Cangliang Shen

Inactivation of Escherichia coli O157:H7 in Nonintact Beefsteaks of Different Thicknesses Cooked by Pan Broiling, Double Pan Broiling,or Roasting by Using Five Types of Cooking Appliances

This study compared thermal inactivation of Escherichia coli O157:H7 in nonintact beefsteaks of different thicknesses by different cooking methods and appliances. Coarsely ground beef was inoculated with rifampin-resistant E. coli O157:H7 (eight-strain composite, 6 to 7 log CFU/g) and then mixed with sodium chloride (0.45%) plus sodium tripolyphosphate (0.23%); the total water added was 10%. The meat was stuffed into bags (10-cm diameter), semifrozen (-20 degrees C, 6 h), and cut into 1.5-, 2.5-, and 4.0-cm-thick steaks. Samples were then individually vacuum packaged, frozen (-20 degrees C, 42 h), and tempered (4 degrees C, 2.5 h) before cooking. Partially thawed (-2 +/- 1 degrees C) steaks were pan broiled (Presto electric skillet and Sanyo grill), double pan broiled (George Foreman grill), or roasted (Oster toaster oven and Magic Chef standard kitchen oven) to a geometric center temperature of 65 degrees C. Extent of pathogen inactivation decreased in order of roasting (2.0 to 4.2 log CFU/g) > pan broiling (1.6 to 2.8 log CFU/g) >/= double pan broiling (1.1 to 2.3 log CFU/g). Cooking of 4.0-cm-thick steaks required a longer time (19.8 to 65.0 min; variation was due to different cooking appliances), and caused greater reductions in counts (2.3 to 4.2 log CFU/g) than it did in thinner samples (1.1 to 2.9 log CFU/g). The time to reach the target temperature increased in order of George Foreman grill (3.9 to 19.8 min) < Oster toaster oven (11.3 to 45.0 min) < Presto electric skillet (16.3 to 55.0 min) < Sanyo grill (14.3 to 65.0 min) < standard kitchen oven (20.0 to 63.0 min); variation was due to steak thickness. Results indicated that increased steak thickness allowed greater inactivation of E. coli O157:H7, as time to reach the target internal temperature increased. Roasting in a kitchen oven was most effective for pathogen inactivation.

Thermal Inactivation of Acid, Cold, Heat, Starvation, and Desiccation Stress–Adapted Escherichia coli O157:H7 in Moisture-Enhanced Nonintact Beef

This study was conducted to compare thermal inactivation of stress-adapted and nonadapted Escherichia coli O157:H7 in nonintact beef moisture enhanced with different brine formulations and cooked to 65°C. Coarsely ground beef was mixed with acid, cold, heat, starvation, or desiccation stress-adapted or nonadapted rifampin-resistant E. coli O157:H7 (eight-strain mixture, 5 to 6 log CFU/g) and a brine solution for a total moisture enhancement level of 10%. The brine treatments included distilled water (control), sodium chloride (0.5% NaCl) plus sodium tripolyphosphate (0.25% STP), or NaCl + STP combined with cetylpyridinium chloride (0.2% CPC), lactic acid (0.3% LA), or sodium metasilicate (0.2% SM). The treated meat was extruded into bags (15 cm diameter), semifrozen (-20°C for 4.5 h), and cut into 2.54-cm (1-in.)-thick portions. Samples were individually vacuum packaged, frozen (-20°C for 42 h), and tempered at 4°C for 2.5 h before cooking. Partially thawed (-1.8 ± 0.4°C) samples were pan broiled to an internal temperature of 65°C. Pathogen counts of partially thawed (before cooking) samples moisture enhanced with brines containing CPC, LA, or SM were 0.7 to 1.1, 0.0 to 0.4, and 0.2 to 0.4 log CFU/g, respectively, lower than those of the control. Compared with microbial count reductions obtained after pan broiling of beef inoculated with nonadapted E. coli O157:H7 cells, count reductions during cooking of meat inoculated with cold and desiccation stress-adapted, acid stress-adapted, and heat and starvation stress-adapted cells indicated sensitization, cross protection, and no effect, respectively, of these stresses on the pathogen during subsequent exposure to heat. Among all stressed cultures, CPC-treated samples (0.8 to 3.6 log CFU/g) and LA-treated samples (0.8 to 3.5 log CFU/g) had the lowest numbers of E. coli O157:H7 survivors after cooking.

Reductions in Natural Microbial Flora, Nonpathogenic Escherichia coli, and Pathogenic Salmonella on Jalapeno Peppers Processed in a Commercial Antimicrobial Cabinet: A Pilot Plant Trial

This experiment aimed to validate the use of antimicrobial solutions in a spray cabinet to inactivate natural microbial flora, nonpathogenic Escherichia coli , and Salmonella on jalapeno peppers. Jalapeno peppers, uninoculated or inoculated with a five-strain mixture of rifampin-resistant E. coli (3.9 log CFU/g) or novobiocin- and nalidixic acid-resistant Salmonella (4.2 log CFU/g), were passed through a commercial antimicrobial cabinet containing both a top and bottom bar spraying (1.38 bar and 2 liters/min) water, sodium hypochlorite (50 ppm), sodium hypochlorite with pH adjusted to 6.7, peroxyacetic acid (PAA; 80 ppm), PAA with pH adjusted to 6.7, lactic with citric acid (1%), lactic with citric acid with sodium lauryl sulfate (1,200 ppm), or chlorine dioxide (5 ppm). Bacteria were recovered in 0.1% buffered peptone water plus 0.1% sodium thiosulfate, which was followed by spread plating onto tryptic soy agar (TSA), TSA plus rifampin (100 μg/ml), and TSA plus novobiocin (25 μg/ml) and nalidixic acid (20 μg/ml). There were no significant differences (P ≥ 0.05) in recovered natural microbial flora, E. coli , and Salmonella populations between untreated peppers (3.5 to 4.2 log CFU/g) and peppers treated with water (3.4 to 3.8 log CFU/g). Significantly fewer (P < 0.05) natural microbial flora, E. coli , and Salmonella populations were recovered on the peppers after they were treated with a majority of the antimicrobials applied in the commercial antimicrobial cabinet. The largest population reduction was observed on peppers sprayed with PAA. Interestingly, the pH adjustment did not make a difference (P ≥ 0.05) in the recovered bacterial populations. These results validate the use of a commercial antimicrobial spray cabinet, and they are useful for developing application protocols for antimicrobials to control Salmonella during the postharvest processing of jalapeno peppers.

Impact of Built-up-Litter and Commercial Antimicrobials on Salmonella and Campylobacter Contamination of Broiler Carcasses Processed at a Pilot Mobile Poultry-Processing Unit

The small-scale mobile poultry-processing unit (MPPU) produced raw poultry products are of particular food safety concern due to exemption of USDA poultry products inspection act. Limited studies reported the microbial quality and safety of MPPU-processed poultry carcasses. This study evaluated the Salmonella and Campylobacter prevalence in broiler ceca and on MPPU-processed carcasses and efficacy of commercial antimicrobials against Campylobacter jejuni on broilers. In study I, straight-run Hubbard × Cobb broilers (147) were reared for 38 days on clean-shavings (CS, 75) or built-up-litter (BUL, 72) and processed at an MPPU. Aerobic plate counts (APCs), coliforms, Escherichia coli, and yeast/molds (Y/M) of carcasses were analyzed on petrifilms. Ceca and carcass samples underwent microbial analyses for Salmonella and Campylobacter spp. using the modified USDA method and confirmed by API-20e test (Salmonella), latex agglutination immunoassay (Campylobacter), and Gram staining (Campylobacter). Quantitative polymerase chain reaction (CadF gene) identified the prevalence of C. jejuni and Campylobacter coli in ceca and on carcasses. In study II, fresh chilled broiler carcasses were spot inoculated with C. jejuni (4.5 log10 CFU/mL) and then undipped, or dipped into peroxyacetic acid (PAA) (1,000 ppm), lactic acid (5%), lactic and citric acid blend (2.5%), sodium hypochlorite (69 ppm), or a H2O2–PAA mix (SaniDate® 5.0, 0.25%) for 30 s. Surviving C. jejuni was recovered onto Brucella agar. APCs, coliforms, and E. coli populations were similar (P > 0.05) on CS and BUL carcasses. Carcasses of broilers raised on BUL contained a greater (P < 0.05) Y/M population (2.2 log10 CFU/mL) than those reared on CS (1.8 log10 CFU/mL). Salmonella was not detected in any ceca samples, whereas 2.8% of the carcasses from BUL were present with Salmonella. Prevalence of Campylobacter spp., C. jejuni was lower (P < 0.05), and C. coli was similar (P > 0.05) in CS-treated ceca than BUL samples. Prevalence of Campylobacter spp., C. jejuni, and C. coli was not different (P > 0.05) on CS- and BUL-treated carcasses. All antimicrobials reduced C. jejuni by 1.2–2.0 log CFU/mL on carcasses compared with controls. Hence, raising broilers on CS and applying post-chilling antimicrobial treatment can reduce Salmonella and Campylobacter on MPPU-processed broiler carcasses.

A Comparison Study of Quality Attributes of Ground Beef and Veal Patties and Thermal Inactivation of Escherichia coli O157:H7 after Double Pan-Broiling Under Dynamic Conditions

This study compared the quality variation and thermal inactivation of Escherichia coli O157:H7 in non-intact beef and veal. Coarse ground beef and veal patties (2.1 cm thick, 12.4 cm diameter, 180 g) inoculated with E. coli O157:H7, aerobically stored before double pan-broiling for 0–360 s without rest or to 55, 62.5, 71.1, and 76 °C (internal temperature) with 0.5- or 3.5-min rest. Microbial population and qualities including color, cooking losses, pH, water activity, fat, and moisture content, were tested. After cooking the beef and veal patties, the weight losses were 17.83–29%, the pH increased from 5.53–5.60 to 5.74–6.09, the moisture content decreased from 70.53–76.02% to 62.60–67.07%, and the fat content increased (p < 0.05) from 2.19–6.46% to 2.92–9.45%. Cooking beef and veal samples with increasing internal temperatures decreased a* and b* values and increased the L* value. Escherichia coli O157:H7 was more sensitive to heat in veal compared to beef with shorter D-value and “shoulder” time. Cooking to 71.1 and 76 °C reduced E. coli O157:H7 by >6 log CFU/g regardless of rest time. Cooking to 55 °C and 62.5 °C with a 3.5-min rest achieved an additional 1–3 log CFU/g reduction compared to the 0.5-min rest. Results should be useful for developing risk assessment of non-intact beef and veal products.

Comparison of the Efficacy of Electrostatic versus Conventional Sprayer with Commercial Antimicrobials To Inactivate Salmonella, Listeria monocytogenes, and Campylobacter jejuni for Eggs and Economic Feasibility Analysis

This study was conducted to compare the efficacy of antimicrobials sprayed by electrostatic versus conventional sprayer for inactivation of Salmonella, Listeria monocytogenes, and Campylobacter jejuni on eggs and to determine the economic feasibility of these treatments. Eggs were dip inoculated with overnight cultures (18 h) of Salmonella Typhimurium, Salmonella Tennessee, a two-strain mixture of L. monocytogenes, and a three-strain mixture of C. jejuni (microaerophilic condition). Inoculated eggs were then not sprayed or subjected to electrostatic and conventional spraying with peroxyacetic acid (PAA; 0.1%), lactic acid (5.0%), lactic and citric acid blend (2.5%), sodium hypochlorite (SH; 50 ppm), and SaniDate-5.0 (SD [a mixture of PAA and H2O2]; 0.25%) for 30 s (15 s each side). Surviving bacteria on eggshells were recovered on xylose lysine Tergitol 4 agar ( Salmonella), modified Oxford agar ( L. monocytogenes), or Brucella agar ( C. jejuni). Compared with conventional spraying, electrostatic spraying of PAA, SD, and SH achieved significant additional reductions ( P < 0.05) of Salmonella, L. monocytogenes, and C. jejuni of 0.96 to 3.18, 1.19 to 3.05, and 0.96 to 1.62 log CFU per egg, respectively. A simple cost comparison suggests that regardless of the antimicrobial agent used, the cost of using an electrostatic sprayer is 20 to 40% lower than that of a conventional sprayer for a small poultry farm that produces 1,500 eggs per day. Among the five antimicrobials, the total sanitizing cost was lowest for SH, followed by PAA and SD. The results indicated that electrostatic spraying of commercial antimicrobials can be considered an effective and economical approach to enhancing the microbial safety of eggs, especially for small poultry processors.

Food Microbiology Laboratory for the Food Science Student

We will provide food microbiology laboratory training for all students taking this class and emphasize the importance of lab notebook record, and finally we will show students the examples of good lab notebook record.