Taze etin bozulma sürecinin tahribatsız optik yöntemlerle incelenmesi
Investigation of freshness of red meat with nondestructive optical methods
Yazar: ELİF OLFAZ HEZER
Danışman: DOÇ. DR. NEŞE ŞAHİN YEŞİLÇUBUK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Gıda Mühendisliği Ana Bilim Dalı / Gıda Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Gıda Mühendisliği = Food Engineering

Özet:
Günümüzde tüketicilerin sağlıklı yaşam bilinci her geçen gün artmaktadır.  Tükettikleri besinlerin içeriğine, kalitesine dikkat ederek ve standartlara uyması gerektiğini düşünerek gıda maddelerini satın almaktadırlar. Günlük diyette yer alması gereken protein, karbonhidrat, yağ, vitamin ve mineralleri hayvansal veya bitkisel kaynaklı tercih edip vücudun gereksinimlerini tamamlamaktadırlar. Kırmızı et ise içerdiği protein içeriği, esansiyel aminoasit miktarı ve çeşidi açısından bitkisel kaynaklı proteinlere göre öncelikli olarak seçilmektedir. 
Taze et kalitesi tüketicilere göre değişkenlik gösterebilen bir kavramdır. Etin rengi, kokusu, lezzeti ve çiğneme kalitesi genel değişkenler olarak görülmektedir. Raf ömrü içerisinde kırmızı et birçok faktöre bağlı olarak bozulabilmektedir. Etin bozulması yağ oksidasyonu ve mikrobiyal gelişim ile meydana gelmektedir. 
Yapılan bu çalışmada aerobik ortamda ambalajlanmış bonfile numuneleri, 00C ve 40C sıcaklık koşullarında 10 gün boyunca muhafaza edilerek, bozulma süreci izlenmiştir. Etin tazeliği tahribatsız yöntemlerden olan fourier dönüşümlü infrared spektroskopisi (FTIR) ve floresan spektroskopisi ile incelenmiştir. İki optik yöntemin etin tazeliğini tahminleme yeteneğini konvansiyonel diğer kalite analizleri (TBA (tiyobarbitürik asit), mikrobiyolojik analiz ve duyusal analizler) yardımıyla karşılaştırılmıştır. 
FTIR analizi sonuçlarına göre, protein ve nem içeriğini temsil eden piklerdeki değişimin konvansiyonel test sonuçları ile paralel olduğu görülmüştür. Muhafaza süresi boyunca mikrobiyolojik gelişimin etkisi ile ortamdaki proteinler mikroorganizmalar tarafından parçalanarak, C-N bağ yapısında azalma meydana getirmiştir.
Floresan spektroskopisi ile etin kalite tayininde potansiyel bozulma göstergesi olarak değerlendirilebilecek porfirin izlenmiştir. Muhafaza süresi boyunca her iki sıcaklık koşulunda muhafaza edilen etlerin floresan yoğunluğu artmıştır. Bu artış, 40C muhafaza sıcaklığına sahip ortamda muhafaza edilen etlerde  daha fazla görülmüş, sıcaklığın bozulmadaki etkisi konvensiyonel testler ile de desteklenmiştir. Porfirin floresan yoğunluk pikleri diğer literatür çalışmalarından genel olarak farklıdır. Etin homojen olmayan yapısı, etin çeşidi, hayvanın cinsi, ve deney parametrelerindeki faktörlerin etkili olduğu düşünülmektedir. Her iki muhafaza sıcaklığı koşulundaki sonuçlara yönelik gerçekleştirilen  temel bileşen analizi sonucuna göre, her iki sıcaklık şartında mikrobiyal bozulma ile birlikte oluşan metabolitlerin floresan özelliğinin 435 nm bulgulama dalga boyunda karakteristik değişiklik gösterdiği tespit edilmiştir. Gelecek çalışmalarda, incelenecek fiziksel parametre sayısının ve aralığının genişletilerek validasyonun sağlanması ile, ette mikrobiyal ve biyokimyasal kaynaklı bozulmaların tespitinde hızlı yanıt verebilen optik yöntemlerin tercih edileceği ve geliştirileceği düşünülmektedir.

Abstract:
In the World, people have become very conscious about healthy life. They consume foods, thinking that they need to obey the standards by paying attention to the quality of foods. Each macro and micronutrients should be taken to the body in the daily diet. These are preferred by animal or vegetable sources and fulfill requirements of the body.
Red meat and other animal animal-derived foods are a better source of protein than vegetable-derived foods. Niacin, vitamin B6, vitamin B12, folic acid, zinc, iron can be supplied with meat consumption which is important in the daily diet. It is possible to supply 25% of these foodstuffs with 100 g of red meat per day. Red meat also contains selenium, riboflavin, pantothenic acid. With 100 g of red meat consumption, more than 10% of these minerals and vitamins can be provided. Meat consumption especially contributes to bone development for children. Meat consumption prevents anemia in pregnant women and children. It is also known that the consumption of high amounts of red meat can relate to cancer and obesity.
Consumption of red meat is parallel to the development of the countries and economic opportunities. While annual meat consumption is high in industrialized countries, meat consumption in developing countries is less than 10 kilograms per year. It is seen as the cause of undernutrition. When meat consumption in the World is investigated, Spain consumes the most meat in Europe while the least meat consuming country is Greece. In our country, annual meat consumption is equivalent to 5.7 kilograms. Looking at other European countries, the consumption rate is quite insufficient.
Fresh meat sensory quality is a concept that can vary according to consumers. The color, flavor, smell, and quality of chewing meat are seen as general variables. Meat appearance is determined according to factors such as meat color, fat content, fat color, and meat texture. Appearance quality traits are the most important parameters when consumers purchase meat. Softness, flavor, and hydration are gathered under the name of eating quality traits. Meat reliability, nutritional value, animal health, price, product presentation, origin, and brand are defined as reliance on quality traits. Sensory quality criteria are color, texture, and taste. 
The microbial quality of raw meat is affected by factors such as the physical condition of the animal at the time of slaughtering, meat processing, and transfer. Unsuitable conditions are unacceptable in terms of human health, which leads to oil oxidation and autocatalytic enzymatic reactions with pH conditions suitable for the development of nutrients and microorganisms in meat. Microbial growth which cause food spoilage varies depending on environmental conditions such as food processing, storage, and distribution. Environmental factors are grouped under four main headings. These are internal factors (pH, water activity etc.), processing factors, external factors (temperature, relative humidity etc.) and other microorganisms. 
Pseudomonas spp.  is the most common deterioration agent in chilled raw meat. Under refrigerator temperatures (4°C) and under aerobic conditions, it develops in raw meat. The gram-negative microorganism is psychrotroph and can survive between 0 and 200C temperatures. The high relative humidity of the refrigerator environment provides an additional ground for deterioration. Excessive amounts of Pseudomonas fluorescence, Pseudomonas fragments, and Shewanella putrefaciens bacteria increase the population, resulting in meaty mildew and bad odor formation in refrigerator conditions.
Lipid oxidation is a decisive factor in deciding food shelf life in foods with muscle content, such as meat. The main products of the reaction between molecular oxygen and unsaturated fatty acids are hydroperoxides and secondary products such as alkenes, alkenes, aldehydes, ketones, alcohols, esters, acids, hydrocarbons. Lipid oxidation is the result of undesirable taste, color and texture changes in meat.
Along with microbial growth and lipid oxidation, meat deterioration and the development of food-borne pathogens are seen. For this reason, several methods have emerged to protect the meat. The most important factors affecting meat shelf life and quality are storage temperature, atmospheric oxygen, enzymes, moisture, light, and microorganisms. Each factor or combination of them affects the color, texture, smell, and taste of the meat. The hiding of the meat can be examined in three categories. These can be categorized as temperature control, moisture control and applied processes (bactericide, ionizer irradiation, packaging, etc.). The novel technologies based on extending shelf life is still continued. Chilling, freezing, high-pressure application, modified atmosphere packaging are known as novel technologies related to storage of meat.
Food safety of meat is an important issue. If it is not ensured and storage conditions are not maintained properly, it can easily deteriorate. As a result of microbial deterioration, odor and color changes, food poisoning can come to the scene by consuming these meats. Microbial deterioration is not always physically identifiable and becomes a dangerous situation for consumers. Chemical and microbiological analyzes are time-consuming, and they are destructive test methods. However, apart from chemical and microbial tests, there is a need for non destructive methods also being fast, reliable and having high-precision. 
The preferred optical methods for quality measurements are based on spectroscopic measurements. It has four main headings. These are visible spectroscopy and color measurement, Raman spectroscopy, infrared spectroscopy and fluorescence spectroscopy. The most important reasons for the widespread use of optical methods in food quality control are non-destructive, fast, cheap, allowing for online measurements and not requiring too much labor cost to use.
In this study, beef samples were packed and stored at 00C and 40C and deterioration process was observed for 10 days. The freshness of samples was investigated by non-destructive methods such as Fourier transform infrared spectroscopy (FTIR) and fluorescence spectroscopy. The performance of the two optical methods was supported by conventional tests such as TBA (thiobarbituric acid), microbiology and sensory analysis.
The change in protein and moisture content by FTIR analysis was done with  conventional tests. The decrease in microbiological development, increase in fat oxidation, and panelist scores in sensory parameters were used . The proteins in the environment are broken down by microorganisms, causing a decrease in C-N bond structure.
Potential porphyrin was used in the determination of the quality of the meat by fluorescence spectroscopy. Fluorescent intensity was increased in both chambers during the storage period. This situation was further observed in the 40C section, and the effect of temperature on deterioration was supported by the conventional tests. Fluorescence peak obtained from two chambers in this study was different from literature. The result of the principal component analysis revelaed that deterioration state with 435 nm detection wavelength at both temperatures could be selected as characteristic.
In the future studies, optical methods that can respond quickly in detecting microbial and biochemical changes in meat, will be preferred and developed by increasing the number of physical parameters to be examined and extending validation range.