Laktik asit bakterilerinden sentezlenen ekzopolisakkaritlerin buğday suyu özelliklerine etkisinin incelenmesi
Effects of exopolysaccharides produced by lactic acid bacteria on the liquid wheat
Yazar: SELİN DAĞ
Danışman: PROF. DR. ZEYNEP DİLEK HEPERKAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Gıda Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Gıda Mühendisliği = Food Engineering

Özet:
Bugünlerde tüketiciler; katkı maddesiz, sağlıklı ve güvenli gıdaları tercih etmektedir. Laktik asit bakterileri (LAB) farklı metabolik aktiviteleri ile gıda endüstrisinde önemli yere sahiptir. LAB, fermantasyonda starter kültür, ürettiği metabolitler ile gıda katkı maddesi veya proses yardımcısı olarak görev almaktadır. Gıdaların teknolojik, besinsel, organoleptik özelliklerini geliştirmekte ve ürettiği antimikrobiyallerle gıdaların korunmasında etkili olmaktadır. Gıdaların yapısını geliştirerek, aroma maddeleri üreterek gıdayı daha çekici hale getirmekte; fajlara dirençli hale getirilerek teknolojik açıdan, toksik bileşikleri azaltarak ve probiyotik özelliklere sahip olarak sağlık açısından avantajlar sağlamaktadır.
Laktik asit bakterilerinin en önemli fonksiyonlarından biri de gıdaların besinsel değerini artıran, istenmeyen ve toksik bileşiklerin yok edilmesine, görünümün iyileştirilmesine, farklı doku ve aroma kazandırılmasına neden olan laktik asit fermantasyonlarını gerçekleştirmektir. Laktik asit fermantasyonu süt ürünlerinde, hububat bazlı ürünlerde, sebzelerin, çeşitli içeceklerin yapımında görülmektedir. Hububatlar arasında buğday düyada yetişen önemli tahıl ürünüdür. Buğday, yazın ve kışın yetişebilen tahıldır. Un, ekmek, makarna, bisküvi, kek, kraker ve yem eldesi gibi birçok amaç için kullanılır. Aynı zamanda nişasta, gluten ve alkol eldesinde de kullanılır. 
Laktik asit bakterilerinin ürettiği metabolitlerden biri de ekzopolisakkaritlerdir. Yüksek molekül ağırlıklı, uzun zincirli polimerler olan ekzopolisakkaritlerin su tutma kapasiteleri bulunmaktadır. Gıda endüstrisinde emülsifikatör, stabilizatör olarak, sineresisin önlenmesinde, kristalizasyonun kontrolünde pek çok amaçta kullanılmaktadır. Bunun yanında sağlık üzerine yararlı metabolitlerdir. Prebiyotik, antitümör, antiülser etkileri olup immün sistemin düzenlemesinde, kalp rahatsızlıklarında etkili olmaktadır. 
Araştırmada, LAB türlerinden elde edilen EPS moleküllerinin buğday suyu üzerine etkileri incelenecektir. Buğday; Türkiye'de doğrudan ve dolaylı tüketim ürünlerinden birisi olup, endüstrisinde özelliklerinin iyileştirilmesi konusunda yapılacak olan bu çalışmanın literatüre, ülke ekonomisi ve toplum sağlığına katkı sağlayacağı düşünülmektedir.
Yapılan çalışmada laktik asit bakterilerinin ekzopolisakkarit oluşturma kapasitelerinin belirlenmesi amaçlanmıştır. Laktik asit bakterilerinden sentezlenen ekzopolisakkaritlerin buğday suyunun reolojik özelliklerine etkisi incelenmiştir. Birçok bakteri türü tarafından üretilen ekzopolisakkaritler (EPS) stabilize edici ve emülgatör özelliği ile gıda endüstrisinin ilgisini çekmektedir. Çalışmada bozadan izole edilmiş olan ekzopolisakkarit üreten Leuconostoc citreum (A31), Lactococcus lactis (A47), Lactobacillus coryniformis (C55), Lactobacillus paracasei (E8) ve Pediococcus parvulus (E42) suşları kullanılmıştır. Çalışmada hazırlanan buğday suyunun kimyasal özellikleri ve reolojik özellikleri ölçülmüştür. Laktik asit bakterilerinin faaliyeti sonrasında bütün buğday suyu ve M-MRS örneklerinde pH değerinin azaldığı tespit edilmiştir.  Hem M-MRS'de hemde buğday suyunda pH en düşük değeri; A47 suşuna aittir. En düşük EPS üretimi M-MRS numunelerinde tespit edilmiştir. A47 suşu iki farklı ortamda da en yüksek EPS üretimine sahiptir. Buğday suyunun reolojik özellikleri plaka-sensör sistemi kullanılarak reometre ile 25°C'de ve 0,01-300 s-1 kayma hızı aralığında ölçülmüştür. Reolojik ölçümlerde farklı  viskozite etkileri farklı ekzopolisakkaritlerden olduğu tespit edilmiştir. Ekzopolisakkarit eklenen buğday sularının tümü Newtonyen olmayan, kayma incelmesine sahip davranış göstermiştir. En yüksek viskozite ve kıvam katsayısı Lactococcus lactis (A47) suşu eklenmiş buğday suyunda tespit edilmiştir. Laktik asit bakterilerinden sentezlenen ekzopolisakkaritlerin buğday suyunun yapısal özelliklerini iyileştirdiği için stabilizör olarak kullanılması tavsiye edilebilir.

Abstract:
Nowadays consumers prefer healthy, safe food that is without artificial preservatives. Lactic acid bacteria (LAB) have important properties in food industry with their diversity of metabolic activities. LAB used in fermentations as a starter culture, or used as an additive or a processing aid with the metabolites they produce. They improve the technologic, nutritional, organoleptic properties of foods and they are effective in preserving foods by the antimicrobials they produce. They improve the texture of foods and make them attractive by producing flavour compounds. They provide technologic advantages by becoming resistant to bacteriophages, nutritional or health promoting advantages by producing nutraceticals, reducing the toxic compounds and having probiotic properties.
Lactic acid bacteria occur in habitats with a rich nutrition supply such as decomposing plant material and fruits as well as in food and in cavities of humans and animals. They can also be found on grapes, in grape must and wine. Only 22 species of the genera Lactobacillus, Leuconostoc, Pediococcus, Oenococcus and Weissella have been isolated during wine making. Lactic acid bacteria ferment different monosaccharides and metabolize organic compounds of must. Lactic acid bacteria (LAB) are a group of Gram-positive, non-spore forming, cocci or rods, which produce lactic acid as the major end product during the fermentation of carbohydrates. 
One of the important properties of LAB is the lactic acid fermentations; contributing to different texture and flavour, increase in nutritional value of foods, elimination of the unwanted and toxic compounds and improvement of appearance. Lactic acid fermentations take place in process of dairy products, cereal based products, vegetable products and some beverages. Wheat is a major cereal crop in many parts of the world. Wheat is grown as both a winter and a spring cereal and, owing to the number of species and varieties and their adaptability, it is grown in many countries around the world. It has many uses. Flour, semolina, bread, pasta, biscuits, cakes, crackers and animal feed is obtained. Starch, gluten and alcohol are used in manufacturing. LAB fermentation is not only of a major economic importance, but it also promotes human health.
Fermentation of various food stuffs by lactic acid bacteria (LAB) is one of the oldest forms of biopreservation practiced by mankind. Bacterial antagonism has been recognized for over a century but in recent years this phenomenon has received more scientific attention , particularly in the use of various strains of lactic acid bacteria One important attribute of many LAB is their ability to produce antimicrobial compounds called bacteriocins. In recent years interest in these compounds has grown substantially due to their potential usefulness as natural substitute for chemical food preservatives in the production of foods with enhanced shelf life and / or safety. There is growing consumer awareness of the link between diet and health. Recent scientific evidence supports the role of probiotic LAB in mediating many positive health effects. Traditional probiotic dairy strains of lactic acid bacteria have a long history of safe use and most strains are considered commensal microorganisms with no pathogenic potential.
Some lactic acid bacteria (LAB) secrete a polysaccharide polymer. This extracellular polysaccharide, or 'exopolysaccharide' (EPS), is economically important because it can impart functional effects to foods and confer beneficial health effects. LAB have a 'Generally Recognized As Safe' (GRAS) classification and are likely candidates for the production of functional EPSs. Current challenges are to improve the productivity of EPSs from LAB and to produce EPSs of a structure and size that impart the desired functionality. The engineering of improvements in these properties will depend on a deep understanding of the EPS biosynthetic metabolism and of how the structure of EPSs relates to a functional effect when incorporated into a food matrix.
One of the metabolites that LAB produces is the exopolysaccharides. Exopolysaccharides are high molecular weight, long chained polimers with water binding capacities. They are used in food industry for many purposes; as an emulsifying agent, stabilizator and used for preventing syneresis, controlling crystallization. Besides, they are health promoting metabolites. They have prebiotic, antitumour, antiulcer activities and effective in heart diseases and regulation of immune system. The ability to produce exopolysaccharides (EPS) is widespread among lactic acid bacteria (LAB), although the physiological role of these molecules has not been clearly established yet. Some EPS confer on LAB a "ropy" character that can be detected in cultures that form long strands when extended with an inoculation loop. When EPS are produced in situ during milk fermentation they can act as natural biothickeners, giving the product a suitable consistency, improving viscosity, and reducing syneresis. The increasing demand by consumers of novel dairy products requires a better understanding of the effect of EPS on existing products and, at the same time, the search for new EPS-producing strains with desirable properties. The use of genetically modified organisms capable of producing high levels of EPS or newly designed biopolymers is still very limited. Therefore, exploration of the biodiversity of wild LAB strains from natural ecological environments is currently the most suitable approach to search for the desired EPS-phenotype. The screening of ropy strains and the isolation and characterization of EPS responsible for this characteristic have led to the application over the past years of a wide variety of techniques.
In this research work, effects of EPS molecules synthesized from LAB on liquid wheat will be investigated. Determination of improved effects of EPS on liquid wheat will add valuable knowledge to the literature, public health and national economy.
In this study, we aimed to determine the exopolysaccharide capacity of lactic acid bacterias. The effect of exopolysaccharides synthesized from lactic acid bacteria on the properties of wheat water were investigated. The exopolysaccharides produced by many species of bacteria (EPS) are attracting interest from the food industry with stabilizing and emulsifying properties. Leuconostoc citreum (A31), Lactococcus lactis (A47), Lactobacillus coryniformis (C55), Lactobacillus paracasei (E8), ve Pediococcus parvulus (E42) strains were isolated boza. Chemical properties and rheological properties of liquid wheat prepared were measured. In all samples it was determined MMRS and liquid wheat the pH decreased. This activity of lactic acid bacteria was determined to occur. The lowest pH value has A47 strain in all media. En düşük EPS üretimi MMRS numunelerinde tespit edilmiştir. A47 strain was found to have the highest EPS production on two different media. Rheological parameters of liquid wheat were determined by using a rheometer with concentric plate-sensor system at a temperature of 25°C and at a shear rate range of 0,01-300 s-1. Rheological measurements showed that the viscosities of liquid wheat were different in the sensory analysis. Liquid wheat with EPS exhibited non-Newtonian behaviour with pseudoplasticity. The highest viscosity and consistency were identified in the A47 strains added liquid wheat. It is recommended to use exopolysaccharides synthesized from lactic acid bacteria as a stabilizer for improving the structural properties of the liquid wheat.