Effect of potassium sorbate washing on the growth of Listeria monocytogenes on fresh poultry

Food Control 18 (2007) 842–846 www.elsevier.com/locate/foodcont

EVect of potassium sorbate washing on the growth of Listeria monocytogenes on fresh poultry E. González-Fandos ¤, J.L. Dominguez Food Technology Department, University of La Rioja, Madre de Dios 51, 26006 Logroño (La Rioja), Spain Received 16 October 2005; received in revised form 15 April 2006; accepted 17 April 2006

Abstract This work evaluated the eVect of potassium sorbate washing on the growth of Listeria monocytogenes on poultry legs stored at 4 °C for 7 days. Fresh inoculated chicken legs were dipped into either a 2.5% (w/v) or 5% potassium sorbate solution or distilled water (control). Changes in mesophiles, pychrotrophic counts and sensorial characteristics (odor, color, texture and overall appearance) were also evaluated. The shelf life of the samples washed with potassium sorbate was extended by at least 2 days over the control samples washed with distilled water. Legs washed with 5% potassium sorbate showed a signiWcant (p < 0.05) inhibitory eVect on L. monocytogenes compared to control legs, with a decrease of about 1.3 log units after 7 days of storage. Sensory quality was not adversely aVected by potassium sorbate. © 2006 Elsevier Ltd. All rights reserved. Keywords: Poultry; Decontamination; Potassium sorbate; Listeria monocytogenes

1. Introduction Meat and poultry products are often identiWed as the source of foodborne outbreaks of listeriosis (ICMSF, 1998). Raw poultry is a well-recognized source of Listeria monocytogenes, and many surveys have conWrmed the presence of this pathogen on fresh poultry (Bailey, Fletcher, & Cox, 1989; Genigeorgis, Dutulescu, & Garazabar, 1989; Uyttendaele, Neyts, Lips, & Devebere, 1997). Some authors have associated cases of listeriosis with the consumption of undercooked chicken (Schuchat, Deaver, Wenger, Swaminathan, & Broome, 1992). The contamination of raw chicken with bacterial pathogens has important implications for public health. There is a great interest in reducing surface microbial contamination of carcass meat, with particular regard to reducing the levels of pathogens. One approach has been the application of decontamination treatments during processing. Some *

Corresponding author. Tel.: +34 941 299728; fax: +34 941 299721. E-mail address: [email protected] (E. González-Fandos).

0956-7135/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2006.04.008

studied decontamination treatments for poultry cacasses are: chlorine, organic acids, phosphates, bacteriocins, hydrogen peroxide, ozone, water, ultrahigh hydrostatic pressure, irradiation, pulsed-Weld electricity, ultrasonic energy and UV light (Bolder, 1987). Organic acids and their salts (acetic, lactic, propionic and sorbic) exert antibacterial activity. They have been traditionally used as food preservatives and are generally recognized as safe substances (GRAS) approved as food additives by E.C., FAO/WHO and FDA (Surekha & Reddy, 2000). Sorbic acid and its salts have several advantages as food preservatives. Initially thought to have only antimycotic activity, they are now known to also inhibit a wide range of bacteria, particularly aerobic catalase-positive organisms (Thomas, 2000). EVective concentrations do not normally alter product taste or odor. These preservatives are also considered harmless (Thomas, 2000). Potassium salt is commonly used because it is more stable. Furthermore, its greater solubility extends the use of sorbate to solutions appropriate for dipping and spraying (Thomas, 2000).

E. González-Fandos, J.L. Dominguez / Food Control 18 (2007) 842–846

Potassium sorbate has been extensively investigated as an antimicrobial agent for use in meat including poultry to extend its shelf life and inhibit the growth of pathogens such as Salmonella or Staphylococcus aureus (Ahmed et al., 2003; Elliot, Tomlins, & Gray, 1985; Robach & Sofos, 1982; To & Robach, 1980). Moreover, eVective concentrations do not aVect sensory characteristics of poultry (Cunningham, 1979). The ability of sorbic acid and its salts to inhibit L. monocytogenes has been studied in laboratory media and in some foods such as cheese, meat products or Wsh (Dorsa, Marshall, & Semien, 1993; El-Shenawy & Marth, 1988; Moir & Eyles, 1992; Ryser & Marth, 1988; Samelis et al., 2001). However, there are few studies on the eVect of sorbic acid or its salts on L. monocytogenes growth on poultry. The aim of this work was to evaluate the eVectiveness of a sorbate dip to control the growth of L. monocytogenes on poultry stored at 4 °C. Microbiological and sensorial quality were also evaluated. 2. Materials and methods 2.1. Preparation of bacterial inoculum The L. monocytogenes serotype 1/2a strain CECT 932 was grown in Tryptone soya broth (Oxoid, Hampshire, UK) at 30 °C for 18 h to achieve a viable cell population of 9 log cfu/ml. The culture was then transferred to a sterile centrifuge bottle and centrifuged at 10,000g for 10 min at 4 °C. The supernatant was decanted and the pellet resuspended in sterile 0.1% peptone solution (Merck, Darmstadt, Germany) (pH 6.2) by vortexing. The washing step was repeated twice. The suspension of washed cells was diluted in a sterile 0.1% peptone solution to obtain an appropriate cell concentration for inoculation of sterile distilled water. 2.2. Inoculation of poultry and treatment A total of 30 fresh chicken legs were obtained from a poultry processing plant (La Rioja, Spain). The legs were placed on crushed ice and transported to the laboratory. Fresh chicken legs were inoculated with L. monocytogenes by dipping them into a suspension of this pathogen (7 log cfu/ml) for 5 min at room temperature. After the inoculation, the legs were removed and kept for 30 min at room temperature to allow the attachment of inoculated cells to the skin. The inoculated poultry legs were divided into three groups, each containing 10 legs. Samples of each group were dipped for 5 min into sterile distilled water (control) (group one), 2.5% (w/v) (group 2) or 5% (group 3) potassium sorbate (Scharlau, Barcelona, Spain). After these treatments, the legs were removed and drained for 5 min and stored individually in sterile bags at 4 °C for 7 days. Samples were taken on days 0 (after dipping treatment), 1, 3, 5 and 7. On the sampling days, two legs of each group

843

were taken out from storage to perform microbiological, pH and sensorial analysis. 2.3. Sensorial analysis The samples were evaluated for overall acceptability with regard to odor, color, texture and overall appearance by a panel of 9 members. A structured hedonic scale (Anzaldúa-Morales, 1994) with numerical scores ranging from 7 (I like it very much) to 1 (I dislike it very much) was used. A score of 3 was considered the borderline of acceptability. 2.4. Microbiological analyses and pH determination Ten grams of skin were aseptically weighed and homogenised in a Stomacher (IUL, Barcelona, Spain) for 2 min with 90 ml of sterile peptone water (Oxoid). Further decimal dilutions were made with the same diluent. The total number of mesophilic microorganisms was determined on plate count agar (PCA, Merck) following the pour plate method, incubating at 30 °C for 72 h (ICMSF, 1978). Psychrotrophs were determined on plate count agar (Merck) with an incubation temperature of 7 °C for 10 days, following the pour plate method (ICMSF, 1978). Listeria spp. were determined following the surface plate method on Palcam agar with an incubation temperature of 30 °C for 48 h (Mossel, Corry, Struijk, & Baird, 1995). All analyses were performed in duplicate. For pH determination, 5 g of skin were blended with 10 ml of distilled water. The pH of the homogenized sample was measured with a Crison model 2002 pH meter (Crison Instruments, Barcelona, Spain). Determinations of pH were performed in duplicate. 2.5. Statistical analysis Analysis of variance was performed using the SYSTAT program for Windows; Statistics version 5.0 (Evanston, IL). Tukey’s test for comparison of means was performed using the same program. Plate count data were converted to logarithms prior to their statistical treatment. All experiments were carried out in duplicate. SigniWcance level was deWned at p < 0.05. 3. Results and discussion The eVect on mesophiles and psychrotrophs of dipping the legs into potassium sorbate is shown in Fig. 1. SigniWcant diVerences (p < 0.05) in mesophiles and psychrotrophs counts were found between the legs treated with 5% potassium sorbate and the control legs. The data obtained showed that a 5 min dip in 5% w/v potassium sorbate reduced mesophiles counts between 0.5 and 1.2 log cycles compared to the control legs throughout storage. However, no signiWcant diVerences were found for these bacterial counts between the samples treated with 2.5% potassium

844

E. González-Fandos, J.L. Dominguez / Food Control 18 (2007) 842–846

(a) Mesophiles

(a) Odor 7

10

6 5

6

Score

log (cfu/g)

8

4

4 3

C

2%SP

2

2%SP

5%SP

1

5%SP

C

0

2 0

2

4

6

0

8

1

2

Days of storage

(b) Psychrotrophs

4

5

6

7

4 3 5 Days of storage

6

7

(b) Color

10

7 6

8

5 Score

log (cfu/g)

3

Days of storage

6 C 4

4

C

3

2%SP

2

5%SP

1

2%SP 5%SP

0

2 0

1

2

3

4

5

6

7

Days of storage

Fig. 1. Evolution of microbial population in chickens legs treated with potassium sorbate. Control (䊏), potassium sorbate 2% (w/v) (2% SP) (䊉), potassium sorbate 5% (w/v) (5% SP) (䉱) (a) mesophile counts and (b) psychrotrophs. The data are the mean values of two replicates.

sorbate and the control samples, although lower counts were observed with 2.5% potassium sorbate. Our results agree with those reported by Morrison and Fleet (1985), who found that immersion of chicken carcass in 2.5% potassium sorbate did not greatly reduce total counts. To and Robach (1980) also observed that dipping a freshly chilled carcass into a 5% (w/v) solution of potassium sorbate for 1 min reduced psychrotrophic counts. Greer (1982) showed that dipping fresh beef into a 10% potassium sorbate solution inhibited growth of psychrotrophic spoilage bacteria by extending the lag phase of growth without aVecting the growth rate. As a result, these authors reported that shelf life was extended by 2 days. Also Mendonca, Molins, Kraft, and Walker (1989) reported that 10% potassium sorbate solutions reduced the mesophiles and psycrotrophs counts in pork meat. Robach and Ivey (1978) reported that a 5% potassium sorbate dip signiWcantly reduced the total plate count of chicken and extended the shelf life of fresh poultry. No signiWcant diVerences were found in pH values among the diVerent treatments. Initial pH values (day 0) were between 6.52 and 6.55. During storage, pH decreased Wrst by about 0.01 units but increased after 3 days, being 6.7–6.8 after 7 days of storage.

0

1

2

Fig. 2. Evolution of sensorial scores in chickens legs treated with sorbate potassium. Control (䊏), potassium sorbate 2% (w/v) (2% SP) (䊉), potassium sorbate 5% (w/v) (5% SP) (䉱); (a) odor and (b) color.

Sensorial data (Fig. 2) indicated that the panel members could not distinguish those legs dipped in 2% or 5% sorbate from those dipped in distilled water on day 0. Thus, sorbate treatment did not have perceived adverse eVects on poultry legs quality characteristics. Other authors have also reported no sensorial negative eVects of sorbate dips. In this sense, Cunningham (1979) reported that a 5% or 10% potassium sorbate dip for 30–60 s did not aVect sensory characteristics of poultry. After 5 days of storage at 4 °C oV-odors were apparent in the control legs, and after 7 days in legs treated with 2.5% of potassium sorbate. These results agree with those reported by Robach and Ivey (1978), who observed oVodor in chicken breasts dipped in 2.5% sorbate two days later than in control legs. OV-odors were noticed by the panel members when the counts approached 9 log cfu/g. To compare our results with those reported by other authors the data were transformed to log cfu/cm2. It was found that 1 g of skin corresponded to an average of 6.88 cm2 of skin. Thus, 9 log cfu/g corresponded to 8.16 log cfu/cm2. Other authors have reported spoilage odors in poultry when counts approached 7–8 cfu/cm2 (Barnes, 1976; Elliot et al., 1985; Studer, Schmidt, Gallo, & Schmidt, 1988). After 5 days of storage, mesophiles and psychrotrophs reached populations above 9 log cfu/g in control legs.

E. González-Fandos, J.L. Dominguez / Food Control 18 (2007) 842–846 10

log (cfu/g)

8

6 C 4

2%SP 5%SP

2 0

1

2

3 4 5 Days of storage

6

7

Fig. 3. EVect of a 5 min potassium sorbate dip on the growth of L. monocytogenes on chicken legs at 4 °C. Control (䊏), potassium sorbate 2% (w/v) (2% SP) (䊉), potassium sorbate 5% (w/v) (5% SP) (䉱).The data are the mean values of two replicates.

However, in the legs treated with 5% of potassium sorbate, mesophiles and psychrotrophs counts were below 9 log cfu/ g after 7 days of storage at 4 °C and signs of spoilage were not detected after 7 days of storage. When the legs were treated with 2% potassium sorbate, populations above 9 log cfu/g were detected after 7 days of storage and sensorial scores were above those reached by the control legs, these legs were rejected after 7 days of storage. Other authors such as Cunningham (1979) reported longer shelf life of poultry parts treated with sorbate maybe due to the higher concentration used (10%), the lower initial counts and the diVerent poultry part studied. It is known that the initial number of microorganisms present greatly inXuences the shelf life of poultry. On the other hand, the pH of poultry parts can aVect the spoilage rate (ICMSF, 1998). It should be pointed out that poultry leg muscle has a pH of 6.4–6.7, while other parts like breast muscle have lower pH values (5.7–5.9). Poultry leg meat spoils more quickly than breast meat, as the higher pH has an impact on the growth of certain spoilage bacteria that can multiply on leg muscle but only slowly or not at all on breast muscle (Barnes, 1976). The high pH of skin must also be considered. To and Robach (1980) also observed that the reWgerated shelf life of fresh whole broilers at 3 °C was extended by dipping a freshly chilled carcass in 5% (w/v) solution of potassium sorbate for 1 min. Fig. 3 shows the eVect of sorbate treatment on the growth of L. monocytogenes inoculated onto legs. SigniWcant reductions in the L. monocytogenes populations were observed on days 1,3, 5 and 7 of storage compared to the control samples. Throughout the 7 days of storage, L. monocytogenes counts on legs treated with 5% potassium sorbate were 0.6–1.3 log cycles lower than on untreated legs. Treated samples showed an extended lag phase of L. monocytogenes and lower counts throughout storage compared with control legs. The ability of sorbic acid and its salts to inhibit L. monocytogenes has been studied in laboratory media and in some

845

foods (El-Shenawy & Marth, 1988; Moir & Eyles, 1992; Ryser & Marth, 1988). Dorsa et al. (1993) also reported that spray application of 0.03 g/kg of potassium sorbate extended the lag phase of L. monocytogenes on crawWsh meat by 2 days. However, they observed that after 10 d at 4 °C, the microorganism achieved the maximum population size. The increase in the initial lag phase had no eVect on the eventual growth rate of the bacterium. Therefore, these authors indicated that potassium sorbate has little or no beneWt in adding any degree of safety against L. monocytogenes on crawWsh tail meat. In contrast, other authors reported the eYcacy of sorbate treatment. Samelis et al. (2001) observed that sliced pork bologna treated with 5% potassium sorbate could be stored for 50 days before a signiWcant increase in L. monocytogenes occured. Nevertheless, sorbate has a bacteriostatic eVect on L. monocytogenes and no listericidal eVect has been observed according to other authors (Buncic, Fitzgerald, Bell, & Hudson, 1995). ConXicting reports on the eYcacy of sorbate against L. monocytogenes may be due to variations in the media or food, pH or sorbate concentration (Thomas, 2000). According to data collected by El-Shenawy and Marth (1988) the ability of potassium sorbate to prevent growth of L. monocytogenes is related to temperature and pH. The lower the storage temperature and pH of the medium, the greater was the eVectiveness of sorbates against L. monocytogenes. It must be highlighted that Uyttendaele et al. (1997) reported that among chicken parts, L. monocytogenes was predominantly isolated from chicken legs and chicken wings, the parts that are still partially covered with skin. This pathogen is mainly located on the skin surface of poultry carcasses and to a lesser extent in the meat. On the other hand, the higher pH of leg meat may provide more favourable conditions for multiplication of L. monocytogenes (ICMSF, 1998). L. monocytogenes can grow at temperatures as low as 4 °C. Thus, this bacterium is a particular food-borne hazard because of the ability to replicate, albeit slowly at refrigeration temperatures. 4. Conclusions Poultry legs treated with 5% potassium sorbate can preserve a reasonable sensorial quality after storage at 4 °C for 7 days, although it must be pointed that high L. monocytogenes populations can be found in inoculated legs. Nevertheless, a dip into sorbate solutions reduced L. monocytogenes populations between 0.6 and 1.3 log units. Acknowledgement The authors thank the Regional Government of La Rioja (Spain) for its Wnancial support (Project Reference ANGI 2002/08).

846

E. González-Fandos, J.L. Dominguez / Food Control 18 (2007) 842–846

References Ahmed, S. N., Chattopadhyay, U. K., Sherikar, A. T., Waskar, V. S., Paturkar, A. M., Latha, C., et al. (2003). Chemical sprays as a method for improvement in microbiological quality and shelf-life of fresh sheep and goat meats during refrigeration storage (5–7 °C). Meat Science, 63, 339–344. Anzaldúa-Morales, A. (1994). La evaluación sensorial de los alimentos en la teoria y en la práctica. Zaragoza: Acribia. Bailey, J. S., Fletcher, D. L., & Cox, N. A. (1989). Recovery and serotype distribution of Listeria monocytogenes from broiler chickens in the southeastern United States. Journal of Food Protection, 52, 148–150. Barnes, E. M. (1976). Microbiological problems of poultry at refrigerator temperatures – a review. Journal Science Food Agriculture, 27, 777–782. Bolder, N. M. (1987). Decontamination of meat and poultry carcasses. Trends in Food Science and Technology, 8, 221–227. Buncic, S., Fitzgerald, C. M., Bell, R. G., & Hudson, J. A. (1995). Individual and combined listericidal eVects of sodium lactate, potassium sorbate, nisin and curing salts at refrigeration temperature. Journal of Food Safety, 15, 247–264. Cunningham, F. E. (1979). Shelf-life and quality characteristics of poultry parts dipped in potassium sorbate. Journal of Food Science, 44, 863– 864. Dorsa, W. J., Marshall, D. L., & Semien, M. (1993). EVect of potassium sorbate and citric acid sprays on growth of Listeria monocytogenes on cooked crawWsh tail meat at 4 °C. Lebensmittel-Wissenschaft und Technology, 26, 480–483. Elliot, P. H., Tomlins, R. J., & Gray, R. J. H. (1985). Control of microbial spoilage on fresh poultry using a combination potassium sorbate/carbon dioxide packaging system. Journal of Food Science, 50, 1360–1363. El-Shenawy, M. A., & Marth, E. H. (1988). Inhibition and inactivation of Listeria monocytogenes by sorbic acid. Journal of Food Protection, 51, 842–847. Genigeorgis, C. A., Dutulescu, D., & Garazabar, J. F. (1989). Prevalence of Listeria spp. in poultry meat at the supermarket and slaughterhouse level. Journal of Food Protection, 52, 618–624. Greer, G. C. (1982). Mechanism of beef shelf life extension by sorbate. Journal of Food Protection, 45, 82–83. ICMSF (International Commission on Microbiological SpeciWcations for Foods) (1978). Microorganisms in foods (2nd ed.). 1: Their signiWcance and methods of enumeration. Toronto: University of Toronto Press. ICMSF (International commission on microbiological speciWcations for foods) (1998). Microorganisms in foods. Microbial speciWcations of food commodities (Vol. 6). London: Blackie Academic & Professional. Mendonca, A. F., Molins, R. A., Kraft, A. A., & Walker, H. W. (1989). EVects of potassium sorbate, sodium acetate, phosphates and sodium

chloride alone or in combination on shelf life of vacuum-packaged pork chops. Journal of Food Science, 54, 302–306. Moir, C. J., & Eyles, M. J. (1992). Inhibition, injury and inactivation of four psychrotrophic foodborne bacteria by the preservatives methyl p-hydroxybenzoate and potassium sorbate. Journal of Food Protection, 55, 360–366. Morrison, G. J., & Fleet, G. H. (1985). Reduction of Salmonella on chicken carcasses by immersion treatments. Journal of Food Protection, 48, 939–943. Mossel, D. A. A., Corry, J. E. L., Struijk, C. B., & Baird, R. M. (1995). Essentials of the microbiology of foods. A textbook for advanced studies Chichester: John Wiley & Sons. Robach, M. C., & Ivey, F. J. (1978). Antimicrobial eYcacy of a potassium sorbate dip on freshly processed poultry. Journal of Food Protection, 41, 284–288. Robach, M. C., & Sofos, J. N. (1982). Use of sorbates in meat products, fresh poultry and poultry products: a review. Journal of Food Protection, 45, 374–383. Ryser, E. T., & Marth, E. H. (1988). Survival of Listeria monocytogenes in cold-pack cheese and food during storage. Journal of Food Protection, 51, 615–621, 625. Samelis, J., Sofos, J. N., Kain, M. L., Scanga, J. A., Belk, K. E., & Smith, G. C. (2001). Organic acids and their salts as dipping solutions to control Listeria monocytogenes inoculated following processing of sliced pork bologna stored at 4 °C in vacuum packages. Journal of Food Protection, 64, 1722–1729. Schuchat, A., Deaver, K., Wenger, J. D., Swaminathan, B., & Broome, C. V. (1992). Role of food in sporadic listeriosis: I Case-control-study of dietary risk factors. Journal of American Medical Association, 267, 2041–2045. Studer, P., Schmidt, R. E., Gallo, L., & Schmidt, W. (1988). Microbial spoilage of refrigerated fresh broilers. II EVect of packaging on microbial association of poultry carcasses. Lebensmittel-Wissenschaft und Technology, 21, 224–228. Surekha, M., & Reddy, S. M. (2000). Preservatives. ClassiWcation and properties. In R. K. Robinson, C. A. Batt, & C. Patel (Eds.), Encyclopedia of food microbiology (pp. 1710–1717). New York: Academic Press. Thomas, L. V. (2000). Preservatives. Sorbic acid. In R. K. Robinson, C. A. Batt, & C. Patel (Eds.), Encyclopedia of food microbiology (pp. 1769– 1776). New York: Academic Press. To, E. C., & Robach, M. C. (1980). Potassium sorbate dip as a method of extending shelf life and inhibiting the growth of Salmonella and Staphylococcus aureus on fresh, whole broilers. Poultry Science, 59, 726–730. Uyttendaele, M. R., Neyts, K. D., Lips, R. M., & Devebere, J. M. (1997). Incidence of Listeria monocytogenes in poultry and poultry products obtained from Belgian and French abbatoirs. Food Microbiology, 14, 339–345.