O”-like substance, are highly flexible and absorbent networks of polymer strings that are frequently used in tissue engineering to act as a scaffold to aid cellular growth and development.

The paper demonstrates for the first time that it is possible to immobilize different proteins simultaneously using a hydrogel. This is critical for controlling the determination of stem cells, which are used to engineer new tissue or organs.

“We know that proteins are very important to define cell function and cell fate. So working with stem cells derived from the brain or retina we have demonstrated we can spatially immobilize proteins that will influence their differentiation in a three-dimensional environment,” explained Professor Molly Shoichet of the Department of Chemical Engineering & Applied Chemistry, the Institute for Biomaterials & Biomedical Engineering and the Department of Chemistry.

Immobilizing proteins maintains their bioactivity, which had previously been difficult to ensure. It is also important to maintain spacial control as the tissue and organs are three-dimensional. Therefore, being able to control cell fate and understanding how cells interact across three dimensions is critical.

“If we think about the retina, the retina is divided into seven layers. And if you start with a retinal stem cell, it has the potential to become all of those different cell types. So what we are doing is immobilizing a protein which will cause their differentiation into photoreceptors or bipolar neurons or other cell types that would make up those seven different cell types,” said Shoichet.

The end result is a new hydrogel that can guide stem cell development in three-dimensions.

Shoichet identifies two long-term outcomes from this discovery.

“We could use... it as a platform technology to look at the interaction of different cells and build tissues and organ,” Shoichet stated, while also noting that it could help lead to a more fundamental understanding of cellular interaction. “By growing cells in a 3D environment, similar to how they grow in our body, we can develop a better understanding of cell processes and interactions.”

The research was led by Shoichet and was conducted by Ryan G. Wylie, Shoeb Ahsan, Yukie Aizawa, Karen L. Maxwell and Cindi M. Morshead.

Provided by University of Toronto (news : web)

Flexible electronics hold promise for consumer applications

New research from Wake Forest University has advanced the field of plastic-based flexible electronics by developing, for the first time, an extremely large molecule that is stable, possesses excellent electrical properties, and inexpensive to produce.

The technology, developed by Oana Jurchescu, assistant professor of physics at Wake Forest, her graduate students Katelyn Goetz and Jeremy Ward, and interdisciplinary collaborators from Stanford University, Imperial College (London), University of Kentucky and Appalachian State University, eventually may turn scientific wonders – including artificial skin, smart bandages, flexible displays, smart windshields, wearable electronics and electronic wallpapers – into everyday realities.

Jurchescu says plastic or organic semiconductors, produced in large volume using roll-to-roll processing, inkjet printing or spray deposition, represent the "electronics everywhere" trend of the future.

In the current consumer market, however, the word "electronic" is generally associated with the word "expensive." This is largely because products such as televisions, computers and cell phones are based on silicon, which is costly to produce. Organic electronics, however, build on carbon-based (plastic) materials, which offer not only ease of manufacturing and low cost, but also lightweight and mechanical flexibility, says Jurchescu.

The team recently published its manuscript in Advanced Materials, one of the most prestigious journals in the field of materials research.

Prior researchers predicted that larger carbon frameworks would have properties superior to their smaller counterparts, but until now there has not been an effective route to make these larger frameworks stable and soluble enough for study.

"To accelerate the use of these technologies, we need to improve our understanding of how they work," Jurchescu says. "The devices we study (field-effect transistors) are the fundamental building blocks in all modern-based electronics. Our findings shed light on the effect of the structure of the molecules on their electrical performance, and pave the way towards a design of improved materials for high-performance, low-cost, plastic-based electronics."

Jurchescu's lab is part of the physics department and the Center for Nanotechnology and Molecular Materials.

The team studied new organic semiconductor materials amenable to transistor applications and explored their structure-property relationships. Organic semiconductors are a type of plastic material characterized by a specific structure that makes them conductive. In modern electronics, a circuit uses transistors to control the current between various regions of the circuit.

The results of the published research may lead to significant technological improvements as the performance of the transistor determines the switching speed, contrast details, and other key properties of the display.

 

Scientists trace gecko footprint, find clue to glue

Geckos' ability to scamper up walls with ease has long inspired scientists who study the fine keratin hairs on these creatures' footpads, believed responsible for the adhesion. Researchers at The University of Akron have discovered that geckos' ability to adhere to surfaces is not all about keratin. Clues lie in the lipids left behind in gecko footprints.

This discovery by researchers Ping Yuan Hsu and Liehui Ge, both UA polymer science graduate students; Alyssa Stark, UA integrated bioscience graduate student; Xiaopeng Li, chemistry research scientist; Chrys Wesdemiotis, distinguished professor ofchemistry; Peter Niewiarowski, interim director, UA Integrated Bioscience, Ph.D. Program; and Ali Dhinojwala, chair of the UA Department of Polymer Science, is published in Interface, the Journal of the Royal Society under the title: Direct evidence of phospholipids in gecko footprints and spatula–substrate contact interface detected using surface-sensitive spectroscopy.

The researchers' analysis of the near-invisible gecko footprints reveals the presence of phospholipids, according to Dhinojwala. This material, he says, has not been considered in current models of gecko adhesion and now provides the missing link in understanding superhydrophobicity, self-cleaning and fluid-like adhesion and release of gecko feet.

Dhinojwala, a pioneer in gecko-inspired adhesive research, says the lipids in gecko footprints have significant implications for scientists working to design synthetic adhesives that could be reused thousands of times over, such as for wall-climbing robots, microelectronics, adhesive tapes and bioadhesives.

More information: Direct evidence of phospholipids in gecko footprints and spatula–substrate contact interface detected using surface-sensitive spectroscopy, J. R. Soc. Interface, Published online before print August 24, 2011, doi: 10.1098/?rsif.2011.0370

Abstract
Observers ranging from Aristotle to young children have long marvelled at the ability of geckos to cling to walls and ceilings. Detailed studies have revealed that geckos are ‘sticky’ without the use of glue or suction devices. Instead, a gecko's stickiness derives from van der Waals interactions between proteinaceous hairs called setae and substrate. Here, we present surprising evidence that although geckos do not use glue, a residue is transferred on surfaces as they walk—geckos leave footprints. Using matrix-free nano-assisted laser desorption-ionization mass spectrometry, we identified the residue as phospholipids with phosphocholine head groups. Moreover, interface-sensitive sum-frequency generation spectroscopy revealed predominantly hydrophobic methyl and methylene groups and the complete absence of water at the contact interface between a gecko toe pad and the substrate. The presence of lipids has never been considered in current models of gecko adhesion. Our analysis of gecko footprints and the toe pad–substrate interface has significant consequences for models of gecko adhesion and by extension, the design of synthetic mimics.

Provided by University of Akron