Siyah Aspergillus Suşları Tarafından Kuru Üzüm Besiyerinde Okratoksin A (ota) Oluşumunun İncelenmesi

Abstract

Tüketiciler, sebze ve meyveleri yaş formda olarak tüketebildikleri gibi, kurutulmuş formda da tüketebilmektedirler. Kurutulmuş olarak tüketilen ürün gruplarından birisi de kuru üzümlerdir. Kuru üzümler çekirdekli olabildiği gibi çekirdeksiz de olabilir. Yaş formdaki üzümler geleneksel ya da modern teknikler kullanılarak kurutma prosesinden geçirilerek kurutulmuş forma getirilir. Kuru üzüm gerek iç piyasaya sürülmesi, gerekse ihracat ürünü olması nedeniyle ekonomik açıdan önem teşkil eden bir gıda maddesi grubudur. Kuru üzüm, bağlarda yetişmeye başladığı yaş halinden itibaren tüketicilere son ürün olarak sunulup, tüketiciler tarafından tüketildiği ana kadar geçen süreçte ürünün uygun üretim ve muhafaza koşulları sağlanmadığı takdirde, mikotoksin içeriği bakımından riskli bir hale gelmektedir. Gıda endüstrisinde, gıda maddelerinin güvenliğinin ve kalitesinin sağlanması en önemli konulardan birisidir. Gıda maddelerinde mikotoksin oluşumu da, mikotoksinlerin hem insan sağlığı üzerindeki olumsuz etkileri hem de ekonomik kayıplara neden olması açılarından, gıda güvenliği ve gıda kalitesini doğrudan etkilemektedir. Bu tez çalışması kapsamında; tüketiciler tarafından sıklıkla tercih edilen bir gıda maddesi olan kuru üzümde okratoksin A (OTA) oluşumu incelenmiştir. Çalışmada, kuru üzümde gelişen 2 farklı Aspergillus suşunun (A.niger ve A.carbonarius) 10 günlük inkubasyon periyodunda 3 farklı besiortamında OTA oluşturma profilleri, Yüksek Performanslı Sıvı Kromatografisi–High Performance Liquid Chromatograpy (HPLC) ile belirlenmiş olup; oluşan OTA miktarları tespit edilmiştir. Çalışmada kullanılan 2 Aspergillus suşu, kuru üzümden izole edilmiştir. Besiortamları ise; Malt Extract Agar (MEA), çekirdekli siyah üzümden elde edilen besiortamı ve çekirdeksiz sarı üzümden elde edilen besiortamı olup, 3 farklı çeşit besiortamı kullanılmıştır. Çalışma sonuçlarına göre; A.carbonarius suşunun hem çekirdekli siyah kuru üzümde hem de çekirdeksiz sarı kuru üzümde OTA oluşturduğu; A.niger suşunun ise her iki kuru üzüm cinsinde OTA oluşturmadığı bulunmuştur. Besiortamlarının 10 günlük gelişme periyodu boyunca pH değerleri ölçülmüş ve besiortamlarına (substrata) ait pH değerlerinin 1.günden 10.güne giderek azaldığı tespit edilmiştir. 2 farklı Aspergillus suşunun (A.niger ve A.carbonarius) gelişme hızlarının belirlenmesi amacıyla 10 günlük gelişme periyodu boyunca 25ºC ve 30°C sıcaklık değerlerindeki, petrilerde gelişen kolonilerin çapları mm cinsinden ölçülmüştür. Çalışmada kullanılan her iki Aspergillus suşunun da 30ºC sıcaklık değerindeki gelişmelerinin daha hızlı olduğu bulunmuştur. Bu yüksek lisans tezinin birinci bölümünde giriş bilgileri; ikinci bölümünde literatür özeti; üçüncü bölümünde kullanılan malzeme ve yöntemler; dördüncü bölümünde çalışmadan elde edilen sonuçlar ve beşinci bölümde ise sonuç ve öneriler konularında bilgi verilecektir.

Consumers prefer eating fruits and vegetables during their daily diet as they have high vitamin content. They may consume fruits and vegetables as either fresh or dried depending on their preference. Grapes are very popular fruits and highly consumed in Turkey. Dried vine fruits that are dried form of grapes are one group of the food products are consumed as in the dried form. Fresh form of grapes are preferred especially in summer because of higher water content in comparison to dried form while dried vine fruit is preferred especially in winter. Dried vine fruit can be either with seed or seedless. Grapes are dried by the application of drying process. Drying process decreases the water content of the food product. Therefore, the water activity of food product is also decreased. Drying process can be applied by using either traditional techniques or modern techniques. For both methods, this is certain that the water activity is decreased. Microorganisms cannot grow or can grow limited at lower water activity values as their metabolic activity is decreased or stopped due to the limited available water. Low water activity value and other factors affect the mold metabolism negatively and this situation causes stress on mold metabolism. In this case, if the other factors are appropriate, the molds synthesize mycotoxins. Mycotoxins have not only harmful effect on human health but also negative effect economically. Dried vine fruits have high economical value since they are both sold in domestic market and exported. Dried vine fruits can become risky due to mycotoxin content if appropriate manufacturing and storage conditions are not satisfied during the period from harvest to the consumption of end product. Ensurance of food safety and food quality is one of the most important topics in food industry. Mycotoxin formation on food products, directly affect food safety and food quality since mycotoxins cause economical loss and have negative effects on human health. There are different types of mycotoxins synthesized by different species of molds. However, the frequency and availability of mycotoxins are not the same. Some of the mycotoxins (aflatoxins, ochratoxins, fumonsins, etc.) are found frequently. That is why, they are called as major mycotoxins. Some of the mycotoxins (sterigmatocystin, 3–nitropiazonic acid, etc.) are found rarely. That is why, these types of mycotoxins are called minor mycotoxins. In this study, one of the most frequent mycotoxins, ochratoxin A (OTA) formation in dried vine fruits that are one of the often preferred food products by consumers was investigated. In this study, the OTA production formation profiles of two Aspergillus strains (A.niger and A.carbonarius) during 10 days incubation period were stated by High Performance Liquid Chromatography (HPLC). The amount of OTA that were formed during incubation period were quantified. Two Aspergillus strains (A.niger and A.carbonarius) used in the study were isolated from dried vine fruits. Three different medias are used in this study and they are: Malt Extract Agar (MEA), grape media obtained from sultanas and grape media obtained from seed bearing raisins. It was found that A.carbonarius strain used in this study synthesized OTA in both types of dried vine fruits that were used in this study while A.niger strain that was used in this study did not synthesize OTA in both types of dried vine fruits that were used in this study. pH values of medias during 10 days incubation period were measured. For A.niger strain, pH values of MEA were measured between 5.13–2.38; pH values of grape media obtained from sultanas were measured between 3.89–1.86; pH values of grape media obtained from seed bearing raisins were measured between 4.07–2.11. For A.carbonarius strain, pH values of MEA were measured between 5.13–2.18; pH values of grape media obtained from sultanas were measured between 3.89–2.05; pH values of grape media obtained from seed bearing raisins were measured between 4.07–1.83. It was determined that pH values of media have been gradually decreasing from the first day to the tenth day. Two Aspergillus strains (A.niger and A.carbonarius) were incubated at both temperatures, 25ºC ve 30ºC, for 10 days in order to determine the growth rate of these two strains. Colony diameters were measured in terms of mm for each day during incubation period. Diameter values started from 0 mm and reached to 85 mm at the end of the incubation period. It is valid for both strains that the surface of the petri dishes was fully covered on the seventh day for 30ºC incubation temperature and on the tenth day for 25ºC incubation temperature. For A.niger strain, the growth rate at 25ºC was found as 8.5595 mm/day; and the growth rate at 30ºC was found as 10.067 mm/day. For A.carbonarius strain, the growth rate at 25ºC was found as 8.7088 mm/day; and the growth rate at 30ºC was found as 10.411 mm/day. These results demonstrated that the growth rate of A.carbonarius is higher than the growth rate of A.niger. In addition to this, it was found that the growth rate at 30ºC was faster than the growth rate at 25ºC for both Aspergillus strains that were used in this study. In order to minimize the risk of OTA that has negative health effect, the producers should ensure the food safety during the period from manufacturing the food product to the consumption of the product by managing this period consciously and carefully. By this way, positive developments on food quality and food safety can be achieved. In the first chapter of the master thesis, information for introduction; in the second chapter, literature survey will be emphasized. In the third chapter, materials and methods that have been used in the study and in the fourth chapter, results obtained from the study will be mentioned. Finally, in the last chapter, discussion part will take place.