Elektroüretimle Nanolif Eldesine Etki Eden Faktörlerin Ve Jelatin-pektin İçeren Nanoliflerin Model Gıdaların Reolojik Özelliklerine Etkilerinin İncelenmesi

Abstract

Nanoölçekteki malzemeler, kütlesel malzemenin özelliklerinden ya da malzemenin moleküler haldeki özelliklerinden çok farklı olan yeni özelliklere sahiptir. Nano boyutlara inildiğinde artan yüzey alanı/hacim oranı ile birlikte maddelerin manyetik, optik, elektriksel, ısıl, kimyasal ve mekanik özellikleri değişmektedir. Nanoteknoloji, nanobilim buluşlarının gerçek hayattaki uygulamalarıyla ilgilidir. Bu nedenle bazı kuruluşlar “nanoteknoloji bir şeyleri meydana getirmenin yeni yollarıyla ilgilidir” şeklinde tanımlamaktadır. Bu nedenle nanotekonoloji özel bir bilim ya da mühendislik alanından çok, birçok teknolojik prosesin ve tekniğin toplamıdır. Nanoteknoloji fizik, kimya, ilaç, elektronik, bilgisayar, malzeme, tekstil ve tıp alanında kullanıldığı gibi gıda ve ziraat alanlarında da çok çeşitli olarak uygulanmaktadır. Gıda işleme, yeni fonksiyonel ürünlerin geliştirilmesi, biyoaktif maddelerin taşınması ve kontrollü salımı, patojenlerin tespiti, yeni ambalaj malzemelerinin ve teknolojilerinin geliştirilerek raf ömrünün uzatılması gibi uygulamalar gıda alanındaki çalışmalar arasında yer almaktadır. Nanoteknolojik çalışmalarda kullanılan yapılar genel itibariyle nanokapsüller, nanatüpler, nanolifler olmak üzere sınıflara ayrılmaktadır. Nanolifler çapları 100 nanometrenin altında olan yapılar olarak ifade edilmektedir. Nanolifler dört farklı şekilde üretilebilmektedir. En yaygın olan yöntem elektrodöndürme yöntemi ile nanolif üretim tekniğidir. Bu teknik ile üretilen nanolifler tekstil, tarım, tıp ve ilaç uygulamaları, savunma endüstrisi ve filtre geliştirme çalışmalarında yaygın olarak kullanılmaktadır. Son yıllarda giderek artan çalışmalarla birlikte gıda sanayinde de nanoliflerin kullanımı artmaya başlamıştır. Gıda endüstrisinde nanolifler özellikle ambalaj geliştirilmesi çalışmalarında kullanılmıştır. Nanoliflerle ilgili yasal düzenlemelerin az olması ve bazı ülkelerde hiç olmaması nanoliflerin gıdalarda kullanılması çalışmalarını kısıtlamıştır. Nanolif üretiminde yaygın olarak sentetik polimerler kullanılmakta ve doğal biyopolimerlerin de kullanımı son zamanlarda artmaktadır. Kolajen, jelatin, kitosan ve selüloz elektrodöndürme yöntemiyle başarılı bir şekilde nanolif üretilen doğal polimerlerdir. Jelatin, gıdalarda genellikle kıvam artırıcı olarak kullanılan bir katkı maddesidir. Jelatinin oluşturduğu saydam, renksiz, kokusuz ve ağızda kolayca eriyen jel yapı başka kıvam artırıcılar tarafından sağlanamamaktadır. Karbonhidrat kaynaklı kıvam artırıcılarla karşılaştırıldığında jelatin bazı üstünlükler göstermekte ve tercih edilmektedir. Literatürde jelatinden elektrodöndürme yöntemiyle çeşitli çözücüler (asetik asit, formik asit gibi) kullanılarak nanolif elde edildiği bildirilmiştir. Pektin gıda, ilaç ve kozmetik endüstrisi için önemli bir polisakkarittir. Gıda teknolojisi açısından, taze veya işlenmiş sebzelerde tekstür, meyve suyu ve şarabın durultulması, pürelerde ve meyve suyunda viskozite, jel oluşturmasından dolayı reçel ve marmelat üretimlerinde önem taşımaktadır. Bu çalışmada gıdalarda yaygın olarak kullanılan jelatin ve pektin karışımından elektrodöndürme yöntemi ile nanolif eldesi sağlanarak elde edilen nanoliflerin model gıdaların reolojik özelliklerine etkisi incelenmiştir. Besleme çözeltisi için jelatin çözeltisi (%20 jelatin / %20 asetik asit / saf su; w/v/v) ile pektin çözeltisinin (%1 pektin/saf su; w/v) farklı konsantrasyonlarda karıştırılarak kullanılmasına karar verilmiştir. Çalışmalar sonucunda %20’lik jelatin çözeltisi(w/v) ile %1’lik pektin çözeltisinin(w/v), 9/1 (v/v) oranında karıştırılarak kullanılmasına karar verilmiştir. Elektrodöndürme yönteminde elde edilen nanoliflerin morfolojisine etki eden faktörler araştırılmıştır. Bu araştırma çalışmaları kapsamında besleme debisi (0,1;0,5;1,0 ve 1,5 ml/sa), plaka mesafesi (5;10;15 cm) ve uygulanan voltaj (14-20 mV) değiştirilerek nanolif morfolojisindeki değişiklik taramalı elektron mikroskop ile incelenmiştir. İnceleme sonucunda tezin ilerleyen aşamalarında kullanılacak elektrodöndürme yöntem koşullarına (0,1 ml/sa debi, 5cm plaka mesafesi ve 18 mV uygulama voltaj değeri) karar verilmiştir. Daha sonra belirlenen koşullarda elde edilen jelatin-pektin nanolifleri farklı konsantrasyonlarda (%1,%1,5 ve %2 (w/w)) model gıdalara ilave edilerek reolojik özellikleri, zeta potansiyelleri ve difüzyon katsayıları ölçülmüştür. Model gıdalara ilave edilen nanoliflerin konsantrasyonunun artmasına paralel olarak model gıdaların viskoziteleri de artış göstermiştir. Aynı miktarda jelatin-pektin karşımınının model gıdalara ilavesi ile nanolifli örnekler karşılaştırıldığında nanolifli örneklerdeki viskozite değişiminin daha yüksek olduğu anlaşılmaktadır. Nanolifli zeyinyağı örneğinde sırasıyla %1, %1,5 ve %2 konsantrasyonlarda viskozite değeri 259,77±66,43; 706,33±254,23; 1968,96±93,42 olarak, aynı konsantrasyonlardaki jelatin-pektin örneklerinde ise 24,40±1,81; 22,12±2,15; 29,19±0,67 mPa.s olarak ölçülmüştür. Nanolifli süt örneklerinde ise %1, %1,5 ve %2 konsantrasyonlarda vizkozite değeri 11,53±0,31; 35,77±8,6; 64,09±18,83 olarak, aynı konsantrasyonlarda jelatin-pektin ilavesi sonucu ise 5,73±0,74; 11,86±1,23; 18,10±0,63 mPa.s olarak ölçülmüştür. Ölçüm sonuçlarına göre nanolif ilavesinin model gıdaların reolojik özelliklerini büyük ölçüde etkilediğini ve konsantrasyondaki artışa bağlı olarak nanolif ilavesinin örneklerin akış tipini değiştirebileceği sonucuna varılmıştır.

Nanotechnology is the first major worldwide research initiative of the 21st century. Nanotechnologies are applied to cross industrial problems and are a general purpose technology that acts as both a basis for technology solutions or at the convergence of other enabling technologies, like biotechnologies, computational sciences, physical sciences, communication technologies, cognitive sciences, social psychology and other social sciences. Nanotechnology is used in many fields such as physics, molecular biology, biology, chemistry, pharmaceuticals, medicine, electronics and environment also used in a wide variety of purposes of food industry. Comparing to other areas, applications of nanotechnology in food industry has been limited. Nanotechnology is used in food for particularly functional products, extend the shelf life of foods, improving food quality, detection of pathogens, improving of the colour-aroma characteristics and food packaging. Nanotechnology, which is generally interested in particles that are between 100 nm or less, has grown in recent years and promises to continue to grown in the future. Especially, developed countries such as the United States and Japan have been working on nanotechnology, and also they separate by a large budget for nanotechnology investigations. Apart from mass materials, structures in the nanoscale have been shown to have unique and novel functional properties. At nanoscale; morphologic, magnetic, optical, electrical, thermal, chemical and mechanical characteristics of materials exhibit very different behavior because of increasing the surface area/volume ratio. These include a possible reduction in the use of preservatives, salt, fat and surfactants in food products; development of new or improved tastes, textures and mouth sensations through nano-scale processing of foodstuffs. Nano-formulations can also improve the uptake, absorption, and bioavailability of nutrients and supplements in the body compared to bulk equivalents. Nanotechnology derived polymer composites offer new lightweight but stronger food packaging materials that can keep food products secure during transportation, fresh for longer during storage, and safe from microbial pathogens. Antibacterial nano-coatings on food preparation surfaces can help maintain hygiene during food processing, whereas the use of ‘Smart’ labels can help protect safety and authenticity of food products in the supply chain. The emerging applications of nanotechnologies for food production include nano formulated agrochemicals (e.g. fertilisers, pesticides, biocides, veterinary medicines) for improved efficacy, less use of farm chemicals, better control of applications (e.g. slow release pesticides), safer and more nutritious animal feeds (e.g. fortified with nano-supplements, antimicrobial additives; detoxifying nanomaterials), and nano-biosensors for animal disease diagnostics. Example applications include nano-sized feed supplements and feed additives, such as nano-form of a biopolymer derived from yeast cell wall that can bind mycotoxins to protect animals against mycotoxicosis, and an aflatoxin-binding nano-additive for animal feed derived from modified nanoclay. Nanostructures used in nanotechnology applications divided into three groups including nanoparticles, nanotubes and nanofibers. Nanofibers defined as having an average diameter of less than 100 nm. Research on the potential applications of nanofibers continues to expand rapidly day by day in worldwide. Nanofibers have large surface area, aspect ratio and porosity. There are several methods used in the production of nanofiber. The simplest and most efficient nanofiber production method is “electrospinning”. Electrospinning method; after dissolving the polymer sample in a suitable solvent such as water, asetic acid, formic acid etc., polymer solution is placed in the syringe; finally, uniform nanofibers are obtained by applying high voltage between the tip and collector plate. Continuous nanofibers can be fabricated by electrospinning which is an application of high voltage to sprayed solution from a capillary tube. Electrospinnning is easier and more economical method comparing to other methods for obtaining nanofibers. Electrospinning is a unique method to prepare electrospun fibers with diameters in the range from micrometers to nanometers that depends on the kinds of polymer and processing conditions. Electrospinning technique has been recognized as an efficient processing method to manufacture nanoscle fibrous structures for a number of applications. Electrospinning method is particularly used for synthetic polymers. Studies on nanofiber production from the natural polymer have been increasing day by day. Natural polymers such as collagen, gelatin, chitosan and cellulose are successfully produced nanofibers by electrospinning method in literature. These natural nanofibers are used with different aims tissue engineering, drug delivery, textile, sensor, filtration, material engineering-characterizations and other sectors. Bio-based nanofibers have become important due to fact that they are biocompatible and biodegradable properties. The foodstuff gelatine has had a long and successful history. In ancient times it was used as a ‘‘biological adhesive’’, and in the course of time it progressed to industrial manufacture and diverse applications. Gelatin is a soluble protein compound obtained by partial hydrolysis of collagen, the main fibrous protein constituent in bones, cartilages and skins; therefore, the source, age of the animal, and type of collagen, are all intrinsic factors influencing the properties of the gelatins. Two types of gelatin are obtainable, depending on the pre-treatment procedure and are known commercially as type-A gelatin (isoelectric point at pH 8.9) and type-B gelatin (isoelectric point at pH 4.5) obtained under acid and alkaline pre-treatment conditions respectively. Industrial applications call for one or the other gelatin type, depending on the degree of collagen crosslinking in the raw material. Because of the acid lability of crosslinking in immature collagens, such as in fish skins, reasonably mild acid treatment is enough to effect collagen solubilisation. The classical food, photographic, cosmetic and pharmaceutical applications of gelatin are based mainly on its gel-forming and viscoelastic properties. Recently, and especially in the food industry, an increasing number of new applications have been found for gelatin in products such as emulsifiers, foaming agents, colloid stabilizers, fining agents, biodegradable packaging materials and micro-encapsulating agents, in line with the growing trend to replace synthetic agents with more natural ones. Gelatin also has been fabricated into ultra-fine fibers by electrospinning method. Gelatin using with variety solvents such as acetic acid, formic acid and trifluoroacetic acid has been successfully prepared nanofiber production via electrospinning method in the literature. Gelatin, a naturally – occurring biopolymer, was electrospun. It has been recognized that although gelatin can be easily dissolved in water the gelatin / water solution was unable to be electrospun into ultra-fine fibers. Pectin is used in a number of foods as a gelling agent, thickener, texturizer, emulsifier and stabilizer. Sugar-beet pulp, the residue left from sugar extraction, is a rich source of pectin. Pectin contains about one-third of the cell-wall dry substance of dicotyledonous and some monocotyledonous plants. Most pectin is in the middle lamella of plants cell walls and structural changes of pectin materials can cause physical and textural changes such as softening. Chemically, D-galacturonic acid polymers form the main component of pectin materials which link together through ɑ-1,4-glycosidic linkages. Pectin has many applications in food and pharmaceutical industries. In foods, pectin is mostly used in jams and jellies as a gelling agent and thickener. It is also used in drinks, sauces, syrups and some other foods to make a desirable texture. In the pre-research of this study, nanofiber from natural polymers such as pectin and gelatin by electrospinning were studied. The applied electrical potential was adjusted between 14-18 kV. The distance between syringe needle and the grounded collector was in between 5 and 15 cm. A syringe pump was used to maintain a solution flow rate between 0.1 and 1.5 ml/h during electrospinning. The collector was covered with aluminum foil, and nanofibers were deposited on the aluminum foil. In the first part of this study, the objective was to determine the influences of the affecting parameters such as flow rate, applied voltage, feed solution properties and distance to the collector plate, during electrospinning process on the morphology of electrospun gelatin-pectin nanofibers. The morphologies of electrospun nanofibers were determined by using field emission scanning electron microscope. Firstly, gelatin (10% and 20% w/v gelatin solutions in 20% v/v acetic acid solution in the pure water) and pectin (1% w/v pectin/pure water) solutions were prepared. Gelatin concentrations at 10% (w/v) and 20% (w/v) were separetely fed to the electrospinning equipment. The applied voltages were in between 14 and 18 kV. The feed rate was in between 0.1 and 1.5 ml/h. The electrospun nanofibers were deposited on the collector plate. Then, pectin solution at 1% (w/v) was fed to the electrospinnig equipment under the same conditions before. However, pectin solution did not produce nanofibers. Therefore, the mixtures of gelatin and pectin solutions were prepared at different concentrations. The amount of pectin solution was increased step by step in the mix solution. The electrospun nanofibers containing pectin and gelatin was examinated by FE-SEM. The average diameters of the resulting electrospun nanofibers were in between 24.6 and 49.2 nm. According the FE-SEM images, smooth nanofibers were obtained at the conditions of 18 kV and 0.1 ml/h. The optimal concentration of pectin-gelatin solution was determined for production of nanofiber. Subsequent studies had been carried out through the electrospinning process parameters at 18 kV applied voltage, 0.1 ml/h feed rate and 5 cm distance between tip and collector plate. Ue to the complexity of the electrospinning process and affecting factors, the evaluation of the morphologies of electrospun nanofibers was a challenge. In the second part of this study, the aim was to obtain nanofiber by electrospinning (18 kV voltage and 0.1 ml/h feed rate) using the mixture of 20% gelatin (w/v)- 1% pectin (w/v) solutions. These electrospun nanofibers were added to olive oil and milk. Electrical conductivity, surface tension, thermal properties and rheological properties of the feed solutions were determined. Electrical conductivity and surface tension of 20% gelatin+1% pectin solution were measured as 4.02 ± 0.01 mS/cm and 33.75 ± 0.03 mN/m, respectively. Thermal properties of gelatin solution, electropsun gelatin nanofiber and bulk gelatin were determined by using a DSC. Rheological parameters such as K and n were determined. The rheological behavior of feed solutions was Newtonian. Bulk gelatin and electrospun gelatin were added to water, olive oil and milk at 0.5%, 1.0% and 1.5%. They were stirred for 4 minutes with Ultra-Turrax at 11000 rpm and 25˚C. The zeta potential, particle size and their rheological properties of bulk gelatin-pectin and electrospun gelatin-pectin nanofibers in olive oil and milk were investigated and compared to each other. The zeta potential of nanofibers in olive oil were higher than zeta potential of gelatin-pectin in olive oil. Viscosities of olive oil with nanofibers at 1.0%, 1.5% and 2.0% were determined as 259.77 ± 66.43 mPa.s, 706.33 ± 254.32 mPa.s and 1968.96 ± 93.42 mPa.s, respectively. At the same concentrations, viscosities of gelatine-pectin were measured as 22.12 ± 2.15 mPa.s, 29.19 ± 0.67 mPa.s and 32.30 ± 1.77 mPa.s, respectively. Bulk gelatin and electrospun gelatin nanofibers in olive oil were showed pseudoplastic behavior. Viscosities of milk with nanofibers at 1.0%, 1.5% and 2.0% were measured 11.53 ± 0.31 and 35.77 ± 8.36 mPa.s, and 64.09 ± 18.83 mPa., respectively. Viscosities of milk with gelatine were 5.73 ± 0.74 mPa.s, 11.86 ± 1.23 mPa.s and 18.10 ± 0.63 mPa.s. Bulk gelatin and electrospun gelatin nanofibers in milk were showed pseudoplastic behavior. In conclusion, gelatin-pectin nanofiber may be used as a thickener in foods similar to bulk gelatin-pectin. At nanoscale gelatin at lower concentrations probably provide more consistency to liquid media than bulk gelation does.