SLOVENIAN VETERINARY RESEARCH

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5,0 4,5 The effect of thyme oil on the shelf life of chicken balls during storage period 23 5,0 4,0 4,5 3,5 4,0 3,0 5,5 5,0 4,5 taste score taste score 3,5 2,5 4,0 3,0 2,0 3,5 2,5 1,5 2,0 0 2 4 6 8 10 12 14 3,0 Storage Time (Day) 1,5 2,5 0 2 4 6 8 10 12 14 Storage Time (Day) 0 2 4 6 8 10 12 14 Storage Time (Day) Figure 3: Changes in the taste (a) and odour (b) of chicken balls, control (A), batter with added thyme EO 0.4% (B) and ball surface thyme EO 0.4% (C). Each point is the mean of three samples taken from two replicate experiments (n: 3 x 2: 6). Error bars show SD. Table 1 shows the colour measurement results of chicken balls. All chicken balls varied insignificant in their L, a and b values (p>0.05). Table 1: Colour properties of experimental chicken balls Group Storage time (day) Analysis 0 3 6 9 12 L* 75.42±0.46 a,z 75.42±0.33 a,z 75.33±0.56 a,z 75.56±0.41 a,z 75.33±0.39 a,z A a* 0.90±0.09 a,z 0.90±0.06 a,z 0.91±0.4 a,z 0.93±0.21 a,z 0.90±0.36 a,z b* 16.77±0.25 a,z 16.77±0.21 a,z 16.81±0.56 a,z 16.85±0.43 a,z 16.77±0.21 a,z L* 75.33±0.19 a,z 76.16±0.26 a,z 76.01±0.31 a,z 75.19±0.18 a,z 75.96±0.16 a,z B a* 0.91±0.04 a,z 0.90±0.02 a,z 0.96±0.05 a,z 0.91±0.04 a,z 0.93±0.04 a,z b* 17.13±0.22 a,z 17.09±0.19 a,z 17.33±0.24 a,z 17.13±0.19 a,z 17.21±0.21 a,z L* 76.01±0.56 a,z 76.81±0.54 a,z 76.16±0.42 a,z 76.21±0.36 a,z 76.33±0.29 a,z C a* 0.93±0.01 a,z 0.91±0.06 a,z 0.94±0.02 a,z 0.90±0.01 a,z 0.92±0.03 a,z b* 16.36±0.12 a,z 16.22±0.21 a,z 16.43±0.23 a,z 16.21±0.19 a,z 16.23±0.21 a,z Texture analysis results for chicken balls are shown as in Table 2. Results regarding hardness, cohesiveness, springiness and chewiness value during storage time were determined to be similar for all groups, therefore, the mean values have been given. Table 2: Textural properties of experimental chicken balls. Group Hardness (kg) Cohesiveness(mm/mm) Springiness (mm/mm) Chewiness (kg/mm) M ± SD A 3.73±0.22 0.67±0.01 12.56±0.42 31.33±1.56 B 3.96±0.19 0.65±0.04 12.93±0.46 35.21±1.41 C 3.52±0.28 0.69±0.02 12.87±0.52 32.56±1.82
24 Ö. Pelin Can Discussion The changes in total viable count (TVC) of the chicken meat balls are given Fig. 1a. The initial value of TVC (day 0) for fresh chicken meat was ca. 4.3 log cfu/g, indicative of good quality chicken meat (19). TVC reached a value of 7 log cfu/g, considered as the upper microbiological limit for good quality fresh poultry meat, as defined by the ICMSF (2), on day 6 for the control samples. Samples treated with thyme oil in groups never reached the limit of 7 log cfu/g during the 12 day storage period. The group B samples were determined to be 4.83 log cfu/g 0 day. This value decreased about 2 log cfu/g on day 3 of storage and reached 5.21 log cfu/g at the end of storage. There was no significant change to the C groups sample during storage. Thyme oil in the additive ball was more effective than in the surface ball on reducing TVC. Thyme oil resulted in a shelf-life extension of six days as compared to the control samples. In related studies, Giatrakou (7) mentioned a shelf-life extension of 2 days after the application of thyme oil 0.2% v/w on chicken, while Ergezer (20) reported that TVC in chicken balls was reduced with whey powder stored at -18 °C for three months. Listeria spp. and Salmonella spp were found in one of the samples. They are also in agreement with those reported by Yavaş et al. (21), who reported no determination in ground chicken balls after 21 days of storage under modified atmosphere pressure (MAP). Pseudomonads (Fig. 1b) are Gram-negative bacteria, comprising the main spoilage microorganisms in meat (22). In other studies, the combined use of thyme oil on chicken products stored aerobically at 4 °C, resulted in about 8.0 log cfu/g of the final population of pseudomonas (6). Deans and Richie (23) showed that thyme oil was very effective against Pseudomonas aeruginosa, in a study where the inhibitory properties of ten plant essential oils were tested using an agar diffusion technique. This is in agreement with Elgayyar et al. (24) who reported that oregano essential oil was less effective in inhibiting P. aeruginosa compared to other microorganisms. Lactic acid bacteria (LAB) (Fig. 1c) facultative anaerobic species were found to be members of the microbial flora of the chicken product. Of all the antimicrobial treatments in this study, thyme oil on surface of ball treatment proved to be the most effective in inhibiting the growth of LAB, almost stable during the storage period. For Georgantelis et al. (25), the combined use of rosemary essential oil and chitosan on fresh pork sausages stored aerobically at 4 °C, resulted in a 2.0 log cfu/g reduction of the final population of LAB. In another study, LAB count reduced by 0.2% in the chicken balls with thyme oil during storage (6). With respect to Enterobacteriaceae (Fig. 1d), considered as a hygiene indicator (26), the initial counts of 2.33 log cfu/g were indicative of good quality chicken meat. Enterobacteriaceae grew under essential oil applications at a slower rate than others. This is in agreement with the results of Choularaia et al. (27), who reported that oregano oil had a strong effect in the reduction of Enterobacteriaceae counts. On day 9 of storage, the use of thyme oil had practically no effect on Enterobacteriaceae counts (p> 0.05). On the same day, the Enterobacteriaceae counts were determined by 7.56 log cfu/g, 2.13 log cfu/g and 2.59 log cfu/g in groups A, B and C, respectively. Giatrokau et al. (7) reported that Enterobacteriaceae of chicken products were inhibited in the presence of thyme oil packaging. As a result, the initial population of yeasts and moulds were very low (2.78 log cfu/g) and no population was determined on day 3 and 6 of storage for B and C group samples. The balls with added thyme oil were a lot more effective in reducing yeast populations in comparison to surface added balls (P
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