R.A. Holley

Evaluation of antilisterial action of cilantro oil on vacuum packed ham.

Cilantro oil is an essential oil preparation extracted from the plant Coriandrum sativium. A series of experiments were conducted to evaluate the ability of cilantro oil to control the growth of Listeria monocytogenes on vacuum-packed ham. The in vitro minimal inhibitory concentration for five strains of L. monocytogenes was found to vary from 0.074% to 0.018% depending on strain. Cilantro oil treatments were then tested on ham disks inoculated with a cocktail of the five L. monocytogenes strains. The treatments studied were 0.1%, 0.5%, and 6% cilantro oil diluted in sterile canola oil or incorporated into a gelatin gel in which lecithin was used to enhance incorporation of the cilantro oil. Gelatin gel treatments were also conducted with 1.4% monolaurin with or without 6% cilantro oil to determine if an interaction between the antimicrobials could increase inhibition of L. monocytogenes. Treated ham was then vacuum-packed and stored at 10 degrees C for up to 4 weeks. The only cilantro oil treatment which inhibited growth of L. monocytogenes on the ham samples was 6% cilantro oil gel. Samples receiving this treatment had populations of L. monocytogenes 1.3 log CFU/ml lower than controls at week 1 of storage, though there was no difference between treatments from week 2 onward. It appears that immobilization of the antimicrobial in a gel enhanced the effect of treatments. Cilantro oil does not appear to be a suitable agent for the control of L. monocytogenes on ham. The possible reasons for reduced effectiveness of cilantro oil against L. monocytogenes on ham are discussed.

Pulsed electric field processing of foods: a review.

Use of pulsed electric fields (PEFs) for inactivation of microorganisms is one of the more promising nonthermal processing methods. Inactivation of microorganisms exposed to high-voltage PEFs is related to the electromechanical instability of the cell membrane. Electric field strength and treatment time are the two most important factors involved in PEF processing. Encouraging results are reported at the laboratory level, but scaling up to the industrial level escalates the cost of the command charging power supply and of the high-speed electrical switch. In this paper, we critically review the results of earlier experimental studies on PEFs and we suggest the future work that is required in this field. Inactivation tests in viscous foods and in liquid food containing particulates must be conducted. A successful continuous PEF processing system for industrial applications has yet to be designed. The high initial cost of setting up the PEF processing system is the major obstacle confronting those who would encourage the systems industrial application. Innovative developments in high-voltage pulse technology will reduce the cost of pulse generation and will make PEF processing competitive with thermal-processing methods.

The effect of different grain diets on fecal shedding of Escherichia coli O157:H7 by steers

Three groups of six yearling steers (three rumen fistulated plus three nonfistulated) fed one of three different grain diets (85% cracked corn, 15% whole cottonseed and 70% barley, or 85% barley) were inoculated with 10(10) CFU of Escherichia coli O157:H7 strain 3081, and the presence of the inoculated strain was followed in the rumen fluid and feces for a 10-week period. E. coli O157:H7 was rapidly eliminated from the rumen of the animals on all three diets but persisted in the feces of some animals up to 67 days after inoculation, suggesting that the bovine hindgut is the site of E. coli O157:H7 persistence. A significant difference existed in the levels of E. coli O157:H7 shed by the animals among diets on days 5, 7, 49, and 63 after inoculation (P < 0.05). No significant difference was found between the levels shed among diets on days 9 through 42 and on day 67 (P > 0.05). The number of animals that were culture positive for E. coli O157:H7 strain 3081 during the 10-week period was significantly higher for the barley fed group (72 of 114 samplings) as opposed to the corn fed group (44 of 114 samplings) (P < 0.005) and the cottonseed and barley fed group (57 of 114 samplings) (P < 0.05). The fecal pH of the animals fed the corn diet was significantly lower (P < 0.05) than the fecal pH of the animals fed the cottonseed and barley and barley diets, likely resulting in a less suitable environment for E. coli O157:H7 in the hindgut of the corn fed animals. E. coli O157:H7 strain 3081 was present in 3 of 30 (corn, 1 of 10; cottonseed, 1 of 10; barley, 1 of 10) animal drinking water samples, 3 of 30 (corn, 1 of 10; cottonseed, 0 of 10; barley, 2 of 10) water trough biofilm swabs, 5 of 30 (corn, 0 of 10; cottonseed, 2 of 10; barley, 3 of 10) feed samples, and 30 of 30 manure samples taken from the pens during the entire experimental period. Mouth swabs of the steers were also culture positive for E. coli O157:H7 strain 3081 in 30 of 180 samples (corn, 7 of 60; cottonseed, 4 of 60; barley, 19 of 60) taken during the 10-week period. Minimizing environmental dissemination of E. coli O157:H7 in conjunction with diet modification may reduce numbers of E. coli O157:H7-positive cattle.

Review of centralized packaging systems for distribution of retail-ready meat.

There is growing interest in centralized preparation of retail-ready meat cuts for distribution to widely dispersed retail stores due to the convenience of having high-quality ready-to-go products that are consistently provided to consumers at lower cost. Various centralized packaging techniques are described. Of all packaging techniques, master packaging is the most economical and shows promise for commercial application. Nevertheless, the master-packaging technique must be integrated with strict temperature control in a narrow range just above freezing (- 1.5 +/- 0.5 degrees C), good processing hygiene, and maintenance of a completely anoxic atmosphere in the package headspace throughout the distribution period to maximize storage life. Packaging using the CAPTECH process reduces the residual O2 present in the headspace to 300 ppm. Oxygen scavengers must be incorporated in the package to absorb the residual O2 and preserve the metmyoglobin reducing activity of meat tissues. Integration of all these technologies can provide a storage life of retail-ready meat up to 10 weeks in the master package followed by 3 days of retail display life. This extension of storage life is sufficient for transporting meat to distant markets.

Centralized Packaging of Retail Meat Cuts: A Review

Centralized packaging of retail meat cuts is growing more popular because of its economies and potential to maintain quality, enhance safety, and extend the shelf life of fresh meat. Requirements for optimizing shelf life of centrally prepared retail cuts for periods up to 15 weeks are slightly different from those needed to extend the shelf life of fresh, chilled meat. Chilled meat primarily deteriorate at the cut or uncut muscle surface. In long-term storage, primal cuts are placed in an atmosphere saturated with carbon dioxide and containing very low residual oxygen. These cuts are held at -1.5+/-0.5 degrees C. When the meat is removed, it is fabricated into retail or food service cuts. New fresh surfaces are created in the process, revitalizing the meats appearance. After being prepared for retail display, the meat normally has four more days of shelf life. Depending on the meat species, shelf life is usually limited by development of undesirable organoleptic changes, usually defects in color, which are independent of microbial presence. The microbes consist of a lactic acid bacterial population that maximizes under storage conditions at about 10(8) CFU/cm2 well before shelf life ends. Circumstances are different with centralized distribution of retail-ready fresh meat. The wholesale storage period following initial packaging of the retail cuts is about 20 to 30 days. Prepared products must withstand retail display for up to 2 days without further manipulation of package contents. Retail packages are simply moved from their storage container (usually a unit or overwrap containing a modified atmosphere) to retail display, where desirable meat color develops upon exposure to air. Three gas atmospheres have some potential to satisfy storage needs for centralized distribution of retail-ready packages: 100% CO2, 100% N2, or 70% N2 + 30% CO2. Shelf life is limited by undesirable changes in surfaces exposed at initial packaging, caused by growth of psychrotrophic bacteria. If 100% CO2 is used, these are all lactic acid bacteria (LAB). Therefore, initial bacterial numbers on the meat and storage temperature become critical to success. The most attractive storage option is 100% CO2 used at - 1.5 +/-0.5 degrees C. This review presents the reason for that recommendation, along with basic concepts of meat chemistry, a discussion of modified atmosphere packaging, meat microbiology, and current results with simulated centralized packaging of retail-ready meats.

Persistence of Escherichia coli O157:H7 in barley silage: effect of a bacterial inoculant.

Aims: The effect of a lactic acid producing bacterial (LAB) inoculant on the elimination of Escherichia coli O157:H7 from barley forage was assessed. 
Methods and Results: Triplicate mini‐silos were prepared for four treatments and six sampling times (1, 3, 7, 15, 30 and 42 d post‐ensiling). The treatments were (i) 105 cfu g−1Pediococcus pentosaceus and Propionibacterium jenzenii (P2); (ii) 105 cfu g−1E. coli O157:H7 strain 3081 and 105 cfu g−1E. coli Biotype 1 strains 719IE10, 719IE14 and 614ME49 (EC); (iii) P2 + EC; and (iv) the control (sterile distilled water). Triplicate mini‐silos were opened at each sampling time for pH, volatile fatty acid (VFA) and lactate determinations and E. coli, E. coli O157:H7 and LAB were enumerated. On d 3 and 7, numbers of E. coli O157:H7 in P2 + EC were significantly lower than in EC (P < 0˙05). Escherichia coli O157:H7 was not detected in P2 + EC and EC at 7 and 15 d post‐ensiling, respectively. On d 15 through 42, E. coli Biotype 1 was not detected in P2 + EC or EC. Populations of LAB were higher in P2 and P2 + EC than in the control and EC on d 3 and 7 (P < 0˙05). After 3 d of ensiling, lactate levels were higher (P < 0˙05) and pH was lower (P < 0˙05) in P2 and P2 + EC as compared to the control and EC. Bacteriocins of P2 were not found to be inhibitory to E. coli O157:H7 using the agar‐spot procedure. Escherichia coli O157:H7 inoculated into the control silage at a level of 103 cfu g−1 and exposed to aerobic conditions at 22°C was not detected after 1 d and remained undetectable for the 28 d exposure period. 
Conclusions: Silage inoculant P2 increased lactate levels and decreased pH more rapidly during ensiling, which appeared to hasten the elimination of E. coli O157:H7 from the silage. 
Significance and Impact of the Study: Results emphasize the importance of adequate ensiling since E. coli O157:H7 may be maintained and spread among cattle through feed.

Enhancing the antimicrobial effects of bovine lactoferrin against Escherichia coli O157:H7 by cation chelation, NaCl and temperature

Aim:  To evaluate the effect of NaCl, growth medium and temperature on the antimicrobial activity of bovine lactoferrin (LF) against Escherichia coli O157:H7 in the presence of different chelating agents.

Cresol Red Thallium Acetate Sucrose Inulin (CTSI) agar for the selective recovery of Carnobacterium spp.

Carnobacterium spp. are commonly isolated from a variety of foods, especially from meats stored under anaerobic atmospheres at refrigeration temperatures, but the role of these organisms in the spoilage of meat and meat products is yet to be determined. Cresol Red Thallium Acetate Sucrose (CTAS) agar was developed as a selective medium for enumeration of carnobacteria, however problems such as poor recovery of Carnobacterium spp. and interference by other microorganisms have precluded its general use. The aim of this study was to improve CTAS agar by broadening its spectrum of selective recovery for carnobacteria while restricting the ability of interfering species to grow. Ten Carnobacterium spp. (five ATCC cultures and five isolates from fresh pork) and 20 other genera were used in testing the agar. A wider range of Carnobacterium spp. recovery was obtained by modifying concentrations of sucrose, manganese sulphate and thallium acetate. Additions of inulin and thiamine hydrochloride also improved growth response. The additions of vancomycin and Chrisin (nisin) eliminated interference from other microorganisms. A two-temperature incubation procedure was included to improve the characteristic growth of Carnobacterium spp. on the modified medium, identified as Cresol Red Thallium Sucrose Inulin (CTSI) agar. Lactic acid bacteria and Enterobacteriaceae were unable to grow on CTSI incubated aerobically. Growth of Carnobacterium spp. on CTSI yielded pink colonies, except for Cb. mobile, which formed gray colonies. In some instances, a red precipitate formed in the center of the colony. Yellowing and clearing of the growth medium was also frequently observed. Recovery of carnobacteria using CTSI was identical to that obtained with All Purpose Tween (APT) agar.

Evaluation of the hygienic performances of the processes for cleaning, dressing and cooling pig carcasses at eight packing plants

The hygienic performances of the processes for the production of cooled carcasses at eight pork packing plants were assessed from small sets of microbiological data. At each plant, a single sample was obtained from a randomly selected site on each of 25 randomly selected carcasses at each of three stages of processing, which were after polishing, after washing at the end of the dressing process, and after cooling. The aerobic bacteria, coliforms and Escherichia coli recovered from each sample were enumerated. When bacteria of one type were recovered from > or = 20 of 25 samples, the log mean number of those bacteria on the population of carcasses undergoing processing was estimated on the assumption that the set of counts was normally distributed. The log of the total number recovered from 25 samples was calculated for each set of counts. The log mean numbers of total aerobic bacteria recovered from the polished carcasses at different plants ranged from about 1.9 to 3.8 log cfu cm(-2). At six of the plants, the log mean numbers of total aerobes on the cooled carcasses did not differ substantially from the log mean numbers on the polished carcasses, but the log mean numbers on the cooled carcasses were substantially higher at one plant and substantially lower at another than on the polished carcasses. Coliforms and E. coli were recovered from too few samples in most sets from cooled carcasses for estimation of their log mean numbers. However, the log total numbers of coliforms and E. coli recovered indicated that substantial numbers of those organisms were added to carcasses during the dressing processes at four of the plants, and that the numbers on the carcasses were substantially reduced by the processes for cooling without spraying at two of the plants. At seven of the plants, the total numbers of coliforms and E. coli recovered from cooled carcasses were <3.1 and <2.2 log cfu 2500 cm(-2), respectively. The findings indicate that production processes for pig carcasses can be operated to give cooled carcasses with log mean numbers of total aerobes < 2 cm(-2), and log total numbers of coliforms and E. coli each < 1 2500 cm(-2).

Predicting survival of Escherichia coli O157:H7 in dry fermented sausage using artificial neural networks.

The Canadian Food Inspection Agency required the meat industry to ensure Escherichia coli O157:H7 does not survive (experiences > or = 5 log CFU/g reduction) in dry fermented sausage (salami) during processing after a series of foodborne illness outbreaks resulting from this pathogenic bacterium occurred. The industry is in need of an effective technique like predictive modeling for estimating bacterial viability, because traditional microbiological enumeration is a time-consuming and laborious method. The accuracy and speed of artificial neural networks (ANNs) for this purpose is an attractive alternative (developed from predictive microbiology), especially for on-line processing in industry. Data from a study of interactive effects of different levels of pH, water activity, and the concentrations of allyl isothiocyanate at various times during sausage manufacture in reducing numbers of E. coli O157:H7 were collected. Data were used to develop predictive models using a general regression neural network (GRNN), a form of ANN, and a statistical linear polynomial regression technique. Both models were compared for their predictive error, using various statistical indices. GRNN predictions for training and test data sets had less serious errors when compared with the statistical model predictions. GRNN models were better and slightly better for training and test sets, respectively, than was the statistical model. Also, GRNN accurately predicted the level of allyl isothiocyanate required, ensuring a 5-log reduction, when an appropriate production set was created by interpolation. Because they are simple to generate, fast, and accurate, ANN models may be of value for industrial use in dry fermented sausage manufacture to reduce the hazard associated with E. coli O157:H7 in fresh beef and permit production of consistently safe products from this raw material.