Rapid Testing Methods: Essential Safety Tools for Forging Greater Confidence in U.S. Food Supply
By Erdogan Ceylan, Ph.D., and John Williams Jr.
Nowadays, U.S. consumer confidence in the safety of food products can aptly be described as unpredictable. In its 2008 grocery trends survey, the Food Marketing Institute (FMI) revealed 81% of participants expressed confidence in the safety of the food they buy and eat. The figure represented a 15-point increase over the previous year.
However, the annual report alluded to the fragility of consumers' confidence. Only 11% of consumers were "completely confident" (down from 15% in 2007), whereas 70% were "somewhat confident." Following a calamitous 2007 – a year marked by major fresh produce and beef recalls – respondents "somewhat" or "strongly" agreed that fresh produce (93%), canned and boxed foods (92%), and meat, poultry and fish (90%) were safe to eat. Of the two statements, higher numbers of FMI survey respondents sided with the "somewhat" affirmation.
Fresh on the heels of an uptick in consumer confidence, it is important for food companies to embrace proven scientific tools and technologies to bolster further trust in the U.S. food supply. Reliable and accurate rapid testing methods are invaluable tools in the ongoing war against Listeria moncoytogenes, E. coli O157:H7 and other potentially deadly foodborne organisms.
Technological Advances
Several years ago, tedious and labor-intensive culture methods dominated the microbiological testing landscape. Today, a wide spectrum of rapid microbiological test kits and automated systems enable the detection and identification of microbial hazards in products prior to their release from the processing plant.
These technologies include biochemical identification test kits and automated systems based on biochemical changes to generate a phenotypic profile such as fatty acid profiles and carbon oxidation profiles; antibody-based assays such as enzyme linked immunosorbent assay (ELISA); enzyme linked fluorescent assay (ELFA); reverse passive latex agglutination (RPLA); latex agglutination and immunoprecipitation; and DNA-based assay such as polymerase chain reaction assay (PCR), probe assay (generally targeting ribosomal RNA (rRNA), and phage assay.
PCR is a method of DNA amplification of a single target copy of DNA by a million fold in a couple of hours to enable detection. The target fragment of DNA is very unique to the test organism. The presence of inhibitors in foods may reduce the sensitivity of PCR. Therefore, when testing foods, PCR methods involve a basic three-step process: sample preparation (cultural enrichment), amplification and detection. Samples are first enriched according to the standard procedures in an enrichment medium designed to promote the growth of the target organism.
The target DNA is exponentially multiplied through of a series of heating and cooling cycles. If the starting genomic material is RNA, for instance in the case of viruses, it is converted to double stranded DNA first by reverse transcriptase PCR. An automated fluorescence based system is used for detecting PCR products via the generation of a fluorescent signal.
With the emergence of DNA-based microarray assays, we can look at DNA sequences of organisms, and even strains within an organism, for very precise identification. DNA microarrays are a revolutionary concept in the evolution of food testing because in a single or small number of assays analysts can screen for a large number of microorganisms. Following the standard PCR protocol, which amplifies the DNA for detection of a microbe, a single DNA chip can be used to identify 40 to 100 species or strains of microorganisms in a single test.
Biosensors, another cutting-edge analytical device, contain a biological sensing element connected to a transducer (such as amperometric, potentiometric, calorimetric, conductimetric, colorimetric, luminescence and fluorescence). Signals are produced that detect the presence or activity of living or dead microorganisms in a food sample.
The New Gold Standard
Unless it is sterile, raw or processed food products will contain indigenous microflora, contaminant organisms or in some cases food borne pathogens. Identification of organisms causing in food product formulations is an important need in the food industry. Recent advances in genetic technology make identification faster, more sensitive, reliable and specific with reproducible results compared to conventional identification methods that require tedious processes such as gram stains, biochemical information or special growth conditions.
Recognized industry-wide as the "gold standard" in culture identification, gene sequencing is based on analysis of ribosomal RNA gene (rDNA) of bacteria and fungi. Identifying microorganism through DNA sequence analysis yield accurate results for biochemical inert species and organisms that are difficult to grow, non-viable, unidentifiable by phenotypic assays or require long cultivation period such as yeasts and molds. Furthermore, one can analyze hundreds of samples in a single day.
Telling Stats
Last year in its report, "Food Micro – 2008 to 2013," Strategic Consulting, Inc. (SCI) noted the global food industry has recognized the benefits offered by faster and better testing methods. (SCI is a broad-based consulting firm serving the food, beverage, environmental, personal care product, and pharmaceutical segments of the industrial diagnostics market.) Over the past decade, according to SCI research, a significant shift to newer, rapid methods has occurred within the food industry.
In 2005, 224.3 million rapid tests were conducted, according to the report. Three years later, rapid tests totaled 306.8 million, an increase of 36.8%. Interviews with hundreds of food QA/QC managers worldwide were used to compile the data cited in the SCI report.
Committed to the advancement of science and technology, members of the Silliker Food Science Center staff will be participating at the following industry events this summer:
May American Society for Microbiology General Meeting
May 17-21, 2009
Philadelphia, PA
Pre-meeting Workshop: Molecular Testing for Foodborne Pathogens – Practical Considerations
Instructors include: Mark Carter, Vice President of R&D, and Sarita Raengpradub, Ph.D., FSC Molecular Biologist
June Institute of Food Technologists Annual Meeting and Exposition
June 6-9, 2009
Anaheim, CA
Symposium: A 10-year Retrospective: Celebrating the Accomplishments of Non-thermal Processing Division
Co-moderator: Dr. Cynthia Stewart, FSC General Manager
IFT Sunrise Symposium: DNA Techniques for Food Pathogens
Co-instructor: Sarita Raengpradub, Ph.D., FSC Molecular Biologist
July International Association for Food Protection Annual Meeting
July 12 -15, 2009
Grapevine, TX
Poster Presentation: Effect of Cooling Rates on Survival and Growth of Escherichia coli O157:H7 in Creamed Cottage Cheese
Presenter: Dr. Erdogan Ceylan, FSC Director
Poster Presentation: Evaluation of Repetitive Extragenic Palindromic Sequence-Based PCR Typing of Bacillus Species
Presenter: Sarita Raengpradub, Ph.D., FSC Molecular Biologist
Oral Presentation: Independent Laboratory Evaluation of a Real-Time PCR Test for Detection of Listeria spp. in Selected Foods from a Single Primary Enrichment
Presenter: Brian Kupski, FSC Operations Supervisor
Poster Presentation: Evaluation of a Rapid Molecular Subtyping Method for Predicting Salmonella Serotypes
Presenter: Sarita Raengpradub, Ph.D., FSC Molecular Biologist
Poster Presentation: Evaluation of VIDAS(r) Recombinant Phage Protein Technology for Detection of Escherichia coli O157:H7 in Produce and Spent Irrigation Water
Presenter: Brian Kupski, FSC Operations Supervisor
August Second Annual Molecular Methods in Food Microbiology Symposium and Workshop Series
August 3 -7, 2009
Colorado State University, Fort Collins, CO
Designed for current and future food safety and quality assurance professionals, this series provides theoretical and hands-on training in molecular subtyping of foodborne pathogens and spoilage organisms.
Instructors include: Mark Carter, Vice President of R&D, and Sarita Raengpradub, Ph.D., Molecular Biologist
FSC News & Notes: Kalinowski Named Research Project Manager
Robin M. Kalinowski has joined the Silliker Food Science Center as a Research Project Manager. With over 20 years of industry experience, Robin most recently served as senior microbiologist at the National Center for Food Safety and Technology in Chicago, IL. In this role, she managed a portfolio of collaborative FDA and industry funded projects involving the microbial validation of new food safety technologies. Before that, she served in managerial and technical positions with ConAgra Foods from 1989 to 2004.
A graduate of the Illinois Institute of Technology with a MS in biology, Robin possesses an extensive background in food microbiology, method validation studies, shelf-life programs, process controls, and environmental sampling.
Nowadays, U.S. consumer confidence in the safety of food products can aptly be described as unpredictable. In its 2008 grocery trends survey, the Food Marketing Institute (FMI) revealed 81% of participants expressed confidence in the safety of the food they buy and eat. The figure represented a 15-point increase over the previous year.
Committed to the advancement of science and technology, members of the Silliker Food Science Center staff will be participating at the following industry events this summer: