Limon otu yağının elma suyunda escherıchıa colı o157:h7 ve lısterıa monocytogenes'in ısıl direnci üzerine etkisi = Effect of lemon grass oil on the heat resistance of escherichia coli o157:h7 and listeria monocytogenes in apple juice

Abstract

Anahtar kelimeler: E. coli O157:H7, L. monocytogenes limon otu yağı, elma suyu, ısıl işlem, D değeri, z değeri Limon otu yağının (LOY) elma suyunda Escherichia coli O157:H7 ve Listeria monocytogenes'in ısıl direnci üzerine etkisi araştırılmıştır. LOY (%0,1 ve 0,2) ilave edilmiş elma suyu örneklerine 7-8 log kob/mL düzeyinde E. coli O157:H7 ve L. monocytogenes inoküle edilmiş, dört farklı sıcaklıkta (55; 57,5; 60; 62,5°C) ısıl işlem uygulanmış ve belirli sürelerde örnekleme yapılarak canlı hücre sayısı belirlenmiştir. Elde edilen veriler GInaFit yazılımında Log-Lineer ve Weibull modeline uyumlanarak D ve z değerleri hesaplanmıştır. Buna göre E. coli O157:H7'nin 55; 57,5; 60; 62,5°C'deki Log-Lineer ve Weibull modeline uyumlanarak hesaplanan D değerleri sırasıyla kontrol örneklerinde (%0 LOY) 10,84-11,18; 2,06-2,00; 1,39-1,53; 0,82-0,85 dak., %0,1 LOY ilave edilmiş örneklerde 10,78-9,90; 1,86-1,86; 1,25-1,28; 0,48-0,60 dak. ve %0,2 LOY ilave edilmiş örneklerde 9,11-8,32; 1,19-1,19; 1,10-1,06; 0,48-0,54 dakikadır. Veriler her iki modele de uyumlu bulunmuştur (r2 > 0,95). E. coli O157:H7'nin %; 0,1 ve 0,2 içeren elma suyu örneklerindeki z değerleri Log-Lineer modele göre sırasıyla 7,09°C (r2=0,89), 5,92°C (r2=0,93) ve 6,45 (r2=0,85), Weibull modele göre ise sırasıyla 7,19°C (r2=0,87), 6,53°C (r2=0,92) ve 6,89°C (r2=0,84) olarak hesaplanmıştır. L. monocytogenes'in 55; 57,5; 60; 62,5°C'deki Log-Lineer ve Weibull modeline uyumlanarak hesaplanan D değerleri sırasıyla kontrol örnekleri için 12,71-11,63; 1,80-1,87; 1,56-1,62; 0,62-0,66 dak., %0,1 LOY ilave edilmiş örneklerde 11,57-10,95; 1,24-1,31; 1,14-1,17; 0,61-0,58 dak. ve %0,2 LOY ilave edilmiş örneklerde 10,41-7,73; 1,18-1,16; 0,94-0,90; 0,53-0,49 dakikadır. L. monocytogenes'in inaktivasyon eğrileri Log-Lineer modele göre (r2=0,91) Weibull modele (r2=0,95) daha uyumlu bulunmuştur. L. monocytogenes'in %; 0,1 ve 0,2 içeren elma suyu örneklerindeki z değerleri Log-Lineer modele göre sırasıyla 6,27°C (r2=0,87), 6,46°C (r2=0,80) ve 6,28 (r2=0,82), Weibull modele göre ise sırasıyla 6,57°C (r2=0,88), 6,43°C (r2=0,83) ve 6,74°C (r2=0,86) olarak hesaplanmıştır. Her iki patojende de sıcaklık ve LOY konsantrasyonu arttıkça membranı zarar görmüş hücre sayısı artmıştır. Çalışmada elde edilen bulgular doğrultusunda LOY'nın elma suyunda E. coli O157:H7 ve L. monocytogenes'in ısıl direncini azalttığı, bu nedenle ısıl işlemle dayanıklı hale getirilen meyve sularında koruyucu olarak kullanılabileceği sonucuna varılmıştır.

Keywords: E. coli O157:H7, L. monocytogenes, lemongrass oil, apple juice, heat treatment, D value, z value The effect of lemongrass oil (LGO) on the heat resistance of Escherichia coli O157:H7 and Listeria monocytogenes in apple juice was investigated. E. coli O157:H7 and L. monocytogenes were inoculated (7-8 log cfu/ml) into apple juice samples added with LGO (0.1 and 0.2%). Then samples were heat treated at isothermal temperatures (55, 57.5, 60, 62.5°C) and the viable counts were determined after sampling at predetermined time intervals. D and z values were calculated by curve fitting to Log-Linear and Weibull models using GInaFit software. According to the Log-Linear model, the D values of E. coli O157:H7 at 55, 57.5, 60 and 62.5°C were 10.84, 2.06, 1.39 and 0.82 min, respectively, in control samples (0%LGO); 10.78, 1.86, 1.25 and 0.48 min, respectively, in 0.1%LGO added samples; and 9.11, 1.19, 1.11 and 0.48 min, respectively, in %0.2 LGO added samples. While, according to the Weibull model, they were 11.18, 2.00, 1.53 and 0.85 min, respectively, in control samples; 9.90, 1.86, 1.28 and 0.60 min, respectively, in 0.1%LOG added samples; and 8.32, 1.19, 1.06 and 0.54 min, respectively, in 0.2%LOG added samples. The survival curves were well fitted to both models (r2>0.95). The z values of E. coli O157:H7 in apple juice with 0, 0.1 and 0.2%LOG were calculated as 7.09°C (r2=0.89), 5.92°C (r2=0.93) ve 6.45 (r2=0.85), respectively, according to Log-Linear model, while they were calculated 7.19°C (r2=0.87), 6.53°C (r2=0.92) ve 6.89°C (r2=0.84), respectively, by fitting to Weibull model. When the data were fitted to the Log-Linear model, the D values of L. monocytogenes at 55, 57.5, 60 and 62.5°C were 12.72, 1.80, 1.56 and 0.62 min, respectively, in control samples, 11.57, 1.24, 1.14 and 0.61 min, respectively, in 0.1%LOG added samples, and 10.41, 1.18, 0.94 and 0.53 min, respectively, in 0.2%LOG added samples. On the other hand, by fitting to the Weibull model, they were 1.63, 1.87, 1.62 and 0.66, respectively, in the control samples, 10.95, 1.31, 1.17 and 0.58, respectively, in 0.1%LOG added samples, and 7.73, 1.16, 0.90 and 0.49 min, respectively, in 0.2%LOG added samples. The survival curves were better fitted to the Weibull model (r2>0.95) than the Log-Linear model (r2>0.91). The z values of L. monocytogenes in apple juice with 0, 0.1 and 0.2%LOG were calculated as 6.27°C (r2=0.87), 6.46°C (r2=0.80) ve 6.28 (r2=0.82), respectively, according to Log-Linear model, while they were 6.57°C (r2=0.88), 6.43°C (r2=0.83) ve 6.74°C (r2=0.86) according to Weibull model.The number of membrane-damaged cells of both pathogens increased with the increasing temperature and LOG concentration. Based on the finding obtained in this study, it was concluded that LOG reduces the thermal resistances of E. coli O157:H7 and L. monocytogenes in apple juice; therefore, it can be used as a preservative in fruit juices preserved by heat treatment.