Article pp.59-71 du Vol.27 n°1 (2007)

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ARTICLE ORIGINAL ORIGINAL PAPER

Effects of selected chemicals on microbial stability of turkey meat

A.H. Dinçer Baysal

^*¹

, A. Ünlütürk

²

SUMMARY

The influence of dipping turkey breast meat in lactic acid (LA), fumaric acid (FA), lactic acid plus fumaric acid (LA + FA), trisodium phosphate (TSP) and sodium tripolyphosphate (STPP) solutions on aerobic mesophilic, psychrotrophic bacteria and yeast counts were assessed. 1-1.5% LA, 0.5% FA and 1% LA + 0.5% FA showed immediate inhibitory effects on aerobic mesophilic bacteria (0.3-0.6, 0.4 and 1.8 log unit reductions, respectively). 0.5% FA reduced psychrotrophic bacteria and yeast counts on fresh turkey breast fillets immediately by 1.1 and 0.4 log units, respectively. 5%

TSP reduced aerobic mesophilic and psychrotrophic bacteria by 0.4 and 0.5 log units, respectively on breast fillets. 5% STPP reduced the yeast count on breast fillets immediately by 0.7 log unit. 1% LA, 0.5% FA and 1% LA + 0.5% FA reduced the psychrotrophic bacteria counts by 0.48, 0.23 and 1.27 log units after 8 days of storage, respectively in comparison to the untreated control samples. 1% LA + 0.5% FA treated fillets had a detectable discoloration and acid odour although there was no microbial spoilage at 14 days of storage. Dipping fillets in both 1% LA and 0.5% FA extended the storage life up to 4 days, without adversely affecting the colour.

Keywords

lactic acid, fumaric acid, trisodium phosphate, sodium tripolyphosphate, turkey breast meat, storage life.

1 – INTRODUCTION

Contamination and growth of bacteria are a major problem to the poultry meat indus- try, even though good manufacturing practices are followed during processing. Therefore, numbers of microorganisms introduced on meat surfaces during slaughter should be reduced during production. The U.S. Department of Agriculture (USDA) Food Safety Inspection Service has proposed that all slaughter establishments should apply at least one antimicrobial treatment or other approved intervention procedure to livestock and poultry carcasses (NISSEN et al., 2001).

1. Izmir Institute of Technology – Department of Food Engineering – 35430 Urla – Izmir – Turkey.

2. Ege University – Department of Food Engineering – 35100 Bornova – Izmir – Turkey.

* Correspondence: Tel.: +90 750 6187; fax: +90 750 6196. E-mail address: handanbaysal@iyte.edu.tr

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Organic acids have been used as antimicrobial surface treatments to decrease pathogens, prevent the growth of spoilage microorganisms and extend the shelf life of fresh poultry meat. Organic acid dips or sprays such as acetic, lactic, citric and propionic acids either individually or combined, are beneficial in controlling undesired microorganisms on refrigerated meats (BELL et al., 1986; HAMBY et al., 1987; LILLARD et al., 1987; MARSHALL and KIM, 1996). Organic acids have been investigated because of their bactericidal activity and they are generally recognised as safe (GRAS) and therefore are utilised for preser- vation in many food applications (IZAT et al., 1989, DICKSON and ANDERSON, 1992).

Lactic acid (LA) is an effective solution for decontaminating fresh meat carcasses and retail cuts (DICKSON and ANDERSON, 1992; GILL and NEWTON, 1982; JAY, 1992;

WOOLTHUIS and SMULDERS, 1985). MARCEL et al. reported that decontamination of broiler carcasses with 1-2% lactic acid before chilling improved the bacterial safety and extended the refrigerated shelf life (HWANG and BEUCHAT, 1995). Fumaric acid (FA) is used for its good antioxidant properties in butter, cheese, powdered milk, frankfurters, nuts and potato chips, as an acidulant in beverages and also as an antimicrobial additive in fruit and vegetable products and in wines during the malolactic acid fermentation.

Esters of fumaric acid have also been reported to retard mould growth on bread (HUHTANEN and GUY, 1984). SHIMUZU et al. (1995) reported that among 9 organic acids commonly used as food additives in Japan, fumaric acid exhibited the strongest growth inhibiting action within 160 s of contact with 0.3% (w/v) solution on 20 gram negative bacteria tested. Fumaric acid at a concentration of 1% (w/v) was the most effective than acetic or lactic acids in reducing the populations of Listeria monocytogenes by up to 1 log unit and E.coli O157:H7 by up to 1.3 log units on lean beef surfaces (PODOLAK et al., 1996b). Although organic acids have antimicrobial effects, there are limited studies on the effects of lactic and fumaric acids on refrigerated turkey breast meat to extend shelf life.

Phosphates have been used widely as texture modifiers, curing agents and to increase water holding capacity and more recently as surface decontaminating agents for meat products (HWANG and BEUCHAT, 1995; SLAVIK et al., 1994). Phosphates have broad- spectrum antimicrobial activity and play an important role on the microbiological shelf life of meat products (MOLINS, 1991). USDA approved the use of trisodium phosphate (TSP) as a post chill processing aid to reduce bacteria on raw poultry carcasses. Chilling of chicken carcasses in commercial blends of pyro- and polyphosphates may also prove to be useful in altering the microbial population of poultry meat (RATHGEBER and WALDROUP, 1995, VARELTZIS et al., 1997). Researchers chilled broiler carcasses in 3%

and 8% solutions of sodium tripolyphosphate (STPP)/tetra sodium pyrophosphate (TSPP) blend for 20 to 24 h and reported increases in shelf life of 17% and 25%, respectively. In a similar study, researchers chilled the broilers in an 8% solution of the same phosphate blend for 6 h and shelf life was increased by 1 to 2 days (RATHGEBER and WALDROUP, 1995). Others have shown that TSP treatments yield superior antimicrobial effects compared to other phosphates (HWANG and BEUCHAT, 1995). Although phosphates have antimicrobial effects, there are limited studies on the effects of phosphate type and concentration for use on refrigerated turkey meat to extend shelf life.

The purpose of the present study was to evaluate microbiological changes and microbiological shelf life of refrigerated turkey breast fillets treated with lactic acid, fumaric acid, their mixtures, trisodium phosphate and sodium tripolyphosphate.

2 – MATERIAL AND METHODS

2.1 Treatments and storage

Solutions of lactic acid (PURAC FCC80) at 1% and 1.5% (v/v), fumaric acid (Merck) at 0.5% (w/v), trisodium phosphate (Merck) at 5% (w/v) and sodium tripolyphosphate (Merck) at 5% (w/v) were prepared in tap water. The pH values of acid and phosphate

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solutions measured at the time of application with a pH meter were as follows: 1% LA (pH = 2.72), 1.5% LA (pH = 2.22), 0.5% FA (pH = 2.70), 1% LA + 0.5% FA (pH = 2.14), 5% TSP (pH = 12.68) and 5% STPP (pH = 8.90). The administration of all the treatments and the sampling of the retail sliced breasts (fillets) were conducted in a commercial poultry processing unit of a plant in zmir. Fillets were dipped in 6 l solutions of 1%, 1.5% LA, 0.5% FA, 1% LA + 0.5% FA, 5% TSP, 5% STPP for 1 min then drained on a sanitised tray for 10 min at 4°C. Fillets not treated with acids or phosphates were non treated control samples. After dipping, 3 fillets were packed in a polystyrene tray with a polyvinyl chloride cover films in an automatic machine and were transported on ice within 30 min to a storage room adjusted 4 ± 1°C and 95% RH for storage.

2.2 Microbiological analyses

Immediately, after acid and phosphate treatment, and during the storage fillets were taken for analyses at defined intervals. 25 g sample was removed aseptically from π of each fillet in the tray, placed in a stomacher bag and 225 ml of sterile 0.1% (w/v) peptone water (Oxoid L37) added. The sample was homogenised for 2 min in a stomacher (Seward Medical, Model 400), and a series of decimal dilutions were prepared. The enu- meration of psychrotrophic microorganisms, total mesophilic aerobic microorganism, and yeast was carried out with the methods described by ANONYMOUS (1989), APHA (1992);

GILILAND et al. (1976); respectively. The results are presented as the means of duplicate plates of triplicate samples.

2.3 Statistical analyses

Data were analysed employing completely randomised factorial design. Analyses of variance was conducted (STAT View) and mean differences were determined using Fisher’s PLSD. The predetermined acceptable level of probability was 5% (P < 0.05) for all comparisons.

3 – RESULTS AND DISCUSSION

3.1 Effects of organic acids and phosphates on aerobic mesophilic microorganisms

The effects of LA, FA and LA+FA, TSP and STPP treatments on the aerobic mesophilic microorganism count in the turkey breast fillets are shown in table 1 and 2. There was a significant difference in aerobic mesophilic count between control, 1% LA, 0.5%

FA and 1% LA + 0.5% FA treated samples after 8 days of storage (P < 0.05, table 1).

Significantly lower counts were observed in 1% LA + 0.5% FA treated samples as compared to control after 8 days of storage (P < 0.05). But there were no significant difference in counts of 1% LA and 0.5% FA treatments after 14 days of storage (P > 0.05). At day 0, samples treated with 1% LA, 0.5% FA and 1% LA + 0.5% FA solutions had aerobic mesophilic counts that were 0.6, 0.4 and 1.8 log units, lower than those of control samples, respectively. The number of aerobic mesophilic microorganisms increased rapidly in the control from an initial population of 4.4 to 8.9 log cfu g^-1 of turkey breast meat in 8 days where off-odour was also detected. In 1% LA and 0.5% FA treated samples off-odour was detected after 14 days of storage and the number of aerobic mesophilic microorganisms reached 9.3 and 9.4 log units, respectively (table 1). However, there was no statistical difference in counts in comparison to the control at day 8. In 1% LA + 0.5% FA treated samples after 14 days of storage the aerobic mesophilic count increased from 2.6 to 8.0 log cfu g^-1 but there was no off-odour. Compared to control, the highest reductions

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of 1.1 and 0.6 log units were observed with 1% LA and 0.5% FA treatments at 6 and 3 days of storage, respectively. The treatment 1% LA + 0.5 FA reached a maximum reduction by 2.2 log units after 6 days of storage in comparison to the untreated control samples.

Table 1

Total aerobic mesophilic counts (log cfu g^-1) of turkey breast meat treated with 1% lactic acid, 0.5% fumaric acid and combined acid solutions during storage at + 4°C.^1,2

In literature the concentration of LA used for decontaminating fresh beef varies from 0.2 to 2.5%. WOOLTHUIS and SMULDER (1985) found that spraying with 1.25% LA reduced the total bacterial counts by 0.8 and 1.3 log units on calf carcass breast and perineum, respectively, after 24 h. IZAT et al. (1989) applied 2% LA using a modified inside-outside birdwasher to prechilled chicken carcasses and obtained 1.03 log cfu reduction of total aerobic bacteria per carcass after spraying. In another study, solutions of lactic acid at 1% (pH = 2.77), 3% (pH = 2.27) and 5% (pH = 2.15) (w/v) were prepared to provide 0.075%, 0.23% and 0.38% (w/w), respectively, of the total weight of the ground beef then vacuum packaged and stored at 4°C. When compared to untreated samples, the total number of aerobic bacteria counts on samples containing 0.075%, 0.23% and 0.38% (w/w) LA were 1.07, 1.89 and 2.04 log units lower than the controls, respectively (PODOLAK et al., 1996b). BAUTISTA et al. (1997) tested the efficacy of a 1.24% LA and 4.25% LA spray at 40 psi for 10 s and found 2.4 and 4.4 log unit reductions compared with initial counts of 6.28 log cfu per carcass in the total number of aerobic bacteria on faecally contaminated turkey carcasses, respectively. They also reported that, increasing the spray pressure did not significantly improve the reduction of total bacteria counts. YANG et al. (1998) sprayed 2% LA (pH = 2.2) for 17 s at 413 kPa using a modified inside-outside birdwasher on chicken carcasses before chilling and reported 1.03 log units per carcass in total aerobic count. Similar results were also reported by others (SAKHARE et al., 1999; XIONG et al., 1998). The results obtained in this study and literature indicates that in addition of acid concentration and pH, the temperature, the time, and the stage of application at processing of acid can vary the antimicrobial effect of lactic acid. This effect also differs depending on the structure (nature or type) of poultry meat, sampling method (procedures) and levels of initial contamination.

In the literature researchers recorded application of 1%, 2%, 3% LA caused decrease in total aerobic counts in the range of 0.8-2.3, 1.03-2.2 and 1.28-4.4 log units, respectively (BAUTISTA et al., 1997; IZAT et al., 1989; SAKHARE et al. 1999; XIONG et al., 1998;

YANG et al., 1998). Most researchers stated that the use of LA solutions at concentrations of 1-2% reduces the bacterial counts on poultry carcasses immediately after slaughter and during storage, without affecting organoleptic characteristics such as colour and fla-

Storage Period

(Day)

Aerobic mesophilic microorganism count

C^a 1% LA^b 0.5% FA^b 1% LA+0.5% FA^c

0 4.4 ± 0.7â 3.8 ± 0.3â 4.0 ± 0.4â 2.6 ± 0.4^b

3 5.1 ± 0.8^a 4.7 ± 0.2^ab 4.5 ± 0.3^b 3.8 ± 0.4^c

6 7.9 ± 0.4^a 6.8 ± 0.2^b 7.7 ± 0.2^a 5.7 ± 0.2^c

8 8.9 ± 0.2â,2 8.5 ± 0.4â 8.6 ± 0.4â 7.1 ± 0.7^b

10 – 8.6 ± 0.3^ab 8.9 ± 0.6^ab 8.4 ± 0.1^b

12 – 8.9 ± 0.1â 8.7 ± 0.1â 9.0 ± 0.3â

14 – 9.3 ± 0.9^a,2 9.4 ± 0.1^a,2 8.0 ± 0.6^b

1. Each value in the table is the mean ± standard deviation of three samples.

Different letters within the same period indicate significantly different means among treatments (P > 0.05).

C: untreated control, LA: dipped in lactic acid solution, FA: dipped in fumaric acid solution.

2. off-odour was detected.

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vour (BOLDER, 1997). BAUTISTA et al. (1997) reported that LA treatment at a concentration of greater than 1.24% caused discoloration on tissues of turkey carcasses and the same negative effect also has been observed with concentrations greater than 1.25% (IZAT et al., 1989; MULDER et al., 1987). In our study no discoloration of the turkey breast fillets has been seen with dipping 1% LA solution. In summary, both lactic and fumaric acid seem to produce the desired initial microbial reduction, when mixtures of the two may possibly enhance the antimicrobial effects. The results obtained in this study are in agree- ment with the findings of others (ARIYAPITIPUN et al., 1999; IZAT et al., 1989; PODOLAK et al., 1996a, b).

There was a significant difference in aerobic mesophilic microorganism count between 1.5% LA, 5% TSP and 5% STPP treated samples after 14 days of storage (P < 0.05, table 2). No significant difference (P > 0.05) was also observed in counts between control and 5% STPP treated samples after 14 days of storage. Samples treated with the 1.5% LA and 5% TSP had significantly lower (P < 0.05) counts than control after 14 days of storage. In control sample, the number of aerobic mesophilic microorganisms was 3.1 log units initially and off-odour when this count reached to 9.2 log cfu g^-1. The samples treated with 1.5% LA, 5% TSP and 5% STPP solutions had counts that were 8.8, 8.7 and 8.8 log cfu g^-1, respectively, when off-odour was noticeable at 14^th day of storage table 2). Results showed that dipping in 1.5% LA solution was more effective in decreasing microbial load than dipping 5% TSP and 5% STPP after storage for 10 days but not after 12 or 14 days.

Table 2

Total aerobic mesophilic counts (log cfu g^-1) of turkey breast meat treated with 1.5%

lactic acid, 5% trisodium phosphate and 5% sodium tripolyphosphate solutions during storage at +4°C.^1,2

BAUTISTA et al. (1997) tested the efficacy of a 2.93% and 10% TSP spray at 40 psi for 10 sec and found 1.8 and 1.94 log unit reductions in the total number of aerobic bacteria on faecally contaminated turkey carcasses, respectively. Also, increasing the spray pressure did not significantly improve the reduction of total bacteria counts. YANG et al. (1998) before chilling sprayed 10% TSP solution (pH = 12.3) for 17 s at 413 kPa using a modified inside-outside birdwasher on chicken carcasses and total aerobic count were reduced by 0.74 log cfu per carcass as compared with an intial counts of 6.56 log cfu on control. KIM and MARSHALL (1999) assessed the influence of dipping chicken legs for 10 min in 5%

TSP solution and they found that chicken legs treated with 5% TSP for 10 min had aero- Storage

Period (Day)

Aerobic mesophilic microorganism count

C^ab 1.5% LA^c 5% TSP^b 5% STPP^a

0 3.1 ± 0.2^b 2.8 ± 0.2^b 2.7 ± 0.1^b 3.8 ± 0.4^a

3 4.2 ± 0.4^ab 2.7 ± 0.2^c 3.7 ± 0.6^b 4.7 ± 0.3^a

6 7.2 ± 0.3â 5.1 ± 0.4^b 7.4 ± 0.3â 7.3 ± 0.1â

8 7.9 ± 0.4^ab 7.1 ± 0.5^c 7.8 ± 0.3^b 8.4 ± 0.1^a

10 8.6 ± 0.1â 7.8 ± 0.5^b 8.7 ± 0.4â 8.5 ± 0.2â

12 9.0 ± 0.2â 8.9 ± 0.3â 8.7 ± 0.4â 8.7 ± 0.1â

14 9.2 ± 0.1â,2 8.8 ± 0.3â,2 8.7 ± 0.3â,2 8.8 ± 0.1â,2

1. Each value in the table is the mean ± standard deviation of three samples.

Different letters within the same period indicate significantly different means among treatments (P > 0.05).

C: untreated control, LA: dipped in lactic acid solution, TSP: dipped in trisodium phosphate solution, STPP: dipped in sodium tripolyphosphate solution.

2 .off-odour was detected.

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bic plate counts nearly 3 log units lower than the controls and other treatments after 12 days of storage at 4°C. The reductions of total mesophilic count in samples dipped in 8%, 10% and 12% TSP for 15 min ranged between 0.95-1.78 and 2.35-3.08 log units, respectively, before storage and on day 5 of storage at 2°C (CAPITA et al., 2000).

MARSHALL and JINDAL (1997) demonstrated that dipping catfish fillets into 10% TSP solution for 5 min reduced aerobic plate count by 1 log unit. In contrast these findings, MORRIS et al. (1997) determined that there was no significant difference in aerobic plate counts between the 10 cm²of pork carcass skins immersed for 5, 10 and 15 sec in 8%

TSP solution and non treated controls. Also, GIESE (1993) reported that TSP treatment resulted in no significant reduction in aerobic plate count.

There is abundant data on the effect of STTP treatment of meat and poultry carcasses or products. In a study dipping chicken carcasses for 10 min in 10% STPP resulted in a reduction of the total aerobic bacteria count from 4.7 log cfu cm^-2 to 3.8 log cfu cm^-2 (VARELTZIS et al., 1997). In another study dipping catfish fillets into 10% TSP solution for 5 min caused 0.3-log unit reduction in aerobic plate count (MARSHALL and JINDAL, 1997). In our study aerobic mesophilic counts of the samples were unaffected by dipping for 1 min in 5% STPP solution.

In the literature there are conflicting results about the shelf life extension with different types of meat under different experiment conditions. GREER and JONES (1991) found that, although 1% LA sprays produced a 0.7 log units reduction in bacteria on beef carcasses, this effect was not extended the shelf life of fillets prepared from these carcasses. Similar results were obtained by PRASAIet al. (1991). In our study dipping 1% LA + 0.5% FA solution was found the most effective treatment among all applications for reduction of microbial load and the extension of shelf life (at least 6 days) of turkey breast fillets. Dip- ping fillets in both 1% LA and 0.5% FA extended the storage life up to 4 days, respectively, without adversely affecting the colour. When the results obtained in this study compared to data in the literature it was found dipping into 1 – 1.5% LA and 1% LA + 0.5% FA solutions provided extension in the shelf life at the same level.

Similar antimicrobial effect of FA at lower concentration (0.5%) than LA (1%) may have been related to its lower acid dissociation constant (pKa) compared to those of lactic acid. The pKa₁ and pKa₂ of FA are 3.03 and 4.44, whereas the pKa of lactic acid is 3.86 (BAIRD-PARKER, 1980). pKa (pH when the 50% of total acid is undissociated) of organic acids that are used as antimicrobial are in the range of 3-5. Microorganisms are not only affected by the concentration of undissociated weak organic acid molecules but also by the level of free H⁺ ions that is the pH (CORLETT and BROWN, 1980). Hence, the higher concentration of free H⁺ ions of FA may have inhibited the microbial cells more effi- ciently than LA. In our study the pH value of fillets (especially at surface) fell immediately after the LA or FA dipping but after a few days the pH value increased again due to the buffering capacity of meat and the diffusion of LA, FA or mixtures of acids into the deeper layers of the meat tissue and/or due to its decomposition. Thus after several days of storage the pH values approached the initial ones of the control samples. Within the same period the pH value of control samples increased as a result of microbial metabolism.

The mechanisms of reductions in bacteria on poultry carcasses with the TSP treatment are still not fully understood. It has been suggested that the high pH and ionic strength of TSP solutions and the ability of these solutions to remove a thin layer of lipids (the « detergent effect ») from skin are responsible for the bactericidal activity (ANONYMOUS, 1994; HWANG and BEUCHAT, 1995; RODRIGUEZ de LEDESMA et al., 1996;

YANG et al., 1998). In the literature researchers recorded that immersion or spraying of 2.93-12% TSP for 17 sec-15 min caused immediate reduction in total aerobic counts in the range of 0.74-1.94 log units. However, the total aerobic bacteria counts of these samples stored at refrigeration temperatures after different storage periods were 2.35-3.08 log units lower than the controls. In our study by dipping breast fillets into 5% TSP solution for 1 min total aerobic bacteria count were reduced by 0.4 log units as compared with initial counts of 3.1 log cfu on control. The result obtained in this study was lower than the data in the literature. The reasons for this can be explained with the concentration of TSP solution, treatment time, temperature and the material differences.

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3.2 Effects of organic acids and phosphates on psychrotrophic bacteria

The effects of LA, FA and combined acid solutions on psychrotrophic bacteria in the turkey breast fillets are shown in table 3. There was a significant difference in psychrotrophic bacteria count between control, 1% LA, 0.5% FA and 1% LA + 0.5% FA treated samples after 10 days of storage (P < 0.05). Similarly, significantly lower counts were observed in 1% LA + 0.5% FA treated samples as compared to 1% LA and 0.5% FA treated samples after 14 days of (P < 0.05). Generally, reduction was greater when the combinations of the acids are treated. At day 0, no significant differences (P > 0.05) were found between the untreated control, 1% LA and 0.5% FA treatments. The highest reduction of 0.90 and 0.36 log units were observed with 1% LA and 0.5% FA at 6 and 8 days of storage, respectively. Compared to control, treatment with the combined acid solutions reduced psychrotrophic bacteria counts by 2.15 (maximum) to 1.94 log units at 6 and 8 days of storage. In control samples the number of psychrotrophic bacteria in 8 days that off-odour was detected increased 5.1 log units and reached 9.3 log cfu g^-1. At day 14, samples treated with 1% LA, 0.5% FA and combined acid solutions had counts reached 8.9, 9.3 and 8.6 log cfu g^-1, respectively.

Table 3

Psychrotrophic bacteria counts (log cfu g^-1) of turkey breast meats treated with 1% lactic acid, 0.5% fumaric acid and combined acid solutions during storage at + 4°C.^1,2

VANDER MAREL et al. (1988) reported that chicken carcasses immersed in 1% or 2%

LA for 15 s shortly before chilling contained significantly lower populations of Enterobac- teriacea, S.aureus, and psychrotrophs compared with carcasses immersed in tap water.

In their study initial numbers of 3.3 log cfu g^-1 and 3.9 log cfu g^-1 of Enterobacteriacea and psychrotroph bacteria, respectively, after LA solution dipping treatment were 2.6 log cfu g- 1 and 2.7 log cfu g^-1. WOOLTHUIS and SMULDERS (1985) observed that when calf carcasses were sprayed with 1.25 LA, Enterobacteriacea counts, which were 1.7 log and 1.9 log in perineum and breast, were reduced below their limit of detection of 1.3 log cfu cm^-

2, after 2.5 h. HWANG and BEUCHAT (1995) reported that washing with 1% LA + 5%

Tween 80 and with 0.5% LA + 0.05 sodium benzoate (SB) significantly reduced numbers of L.monocytogenes and the total number of psychrotrophic bacteria on chicken skin. In another study researchers reported that at pH 6, 1% acetic acid (AA) effectively sup- pressed growth of some gram negative bacteria, but 1% LA could not. 2% LA keep the psychrotrophic bacteria count approximately 2 log cfu cm^-2 lower than that of the control and water treatments vacuum packaged beef (MARSHALL and KIM, 1996). ARIYAPITIPUN et al. (1999) reported that compared to controls, dipping in 2% (w/w) LA (pH = 2.2) solu- tions reduced psychrotrophic bacteria, psychrotrophic Enterobacteriaceae and Pseu- domonas counts significantly. In the study after dipping LA solution psychrotrophic

Storage period

(Day)

Psychrotrophic bacteria counts

C^a 1% LA^c 0.5% FA^b 1% LA+0.5% FA^d

0 4.2 ± 0.1â 4.0 ± 0.2â 4.2 ± 0.5â 3.1 ± 0.5^b

3 5.2 ± 0.6^a 4.5 ± 0.5^b 4.8 ± 0.1^ab 3.9 ± 0.4^c

6 7.9 ± 0.4^a 7.0 ± 0.3^b 7.9 ± 0.1^a 5.8 ± 0.2^c

8 9.0 ± 0.1 8.6 ± 0.3^a 8.6 ± 0.3^a 7.1 ± 0.7^b

10 9.3 ± 0.3â,2 8.7 ± 0.3âb 8.9 ± 0.5âb 8.4 ± 0.2^b

12 – 8.9 ± 0.3â 8.8 ± 0.1â 8.6 ± 0.5â

14 – 8.9 ± 0.5^a,2 9.3 ± 0.1^a,2 8.6 ± 0.5^b

1. 2. Same as in table 1.

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bacteria, psychrotrophic Enterobacteriaceae and Pseudomonas counts become 2.36 log cfu cm^-2, 1.86 log cfu cm^-2 and 1.57 log cfu cm^-2, respectively, with initial counts of 4.10 log cfu cm^-2, 2.47 log cfu cm^-2 and 2.50 log cfu cm^-2. The number of psychrotrophic bacteria, psychrotrophic Enterobacteriaceae and Pseudomonas in raw beef carcasses dipped 2% LA solution were 1.7, 3.0 and 3.0 log units lower than the controls after 56 days storage at 4°C, respectively.

In another study, solutions of lactic acid at 1% (pH = 2.77), 3% (pH = 2.27) and 5%

(pH = 2.15) (w/v) were prepared to provide 0.075%, 0.23% and 0.38% (w/w), respectively, of the total weight of the ground beef then vacuum packaged and stored at 4°C.

When compared to untreated samples, the number of psychrotroph bacteria counts containing 0.075%, 0.23% and 0.38% (w/w) LA were 0.64, 1.82 and 2.22 log units lower than the controls, respectively (PODOLAK et al., 1996a). In our study dipping turkey breast meat in 1% and 1.5% LA for 1 min reduced the psychrotroph counts by 0.2 and 0.6 log units reductions, respectively and the results obtained in this study from the standpoint of both immediate and delayed effect of LA on psychrotrophic counts are in parallel with the data presented in the literature.

The results of the treatments carried out with LA and phosphates are given in table 4.

There was a significant difference in psychrotrophic bacteria count between control, 1.5% LA, 5% TSP and 5% STPP treated samples after 14 days of storage (P < 0.05, table 4). 1.5% LA and 5% TSP treatments gave significantly lower psychrotroph counts than the control and 5% STPP treated samples after 14 days of storage (P < 0.05). In control the number of psychrotrophs increased 5.9 log units and reached 9.1-log cfu g^-1 when off odour was noticable at 14^th day of storage. The samples treated with 1.5% LA, 5% TSP and 5% STPP solutions had psychrotroph bacteria counts that were become 8.9, 8.8 and 8.7 log cfu g^-1, respectively, with initial counts of 2.6, 2.7 and 3.7 log cfu g^-1. In literature there are studies made with different materials by the application of various concentrations of TSP and STPP solutions either dipping or spraying method.

RODRIGUEZ de LEDESMA et al. (1996) reported that a combined 10% TSP and hot water treatment of chicken skin was effective in reducing counts of S.typhimurium, S.aureus, and L.monocytogenes by 95 to 99.7%, 84 to 97% and 79 to 95%, respectively. KIM et al.

(1996) investigated the effect of 10% TSP on S.typhimurium attached to chicken skin. In their research control samples had concentrations of up to 10⁶ cfu cm^-2, whereas treated skins showed less than 10⁴ cfu cm^-2. The authors suggested that one of the major mechanisms of action of TSP on Salmonella reduction is detachment of bacterial cells from poultry skin surface and TSP at 8% (pH > 12) is active against gram-negative bacteria, including coliforms, pseudomonads, Salmonella serovars and Campylobacter spp. and on the skin of chickens. The bactericidal effect of TSP is caused by its high pH, and by effects on cell wall and on adherence factors, as well as direct killing effects. HWANG and BEUCHAT (1995) demonstrated that psychrotroph bacteria counts of chicken skins dipped into 10% TSP solution for 30 min significantly lower than the control samples, but there were no significant difference in counts between 10% STPP and control samples. In the same study psychrotroph bacteria counts of 10% TSP and 10% STPP treated samples reduced by 1.8 and 0.4 log units, respectively, reached 3.0 and 3.7 log cfu g^-1. Again CAPITA et al. (2000) reported that dipping treatment of 8%, 10% and 12% TSP solutions caused decrease in psychrotrophic bacteria counts after dipping and on day 5 of storage at 2°C in the range of 0.92-1.94 and 2.79-4.09 log units, respectively. In our study dipping 5% TSP keep the psychrotroph bacteria count 0.5 log units lower than that of the control but when off odour was noticeable at 14^th day the difference was reduced 0.3 log unit.

The results obtained in this study are lower than the data given in the literature about the reduction in psychrotroph bacteria count and this may be explained by the use of lower concentrations of phosphates, difference in time of application and the type (nature) of poultry meat.

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Table 4

Psychrotrophic bacteria counts (log cfu g^-1) of turkey breast meat treated with 1.5%

lactic acid, 5% trisodium phosphate and 5% sodium tripolyphosphate solutions during storage at + 4°C.^1,2

3.3 Effects of organic acids and phosphates on yeast

The effects of LA, FA and combined acid solutions on yeast in the turkey breast fillets are summarised in table 5. There was a significant difference in yeast count between control, 1% LA, 0.5% FA and 1% LA + 0.5% FA treated samples after 8 days of storage (P <

0.05, table 5). Samples treated with the 1% LA and 1% LA+0.5% FA had significantly lower (P < 0.05) counts than control and the number of yeast in 1% LA + 0.5% FA treated samples was significantly lower than that of the counts of 1% LA and 0.5% FA treated samples (P < 0.05) at day 8. The number of yeast increased rapidly in the control from an initial population of 2.3 to 7.3 log cfu g^-1 of turkey breast fillet in 8 days where that off- odour was also detected. But in 1% LA and 0.5 % FA treated samples off-odour was detected after 14 days of storage and the number of yeast reached 7.1 and 7.6 log units, respectively. Compared to control, the highest reductions of 1.2 and 1.0 log units were observed with 1% LA and 0.5% FA at 6 and 8 days of storage, respectively. The treatment 1% LA + 0.5% FA reached a maximum reduction by 1.7 log units after 6 days of storage in comparison to the control samples and the number of yeast reached 6.2 log units after 14 days of storage.

The effects of LA, TSP and STPP treatments on yeast in the turkey breast fillets are summarised in table 6. There was a significant difference in yeast count between control, 1.5% LA, 5% TSP and 5% STPP treated samples after 14 days of storage (P < 0.05), but samples treated with the 1.5% LA and 5% TSP had significantly lower (P < 0.05, table 6) counts than control and 5% STPP treated samples. The number of yeast increased in the control from an initial population of 1.7 to 7.2 log cfu g-1 of turkey breast fillet in 14 days where off-odour was also detected. The samples treated with 1.5% LA, 5% TSP and 5%

STPP solutions had counts that were 7.2, 7.0 and 7.1 log units, respectively.

Although many researchers have followed the effects of decontamination on poultry meat there are few published data about the effects of organic acids on yeast count.

WOOLTHUIS and SMULDERS (1985) found that there was no significant difference between the yeast counts of control and 1.25% LA sprayed calf carcass samples and after 17 days of storage at 3°C the number of yeast in control and LA sprayed samples were 4.2 and 4.1 log cfu cm^-2, respectively. SAKHARE et al. (1999) found that after dipping 0.25%

LA solution yeast counts were reduced 0.5 and 0.45 log units respectively, when compared to controls, with initial counts of 1.5 log cfu cm^-2 and 1.25 log cfu cm^-2 at scalding (58°C, 2 min) and defeathering steps during processing of broiler chicken carcasses. In a

(Day)

Psychrotrophic bacteria counts

C^ab 1.5% LA^c 5% TSP^b 5% STPP^a

0 3.2 ± 0.2^ab 2.6 ± 0.1^b 2.7 ± 0.2^b 3.7 ± 0.8^a

3 4.8 ± 0.7^a 2.7 ± 0.1^c 3.9 ± 0.6^b 5.0 ± 0.4^a

6 7.0 ± 0.2â 5.2 ± 0.6^b 7.2 ± 0.1â 7.1 ± 0.1â

8 8.1 ± 0.5^ab 7.3 ± 0.6^c 7.8 ± 0.4^bc 8.5 ± 0.1^a

10 8.7 ± 0.1âb 8.1 ± 0.5^b 8.8 ± 0.1â 9.2 ± 0.6â

12 9.0 ± 0.1â 8.6 ± 0.2âb 8.8 ± 0.4â 8.1 ± 1.0^b

14 9.1 ± 0.2â,2 8.9 ± 0.2â,2 8.8 ± 0.2â,2 8.7 ± 0.1â,2

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similar study, where 0.25% LA sprayed on broiler chicken carcasses, yeast counts were reduced by 0.76, 0.63 and 0.82 log units, respectively, as compared with an initial counts of the controls 2.01 log cfu cm^-2, 2.37 log cfu cm^-2 and 1.95 log cfu cm^-2. Results obtained in our study are in accordance with the data presented in the literature. Although there is an abundant of published data on poultry carcass decontamination no researchers have followed the effects of phosphates on yeast count.

Table 5

Yeast counts (log cfu g^-1) of turkey breast meat treated with 1% lactic acid, 0.5% fumaric acid and combined acid solutions during storage at + 4°C.^1,2

Table 6

Yeast counts (log cfu g^-1) of turkey breast meats treated with 1.5% lactic acid, 5% trisodium phosphate and 5% sodium tripolyphosphate solutions during storage at + 4°C.^1,2

(Day)

Yeast Counts

C^a 1% LA^b 0.5% FA^ab 1% LA+0.5% FA^c

0 2.3 ± 0.4âb 2.5 ± 0.2â 2.3 ± 0.2âb 1.9 ± 0.4^b

3 3.6 ± 0.0â 3.8 ± 0.5â 3.9 ± 0.3â 3.6 ± 0.4â

6 6.4 ± 0.0^a 5.2 ± 0.4^b 5.5 ± 0.4^b 4.7 ± 0.1^c

8 7.3 ± 0.1^a,2 6.8 ± 0.1^b 6.3 ± 0.6^c 6.0 ± 0.3^c

10 – 6.8 ± 0.1^a 6.9 ± 0.1^a 6.2 ± 0.2^b

12 – 7.0 ± 0.1â 6.9 ± 0.1â 6.8 ± 0.2â

14 – 7.1 ± 0.4^b,2 7.6 ± 0.4^a,2 6.2 ± 0.2^c

(Day)

Yeast Counts

K^a 1.5% LA^b 5% TSP^b 5% STPP^a

0 1.v.2âb 1.6 ± 0.1âb 1.8 ± 0.5â 1.0 ± 0.3^b

3 3.0 ± 0.6^a 1.8 ± 0.6^b 1.8 ± 0.2^b 2.6 ± 0.4^a

6 5.3 ± 0.3â 3.8 ± 0.7^b 5.2 ± 0.2â 5.0 ± 0.1â

8 6.3 ± 0.5^b 5.4 ± 0.9^c 5.5 ± 0.1^c 7.0 ± 0.1^a

10 6.9 ± 0.3^ab 6.5 ± 0.7^b 6.7 ± 0.3^b 7.5 ± 0.5^a

12 7.6 ± 0.1^a 7.2 ± 0.6^ab 6.8 ± 0.1^b 6.9 ± 0.4^b

14 7.2 ± 0.1â,2 7.2 ± 0.2â,2 7.0 ± 0.2â,2 7.1 ± 0.0â,2

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4 – CONCLUSIONS

It was concluded that, in this study dipping turkey breast fillets in both 0.5% FA and 1% LA could extend the storage life up to 4 day, without adversely affecting the colour.

1% LA + 0.5% FA treated breast fillets had a detectable discoloration and acid odour although there was no microbiological spoilage at 14 days of storage. The off-odour in fillets generally observed when both aerobic mesophilic and psychrotrophic counts exceeded 10⁸cfu g^-1. When compared with the results presented in literature, discrepan- cies may result from different experimental conditions such as decontamination tech- niques, exposure time and storage conditions. The application of organic acids or phosphates cannot replace the rules of high hygiene and good manufacturing practice, but it may be used as an additional hurdle contributing to the extending the shelf life of the refrigerated turkey meat.

5 – ACKNOWLEDGEMENTS

The authors are sincerely grateful for the support of PINAR Entegre Et ve Yem San.

A.S.

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