Food Safety Magazine, June/July 2012

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Testing Product and equipment testing: Because microbes usually enter the production stream based on an ingredient or Good Manufacturing Practice lapse, one dominant organism is often responsible for spoilage. Alternatively, there may be one genus but multiple species involved. Microbial identification takes expertise and precision. Selecting a lab that has such expertise will save time. Ideally, the lab should use the data gathered to assist with formulation of corrective and preventive actions as quickly and efficiently as possible. It is often perplexing why pre-ship test results can be within specifications, but product defects occur later in shelf life. At shipment, if present, gas-forming concentration is usually low or below the limit of detection. This is why reviews of pre-ship results do not always provide helpful data. Routine monitoring of equipment for indicator organisms and data trending provide a picture of the microbial milieu and exposure the products face during production. When setting pre-ship product specifications, the lowest possible pre-ship numbers for common spoilage organisms is the best plan because any presence at this stage may indicate future spoilage. Tracking and trending resultant data may identify whether there may be a spoilage event later in shelf life. Gas production does not occur until bacterial concentrations reach approximately 1.0 × 10 7 colonyforming units/gram (CFU/g). 2 This is why the product can test within specifications when shipped only to swell later in shelf life. 3 Laboratory analysis: For any microbial identification, testing labs usually take a three-pronged approach: 1) cultivation, 2) isolation and enrichment and 3) identification. Cultivation allows for quantitative results. Only approved cultivation methods found in Compendium of Methods for the Microbiological Examination of Foods, 4 Standard Methods for the Examination of Dairy Products 5 or AOAC International, 6 depending on the food type, should be used. However, some scientists may use nonapproved methods to resuscitate injured cells followed by isolation and identification if traditional direct plate counts are ineffective. Isolation and enrichment allows the microbes to be separated and multiplied so that each type may be successfully identified. All three steps are needed. Since each step takes 2–3 days, the entire process will require up to 9 days for final results. Further, if there are not a high number of organisms in the sample, cultivation may take longer. Consequently, obtaining a product sample during bloating will greatly aid in identification because there is a plethora of organisms available for culture. Of note, some organisms such as lactic acid bacteria are difficult to identify. Verify that the laboratory conducting the testing has experience working with them. Gas-Producing Spoilage Organisms Coliforms: Coliforms are a subgroup within the genera of Gram-negative Enterobacteriaceae and are widely known to inhabit the gastrointestinal tracts of animals and humans. Their presence in production facilities indicates unsanitary conditions or contamination with soils exposed to feces. 5 Coliforms grow over a wide pH range (4.4 to 9.0) and at temperatures ranging from 3 °C to 50 °C. They are susceptible to heat, and while some are psychrotrophic (cold-loving), the majority are sensitive to cold. Thus, refrigeration will reduce populations. Lactic Acid Bacteria: Lactic acid bacteria are Gram-positive, nonsporeforming organisms that ferment glucose to lactic acid (homofermentative) or to lactic acid, carbon dioxide and ethanol (heterofermentative). Their presence will cause a sour note; together with heterofermentative organisms, they will cause swelling (Table 1). They can grow in low oxygen tensions (vacuum or modified atmosphere packaging), which enables them to outcompete other spoilage bacteria. Growth in refrigeration and in highly acidic environments will occur, allowing for spoilage multiple weeks into shelf life. 2 Many times, raw ingredients have high lactic acid bacteria counts. Since these bacteria are heat resistant, they can undergo thermal treatments and small numbers can survive. Spoilage can occur with cell concentrations of less than 10 CFU/g in finished products. Yeast: Yeasts ferment carbohydrates to form ethanol and carbon dioxide. They are commonly found in the environment and can cause contamination through airborne transmission. They grow more slowly than bacteria. Yeast spoilage can occur in products with low pH, low water activity and low temperatures. Since most are heat sensitive, yeast contamination of heat-processed foods is due to post-processing contamination (Table 1). Group Coliforms Lactic acid bacteria Specific organisms (genus) Citrobacter Serratia Proteus Escherichia Enterobacter Erwinia Klebsiella Hafnia Lactobacillus Streptococcus Leuconostoc Pediococcus Yeast Candida Saccharomyces Zygosaccharomyces Torulaspora Rhodotorula Pichia Table 1: Organisms Commonly Responsible for Product Spoilage Visible, detectable levels of yeast spoilage occur at approximately 1.0 × 10 6 CFU/g but can go undetected when weak gas production occurs due to a lack of organoleptic clues. 7, 8 Of interest, some yeasts can produce sufficient pressure to explode plastic food packages and glass bottles. 7 Corrective and Preventive Actions Once the organism is identified, the likelihood of elimination is greater. For each genus implicated, the corrective and preventive actions may differ. However, in all cases, comprehensive equipment disassembly, cleaning and sanitizing are 16 F o o d S a f e t y M a g a z i n e
Testing in order since their presence often indicates post-processing contamination. 9 Prerequisite programs and process controls should be reviewed and revised if necessary. For example, implementation or revision of a supplier-monitoring program and skip-lot testing, using one of the listed accredited methods, should be done to ensure raw ingredients are not entering the process at an unacceptable level. Conclusions When the packaging is bursting with gas rather than with flavor, a spoilage organism is often the culprit. An essential step in resolving and correcting this defect is to first identify the organism. Coliforms, lactic acid bacteria and yeasts are gas-forming spoilage organisms. Their presence indicates either pre- or post-processing contamination. Working with an experienced and knowledgeable laboratory in the resolution will help save time and avoid future occurrences. • Advancing Food Science Throughout the Global Food Chain examination of foods, 4th ed. Washington, DC: American Public Health Association. 5. Wehr, H. and J. Frank (eds.). 2004. Standard methods for the examination of dairy products. Washington, DC: American Public Health Association. 6. www.aoac.org/. 7. Stratford, M. 2006. Food and beverage spoilage yeasts. In Yeasts in food and beverages, eds. A. Querol and G. H. Fleet, 335–379. Berlin: Springer Verlag. 8. Hui, Yu (ed.). 2006. Handbook of food science, technology, and engineering. Boca Raton, FL: CRC Press. 9. Doyle, E. M. 2007. Microbial food spoilage — losses and control strategies. Madison, WI: Food Research Institute, University of Wisconsin–Madison. Kara Baldus, M.B.A., is a study coordinator/lead Hazard Analysis and Critical Control Points instructor at Covance Inc. in Madison, WI. She can be reached at kara.baldus@ covance.com. Virginia Deibel, Ph.D., is the director of microbiological consulting within nutritional chemistry and food safety at Covance Inc. References 1. www.docstoc.com/docs/25959301/Using- Contemporary-Archaeology-and-Applied- Anthropology-to. 2. Sperber, W. H. and M. P. Doyle (eds.). 2009. Compendium of the microbiological spoilage of foods and beverages. New York: Springer. 3. Hamasaki, Y., A. Mitsuko, F. Hidetaka and M. Sugiyama. 2003. Behavior of psychrotrophic lactic acid bacteria isolated from spoiling cooked meat products. Appl Environ Microbiol 69(6):3668–3671. 4. Downes, F. and K. Ito (eds.). 2001. Compendium of methods for the microbiological Silliker is dedicated to helping companies worldwide find practical solutions to food safety and quality challenges throughout the supply chain. Our commitment to helping processors, retailers and distributors find workable solutions has made us the trusted food safety and quality resource of companies around the globe. IFT Annual Meeting & Food Expo Silliker, Inc. Booth #1635 IAFP 2012 Annual Meeting Silliker, Inc. Booth #608 Subscribe to receive our free “Industry Insights” newsletter at the trade shows or go online to: http://info.silliker.com/industryinsights/ Silliker, Inc. 111 E. Wacker Drive Suite 2300 Chicago, IL 60601 / USA email. info@silliker.com www.silliker.com email. info@silliker.com J u n e • J u l y 2 0 1 2 17
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