Modeling the effects of sucuk production technique on Listeria monocytogenes, aerobic bacteria and lactic acid bacteria during ripening and storage

food and bioproducts processing 86 (2008) 220–226

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Modeling the effects of sucuk production technique on Listeria monocytogenes, aerobic bacteria and lactic acid bacteria during ripening and storage Osman Erkmen Department of Food Engineering, University of Gaziantep, Faculty of Engineering, 27310 Gaziantep, Turkey

article info

abstract

Article history:

The modeling of sucuk (Turkish dry-fermented sausage) production techniques on the

Received 30 May 2007

survival of Listeria monocytogenes, aerobic bacteria (AB), lactic acid bacteria (LAB), and yeasts

Accepted 24 July 2007

and molds (YM) during ripening and storage periods were studied. Effect of L. monocytogenes initially contaminated level (low, medium and high contaminated levels) with sucuk dough was also studied. Survival data were analyzed by non-linear regression of modified-Gom-

Keywords:

pertz and logistic equations to generate ‘‘best fit’’. L. monocytogenes was immediately reduced

Sucuk

during ripening period (during 15 days) in sucuks produced from both controlled and

Listeria monocytogenes

traditional methods. The reduction in the number of L. monocytogenes was also continued

Modified-Gompertz model

during storage periods (15 days). There was no survival of L. monocytogenes after 25 days (10

Logistic model

days storage) in sucuks contaminated with low level of L. monocytogenes ripened in both

Production techniques

methods. AB, LAB and MY were also reduced during ripening and storage periods. Parameters of non-linear modified-Gompertz and logistic models of L. monocytogenes, AB, LAB and YM in sucuks ripened in controlled and traditional methods were matched in a satisfactory way during ripening and storage periods. Both the modified-Gompertz and logistic models showed good fit to all the survival curves as assessed using the root mean square error (RMSE) and the correlation coefficient (R2) between the experimental and predicted values but the modified-Gompertz model best fit (R2  0.98) than the logistic model (R2  0.96). As a consequence, the model provides parameters for different production methods in modified-Gompertz model against microorganisms. # 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1.

Introduction

Traditional sucuks (Turkish dry-fermented sausages) are wellknown and very popular meat products in Turkey. Nowadays, sucuks are produced throughout the year at butcher shops and by manufacturing companies from sheep and/or beef meat, beef fat or tail fat, salt, sugar, nitrite/nitrate, garlic and various spices such as black pepper, red pepper, cumin, cinnamon, allspice, clove (Bozkurt and Erkmen, 2003; Aksu and Kaya, 2004). Sucuk dough is stuffed into natural cattle small intestine cases which are then hung to ripening in dry in air at 18–22 8C for 15 days and stored at 4 8C. Like all fermented sausages, sucuks have a long storage life due to the added salt, the antimicrobial compounds such as additives (nitrite,

nitrate), low pH and water activity (Bozkurt and Erkmen, 2003; Soyer et al., 2005). Listeria monocytogenes, the causal agent of listeriosis, is a Gram-positive, rod-shaped and psychrotrophic pathogen which is widely distributed in the natural environment and consequently present in various animal products and in vegetables (Johnson et al., 1990; Erkmen, 2007). L. monocytogenes can contaminate meat and meat products during slaughter, processing and production, can persist and grow at low and high pH values, at low water activity and at refrigeration temperatures, and may cause serious food safety problems for consumers (Johnson et al., 1990; Tyopponen et al., 2003; Colak et al., 2007; Thevenot et al., 2005). L. monocytogenes is known to survive at the commercial dry

E-mail address: [email protected]. 0960-3085/$ – see front matter # 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fbp.2007.10.002

food and bioproducts processing 86 (2008) 220–226

sausage manufacturing process (Goulet et al., 1998; Ryser and Donnelly, 2001; Frye et al., 2002). In addition, studies have shown that L. monocytogenes is capable of contaminating food processing machines with bacterial attachment and biofilm formation, representing a source of potential contamination of food products. Once attached to a surface, microorganisms appear to be more difficult to be removed (Autio et al., 1999; Johnson et al., 1990; Soyer et al., 2005). Listeriosis has various symptoms such as meningitis, spontaneous abortion, etc., and a mortality rate of 20–30% (Rocourt et al., 2000; Ryser and Donnelly, 2001). Consumption of meat products contaminated with L. monocytogenes can lead to listeriosis (Hugas et al., 2002). L. monocytogenes has been isolated at levels from 3.7 to 20.3% in cured meat, fresh meat, uncooked and cooked sausages, and intermediate meat products (Noack and Jockel, 1993; Gallarda et al., 1998). Colak et al. (2007) reported that 21.0 and 11.6% of sucuk samples from the wider area of I˙stanbul (Turkey) were found to be positive for Listeria spp. and L. monocytogenes, respectively. Siriken et al. (2006) found that 7% of sucuk samples from the wider area of Afyon (Turkey) were found to be positive for L. monocytogenes. Mathematical models are mainly used for predicting the survival of microorganisms in foods. They include the effect of factors such as temperature, aw, pH, production technique, gaseous atmosphere, the content of organic acids or other preserving methods. The process of modeling usually begins with the fitting of experimental data to models which are mathematical formulas describing microorganisms survival curves (McMeeken et al., 1993; Walker and Jones, 1994). Among meat products, the consumption and production of sucuk is widespread in Turkey. In spite of its popularity, little data is available on the survival of L. monocytogenes and characterization of potential bacterial health risks in sucuks. Therefore, the present study was designed to investigate and to model the effect of production techniques of sucuks (controlled and traditional) on L. monocytogenes, aerobic bacteria, lactic acid bacteria, and yeasts and molds during ripening and storage periods. Modeling the survival of L. monocytogenes depending on initial contamination (addition) levels was also studied. The changes in time of the number of microorganisms and obtaining information about the number of log cycles of survival (log(cfu) g)), the time required to reach the maximum inactivation rate (days); the specific inactivation rate (day1), the maximum specific inactivation rate (cfu g1 day1) were predicted using modified-Gompertz and logistic models.

2.

Materials and methods

2.1.

Culture

level about 1.26  106 colony forming unit (cfu) g1, (ii) medium contamination level (MCL) to obtain the inoculation level about 2.0  105 cfu g1 and (iii) low contamination level (LCL) to obtain the inoculation level about 2.60  104 cfu g1. The final number of L. monocytogenes in sucuk dough was detected by spread plate counting method on duplicate plates of Listeria selective agar (LSA; Difco) (Erkmen, 2007). The cultures used in all experiments were freshly prepared by the same procedure. After inoculation of working culture, the dough was mixed thoroughly.

2.2.

Sucuk preparation

Meat and spices were used to prepare sucuk dough according to the following recipe: 750 g/kg sheep red meat (about 18% fat), 180.74 g/kg tail fat, 5.5 g/kg cumin, 1.1 g/kg cinnamon, 11.42 g/kg allspice, 0.48 g/kg clove, 5.5 g/kg red pepper, 11 g/kg black pepper, 20.76 g/kg garlic, 4.4 g/kg sugar (sucrose), 18 g/kg salt, 300 mg/kg nitrite and 2.1 g/kg olive oil. The meat was minced in a meat grinder (Tefal Prep’Line 1600, France) to about 1.3–2.5 cm, and spices were added and mixed with minced meat. Each dough was held for 24 h at 4 8C (conditioning) and then refrigerated (4 8C) tailed fat was added, mixed and minced to about 3 mm in the meat grinder. After that, each dough was filled (about 100 g) into natural casings (38 mm diameter) under aseptic conditions using a filling machine (Tefal, Prep’Line 1600, France) at 4 8C. After the preparation of sucuk, they were divided into two groups. One group was ripened in room temperature (traditional method) and the other in an incubator (controlled method). Two control sucuk doughs (without L. monocytogenes inoculation) were also ripened for both of traditional and controlled methods. The duplicate batches for each sucuk type were prepared. In the traditional method, sucuks were ripened (manufactured) during 15 days at room temperature (at 24 8C with about 48% RH). In the controlled method, sucuks were ripened under controlled conditions in an incubator. Controlled ripening was carried out from 95 to 60% RH and from 22 to 18 8C during 15 days as; for 2 days at 25 8C with 90% RH, for 2 days at 20 8C with 80% RH, for 3 days at 18 8C with 75% RH, for 3 days at 18 8C with 67% RH, for 5 days at 18 8C with 60% RH. Ripened sucuks (for 15 days) from the traditional and controlled methods were immediately stored at refrigerated temperature (4 8C for 15 days). This production conditions were chosen according to the Turkish Standard indicated for sucuk production (Bozkurt and Erkmen, 2003). Storage was not extended beyond 15 days since the most of sucuks were consumed in Turkey after ripening.

2.3.

L. monocytogenes type 4a KUEN 136 was obtained from Microorganisms Collection Center, Faculty of Medicine, University of I˙stanbul (I˙stanbul, Turkey). The working cultures were maintained on brain heart infusion agar (BHIA; Difco, Detroit) slants and stored at 4 8C. The cultures for experiments were subcultured twice in brain heart infusion broth (BHIB; Difco, Detroit), and incubated at 35 8C for 24 h. Overnight culture was centrifuged at 4000  g for 30 min under aseptic conditions at 25 8C. The cells were used as working culture for inoculation into sucuk dough. The working culture was added to sucuk dough to obtain: (i) high contamination level (HCL): L. monocytogenes (working culture) was added to obtain the inoculation

221

Preparation of sucuk samples for analysis

Analyses were conducted on minced meat, sucuk dough after 1, 2, 7, 15, 20, 25 and 30 days of production. Two sucuks (each about 100 g) were removed and cut into small pieces (about 5 mm  5 mm  5 mm) under aseptic condition. Fifty grams of sucuk sample was homogenized in sterile Warring blender (Torrington, CT, USA) containing 450 ml 0.1% sterile peptone water. Homogenized sucuk samples were serially diluted using 0.1% sterile peptone water.

2.4.

Microbiological determinations and pH

Aerobic bacteria (AB), yeasts and molds (YM) and lactic acid bacteria (LAB) counts were determined by spread plating

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food and bioproducts processing 86 (2008) 220–226

0.5 ml of diluted samples on duplicate plates of plate count agar (PCA; Merck, Darmstadt, Germany), potato dextrose agar (PDA; Merck, Darmstadt, Germany), de Man Rogosa Sharpe (MRS) agar (Merck, Darmstadt, Germany), respectively. The plates were incubated at 37 8C for 24 h for AB counts, at 25 8C for 3 days for YM counts and at 30 8C for 2 days for LAB counts (Erkmen, 2007). L. monocytogenes was counted by spread plating

Fig. 2 – Fitting of logistic model to experimental data (data point) of L. monocytogenes (*, *), aerobic bacteria (AB) (&, &), lactic acid bacteria (LAB) (~, ~) and yeasts and molds (YM) (^, ^) survival in sucuks with LCL (a), MCL (b) and HCL (c) produced at controlled (empty symbols) and traditional (full symbols) methods during ripening (15 days) and storage (15 days) periods.

Fig. 1 – Fitting of modified-Gompertz model to experimental data (data point) of Listeria monocytogenes (*, *), aerobic bacteria (AB) (&, &), lactic acid bacteria (LAB) (~, ~) and yeasts and molds (YM) (^, ^) survival in sucuks with LCL (a), MCL (b) and HCL (c) produced at controlled (empty symbols) and traditional full symbols) methods during ripening (15 days) and storage (15 days) periods.

0.5 ml of diluted samples on duplicate plates of LSA. The plates were incubated at 35 8C for 48 h, after which all the characteristic visible black-blue colonies with black zone on LSA were counted (Erkmen, 2007). The average number of colonies from the duplicate plates was then recorded for each sample. The average value of microbial counts was recorded for each time point from four data (two from each of duplicate batches of sucuk and two analyses for each of them). The

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Table 1 – Modified-Gompertz and logistic parameters for Listeria monocytogenes, aerobic bacteria, and yeasts and molds survival in sucuks produced in controlled (Cont) and traditional (Trad) methods with low level of contamination of L. monocytogenes Parameters

Microorganisms L. monocytogenes

Aerobic bacteria

Lactic acid bacteria

Yeasts and molds

Cont

Trad

Cont

Trad

Cont

Trad

Cont

Gompertz log N0 a b m R2 RMSE m

4.13 4.20  0.24 0.18  0.03 6.44  0.73 0.99 0.20 0.28

4.25 4.98  0.40 0.12  0.02 10.61  0.99 0.99 0.13 0.22

5.65 8.35  1.83 0.05  0.01 28.42  3.30 0.98 0.21 0.15

5.83 5.37  0.81 0.08  0.02 16.09  2.85 0.99 0.20 0.16

5.04 4.89  1.21 0.10  0.02 17.59  2.97 0.99 0.29 0.18

5.11 7.53  2.50 0.08  0.01 18.97  4.84 0.99 0.21 0.22

3.55 3.39  0.31 0.09  0.01 15.86  1.34 0.99 0.09 0.11

3.60 3.62  0.25 0.10  0.01 13.80  0.96 0.99 0.08 0.13

Logistic log N0 a d c R2 RMSE m

4.13 4.01  0.26 2.52  0.53 0.30  0.08 0.98 0.30 0.30

4.25 4.44  0.36 2.89  0.39 0.23  0.04 0.99 0.22 0.32

5.65 4.74  1.64 3.28  0.43 0.14  0.04 0.97 0.24 0.17

5.83 4.35  0.56 2.97  0.46 0.17  0.04 0.98 0.26 0.74

5.04 4.09  0.67 3.79  1.09 0.21  0.07 0.96 0.37 0.86

5.11 5.21  0.91 3.86  0.63 0.18  0.05 0.98 0.27 0.94

3.55 2.74  0.19 3.09  0.29 0.18  0.02 0.99 0.10 0.12

3.60 3.12  0.18 3.08  0.31 0.19  0.02 0.99 0.12 0.15

number of survivors was expressed as log(cfu) g1 of sucuk. Meat and additives were also tested with enriching the samples to ensure that the sucuk formulation were free from Listeria (Erkmen, 2007). The pH values of sucuks (homogenized sucuks in 0.1% peptone water) were determined with a Corning pH meter (EM78X). Analyses of variance were performed on data obtained at different stages of processing by means of a computer program, Statgraphics 2.0 (Stsc. Inc., Rockville, MD).

2.5.

Trad

where N is log(cfu) g1 of cell number at time t; log N0 the asymptotic log counts as time decreases indefinitely, approximately equivalent to the log of the initial level of bacteria (log(cfu) g)); a the count increment as time increases indefinitely, that is number of log cycles of survival (log(cfu) g); m the time required to reach the minimum inactivation rate (day); and b is the specific inactivation rate at time m (day1). From these parameters, the maximum specific inactivation rate [m (log(cfu) g1 day1) = ba/e, where e = 2.7182] was obtained. A logistic model (symmetrical curve) was also applied in order to test its suitability:

Modeling of microbial growth

One of the recommended models for describing microbial survival is modified-Gompertz equation (Zwietering et al., 1990):

log N ¼ log N0 þ

a 1 þ expðd  ctÞ

where log N and log N0 have the same meaning as above; d a dimensionless parameter; and c is the specific inactivation

log N ¼ log N0 þ a expðexpðbðt  mÞÞÞ

Table 2 – Modified-Gompertz and logistic parameters for L. monocytogenes, aerobic bacteria, and yeasts and molds survival in sucuks produced in controlled (Cont) and traditional (Trad) methods with medium contamination level of monocytogenes Parameters

Microorganisms L. monocytogenes

Aerobic bacteria

Lactic acid bacteria

Yeasts and molds

Cont

Trad

Cont

Trad

Cont

Trad

Cont

Gompertz log N0 a b m R2 RMSE m

5.10 4.92  0.26 0.14  0.02 9.08  0.77 0.99 0.18 0.25

5.00 4.74  0.25 0.18  0.04 6.05  0.81 0.99 0.29 0.31

6.40 7.01  1.26 0.08  0.01 15.27  2.78 0.99 0.26 0.21

6.94 10.69  3.41 0.07  0.01 16.75  6.08 0.99 0.28 0.28

5.10 4.90  0.51 0.12  0.03 11.42  1.37 0.99 0.24 0.22

5.20 5.14  0.56 0.15  0.04 9.28  1.59 0.98 0.43 0.28

3.60 2.55  0.16 0.13  0.02 10.05  0.89 0.99 0.10 0.12

3.50 2.91  0.3 0.12  0.03 9.40  1.61 0.98 0.20 0.13

Logistic log N0 a d c R2 RMSE m

5.10 4.63  0.26 2.66  0.42 0.27  0.04 0.98 0.28 0.31

5.00 4.59  0.28 2.28  0.54 0.28  0.08 0.97 0.41 0.32

6.40 5.81  0.74 2.78  0.08 0.16  0.04 0.98 0.34 0.23

5.10 4.44  0.37 3.29  0.68 0.22  0.05 0.98 0.32 0.26

5.20 4.95  0.51 2.83  0.81 0.23  0.07 0.96 0.54 0.28

3.60 2.36  0.12 2.91  0.40 0.23  0.03 0.99 0.12 0.14

3.50 2.76  0.28 2.14  0.47 0.19  0.05 0.96 0.25 0.13

6.94 6.64  0.96 3.021  0.28 0.15  0.02 0.99 0.24 0.25

Trad

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rate at the half-time value of the exponential phase (day1). From these parameters, the exponential microbial inactivation rate [m (log(cfu) ml day1) = ac/4] was derived. The models were applied to ripening methods and initial contamination (adding) level of L. monocytogenes storage temperature where microbial survival occurred.

2.6.

Erkmen, 2003; Gallo et al., 2007; Chowdhury et al., 2007). Microbial numbers were increased during 1 day of ripening at 90% RH. This growth was not included in modeling. The models were applied after 1 day of ripening. The pH values of sucuks ranged from 5.00 to 5.23 and from 5.03 to 5.20 after 15 days of ripening under the controlled and traditional methods, respectively. After that, the pH was increased slightly due to the metabolism of acids and nitrogenous compounds (such as proteins and amino acids). The pH values were ranged from 5.16 to 5.41 and 5.28 to 5.37 in sucuks ripened under the controlled and traditional methods, respectively, after 15 days of storage. The modified-Gompertz and logistic models were applied to L. monocytogenes, AB, LAB and YM in which microbial survival was detected and allowed the prediction of the entire survival curve. Figs. 1 and 2 show the fitting of modifiedGompertz and logistic models, respectively, to these microorganisms during storage in sucuks contaminated with LCL, MCL and HCL of L. monocytogenes, respectively. The survival of L. monocytogenes was about 0.28 log(cfu) g1 sucuk after 30 days with MLC and 0.69 log(cfu) g1 with HCL. The derived parameter from modified-Gompertz model, as the maximum specific inactivation rate (m) depending on the contamination level is given in Tables 1 and 2. It is quite clear visible that with the increase of the initial contamination level, the m increases for L. monocytogenes, AB, LB and MY. The inactivation rate of microorganisms during ripening and storage period of sucuks was higher in sucuks ripened at traditional method than controlled method. This was due to the production of sucuks at low water activity in traditional method than controlled method. Ripening of sucuk at the high relative humidity allowed higher survival rate than low relative humidity. Higher inactivation rates (from modified-Gompertz and logistic models) for L. monocytogenes and AB were also obtained with increasing initial level of organisms. All values of the calculated parameters from modified-Gompertz values (Tables 1 and 2) are statistically significant ( p < 0.05). The modified-Gompertz equation has become the most widely used primary model for describing microbial survival and was regarded as sufficient to describe the inactivation of bacteria in

Statistical analysis

In modeling, the equations were fitted to experimental data by non-linear regression using SigmaPlot 2002 for Windows Version 8.0 (SPSS Inc.). The selected algorithm calculates the set of parameters with the lowest residual sum of squares and their 95% confidence interval for the different conditions tested. Analysis of variance was applied to the parameters to determine statistical differences between different parameters and was compared using the Student’s t-test for significant effects identified in the SigmaPlot 2002 ( p < 0.05). To compare the performance of different models, the correlation coefficient (R2) and the root mean square error (RMSE) between experimental data and those predicted using different models were obtained from plot using SigmaPlot 2002 for Windows Version 8.0 (SPSS Inc.). Additionally, the accuracy of models can be assessed graphically by plotting the predicted values from both models versus the observed values. A simple linear regression was fitted to the points and the intercept, the R2 was obtained (Zhao et al., 2001).

3.

Results and discussion

All the experimental data obtained from two production methods and initial inoculation levels (LCL, MCL and HCL) were fitted into two models (modified-Gompertz and logistic) to detect the survival of L. monocytogenes during ripening and storage periods in sucuks. The application of the modifiedGompertz and logistic models for the description of microbial survival is widely used and described in literature (Zwietering et al., 1990; Van Impe et al., 1992; Buchanan, 1993; Bozkurt and

Table 3 – Modified-Gompertz and logistic parameters for L. monocytogenes, aerobic bacteria, and yeasts and molds survival in sucuks produced in controlled (Cont) and traditional (Trad) methods with high contamination level of L. monocytogenes Parameters

Microorganisms L. monocytogenes

Aerobic bacteria

Lactic acid bacteria

Yeasts and molds

Cont

Trad

Cont

Trad

Cont

Trad

Cont

Trad

Gompertz log N0 a b m R2 RMSE m

5.80 5.61  0.41 0.12  0.02 10.94  1.02 0.99 0.21 0.25

5.78 5.69  0.33 0.14  0.02 8.34  0.86 0.99 0.25 0.29

7.60 5.90  0.65 0.10  0.02 13.64  1.50 0.99 0.21 0.22

7.25 7.51  1.28 0.09  0.02 13.40  2.57 0.98 0.36 0.25

4.90 3.73  0.17 0.17  0.02 9.28  0.66 0.99 0.15 0.23

4.70 4.52  0.37 0.15  0.03 8.72  1.25 0.98 0.31 0.25

3.50 3.28  0.16 0.12  0.01 10.10  0.71 0.99 0.90 0.14

3.40 3.56  0.39 0.12  0.03 9.60  1.65 0.98 0.23 0.16

Logistic log N0 a d c R2 RMSE m

5.80 5.15  0.35 2.83  0.45 0.21  0.04 0.99 0.31 0.27

5.78 5.45  0.35 2.47  0.42 0.22  0.04 0.97 0.38 0.30

7.60 5.14  0.44 3.55  0.50 0.20  0.04 0.98 0.30 0.26

7.25 6.48  0.74 2.69  0.43 0.17  0.04 0.98 0.42 0.28

4.90 3.57  0.20 3.19  0.60 0.27  0.05 0.98 0.24 0.24

4.70 4.28  0.37 2.77  0.69 0.24  0.07 0.96 0.42 0.26

3.50 3.05  0.15 2.70  0.32 0.21  0.03 0.99 0.14 0.16

3.40 3.33  0.32 2.19  0.42 0.18  0.04 0.97 0.27 0.15

food and bioproducts processing 86 (2008) 220–226

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foods (Gil et al., 2006; Walker and Jones, 1994; Van Impe et al., 1992). The correlation between observed and estimated data for the behavior of L. monocytogenes, AB, LAB and YM in sucuks at various levels of L. monocytogenes and production methods calculated with modified-Gompertz and logistic models are given in Figs. 3 and 4, respectively. Both the modifiedGompertz and logistic models showed good fit to all the survival curves as assessed using the root mean square error (RMSE) and the correlation coefficient (R2) between the

Fig. 4 – Correlation between observed and estimated data for the behavior of L. monocytogenes, aerobic bacteria (AB), lactic acid bacteria (LAB) and yeasts and molds (YM) survival in sucuks with LCL (a), MCL (b) and HCL (c) calculated with logistic model for controlled and traditional methods.

Fig. 3 – Correlation between observed and estimated data for the behavior of L. monocytogenes, aerobic bacteria (AB), lactic acid bacteria (LAB) and yeasts and molds (YM) survival in sucuks with LCL (a), MCL (b) and HCL (c) calculated with Gompertz model for controlled and traditional methods.

experimental and predicted values but the modified-Gompertz model best fit (R2  0.99) than the logistic model (R2  0.97). Additionally, good agreement between experimental data and predicted values of AB, LAB and YM were obtained with R2  0.98 for the modified-Gompertz model than logistic model (R2  0.96). Thus these equations allowed a good prediction of the effects of effect of production conditions

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of sucuks during ripening period on L. monocytogenes, AB, LAB and YM because of the closer fit. High R2 values result from a small number of degree of freedom. In such a situation a very good matching of a model to the data is not surprising (McMeeken et al., 1993). It seems that the survival parameters of microorganisms occurring in sucuks with different production methods and contamination levels were estimated relatively well (Tables 1–3). Most of them are statistically significant at the level of p-value = 0.05. It seems that quite clear differences occur among parameters (ripening methods and contamination levels) of survival characteristics of L. monocytogenes, AB, LAB and YM ( p < 0.05). In consequence, m values achieved were dependent on the level of initial level of microorganisms, highly affected by production techniques. These data shows the importance of production technique and level of contaminants at initial as a controlling factor for survival of L. monocytogenes, AB, LAB and YM in sucuks. It is possible to obtain an important reduction of L. monocytogenes, AB, LAB and YM in sucuks during ripening and storage at 4 8C with the production of sucuks with lower level of microbial load in sucuk dough. Storage of sucuk at low temperature (4 8C) showed a dramatic reduction of L. monocytogenes, AB, LAB and YM population and allowed a level of survival after 30 days depending on initial contamination level of microorganisms without re-growth of the microorganisms. On the basis of data obtained in the experiment parameters of non-linear modified-Gompertz and logistic models of the L. monocytogenes, AB, LAB and YM survival in sucuks at various production techniques with different contamination levels were matched in a satisfactory way.

Acknowledgement This work was supported by the Gaziantep University Research Fund.

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