scierice/t#^ii|i^(^^H m^

EATING SAFELY IN A DIRTY WORLD Science battles foodborne pathogens and speeds up bacterial detection methods

Sophie L. Wilkinson C&EN Washington

I t's a wonder we all don't get sick more often. After all, food safety is far more complex than simply remem­

bering to clean the kitchen counter after you prepare your Thanksgiving turkey.

Contaminants can creep into the food supply at many different points. They can get in early on, as with veterinary drugs or sewage and toxins picked up from water by seafood. Produce may carry pesticides or naturally occurring toxicants such as so-

lanine in potatoes. Food can be contaminat­ed during transit—if a truck isn't cleaned properly between loads, for example. Food handlers and equipment all along the chain can introduce contaminants, ranging from hair to metal filings to bacteria. And con­sumers themselves may not cook or store the food appropriately to limit the growth of or to kill microorganisms.

Ensuring food safety requires vigilance on many fronts, from pork to seafood and from dairy products to produce.

Of all these possible sources of food contamination, microorganisms are "gen­erally recognized to be the biggest prob­lem," says Myron Solberg, director of the Center for Advanced Food Technology and professor of food science at Rutgers University, New Brunswick, N.J. At least 90% of reported outbreaks of food-related illness are associated with microorgan­isms, notes Michael P. Doyle, director of the Center for Food Safety & Quality En­hancement, University of Georgia, Griffin.

Each year, millions of Americans are hit with such illnesses. Symptoms can show up anywhere from 12 hours to 10 days af­ter exposure. And as many as 9,000 vic­tims die, according to the Council for Ag­ricultural Science & Technology, Ames, Iowa.

The Department of Agriculture at­tributes over half the illnesses and deaths to contaminated meat and poultry. Medical ex­penses and productivity losses resulting from the impact of just seven pathogens in food may total anywhere from $7 billion to $35 billion annually, USDA estimates. The Centers for Disease Control & Prevention (CDQ considers Escherichia coli 0157:H7, Salmonella, Listeria monocytogenes, and Campylobacter jejuni to be of greatest con­cern because of the severity and number of illnesses they cause.

The risk of foodborne illness has grown over the past 20 years because of both pathogenic and demographic chang­es, according to the General Accounting Office. The number of potential victims in high-risk groups—the elderly, children, and people with suppressed immune sys­

tems—is increasing. Large-scale food pro­duction and distri­bution can spread illness to a great number of people. New, more-resis­tant, and more-viru­lent strains of bacte­ria are emerging. And they're showing up in foods that pre­viously were consid­ered safe, such as to­matoes and orange juice.

The Food & Drug Administrat ion, USDA, the Environ­mental Protection Agency, and CDC— the agencies charged with verifying that industry is fulfilling

24 NOVEMBER 10, 1997 C&EN

Some microbial pathogens and their role in foodborne illness

Pathogen

Bacteria

Salmonella

Campylobacter

Escherichia coli 0157: H7

Vibrio

Protozoa

Toxoplasma gondii

Cryptosporidium parvum

Viruses

Norwalk

Hepatitis A

Sources

Eggs, poultry, meat, dairy products, seafood, fresh produce

Raw or undercooked chicken, unpasteurized milk, untreated water

Ground beef, raw milk, lettuce, fruit juice

Seafood

Raw or undercooked meat, unwashed fruits and vegetables, cat feces

Water, apple cider, manure

Water, salads, frosting, shellfish, person-to-person contact

Person-to-person (fecal-oral) contact, shellfish, lettuce, frozen raspberries and strawberries

Symptoms

Diarrhea, reactive arthritis, systemic infections, death

Acute infectious diarrhea, death

Hemorrhagic colitis, kidney failure, death

Diarrhea, abdominal pain, death

None, or diarrhea, mental retardation, death

Diarrhea, death

Gastrointestinal disease with overwhelming diarrhea

Hepatitis A (which may include fever, malaise, nausea, abdominal discomfort, jaundice, and death)

Notes

About 800,000 to 4 million people are infected each year. In one outbreak in 1994, 224,000 people became ill from eating ice cream.

Is the most frequently identified cause of acute infectious diarrhea in developed countries; 2 million to 4 million cases occur each year, with 120 to 360 deaths.

Causes 25,000 cases each year, and as many as 100 deaths; in a 1996 incident, sickened 66 people and killed one person in three western states and British Columbia; 25 million lb of ground beef were recalled in a 1997 incident after about 20 people became sick.

V. vulnificus kills half of those it infects, many of whom already have an underlying illness, such as liver disorders.

About 1.4 million cases and 310 deaths occur each year. May kill or cause birth defects in fetuses.

In 1993, a Milwaukee outbreak affected more than 400,000 people. The first large outbreak associated with food resulted from fresh apple cider in 1993.

Approximately 181,000 people are affected each year. Many cases associated with oysters are believed to have been caused by sewage dumping by boaters.

Strawberries served in a school lunch program led to an outbreak in 1997; only 5% or less of reported U.S. hepatitis A cases are believed to be due to food.

Note: All figures are for the U.S. only. Source: "Food Safety from Farm to Table: A National Food Safety Intiative," FDA, USDA, EPA, CDC, May 1997.

its food safety responsibilities—note in their May 1997 report, "Food Safety from Farm to Table: A National Food Safety Ini­tiative," that limited knowledge and re­sources are hampering the battle against such food-related illnesses. The agencies are taking a number of steps to improve food safety, including:

• Development of a system to detect and respond to outbreaks of illness early and to generate data to prevent future outbreaks.

• Improvement of methods to assess risks from particular foodborne hazards to assist in allocating resources.

• Development of fast, cost-effective tests for pathogens in food; research into how the pathogens develop resistance; and new methods to control them.

• Better inspections. Despite these intentions, thorough gov­

ernment oversight is impossible. FDA-regulated plants, for example, are visited on average just once every 10 years. That

compares with a visit rate of once every two or three years in 1981.

As a result, much of the responsibility for improving food safety must be borne by industry, notes liSDA's Parthapratim (Pat) Basu. director of the Chemistry & Toxicology Division, Office of Public Health & Science, Food Safety & Inspec­tion Service. One tool that will be increas­ingly used is the Hazard Analysis & Critical Control Point (HACCP) system, in which the entire production process for a partic­ular food category is analyzed for potential safety hazards. The food industry will be required to take preventive measures to control microbial, chemical, and physical hazards revealed in these analyses and to initiate monitoring procedures.

Ensuring safe handling The program will attempt to "identify

those places in production, storage, and delivery of food at which something could happen, Solberg says, "and to try

to set up procedures that will make sure that those areas are areas where things don't happen." Examples include food kept at the wrong temperature or con­taminated by contact with other food or surfaces that food had been on.

HACCP regulatory programs, which be­come effective late this year for seafood, will be phased in for meat and poultry over the next three years. Proposals for fruit and vegetable juices and eggs and egg products will follow in the next few months. When President Bill Clinton an­nounced the new meat and poultry rules in 1996, USDA said they would "replace a system based on sight and smell with more scientific methods and will, for the first time, require plants that slaughter and process meat and poultry to target and re­duce harmful bacteria on their products."

Of course, the key to detecting a par­ticular microorganism in food is to real­ize that it could cause disease in humans in the first place. Campylobacter is a

NOVEMBER 10, 1997 C&EN 2 5

Testing for pathogens speeds up, aims for instantaneous results

While progress continues in microbial abatement, researchers are also fighting the antibacterial battle with advances in pathogen detection.

Unfortunately, food testing is a statisti­cal "game" that can never be completely thorough, warns Wafa Birbari, director of analytical microbiology and director of product development at ABC Research, Gainesville, Fla. ABC provides analytical and technical services to the food indus­try. "In any test for microbiology, there are no 100% guarantees. No matter what you do, there still are going to be some samples or food products that will be positive" even though they test negative, she explains. After all, "what are you go­ing to eat if you test the whole thing?"

Another frustration with food testing is its time requirements. "Everybody wants results yesterday, [practically] before they have the samples in," Birbari says. Meat products, for example, have to wait for the all-clear before they can be shipped.

Tests for Salmonella, Escherichia coli 0157:H7, and other microorganisms used to take five to seven days, says Daniel Y. C. Fung, professor of food sci­ence and microbiology at Kansas State University, Manhattan. Those tests took several days just to isolate and grow the necessary amount of the relevant bacte­ria in broth and on agar plates. The bac­teria's identity could then be narrowed down by allowing it to interact with a number of different types of antibodies to pinpoint whether it was, say, E. coli 0157 or Salmonella, Fung says.

By improving the bacterial amplifica­tion techniques and the specificity of the antibodies, the time requirement for some of these tests has been shrunk to just a day or so, Fung says. "And now," he says, "we are trying to move this to eight hours." The good news is that these tests can be used to quickly con­firm the absence of a particular patho­gen. But "if you have a positive [test], you still have to go through the conven­tional methods to identify" the microbe.

Myron Solberg, director of the Center for Advanced Food Technology and pro­fessor of food science at Rutgers Universi­ty, New Brunswick, N.J., says the ultimate goal for researchers is on-line detection of potentially hazardous microorgan­isms. But Fung predicts that "it will be an­other 10 years before you can instanta­neously detect an E. coli in 25 g" of food.

Solberg says there are "many con­founding issues" impeding such rapid tests. For one, microbes are usually present in small numbers, "and the food material, which is as organic as the mi­crobes, gets in the way."

In addition, food often contains a lot of other bacteria in addition to the harmful organisms. "There can be thousands to millions of other bacteria per gram present," notes the University of Geor­gia's Michael P. Doyle, director of the Center for Food Safety & Quality En­hancement in Griffin. "To detect very small populations of a target organism like 0157," the target population has to be selectively enhanced, typically up to about 100,000 organisms. The desired population can be boosted in enrichment cultures that use selective agents to sup­press growth of the other bacteria. Or an­tibodies against a particular bacteria can be put on immunomagnetic beads and placed into a liquid sample containing the suspected pathogen. A magnet can then be used to separate the beads from the solution, and the beads are then placed on agar to grow the population of the captured bacteria. Fung says this con­centration technique can save a whole day in incubation.

Several techniques can be used to de­tect the pathogen once it has been am­plified to a sufficient level, including ELISA (enzyme-linked immunosorbent assay). Another popular technique in­volves the polymerase chain reaction (PCR) used to amplify the DNA of a con­taminating microorganism to a level at which it can be detected. DuPont's Qual-icon subsidiary, based in Wilmington,

Del., says it developed the first commer­cial products to use PCR to screen for specific pathogens in food and environ­mental samples. Its BAX systems take about a day to test for Salmonella, E. coli 0157:H7, or Listeria monocytogenes.

The government plans to encourage ef­forts to develop DNA-amplification-based tests for bacteria that are hard to detect by culture. Because each strain of bacteria has a specific genetic fingerprint, govern­ment agencies will also work on a nation­al electronic database of DNA fingerprint patterns of bacterial pathogens. The gov­ernment's recent food safety report says this database would, for example, "per­mit rapid recognition that an E coli 0157:H7 bacterium cultured from a pa­tient in Washington was indistinguishable from one isolated from another patient in California. That [information] might sug­gest to public-health investigators that a product distributed in California and Washington was contaminated with the same organism."

Qualicon markets the automated Ri-boPrinter system, which generates such genetic fingerprints to identify the sub­species and pinpoint the source of an organism. Starting with a pure culture of the organism of interest, the ribotyp-ing can be done in about eight hours.

Such sophisticated analyses are not al­ways necessary, however. So-called indi­cator organisms can be used as a flag of contamination, without the need to spe­cifically identify the particular microbe involved. "Generic E. coif tests fall into this category. "If you can find an E coli, regardless of what E. coli, then there must be some fecal contamination in the environment or food, and it is not clean enough," Fung explains.

Even simpler is the adenosine triphos­phate (ATP) test, which a number of firms produce. Counter surfaces—in a food preparation facility, for example— can be swabbed after they have been cleaned and then checked in an easy 10-minute test for the presence of ATP, Fung

good example. It was recognized for de­cades to be an animal pathogen, but it wasn't until 1978 that the connection was made between the microbe and hu­man diarrheal illness, Doyle says.

On the other hand, some microorgan­isms are simply late bloomers. Doyle says E. coli 0157 was first recognized as a hu­man pathogen in 1982. It may have start­ed out in a less virulent form, simply causing mild diarrhea. But he says it may then have been hijacked by a Shigella

gene that codes for shiga toxin, turning it into a much fiercer organism.

CDC estimates that E. coli 0157 causes just 20,000 cases of illness a y e a r -compared with more than 2 million for Salmonella and Campylobacter—but "the severity of symptoms puts 0157 in a category of its own," Doyle stresses. Many cases start out with severe abdominal cramping, which men compare to an ap­pendicitis attack and women to labor pains, he says. Victims then get bloody di­

arrhea, and in about 10% of cases, kidney failure. Many will have to have blood transfusions and dialysis. And some will lapse into a coma and die.

The organism is "rewriting the rule book of food microbiologists from several different perspectives," Doyle continues. "One is that it has an unusual tolerance to acid. Highly acidic foods that we've recog­nized for many years to be safe from most foodborne pathogens—like fermented sau­sage and apple juice—are now considered

2 6 NOVEMBER 10, 1997 C&EN

s c i e n c e / t e c h n o l o g y

says. The swab is put in a chamber with a test unit containing an enzyme that gives off light if ATP is present Although "the test wi l l n o t tell y o u what is o n your counter," it will indicate the presence of "some biological material," Fung says. If so, the counter is cleaned again and re-tested. Once the test comes back negative, "you a s s u m e there are n o o r g a n i s m s there that can cause harm to humans."

Quick and s imple tests wou ld be wel­c o m e d o w n o n the farm as well . An easy assay would, for instance, be useful to find and isolate infected animals. "Stud­ies suggest about 2% of feed-lot cattle and 3 % of dairy calves" are infected wi th E. coli 0 1 5 7 , Doyle says. "It m a y be helpful to identify those animals that are shedding [the organism] s o w e can h o l d those back and treat t h e m before t h e y g o off to market." On the o ther hand, this test would be useless with, say, a flock of chickens, because "90 to 100% of a flock is often contaminated with Campylobacter."

D o y l e is w o r k i n g o n d e v e l o p i n g a rapid test for cattle that could be used o n the farm, though further testing is n e e d e d to d e t e r m i n e t h e n u m b e r o f false positive or negative results that it wou ld generate. The assay is based o n a two-minute serum agglutination test, in w h i c h serum from an animal's b lood is c o m b i n e d w i t h a reagent . If c l u m p s form, ant ibod ie s to E. coli 0 1 5 7 are present in the blood.

E. coli and Listeria are getting a lot o f attention, but Birbari notes that para­sites such as Cyclospora, Cryptosporid­ium, and Giardia are also the target o f c o n s i d e r a b l e r e s e a r c h . T h e s e smal l , one-ce l led organ i sms are hard to iso­late, and their infectious dose is low, s o "it's very hard to find them," s h e says. In severa l o u t b r e a k s o v e r t h e pas t f e w years involving foods such as berries, the microorganisms themse lves could not be found in the food. But their pres­ence was indicated by epidemiological evaluations, Birbari says.

to be potentially hazardous if we don't give them a heat treatment or other treat­ment to control 0157. This organism can survive for weeks or months in these types of foods, depending on temperature."

Perhaps even worse, "this organism ap­pears to have a low infectious dose . . . [fewer] than 10 cells can cause illness," says Doyle. In the investigation following the 1992-93 outbreak associated with Jack in the Box hamburgers in the west­ern U.S., the "highest population we found in any contaminated lot was 15 E. coli 0157 per g."

This low-dose characteristic may be tied to 0 1 5 7 s tolerance to acid "because the acidity of the stomach is one of the first lines of defense that we have to pre­vent foodborne infection," Doyle ex­plains. It also means 0157 is "easily transmitted," and unlike certain patho­gens such as Listeria, "it's not uniquely specific for high-risk populations. 0157 can cause illness in most people."

Like many pathogens, however, prop­er care can vanquish this bacteria. "As long as you cook your hamburgers and use pasteurized apple juice," you're safe, Doyle says. Solberg agrees: "The wonder­ful thing that has kept us all as healthy as we are is that heat destroys most of these bacteria," he says.

In fact, many cases of food-related ill­ness could easily be prevented if the public and food handlers were better ed­ucated about protective measures, such as thoroughly washing hands and cook­ing foods to proper temperatures. But the battle against microbes must be fought on numerous fronts, so other pre­ventive measures are being developed.

Significant improvements have been a long time in coming, according to Ken Lee, department chairman and professor of food science and technology at Ohio State University, Columbus. Not since the Napoleonic era has there been "a major advance in the way we keep food safe." Lee is referring to Nicolas Appert's discov­ery that food could be preserved by heat­ing it in a sealed glass bottle, which led to the development of the canning industry. In 1810, Appert, a Parisian con­fectioner and chef, won 12,000 francs for the discovery from Na­poleon, who was interested in techniques that could improve the way he conserved food for transport to his army.

Now, says Lee, "we are on the verge of another breakthrough. And, ironically, it's partly funded by the same [segment] of soci­ety." The Department of Defense "is looking for ways to give their troops the highest quality food possible, because they have fig­ured out that the morale of their troops is related to what they eat," he says.

One way to keep food at its most palatable is to ininimize the impact of antipathogen treat­ments on the food itself. Several of the techniques under develop­ment ieave foods in their fresh, natural, wholesome state, yet still

remove any pathogens or spoilage bacte­ria," Lee says. "We have a revolution under way, in that we no longer will have to cook foods to keep them safe."

Keeping the pathogens at bay The diversity among food "safening"

techniques is impressive. Improvements can be made all along the chain—even be­fore food becomes food, so to speak. Cattle, for example, are "largely identified as the vehicle of 0157, and hamburger, raw milk, and cattle by-products have been associated with many outbreaks," Doyle says. He and his colleagues found that 0157 grows in the stomachs of infected cattle. The bacteria are then shed into the intestinal tract and ulti­mately excreted. Doyle notes that several in­cidents of human infection have been linked to direct or indirect exposure to cat­tle feces, including via runoff from feed lots (which could infect swimmers in a con­taminated lake) or manure used as fertiliz­er (which could contaminate crops).

Doyle and his fellow researchers have come up with a "competitive inhibition" method that could be used to rid infected cattle of 0157 or to prevent infection in the first place. They isolated several strains of nonpathogenic bacteria from cattle that were naturally free of 0157. These good bacteria, which also are E coli but which produce metabolites that inhibit or kill E coli 0157, can then be fed to calves as a prophylactic or treatment. In a trial with in­fected calves, the benevolent E coli "elimi­nated 0157 within two to three weeks in most of the animals we tested," Doyle says.

USD A inspector checks temperature of chicken carcasses at various control points to compare them with those recorded by the plant to prevent the multiplication of pathogenic bacteria.

NOVEMBER 10, 1997 C&EN 27

science/tei^^^H Likewise, the Institute of Food Technol­

ogists (JFT), Chicago, reports that lactic acid bacteria (LAB) can be used to inhibit the growth of pathogens on minimally pro­cessed, refrigerated fruits and vegetables. This technique could potentially be used to prevent the growth of Salmonella, Shigella, E. coli, Staphylococcus aureus, and other rnicroorganisms on peeled, sliced, grated, or shredded produce.

The lactobacilli generate metabolites including lactic and acetic acids that boost acidity, making the food a less hos­pitable environment for the pathogens. Other inhibitory metabolites include hy­drogen peroxide, enzymes, and bacterio-cins. IFT notes that competitive inhibi­tion is already used in the "Wisconsin process," in which LAB cultures and re­duced levels of nitrite are used to pre­vent the growth of pathogens in bacon.

Less sophisticated techniques are also effective. For example, farm animals defe­cate in their water troughs and thereby contaminate them with 0157, Doyle says. Cleaning the troughs out more often would fix that problem. And at the meat-processing plant, carcass surfaces can be heated briefly with steam to kill 0157 without cooking the meat, he says. The technique can cut populations of the mi­crobe 1,000-fold.

Although some methods to control pathogens are effective, they have been held back by consumer resistance. One controversial option is to irradiate food to kill microorganisms while leaving the food raw. Food is exposed to an ionizing ener­gy source such as cobalt-60 in an enclosed chamber. Depending on dose, the radia­tion controls pathogens such as the Trichinella spiralis parasite in pork, bacte­ria in poultry, and microorganisms in herbs, according to the American Dietetic

Dioxin, antibiotics among potential contaminants under surveillance Authorities responsible for food safety must keep an eye on contaminants other than microorganisms. The Department of Agricultures's Food Safety & Inspection Service, which is responsible for testing for residues including pesticides and other chemicals, just finished a "clean-up action on a finding of dioxin in some poultry," says Parthapratim (Pat) Basu, director of the agency's Chemistry & Toxicology Divi­sion. The agency hooked up with the Envi­ronmental Protection Agency and the Food & Drug Administration to find the source of contamination, where it oc­curred, and how far it had gone and to "make sure the public doesn't get any con­taminated product''

Working days, nights, and weekends for a couple of months, the investiga­tors found that the dioxin came from a clay used as an anticaking agent in feed for poultry and other animals. Basu says as a result, FDA has put restrictions on the use of the clay in animal feed.

Basu's agency also works with FDA's Center for Veterinary Medicine to make

sure antibiotic residues in meat are "un­der control." He terms this a "very criti­cal issue," noting that "because of the use of antibiotics, we have resistant or­ganisms growing in the population, af­fecting humans and animals."

A recent article in Nature [389, 801 (1997)] pointed out that "nutritive and therapeutic treatment of farm animals, amounting to half of the world's antibiot­ic output, has selected for resistant bacte­ria that may contaminate the food pro­duced." These include enterococci and staphylococci in raw cured sausages and raw milk cheeses. Antibiotic-resistance genes are exchanged between pathogen­ic and nonpathogenic bacteria in food-as­sociated environments, according to the article. In the cheese, the transfer could have occurred in the animals or during the cheese-making process. The article, by Michael Teuber and coworkers at the Swiss Federal Institute of Technology's department of food science, urged that "inappropriate use" of antibiotics be curbed.

Association (ADA), Chicago. Irradiation is used on meat sent on space missions, and it also has been used to treat Hawaiian pa­payas, apples in Missouri, and strawberries in Florida, among other products. Doyle expects the process will soon receive gov­ernment approval for beef as well.

This technique has been around for years and is used abroad, but it faces resis­tance in the U.S. in part because of the public's concern about the safety of food treated this way. ADA concedes that "irra­diation does cause changes in food," but says these have been "found to be benign."

And ADA notes that irradiation benefits include "replacement of

Cattle carry E. coli 0157:H7, which can cause severe illness and even death in humans who eat food contaminated with the bacteria.

chemical treatments" (such as the mmigant ethylene oxide for spices) and extended shelf life. Some believe it is simply the best available technology to ensure safely. Sol-berg, for one, believes "there is no way in which raw meats can be distributed and be guaranteed free of potentially hazard­ous microorganisms except through the use of ionizing radiation."

Even though there is "a public accep­tance problem with irradiation, there is no such thing with pulsed-electric-field (PEF) technology, yet it potentially allows us to achieve the same result," says Lee. He terms the technique, in which food is subjected to high-voltage pulses of electricity, "friendly ir­radiation. I would hypothesize that consum­ers don't have a problem with electricity. It's in their homes, and it's safe when han­dled properly." PEF yields "fresh food that has not been cooked, yet it's 100% safe."

Lee says researchers are also revisiting ohmic heating, in which a current is run through the food to heat it. "About 20 years ago, you could buy hot dog warm­ers," he recalls. "You would stick a hot dog on two electrodes, and it would heat up. That's ohmic heating." The technique is "great for things like particulate foods or soups, which are partly fluid and partly solid" and susceptible to uneven heating.

Another method that is currently being studied is the use of high pressure to rid

2 8 NOVEMRFR 10 1QQ7 OtFNF

Soar toNew

Heights! Announcing Version 4.0 for Windows and Macintosh

Now is the perfect time for you to rise to the occasion and discover how STN Express can help you do your online searching of scientific or technical databases-better, faster, and with more confidence.

STN Express

• provides flexible autologon to major vendors

• saves time (and money) with offline query preparation

• includes structure and reaction query drawing with easy-to-use menus and tools

• enhances TIFF image handling

• offers Internet access to online vendors via Windows sockets

• supports fast communication speeds

• permits network sharing

And now-for ONLY $195 (new order; single-user license); $49 (single-user upgrade from any previous version)!

TO PLACE YOUR ORDER

Phone 800-753-4227 or 6H-447-3731

Fax 614-447-3751 E-mail help@cas.org

(SB A division of the American Chemical Society®

CTN Ε*! irt «s

Better

K -.

\^fiTi/rt*wt^groprry oysw^fi

w " » » i

&k££tiiSk*arttell

$\$\v

*

. / '

I

fWBSS^^l^^S&^^^SSSS^^NSSm

sohinons i ï»Si I il Gilson 11 lw< I i I

man collection for samble brebaration tmection ana jracrion collection

LAJfMA interrace xwtem 5fl3«ïiTsrrv.~":

wmàiû\mù!AM^^^mi^mszr:: jot leaa generawm mm leaa optmuzmwn libraries

Better drug discovery • Increase throughput and save time in ?t

HPLC purification and analysis

- Single point software control

- High capacity system accommodates up to

12 standard or deep well microplates

Personal Synthesizer System increases

throughput in organic synthesis

- Low cost, simple to use and flexible

system for lead generation and optimization

techniques, and solid- and solution-phase

combinatorial chemistry

* Open platform architecture supports a

variety of vendors' reaction blocks or your

own design

Gilson LC/MS Interface System

improves throughput in compound

characterization process

- Direct injection from up to 12 standard

or deep well microplates

- Compatible with most leading

LC/MS systems

With just the click of a mouse, our exclusive

Graphic Sample Tracking software matches

injections, peaks and fractions

• Automate a variety of pre- and post-

synthesis liquid handling tasks

- The versatile Gilson 215 Liquid Handler

can be used to streamline virtually any

reagent and precursor preparation task

- Open architecture makes rack loading

fast and easy

fisot i900li

4P GILSON ®

Solutions that tvork for you

www.gilson.com

3000 W. Beltline Hwy., P.O. Box 620027 • Middleton, WI 53562-0027 USA • Tel: (1) 608-836-1551, Fax: (1) 608-831-4451 72 rue Gambetta, B.P. 45 • 95400 Villiers-le-Bel, France • Tel: (33) 1-34-29-50-00, Fax: (33) 1-34-29-50-80

, WE JUST HADE -CVtf° THE WEB

16 TINES

¥^

s

* ^ ^ &

^s^>

It's a cyberspace science milestone! All 26 journals of the American Chemical Society are now on the Web.

These electronic versions offer a wide range of subscription options plus interactive features not available in the print journals, such as:

msk % . . ^ »

•Two separate formats to view articles, interactive text (HTML) and complete page image (PDF).

•Interactive links to other data­bases such as Medline, GenBank, and Chemport.

•Articles ASAR peer-reviewed and available weeks before the print versions.

You won't find such a flexible, comprehensive, feature-rich offer from any other publisher on the Web today.

For ordering/pricing information, call 800-333-95 I I or 614-447-3671 or see About ACS Electronic Editions at

http://pubs.acs.org

ACSfflPUBUOfflONS Essential Resources for the Chemical Sciences

BETTER

•#"? i i s i s i r *

food of microbes like R. coli 0157:H7, Sal­monella, and L. monocytogenes. The tech­nique uses hydrostatic pressures of 50,000 to 100,000 psi to inactivate microbes by dis-mpting their membranes, says Daniel F. Far-kas, head of the department of food science and technology at Oregon State University, Corvallis. Food can be pressure-treated in flexible packages by placing the packages in water in an isostatic press. Water is forced into this cylindrical vessel—which can con­tain up to several hundred liters—until the desired pressure is reached. After a suitable interval, the pressure is released and the packages are removed. If the food is a liq­uid, it can be pumped into a pressure vessel and, after pressure treatment, put into ster­ile packages.

Unlike heat, high pressure "doesn't break the covalent bonds in food, so you don't change the chemistry of the food," says Farkas, who has been affectionately dubbed Mr. Pressure" by another research­er in the food-safety field. "Essentially, you sterilize the food without losing its fresh taste. Of course, Murphy's law is always there: The process is not very effective against spores, which are very pressure- and heat-resistant forms of microbes." The worst of these, Farkas notes, is Clostridium botu-linum, which grows in hermetically sealed containers and can form a deadly toxin.

To deal with this microorganism, he acidifies the food to pH 4.2 or less. "We're dealing initially with acid products for shelf1

stable foods that can be stored at room tem­perature," he says. "For foods that can't be acidified, you have to combine high-pressure treatment with refrigeration or possibly chemical preservatives." In work supported by the Army, Farkas has demon­strated the technique with a yogurt drink, lemon pudding, fruit mix (pineapple, or­ange, and grapefruit "without the sodium benzoate taste," he notes), Spanish rice, spa­ghetti and meat sauce, and yogurt contain­ing peaches.

These products can keep for about 30 days at room temperature, but such con­ditions "allow the chemical breakdown of any food," Farkas says. "It's like taking sterilized leftovers and leaving them out. Even though they wouldn't spoil micro-biologically, the flavors would slowly dis­appear. They would lose their fresh fla­vor notes. So these foods are best refrig­erated to protect the chemistry of these very delicate flavors."

Farkas is aware of only one pressure-treated product on the U.S. market—a re­frigerated guacamole—but says Japanese consumers have access to pressure-treated jams, jellies, yogurts, and pourable salad

Oregon State University researcher Marcia I killing microorganisms in food by treating it

dressings. He notes that the Japanese prod- I ucts are "extremely expensive." Farkas says there is interest in applying the technology to orange juice and apple juice "because you are essentially knocking out the mi­crobes without changing the flavor of the juice, which is a little more difficult to do with heat. On the other hand, "R. coli 01S^:ir in beef is still a stretch for us," partly because of the tonnage required and the cost, but also because the high-pressure treatment can denature the protein in the meat, giving it a slightly cooked appearance (although texture and flavor are unaffected).

Microwave pasteurization is starting to come on the market to treat orange juice, milk, and cheese, according to Seifollah Nikdel, research scientist at the Florida De­partment of Citrus, Like Alfred. The tech­nique avc )ids the uneven heating as well as the overheating and consequent generation of off-tlavors that can occur when pasteur­ization is done by transferring heat through the walls of stainless-steel pipes, he says.

Another technology coming down the pike is treatment with ozone—"a really good substitute for chlorine," Lee says. "Chlorine in food is bad news, because it combines with organic material to form chlorinated hydrocarbons." Ozone could be used to treat chicken or turkey, he says. "A little bit of ozone in the final wash wa­ter will give you a Salmonella-free bird." Once that can be guaranteed, Lee adds, "we have a poultry processor here in Ohio who says, I can get a premium for my birds if I can label them Salmonella-free.'"

Other advances include "modified at­mosphere packaging, in which the air in a package is replaced by a mixture of gas-

Nalker runs a 2-L isostatic press capable of with pressures up to 100; 000 psi.

es tailored to extend the life of the con­tents, Solberg says. Cheese or fish can be packaged with nitrogen or a nitrogen/

i carbon dioxide blend, for example. This treatment stunts the growth of oxygen-loving microbes, but he warns that organ­isms that grow well in the absence of oxy­gen may then become the dominant prob­lem. And in that case, Solberg asks: "Will the consumer recognize spoilage when it has occurred? A great deal of testing is on­going to try to resolve these issues."

The fast-food chain McDonald's re­portedly is working with researchers to develop packaging that can take an ac­tive role in the reduction of microbes.

Other packaging-related research fo­cuses on sensors to go either on or in packages to indicate to consumers that the products have not been stored safely. FDA and USDA plan to work with indus­try and academia to develop and assess the effectiveness of such sensors.

Although many of these techniques look promising, food safety currently cannot be guaranteed. Not everyone is aware of that.

"A lot of consumers are surprised to find out our foods aren't sterile," Lee says. "You can eat a hamburger and potentially die from it. Or you can go to a salad bar and in­nocently pick up some lettuce, strawber­ries, raspberries, or whatever is there. And it might have R coli 0157:H7 on it or Salmo­nella, and you can get very sick."

But Lee expects "within a 10- or 20-year window, consumers will demand ab­solute safety from food." And if that is the case, he says, we'll have "the technology

I to do it."^

NOVFMRFR UL 1997 C&FN 3 3

science