Thermal inactivation of Salmonella spp. in ground chicken breast or thigh meat

Thermal inactivation of a four‐strain mixture of Salmonella spp. was determined in chicken breast and thigh meat. Inoculated meat was packaged in bags and then completely immersed in a circulating water bath and held at 55, 57.5, 60 and 62.5 °C for pre‐determined lengths of time. When the surviving bacteria were enumerated on tryptic soya agar supplemented with 0.6% yeast extract and 1% pyruvate (non‐selective medium), D‐values (time to inactivate 90% of bacteria) in chicken breast meat were 6.08, 4.77, 3.00 and 0.66 min at 55, 57.5, 60 and 62.5 °C, respectively; the values in thigh meat ranged from 11.48 min at 55 °C to 0.84 min at 62.5 °C. As expected, the measured heat resistance was lower when the recovery medium was selective (xylose lysine deoxycholate agar). Thermal death time values from this study will assist food processors in designing the HACCP plans to effectively eliminate Salmonella spp. in cooked chicken breast and thigh meat.     

Residual glutamic-oxaloacetic transaminase (GOT) activity in thermally processed poultry and poultry products as an indicator of end-point temperatures

Glutamic-oxaloacetic transaminase (GOT) activities in chicken and turkey thigh and breast meat samples, thermally processed at 60–84°C in a model heat-treating system, were evaluated for use as indicators of end-point cooking temperatures (EPT). Wings, breasts, thighs and legs from commercially cooked, whole, roasted chickens and commercially processed products containing chicken and turkey meat were analyzed also to determine if residual GOT activities would indicate compliance with recent FDA/FSIS EPT recommendations. Activities of samples processed in the model system decreased logarithmically with increasing temperatures. GOT activities were higher (P < 0·05) in thigh meat than breast meat in both chicken and turkey samples; activities were higher in turkey than chicken. GOT values for chicken thigh and breast meat at 74°C, the FDA/FSIS recommended EPT for use by food handlers and retailers, were 735 and 164 Sigma-Frankel units ml^?1 (SFU ml^?1), respectively. Values for turkey thigh and breast meat at this temperature were 1080 and 450 SFU ml^?1, respectively. The range of activities was 7–13 SFU ml^?1 in commercially prepared chicken products and 27–161 SFU ml^?1 in turkey products. Analysis of these products showed adequate cooking and compliance with FDA/FSIS recommended EPT for retail sale. These data indicate that residual GOT activity in processed poultry has potential for use as an indicator of EPT.     

Combined effect of salt addition and high-pressure processing on formation of free radicals in chicken thigh and breast muscle

The effect of working pressure, processing time, and salt addition on formation of free radicals in chicken breast and thigh muscle was investigated by electron spin resonance (ESR) spectroscopy using α-(pyridyl-1-oxide)-N-tert-butylnitrone (POBN) as spin trap in order to detect early events in lipid oxidation following high-pressure meat processing. Chicken breast and thigh with and without 3.0% salt added were subjected to high hydrostatic pressure at 200, 400, 600, 800, and 1000 MPa for 5, 15 (only breast), and 30 min. Radical formation increased with increasing pressure and processing time and reached a maximum value in chicken breast for 15 min of processing at 1000 MPa and in chicken thigh for 5 min of processing at 600 MPa. Radical formation was found to be more significant in thigh meat compared to breast meat and salt addition further promoted radical formation in chicken breast and especially in chicken thigh.     

The influence of time elapsed after milking and lactation stage on the lactoperoxidase system of milk in Sahiwal cattle and Nili‐Ravi buffaloes

The effects of time elapsed after milking and lactation stage were assessed on the lactoperoxidase (LP) enzyme activity and concentrations of thiocyanate in Sahiwal cattle (N = 15) and Nili‐Ravi buffaloes (N = 15). The LP activity and thiocyanate concentrations decreased as the time elapsed after milking (P < 0.05) but the concentration of these components increased as the lactation advanced. The LP enzyme activity was sufficient until 12 h post milking but the thiocyanate concentration after 8 h decreased to an insufficient level to activate the LP System, hence additional thiocyanate would be beneficial from external sources. No difference was noted regarding the LPS activity in cattle and buffaloes at the time of collection and subsequently after storage. However, at the end of lactation, the thiocyanate concentration was lower in buffaloes than that in cattle. (P < 0.05).     

Decontamination of deboned chicken legs by vacuum-tumbling in lactic acid solution

Vacuum tumbling in a 1–5% lactic acid solution for a short time (1–10 min) improves the microbiological quality of deboned chicken legs, while inducing a light acidification and water absorption. The most significant variable of the process is the tumbling speed. High tumbling speeds lead to a high decontamination level of the chicken legs with regard to total viable counts and Enterobacteriaceae. Sodium lactate alone is unable to induce any decontamination at the same concentrations. Decontamination is probably more linked to acidification than to lactate ions. The use of vacuum tumbled (1 min in a 1% lactic acid solution) deboned chicken legs in the industrial manufacture of fresh chicken sausages led to a clear decrease in the number of Salmonella‐positive batches. The incidence of positive batches was reduced threefold and the acid decontamination process did not adversely affect the sensory quality of the sausages.     

ANALYSIS AND FORMATION OF ACRYLAMIDE IN FRENCH FRIES AND CHICKEN LEGS DURING FRYING

The analysis and formation of acrylamide in French fries and chicken legs during frying were studied. Results showed that the most appropriate extraction solvent was ethyl acetate, with C‐18 cartridge for purification and 5‐mL deionized water as elution solvent. Dibromination of acrylamide followed by dehydrobromination to 2‐bromopropionamide in the presence of triethylamine was necessary for subsequent analysis by gas chromatography–mass spectrometry. The most appropriate temperature programming condition was as follows: 70C in the beginning, raised to 150C at a rate of 10C/min, maintained for 1 min and to 240C at a rate of 30C/min, maintained for 5 min. Detection was carried out using selected‐ion monitoring mode, and N,N‐dimethylacrylamide was used as internal standard for quantification. French fries and the outer flour portion of chicken legs fried at 180C generated a higher level of acrylamide than at 160C. Compared to soybean oil and palm oil, a lower amount of acrylamide was produced in French fries and the outer flour portion of chicken legs fried in lard. However, no acrylamide was detected in the inner meat portion of fried chicken legs.     

Antimicrobial effect of the lactoperoxidase system in milk activated by immobilized enzymes

Immobilized lactase and glucose oxidase were used to produce H₂O₂ to activate the lactoperoxidase system in milk. The enzymes were immobilized on nylon pellets. With a ratio of 35 g of catalyst/L of milk, a concentration of 0.75 mM was produced in 3 min. Raw milk treatment with the catalyst reduced coliforms by 79%; Staphylococcus aureus reduction was 68%, psychrotrophs 91%, and fungi 100%. Results were similar when milk was treated by addition of H₂O₂. Thiocyanate was not limiting because addition of NaSCN did not increase the effectiveness of the lactoperoxidase system.

The stability of the catalyst was poor when successive treatments were applied to milk, having lost one half of the activity every eight determinations. Activation of the lactoperoxidase system by immobilized enzymes could be of interest if stability could be ensured.     

Effect of activating lactoperoxidase system in cheese milk on the quality of Saint‐Paulin cheese

Saint‐Paulin cheese was made from cow’s milk refrigerated at 4 °C for 72 h and preserved by the lactoperoxidase (LP) system. The effect of the LP system on the microbiological, physicochemical and biochemical properties of cheese over a ripening period of 23 days was investigated, using a control (C0), refrigerated LP‐inactivated cow’s milk (C1) and refrigerated LP‐activated cow’s milk (LPA). The LPA treatment showed the least contamination in flora count, particularly salt‐tolerant bacteria at the end of the ripening period. LPA cheese had significantly lower coliform, yeasts and mould counts (P < 0.05) than the other cheeses; this demonstrated the bacteriostatic effect of the LP system. The proteolysis results showed the least value for LPA cheese as compared with the two other samples, as determined by using sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of casein fractions extracted from the three samples. The findings indicated that the preservation of cow’s cheese milk by the LP system can be used to improve the microbiological quality, inhibit psychotropic germs, correct the losses of soluble nitrogen fractions in the whey and conserve the cheese yield affected by refrigeration.     

Lipid oxidation and colour in pressure‐ and heat‐treated minced chicken thighs

Lipid oxidation and colour in pressurised and heated chicken samples were evaluated. In a preliminary test, raw and overcooked (100 °C/60 min) minced chicken thighs were pressurised (500 MPa/50 °C/30 min). Samples were stored at 4 °C in contact with air. Thiobarbituric acid reactive substances (TBARS) were quantified at 1, 6 and 9 days. Pressure induced oxidation in chicken, but overcooking generated many more secondary oxidation compounds. In a second experiment, raw minced chicken thighs were pressurised (500 MPa/?10, 5, 20 and 50 °C/30 and 60 min) or cooked (90 °C/15 min). Samples were vacuum stored at 4 °C. TBARS were measured at 1 and 9 days, whereas colour parameters (L, a, b and ΔE) were determined at 1 day. No differences in TBARS values were observed between untreated and pressurised samples, whereas cooked samples presented the highest values. Pressurisation for 30 and 60 min generated similar TBARS contents. At 9 days, oxidation values did not increase. Pressurisation and cooking induced marked colour changes. Pressurised samples were lighter and less red than untreated ones. Samples pressurised at 50 °C were the palest and, together with cooked samples, presented the lowest a values. Therefore pressurised chicken thigh cannot be marketed as a fresh product but can be incorporated as an ingredient in ready‐to‐eat meals. Copyright © 2004 Society of Chemical Industry     

Heat resistance of Escherichia coli O157:H7 in cook‐in‐bag ground beef as affected by pH and acidulant†

Summary The heat resistance of a four‐strain mixture of Escherichia coli O157:H7 was tested. The temperature range was 55–62.5 °C and the substrate was beef at pH 4.5 or 5.5, adjusted with either acetic or lactic acid. Inoculated meat, packaged in bags, was completely immersed in a circulating water bath and cooked to an internal temperature of 55, 58, 60, or 62.5 °C in 1 h, and then held for pre‐determined lengths of time. The surviving cell population was enumerated by spiral plating meat samples on tryptic soy agar overlaid with Sorbitol MacConkey agar. Regardless of the acidulant used to modify the pH, the D ‐values at all temperatures were significantly lower (P < 0.05) in ground beef at pH 4.5 as compared with the beef at pH 5.5. At the same pH levels, acetic acid rendered E. coli O157:H7 more sensitive to the lethal effect of heat. The analysis of covariance showed evidence of a significant acidulant and pH interaction on the slopes of the survivor curves at 55 °C. Based on the thermal‐death–time values, contaminated ground beef (pH 5.5/lactic acid) should be heated to an internal temperature of 55 °C for at least 116.3 min and beef (pH 4.5/acetic acid) for 64.8 min to achieve a 4‐log reduction of the pathogen. The heating time at 62.5 °C, to achieve the same level of reduction, was 4.4 and 2.6 min, respectively. Thermal‐death–time values from this study will assist the retail food processors in designing acceptance limits on critical control points that ensure safety of beef originally contaminated with E. coli O157:H7.     

Efficacy of citric acid against Listeria monocytogenes attached to poultry skin during refrigerated storage

The aim of this study was to evaluate the effect of citric acid washing on the growth of Listeria monocytogenes on poultry legs stored at 4 °C for 8 days. Fresh inoculated chicken legs were dipped into either a 0.052, 0.104 or 0.156  m citric acid solution for 5 min or distilled water (control). Surface pH values, sensorial characteristics and L . monocytogenes , mesophiles and psychrotrophs counts were evaluated. Legs washed with 0.156  m citric acid for 5 min showed a significant ( P  < 0.05) inhibitory effect on L . monocytogenes compared with control legs, being about 1.55 log units lower in the first ones than in control legs after 1 day of storage. Treatments with 0.156  m citric acid reduced bacterial growth and preserved reasonable sensorial quality after storage at 4 °C for 8 days.     

Effect of Different Cooking Conditions on the Pasting Properties of Flours of Glutinous Rice Varieties from Lao People’s Democratic Republic

The effect of different rehydration temperatures (30, 40, and 50°C) and cooking times (2.7, 4.7, 6.7, 8.7, and 10.7 min) at 95°C on the pasting properties of three glutinous varieties (Thadokkham-11, Thadokkham-8, and Hom Mali Niaw) from Lao People’s Democratic Republic was investigated using rapid visco analyzer. Non-glutinous varieties (IR64 and Doongara) were also analyzed to compare glutinous (amylose <4.5%) and non-glutinous (amylose >15%) varieties. All rice flours took up water at significantly (p < 0.05) higher rates in the case of increased temperature and soaking time, resulting in a decrease in the onset temperature for pasting. Among the glutinous rices, Thadokkham-8 showed a significant (p < 0.05) decrease in peak viscosity in response to increased rehydration time and temperature. For this variety maximum viscosity (2403.3 mPas) was observed at 1 min of rehydration at 30°C and minimum viscosity (1852.0 mPas) at 15 min of rehydration at 50°C. The viscosity values of Thadokkham-11 and Hom Mali Niaw varieties increased to their highest values (1608.7 and 1477.7 mPa.s, respectively) with an increase in temperature to 40°C for 1 min. In general, the glutinous rices produced weaker gel than non-glutinous rices. Extended holding at cooking temperature (95°C) had a more significant (p < 0.05) effect on the glutinous varieties Thadokkham-8 and Thadokkham-11 than on the non-glutinous varieties (IR64 and Doongara) used in this study.     

Characterizing endogenous and exogenous peroxidase activity for bleaching of fluid whey and retentate

The lactoperoxidase (LP) system may be used to achieve the desired bleaching of fluid whey with the addition of low concentrations (<50 mg/kg) of hydrogen peroxide. The addition of an exogenous peroxidase (EP) to whey may also be used to aid in whey bleaching when the LP system is not fully active. The objectives of this study were to monitor LP activity in previously refrigerated or frozen milk, fluid whey, and whey retentate (10% solids) and to evaluate peroxidase activity in fluid whey and whey retentate (10% solids), with and without additional EP (2, 1, or 0.5 dairy bleaching units), over a range of pH (5.5–6.5) and temperatures (4–60°C). Subsequent experiments were conducted to determine the relationship between enzyme activity and bleaching efficacy. Raw and pasteurized milk, fat-separated pasteurized whey, and whey retentate (10% solids) were evaluated for LP activity following storage at 4 or −20°C, using an established colorimetric method. A response surface model was applied to evaluate both endogenous and EP activity at various temperatures and pH in freshly manufactured whey and retentate. Refrigerated or frozen storage at the parameters evaluated did not affect LP activity in milk, whey, or retentate. In fluid whey, with and without added EP, as pH decreased (to 5.5) and temperature increased (to 60°C), peroxidase activity increased. Retentate with EP exhibited behavior similar to that of fluid whey: as pH decreased and temperature increased, activity increased. However, in retentate without EP, as pH increased and temperature increased, activity increased. Enzyme activity was negatively correlated to bleaching time (time for >80% norbixin destruction) in fluid whey but a linear relationship was not evident in retentate. When fluid whey is bleached enzymatically, if pH is decreased and temperature is increased, the rate of reaction increases (e.g., bleaching occurs in less time). When bleaching in retentate, a higher pH (pH 6.5 vs. pH 5.5) is desired for optimal bleaching by the LP system. Due to processing restraints, this may not be possible for all dairy producers to achieve and, thus, addition of EP could be beneficial to improve bleaching efficacy.     

Inactivation of Salmonella in Shell Eggs by Hot Water Immersion and Its Effect on Quality

Thermal inactivation kinetics of heat resistant strains of Salmonella Enteritidis in shell eggs processed by hot water immersion were determined and the effects of the processing on egg quality were evaluated. Shell eggs were inoculated with a composite of heat resistant Salmonella Enteritidis (SE) strains PT8 C405, 2 (FSIS #OB030832), and 6 (FSIS #OB040159). Eggs were immersed in a circulating hot water bath for various times and temperatures. Come‐up time of the coldest location within the egg was 21 min. SE was reduced by 4.5 log at both hot water immersion treatments of 56.7 C for 60 min and 55.6 °C for 100 min. Decimal reduction times (D‐values) at 54.4, 55.6, and 56.7 °C were 51.8, 14.6, and 9.33 min, respectively. The z‐value was 3.07 °C. Following treatments that resulted in a 4.5 log reduction (56.7 °C/60 min and 55.6 °C/100 min), the surviving population of SE remained static during 4 wk of refrigerated storage. After processing under conditions resulting in 4.5 log reductions, the Haugh unit and albumen height significantly increased (P < 0.01) and yolk index significantly decreased (P < 0.05). The shell dynamic stiffness significantly increased (P < 0.05), while static compression shell strength showed no significant difference (P < 0.05). Vitelline membrane strength significantly increased (P < 0.05); although, no significant difference (P < 0.05) was observed in vitelline membrane elasticity. In summary, the hot water immersion process inactivated heat resistant SE in shell eggs by 4.5 log, but also significantly affected several egg quality characteristics.     

Effect of tumbling time and cooking temperature on quality attributes of cooked ham

This study evaluates effect of tumbling time and cooking temperature on cooking rate, cooking loss (CL), colour, water activity and water‐holding capacity of cooked restructured ham rolls. In experiment were investigated three tumbling times (2, 4 and 6 h) at constant temperature (+4 °C) and three cooking temperatures (76, 86 and 96 °C). It was observed that CL decreased (P < 0.01) from 5.41% to 3.22% with tumbling time (2 h vs. 6 h) but increased (P < 0.01) from 2.35% to 7.25% along with cooking temperature (76 °C vs. 96 °C). In contrast, pH value increased (P < 0.01) from 6.18 to 6.24 with tumbling time (2 h vs. 6 h) but decreased (P < 0.01) from 6.22 to 6.17 along with cooking temperature (76 °C vs. 96 °C). In addition, high temperature had higher efficiency for thermal lethality than low temperature (F₀ values were 19 and 92 min at 96 and 76 °C, respectively). Intermediate tumbling (4 h) and cooking (86 °C) could be preferential.     

The resistance ofListeria monocytogenesto high hydrostatic pressure in foods

Two strains ofListeria monocytogenes(NCTC 11994, Lm1 and a poultry isolate, Lm2) were exposed to high pressure (375MPa) in ultra high temperature (UHT) treated milk, raw chicken mince, raw beef mince, cooked chicken mince and cooked beef mince for up to 30min at ambient temperature. Survival of the two strains in UHT milk was significantly greater than previously observed in non-nutrient phosphate buffered saline (PBS). Survival in cooked chicken mince and cooked beef mince was only marginally greater than survival in PBS, whilst survival in raw chicken and raw beef mince was generally less than observed in PBS. In all food substrates, the proportion of survivors sustaining injury increased with increasing duration of compression.The two strains were also treated at 375MPa in cooked beef mince for up to 30min at 45°C. Inactivation of both strains was greater at 45°C than at ambient temperature. Treatment at 375MPa for 5min at 45°C resulted in approximately 4.5log₈-cycle reduction; however extending the treatment time resulted in only a slight further decrease in cell counts. The effects of temperature (25, 35, 45 and 55°C) on survival at 200 and 375MPa (15min) in UHT milk was also assessed. Increasing the temperature resulted in increasing levels of inactivation.     

Mitochondrial DNA Fragmentation to Monitor Processing Parameters in High Acid,Plant‐Derived Foods

Mitochondrial DNA (mtDNA) fragmentation was assessed in acidified foods. Using quantitative polymerase chain reaction, C_t values measured from fresh, fermented, pasteurized, and stored cucumber mtDNA were determined to be significantly different (P > 0.05) based on processing and shelf‐life. This indicated that the combination of lower temperature thermal processes (hot‐fill at 75 °C for 15 min) and acidified conditions (pH = 3.8) was sufficient to cause mtDNA fragmentation. In studies modeling high acid juices, pasteurization (96 °C, 0 to 24 min) of tomato serum produced C_t values which had high correlation to time‐temperature treatment. Primers producing longer amplicons (approximately 1 kb) targeting the same mitochondrial gene gave greater sensitivity in correlating time‐temperature treatments to C_t values. Lab‐scale pasteurization studies using C_t values derived from the longer amplicon differentiated between heat treatments of tomato serum (95 °C for <2 min). MtDNA fragmentation was shown to be a potential new tool to characterize low temperature (<100 °C) high acid processes (pH < 4.6), nonthermal processes such as vegetable fermentation and holding times of acidified, plant‐derived products.     

Effects of mono- and disaccharides on the antimicrobial activity of bovine lactoperoxidase system

The effects of mono- and disaccharides on the antimicrobial activity of the lactoperoxidase (LPO) system against Salmonella Enteritidis were investigated. The results clearly reveal that most of the sugars inhibit the antimicrobial activity of the LPO system. The inhibitory potency varies depending on the structure of sugar. L-Fructose and D-allose were strongly inhibitive to the action of the LPO system, while sucrose was the weakest inhibitor. The decreased antimicrobial activity is due to the reduction of LPO catalytic activity by sugar. An inhibitory kinetic study showed the noncompetitive inhibitor. D-Allose and L-fructose yielded strikingly low K(i) values of 0.36 and 0.42 mM, respectively, while the K(i) values of the other sugars ranged from 1.37 to 3.60 mM. Since LPO activity is inhibited by the saccharides, the sugar content in food should be considered when the LPO system is applied to the preservation of food.     

Enhanced elimination of Salmonella Typhimurium and Campylobacter jejuni on chicken skin by sequential exposure to ultrasound and peroxyacetic acid

The present study investigated the effects of combined ultrasound (37 kHz, 380 W for 5 min) and peroxyacetic acid (PAA; 50–200 ppm) treatment on the reduction of Salmonella Typhimurium and Campylobacter jejuni on chicken skin. Ultrasound was not sufficient to inactivate S. Typhimurium (0.48 log CFU/g reduction) or C. jejuni (0.25 log CFU/g reduction), whereas PAA significantly (p < .05) reduced S. Typhimurium (0.93–1.59 log CFU/g reduction) and C. jejuni (0.77–1.52 log CFU/g reduction). However, maximum reductions of 2.21 and 2.08 log CFU/g were observed for S. Typhimurium and C. jejuni, respectively, for combined treatment with 5 min of ultrasound and 200 ppm PAA. Our results indicate that a combination of ultrasound treatment for 5 min and 200 ppm PAA was more effective in reducing S. Typhimurium and C. jejuni compared to the individual treatments, without significantly affecting the color or texture of the chicken skin, thus, demonstrating its potential to increase the microbial safety during poultry processing.