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of food, to verify products with protected labels such as Parma ham or Champagne, or to justify hopes for a new label. The first step, according to Sforza, is to track down unique DNA sequences for the plant, animal, or microbe you want to detect. The current gold-standard technique for detecting these DNA sequences in food is to employ the polymerase chain reaction. Using PCR, scientists try to amplify sequences of suspect DNA in food to discern contaminants or substitutions. Although PCR is widely used in the food industry, the technique is not always perfect. “Real-time PCR can quantitate a few molecules of DNA in optimal conditions, but food is basically anything but optimal,” Sforza says. Besides the difficulty of dealing with tricky, diverse matrices (think tomato sauce, chocolate, or biscuits), some constituents in food such as polyphenols or calcium can inhibit the enzymes required for PCR. Also, food processing wreaks havoc with the DNA present in food, so the fingerprint sequences of suspect ingredients can be present in extremely low quality and quantity. Because of all these challenges, PCR analysis of food can lead to both false positives and negatives. So Sforza and his Parma coworkers Rosangela Marchelli and Roberto Corradini decided to apply peptide nucleic acids (PNAs)—which are more commonly studied for medical applications—for use in the food industry. Their hope is to exploit the ability of PNAs to hybridize with DNA as an additional tool to support and complement the results obtained by PCR.
PRECIOUS PRODUCTS
Olive oil is in such high demand that some products are fraudulent.
AUTHENTICATING FOOD Researchers are developing PEPTIDE NUCLEIC ACIDS as a way to detect DNA in food SARAH EVERTS, C&EN BERLIN
OLIVE OIL is serious business in Italy.
Although people outside the country may consider a preference for extra-virgin olive oil as evidence of a refined palate, locals take things a step further, discussing the relative merits of olive cultivars such as Canino or Ogliarola, which differ in some genes by only a few base pairs. Then there’s the financial side of things: Because olive oil can sell at a high price, the country, and indeed all of Europe, battles olive oil fraud. In the late ’90s, adulteration of olive oil with hazelnut, soybean, and other oil became such an issue that the European Union set up an antifraud task force to examine the problem. To catch adulterant ingredients or to
authenticate upscale products, one of the best strategies is to look for the presence of DNA from an unwelcome additive—such as hazelnut or a low-quality olive varietal, says Stefano Sforza, an organic and food chemist at the University of Parma. There is a bounty of other reasons that scientists such as Sforza want to search for DNA in food: These studies can reveal the presence of bacterial contaminants and allergens, such as nuts or seafood. Or they can disclose the use of genetically modified organisms (GMOs), the commercial use of which is a touchy issue in Europe. Increasingly, food scientists are also being asked to use genetic sequences to help authenticate the geographical provenance
PNAS ARE HYBRIDS between DNA and proteins. Like DNA, PNAs have a primary backbone bearing purine and pyrimidine bases that can hydrogen bond with complementary bases. However, instead of the deoxyribose backbone of DNA, PNAs have a pseudopeptide backbone. The main benefit of PNAs is that they bind DNA tighter than DNA can bind itself, Sforza explains. This is because neutral or positively charged PNAs sidestep the electrostatic repulsion between two strands of negatively charged DNA. As such, short sequences of eight to 12 PNA base pairs can more selectively and sensitively bind DNA than say, the 15- to 20-base-pair WWW.C EN-ONLINE .ORG
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H2N
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HN Base Base Base get “wild and crazy” about authen“primer” sequences required for PCR. tication for their local products. In particular, the team has found O O O O O O Take tomatoes, he says. Some Italian that making its PNAs chiral and N N N varietals, such as San Marzano, sell positively charged improves DNA seN N N H H H at higher prices, even in their canned lectivity and affinity, which improves form, because the tomatoes are recognition in difficult matrices DNA GRABBER Posithought to have an appealing bittersuch as food. To observe the PNA tively charged PNAs, such sweet taste. and DNA pairs, the Parma team has + as this arginine-derivatized Although production of appealemployed a variety of detection techNH2 H2N one, bind DNA selectively ing tastes and aromas is sometimes niques, such as high-performance and sensitively. more influenced by the weather durliquid chromatography, surface plasing a particular growing season than mon resonance, and microarrays, slight genetic differences among closely Still, the PNA technique seems “like a in combination with PNAs that fluoresce related varieties, people want a way to “uppromising tool” to develop for eventual when bound to DNA. grade a tomato” if they can, Battaglia says. quantitative analysis of DNA in food, says In proof-of-principle studies using these Sforza agrees that “DNA is only part of Josef Schlatter, the head of the Nutritional techniques, they’ve been able to detect the story” and that genetic markers used to & Toxicological Risks Section at the Swiss femtomoles of hazelnut DNA in olive oil— identify a food’s geographical origin, and Federal Office of Public Health. which corresponds to a 5% hazelnut adultherefore its authenticity, may not relate The PNA approach is already gaining teration. They have also been able to detect to flavor molecules produced during the traction in the Italian food industry, Sforza half a dozen GMO genes in maize and soygrowing season. But, he says, “I feel my says. For example, his team is working on beans and the joint presence of allergenic work is to provide the consumer with tools the authentication of olive and tomato varipeanut and hazelnut DNA in cereal snacks. that give confidence that products labeled etals perceived to have singular and excepAlthough the PNAs can bind suspect as San Marzano-varietal tomatoes are in tional flavors. sequences of DNA in food better than PCR fact San Marzano, or that Canino-varietal According to Reto Battaglia, a chemist primers, PNA-DNA hybrids have provided olive oil is in fact Canino. Consumers can and food safety consultant based in Gossimilar levels of signal as PCR in only a few decide whether they like the taste.” ■ sau, Switzerland, some people in Europe applications, Sforza says. HN
13th Annual Green Chemistry & Engineering Conference JUNE 23–25, 2009
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COLLEGE PARK, MD
Sustainability is a complex economic, environmental, and social challenge. This year’s 13th Annual Green Chemistry & Engineering Conference will highlight progress being made in response to the 2006 National Academy of Sciences report, “Sustainability in the Chemical Industry: Grand Challenges and Research Needs.” Moving towards sustainability within the chemical enterprise will require: Q Q Q
Strategic connections between scientific research, technological development, and society; Creative design of products, processes, systems, and organizations; and Implementation of smart management strategies that effectively harness technology and ideas to avoid environmental problems before they arise.
These issues and others will be discussed at the 13th Annual Green Chemistry & Engineering Conference, June 23–25, 2009.
Abstract submission is only open until February 13. Visit www.GCandE.org for more information on tracks and how to submit. Be sure to get your submission in right away. Registration and housing are also open.
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