Doktora Tezleri

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Antimicrobial, antioxidant properties and chemical composition of some spices/herbs
(Izmir Institute of Technology, 2013-12) Yavuzdurmaz, Hatice; Baysal, Ayşe Handan
The present study aims to investigate the chemical composition, antimicrobial activity, and mechanism of antimicrobial activity, antioxidant properties of essential oils and extracts and the effects of them when applied to minced beef samples. For this purposes; four essential oils (bay leaf, thyme, clove and cumin), two extracts (grape seed and olive leaf) and constituents of essential oils (eucalyptol, linalool, α-terpineol and α-pinene) were subjected to related tests. Chemical characterization was complemented for all essential oils and extracts. Antimicrobial activity was examined against Staphylococcus aureus, Escherichia coli O157:H7, Salmonella Typhimurium, Listeria innocua, Shewanella putrefaciens, Carnobacterium divergens and Serratia liquefaciens. All tested compounds were effective on the bacteria with different concentrations. Antioxidant activity was proved by FRAP and DPPH methods. Physical disturbance and changes in the structures of bacteria was demonstrated by various techniques. The activity of two most potent essential oils (thyme and clove) was investigated in the minced meat application study. The findings represented that clove essential oil restricted the growth of S. Typhimurium and coliform bacteria. They did not have a significant inhibition effect on the aerobic mesophilic bacteria, total yeasts and molds and also psychrotrophic organisms. The results indicated that L* and a* values were maintained during the storage period. The featured effect of essential oils was antioxidant characteristic in meat application study. All treatment showed significant reduction in oxidation comparing with control. The obtained results may suggest that tested essential oils possess compounds with antimicrobial characteristic as well as antioxidant activity and therefore they can be used as natural preservatives in food especially in meat products.
Applications of mid-IR spectroscopy for identification of wine and olive yeasts and characterization of antimicrobial activities of phenolics on yeasts
(Izmir Institute of Technology, 2015-12) Canal, Canan; Özen, Fatma Banu; Baysal, Ayşe Handan
The aim of this study was application of mid-IR spectroscopy in combination with multivariate statistical analysis for characterization of yeasts from two fermented products, wine and olive, in comparison with cultural and molecular tests and characterization of antimicrobial effects induced by olive phenolics on yeasts. Totally 19 wine yeasts were molecularly identified as M. pulcherrima (11%), P. membranifaciens (16%), H. uvarum (5%) and S. cerevisiae (68%). According to FTIR spectroscopic data of wine samples, S. cerevisiae isolates formed a cluster which were generally separated from all other yeasts. Totally 182 olive yeasts were identified from naturally debittered Hurma and a common olive variety and their leaves. The most common yeasts were Metschnikowia sp. (39%) and Aureobasidium sp (78%) in the first and the second harvest years, respectively. Since only Aureobasidium sp. was the common yeast isolated from Hurma during both years, any link between natural debittering of Hurma and the yeast population of this olive type might be related to Aureobasidium sp. Molecularly identified yeast types generally formed different clusters and showed spectral differences. For antimicrobial activity tests, all phenolic compounds were found effective on both S. cerevisiae and A. pullulans; however, A. pullulans was observed to be more sensitive. Antimicrobial activity was differentiated with respect to treatment time and phenol concentration with statistical treatment of FTIR data. As a complementary technique, FTIR could be successfully used for identification of yeasts and characterization of antimicrobial activity of phenolics against yeasts.
Assesment of the efficiency of UV light emitting diodes (UV-LEDS) for fruit juice pasteurization
(Izmir Institute of Technology, 2019-06) Akgün, Merve; Ünlütürk, Sevcan
The objectives of this thesis are to evaluate the application of ultraviolet light emitting diodes (UV-LEDs) with various wavelengths for pasteurization of cloudy (CAJ) and clear apple juices (AJ), to assess the disinfection efficiency of combined UV-LED irradiation and mild heat (UV-LED+MH) treatments, to investigate the effect of individual and combined processes on the activity of enzyme, physicochemical and microbiological quality of AJ, to determine the shelf life of UV-LED irradiated juice during storage, to reveal the reactivation potential of target microorganism (E. coli K12) in juice medium with different optical properties, and to elucidate the mechanism of microbial inactivation by UV-LEDs. 280/365 nm UV-LED irradiation assisted by mild heat at 55ºC and 15 min exposure time enhanced the inactivation of E. coli K12 and polyphenoloxidase and satisfied the 5-log reduction pasteurization criterion in apple juice. UV-LED+MH treatment extended the shelf life of CAJ from 3 to 30 days and increased its total phenolic content. However, the color properties were slightly affected by ultraviolet treatment. Subsequent photoreactivation of E. coli K12 after inactivation by UV-LEDs was observed in both CAJ and AJ. Contrarily, dark repair was repressed at 4ºC and 22ºC, furthermore, a decrease in the survival ratio was recorded in both medium. It was revealed that the damage of DNA repair enzymes and the proteins that form the outer cellular membrane of bacteria was highly induced by UV-C light at 280 nm. Additionally, the bactericidal effect of 365 nm (UV-A) wavelength was attributed to enhanced production of reactive oxygen species (ROS) resulting in oxidative damage to cellular lipids, proteins and DNA. The combination of these two wavelengths provided more efficient disinfection than that of UV-C light used alone. UV-LED irradiation assisted by mild heat has a potential to be used as an alternative technique to traditional thermal pasteurization process for juice products. This study leads to useful information for the future design of UV-LED treatment systems.
Bioactive compound retention and shelf life extension of strawberry juice by selected nonthermal processing technologies
(Izmir Institute of Technology, 2017-04) Yıldız, Semanur; Ünlütürk, Sevcan; Barbosa-Canovas, Gustavo V.
Shelf life extension of fruit juices while maintaining quality and functional properties is of great interest. Nonthermal food processing technologies have been emerged as innovative preservation methods alternative to thermal pasteurization of fruit juices. The objectives of this Ph.D. thesis were to (i) ensure microbial safety of strawberry juice (SJ) by thermal and nonthermal technologies, i.e. high pressure processing (HPP), ultrasound (US), pulsed electric field (PEF) and UV-C irradiation; (ii) evaluate physicochemical and phytochemical properties of SJ after processing and during storage; (iii) extend microbial shelf life of SJ without unduly affecting quality. HPP (300 MPa, 1 min), US (120 m, 5.15 J/mL, 55 C, 3 min), PEF (35 kV/cm, 27 s, 155 Hz), and thermal pasteurization (71.7 C, 15 s) conditions were determined based on equivalent inactivation of E.coli (ATCC 11775) in SJ studied at Washington State University. UV-C irradiation (1.01 J/mL, 53.9 C, 6 cycles, 5.8 min) and thermal pasteurization (72 C, 101 s) conditions were determined considering inactivation of E. coli K-12 (ATCC 25253) in SJ studied at IZTECH. Consequently, microbial shelf life of SJ treated by HPP, thermosonication, UVC+mild heating, thermal pasteurization was extended up to 42 days while PEF prolonged up to 35 days at refrigerated storage. Multivariate data analysis revealed that HPP and PEF enhanced phytochemical characteristics of SJ compared to thermosonication and thermal pasteurization. Although UV-C irradiation did not alter physcicochemical properties, total phenolic content, and antioxidant activities of SJ, total anthocyanin content was significantly decreased by UV-C light compared to untreated juice.
Characterization and classification of wines from grape varieties grovn in Turkey
(Izmir Institute of Technology, 2014) Şen, İlknur; Tokatlı, Figen
The wines of Turkish grapes from four vintages (2006-2009) were classified according to variety, geographical origin and vintage based on their chemical composition (element, polyphenol, color, acid, sugar, alcohol, pH, total phenol and brix) by using multivariate statistical techniques. In the varietal classification of red wines, the partial least square-discriminant analysis (PLS-DA) demonstrated the discrimination of Boğazkere-Öküzgözü, Kalecik Karası, Syrah and Cabernet Sauvignon varieties from each other as the significant element, polyphenol, organic acid, sugar and alcohol parameters were combined in the model. Boğazkere and Öküzgözü wines of East Anatolia were characterized with their high coumaroylated anthocyanin derivatives, while Syrah wines of West Anatolia were rich in anthocyanins and flavonols. Kalecik Karası wines were the poorest in terms of total phenol content. In the classification of white wines, Emir wines of Kapadokya region were characterized with their high Li, Sr and resveratrol contents. Sultaniye wines were the lowest in polyphenol content and Muscat wines were the richest in hydroxycinnamic acids. The regional discrimination of red and white wines was achieved with the significant element and polyphenol compositions. The western region wines were characterized with their higher Pb content which may be due to the industrialization of West Anatolia. Moreover, red wines of Tekirdağ region were recognized with their low flavonol-glycoside contents. 2009 vintage red wines were characterized with their high anthocyanin and flavonol contents. In the same way, 2009 vintage white wines had higher flavonols, flavonol-glycosides, phenolic acids and flavan-3-ols.
Chemical and enzymatic interesterification of tallow with different oils
(Izmir Institute of Technology, 2019-04) Aktaş, Ayşe Burcu; Özen, Fatma Banu; Yemişçioğlu, Fahri
The purpose of this study is to manufacture structured lipids by enzymatic and chemical interesterification of tallow with corn, canola and safflower oils individually and to investigate the effects of several process parameters on various chemical and physical properties of structured lipids. Moreover, collection of Fourier-transform mid infrared (FT-MIR) and near infrared (FT-NIR) spectra during interesterification process is also aimed in order to monitor the processes and to construct chemometric models for the prediction of chemical and physical properties of the interesterified products. Both enzymatic and chemical interesterification provided modification of the properties of tallow. The blend ratio is the most significant factor among the parameters investigated for both types of interesterification. Longer reaction time for enzymatic interesterification caused undesirable changes in physical properties of fats. Interesterified lipids have generally low trans fatty acids and they tend to have lower consistencies and solid fat contents compared to their physical blends and the tallow; as a result, they also acquired better spreadable and plastic behaviors. The structured lipids produced with chemical interesterification of tallow with corn oil have better physical properties, higher oxidative stability and lower free fatty acid content compared to structured lipids produced with other vegetable oils. Chemical and physical properties of interesterified fats could be predicted accurately with chemometric analysis of FT-NIR spectra.
Design of a continuous flow UV reactor for opaque liquid foods by using computational fluid dynamics (CFD)
(Izmir Institute of Technology, 2013-06) Atılgan, Mehmet Reşat; Ünlütürk, Sevcan
UV-C radiation is usually applied as an alternative non-thermal process for clear liquid food products in order to achieve microbiologically safe and shelf stable products. The main objective of this Ph.D. study was to design a UV reactor inorder to provide efficient UV dose/intensity distribution to reach minimum 5 log microbial reduction in opaque liquid foods. For this purpose, a S-shaped, thin film, continuous flow UV reactor was designed and constructed. UV dose/intensity delivered in the UV system was measured and determined by means of biodosimetric, actinometric and computational fluid dynamics (CFD) methods. Inactivation performance of the UV reactor was assesed by using both clear and freshly squeezed opaque white grape juices. The number of spoilage yeast, lactic acid bacteria and E.coli K-12 (ATCC 25253) in opaque grape juice was reduced to 1.604, 4.133 and 5.431 log at UV dose levels of 247.302, 301.113 and 273.520 mJ/cm2 respectively. For clear grape juice samples inoculated with S.cerevisiae and E.coli K-12 (ATCC 25253), 6.498 and 5.986 log reductions were achieved at UV dose levels of 1001.618 and 577.245 mJ/cm2. The microbial shelf life of freshly squeezed grape juice was extended up to fourteen days which was two times longer compared to untreated samples at refrigerated conditions. The physicochemical properties of UV-C processed grape juice were also evaluated during storage. Although pH, total soluble content (Bix %) and total titratable acidity were not affected from UV treatment, significant changes observed in pH, turbidity, color properties, total soluble content (Brix %), total titratable acidity and ascorbic acid (Vitamin C) content during storage.
Detection of staphylococcus aureus using quqntitative real-time polymerase chain reaction and loop-mediated isothermal amplification methods in Turkish white cheese
(Izmir Institute of Technology, 2013-12) Kadiroğlu, Pınar; Korel, Figen
The aim of this study was to utilize the quantitative real-time polymerase chain reaction (qPCR) method for direct quantitative detection of S. aureus in Turkish white cheese samples and identification of the isolated colonies using phenotypic and molecular methods. The TaqMan and LNA probe-based qPCR analyses were compared by targeting the nuc gene of S. aureus cells to improve the performance of qPCR analyses to quantify low levels of S. aureus cells. TaqMan probe-based assay was found to be more sensitive than LNA probe based assay in S. aureus pure culture and artificially contaminated white cheese sample studies. For direct bacterial DNA extraction from cheese samples, four different methods were compared. The detection range of S. aureus quantification was improved down to 13.2 CFU/g with the combined DNA extraction method of using trypsin and the food DNA extraction kit in artificially contaminated cheese samples. In the naturally contaminated cheese samples, the bacterial numbers calculated by the qPCR method were higher than the plate counts which can be related to detection of live and dead cells together. Loop-mediated isothermal amplification (LAMP) method was found to have some weak points in giving consistent results with lower efficiency value for detection of S. aureus. In the identification part of the study, 207 pure cultures were obtained. Among the 24 phenotypically and genotypically characterized isolates, 3 isolates were found to be S. aureus according to the sequence analyses of the 16S ribosomal DNA genomic region.
Development and characterization of whey based alpha-lactalbumin protein nanotubes for food applications
(Izmir Institute of Technology, 2013) Tarhan, Özgür; Harsa, Hayriye Şebnem
Alpha-lactalbumin (α-La) is one of the major proteins in whey. When partially hydrolyzed with protease, it produces nanotubular structures by self-assembly process. The aim of this PhD thesis is to develop and characterize whey based α-La nanotubes. In this study, purification of α-La from whey using ultrafiltration and chromatography, development of protein nanotubes with standard and purified α-La fractions, their characterization by microscopic, optical and spectrophotometric methods, analysis of hydrolysis process, and investigation of these nanotubes in relation to food applications were presented. Lactose was eliminated and proteins were concentrated in whey powder by diafiltration assisted ultrafiltration prior to chromatography. α-La and besides β- lactoglobulin were purified individually from whey protein concentrate with high purity (95–99 %). The obtained protein nanotubes were longer than 100 nm up to few microns with ~20 nm width in bundled, rod and chain-like fashions. Remarkable conformational changes occurred in the protein secondary structure during nanotube formation. Calcium to protein ratio critically affected nanotube formation and stability. Both hydrolysis and nanotube growth triggered gelation, but stiffer gel network was obtained with nanotubes. Viscoelasticity and stiffness were improved by blending with cellulose. As the calcium content increased the transparent appearance of the gels got turbid due to aggregation. α-La nanotubes were stable up to ~ 60 °C. The nanotubular gels entrapped a coloring agent by enhancing transparency. Binding of catechin to nanotubes was occured as reversible with low stability. α-La nanotubes and gels can be used as functional ingredients in food processing involving low and moderate heat treatments.
Development of different koruk (Unripe grape) products by using several processing techniques
(Izmir Institute of Technology, 2018-07) Kaya, Zehra; Ünlütürk, Sevcan
Verjuice, obtained by pressing unripe grapes, is mostly used as an alternative to lemon juice and vinegar in salads and traditional meals due to its unique sour taste and flavour. It has a short shelf life due to growth of yeasts and molds when produced at household conditions. Verjuice products in the market are not meeting desirable quality characteristics. The high quality verjuice and its derivatives required to be produced by considering several processing techniques. The objectives of this Ph.D. thesis are to (i) produce long shelf life verjuice with minimum change in its “fresh like” properties by using the combination of UV-C irradiation or Pulsed-UV light (PUV) with mild heating, (ii) produce verjuice powder with a good storage stability by using freeze drying, (iii) produce concentrated verjuice with minimal quality loss by using vacuum evaporation. Verjuice was successfully pasteurized without loosing its desirable quality by a combined UV-C and mild heating (78.0 mJ/mL, 6.2 min, 51.2°C) and PUV assisted with mild heating (6.12 J/cm2, 8.5 min, 47°C) and mild thermal (72°C, 18 s) treatments. 5-log reduction of target S. cerevisiae (NRRL Y-139) was aimed for the pasteurization of verjuice. No microorganism was developed in pasteurized verjuice during 12 and 6 weeks of refrigerated storage after UV+MH and PUV+MH treatments, respectively. Freezedried verjuice powder containing maltodextrin (FD 48h, 20% MD), was highly stable under the accelerated storage conditions (40°C, 90%RH) for 70 days. Concentrated verjuice obtained under vacuum conditions of 45°C/913 mbar, showed minimal quality change and was consumable up to 12 weeks at refrigerated storage.
Development of functional composite edible packaging materials for controlled release of bioactive substances
(Izmir Institute of Technology, 2013) Arcan, İskender; Yemenicioğlu, Ahmet
The aim of this study was to control the release of bioactive agents by modification of hydrophobicity and morphology of zein films using composite and blend film making methods. The bioactive agents incorporated into zein based films were lysozyme and phenolic compounds. The incorporation of beeswax, carnauba or candelilla wax into films gave composite films containing amorphous wax particles, while the incorporation of oleic, lauric or linoleic acid into films caused formation of blend films containing many spherical zein capsules within their matrix. The release profiles of phenolic compounds from zein films were successfully altered by the development of composite and blend films. The composites and blends can show 2.5 to 17 fold lower lysozyme release rates than the controls. The lysozyme release rates of composites reduced as the melting point of waxes increased. The chain length and the concentration of fatty acid used in blend films could also have affected the release rates of lysozyme. The phenolic antioxidants, catechin, gallic acid, p-hydroxy benzoic acid and ferulic acid are effective plasticizers of zein films. These phenolic compounds eliminate the classical brittleness problem of zein films and increase their flexibility considerably (up to 196%). Furthermore, catechin contributed to controlled release properties of films by reducing the film porosity. The phenolic compounds also provided antioxidant activity to films (up to 86 μmol Trolox/cm2). The blends and composites of zein films containing phenolic compounds or lysozyme and phenolic compounds showed antimicrobial activity on critical food pathogenic bacteria or indicator microorganisms including Escherchia coli O157:H7, Listeria monocytogenes, Listeria innocua and Campylobacter jejuni. This work showed the possibility of obtaining advanced edible films having flexibility, antimicrobial and antioxidant activity and controlled release properties.
Development of gluten-free bread formulations based on chickpea flour: Optimization of formulation, evaluation of dough properties and bread quality
(Izmir Institute of Technology, 2016-12) Kahraman, Gökçen; Harsa, Hayriye Şebnem; Lucisano, Mara
The main objective of this study was to develop chickpea flour-containing gluten-free bread formulations having improved physicochemical, nutritional and sensory properties. Increasing roasted chickpea flour (RCF) levels resulted in decreased cohesiveness and springiness, and darker color. Hardness and chewiness decreased and specific volume increased when water level increased. With increasing hydroxypropyl methylcellulose levels, softer crumb was obtained. Optimized formulation contained almost 25% RCF. Model validation revealed good agreement between predicted and measured responses. Based on the optimized formulation, roasted, raw or dehulled chickpea flour-containing rice flour blends, doughs and breads were prepared and analyzed. Compared to rice flour control, reduced retrogradation tendency was observed for chickpea flour-containing blends. Although gas retention capacities of chickpea flour-containing doughs were slightly lower than rice dough, 5-12% higher CO2 was produced. Chickpea flour addition increased both storage (G') and loss (G'') moduli. Bread containing RCF exhibited higher specific volume (2.89 mL/g), ~2.5 fold softer crumb and lower staling rate than raw and dehulled chickpea-containing formulations. Chickpea enrichment resulted with increased protein (24-36%), ash, fat and total phenolic contents; besides, reduced available starch levels (~14%). Breads fortified with dehulled and roasted chickpea flour were superior in terms of low rapidly digestible starch and high in vitro protein digestibility, respectively. Improved sensory quality was observed with an increased overall acceptability from 5.31 to 6.58-6.84. Addition of sourdough (30%) increased in vitro protein digestibility; however, slight decrease occurred in sensory attributes. Chickpea flour-enriched gluten-free rice bread resulted in improved quality characteristics depending on pretreatments applied to chickpea grain.
Development of novel antimicrobial, antioxidant and bioactive edible gels intended for food preservation and promotion of human health
(Izmir Institute of Technology, 2017-12) Boyacı, Derya; Yemenicioğlu, Ahmet
The aim of this thesis was the development of edible gelatin (GEL) based composite gels with antimicrobial, antioxidant, and bioactive properties. For this purpose, composite gels of gelatin with rice starch (RS), candelilla wax (CW) and soy protein isolate (SPI) were incorporated with lysozyme (LYS) and green tea extract (GTE). LYS and GTE release profiles of GEL and its composites were tested in aqueous media and cold-smoked salmon selected as a model food. GEL, GEL/RS and GEL/CW gels did not show considerably different LYS and GTE release profiles in aqueous media, but their release profiles in the model food system were different. GEL/SPI gels bound LYS and prevented its release from the gels, but they released GTE. GEL showed the most rapid LYS delivery onto smoked salmon, while GEL/RS and GEL/CW caused sustained LYS delivery profiles. The total LYS delivered from GEL and GEL/RS gels onto smoked salmon were similar while GEL/CW gels caused almost 30% lower LYS delivery onto food samples. On the other hand, GEL/CW gels caused the highest amounts of GTE delivery onto model food. In broth media at 4°C, all LYS containing gels (with or without GTE) showed antimicrobial activity with a minimum 1.5 decimal reduction in L. innocua that was used as a target bacterium. In smoked salmon samples, the LYS containing gels inhibited the growth of L. innocua, but they did not cause a significant reduction in its counts. Antioxidant capacity, antihypertensive and antidiabetic activity, and cytotoxicity tests against human colon carcinoma cells (Caco-2) conducted with released GTE proved the bioactive potential of developed gels. The gels were also tested for their water binding capacity, and physical (textural properties) and morphological (SEM images) properties. This work clearly showed the possibility of using active gels as multifunctional delivery tools (as coating material, pad or pre-cast film) to prevent microbial and oxidative changes in food and to enhance their bioactive properties.
Development of novel bio-based methods for inhibition of plant pathogens
(Izmir Institute of Technology, 2013) Alkan, Derya; Yemenicioğlu, Ahmet
In this thesis, to develop a post-harvest bio-based preservation method for spoilage of fresh fruits and vegetables, antimicrobial packaging commonly applied for inhibition of human pathogenic bacteria was adapted for inhibition of plant pathogenic bacteria including Pseudomonas syringae, Erwinia amylovora, Xanthomonas vesicatoria and Erwinia carotovora. The zein based films were developed by incorporation of pure phenolic acids such as gallic acid (GA), cinnamic acid (CA), vanillic acid (VA); essential oils such as carvacrol (CAR), thymol (THY), eugenol (EUG) and citral (CIT) and phenolic extracts obtained from clove, artichoke, oregano and walnut shells into film forming solutions. The films containing phenolic acids between 1 and 4 mg/cm2 were effective on all bacteria. Essential oils at concentrations between 2 and 4 mg/cm2 and clove extract at concentrations between 4 and 8 mg/cm2 were found effective against pathogens except P. syringae. The HPLC analysis showed that the clove extracts owe its inhibitory activity to high concentration of GA which is a potent antimicrobial. The incorporation of natural compounds and extracts into films caused significant changes in morphologies and mechanical properties of films. This thesis showed the good potential of antimicrobial films against plant pathogens for the first time in the literature.
Development of sensor systems for food quality monitoring
(01. Izmir Institute of Technology, 2022-12) Büyüktaş, Duygu; Farris, Stefano; Korel, Figen
The main objective of this thesis is to fabricate electrochemical sensors for the detection of 2,4-diaminotoluene (2,4 TDA), 2,6-diaminotoluene (2,6 TDA), and 4,4´-methylene diphenyl diamine (MDA), possibly carcinogenic primary aromatic amines (PAAs) that poses a serious health risk because they can transfer from multilayer food packages including adhesives based on aromatic polyurethane (PU) systems, to the food. The thesis is based on the following three chapters: (1) Development of a nano-modified glassy carbon electrode for the determination of 2,6-diaminotoluene (2) A screen-printed electrode modified with gold nanoparticles/cellulose nanocrystals for electrochemical detection of 4,4´-methylene diphenyl diamine (3) Development of a nano-modified screen-printed electrode for the determination of 2,4-diaminotoluene. In this work, full electrochemical characterization of the nano-modified electrodes was carried out, and the electrochemical properties were described. Migration tests were also conducted to modified sensors in order to investigate their potential application in real food systems. The results of this work clearly showed that modified electrochemical sensors allow reliable quantification of the most important primary aromatic amines migrating from packaging materials to food and can be used as an alternative to the commonly used conventional analytical techniques for the detection of these toxic compounds.
Development of whey protein-pullulan microcapsules for the encapsulation of Lactobacillus acidophilus NRRL-B 4495 as a functional food ingredient
(Izmir Institute of Technology, 2014-07) Çabuk, Burcu; Harsa, Hayriye Şebnem
The aim of this study was to develop whey protein-pullulan (WPI-pullulan) microcapsules in order to assess its protective effect on the viability probiotic bacteria under in vitro gastrointestinal conditions. The probiotic bacteria used in this study was of Lactobacillus acidophilus NRRL-B 4495. This study demonstrated that probiotic bacterial cells were successfully encapsulated into WPI-pullulan gel matrix. The appropriate microcapsule formation parameters include formation of primary emulsion having 50% inner polymer aqueous phase having whey protein in the presence of 10.8% pullulan with sunflower oil. Optimal concentration of bacteria for microencapsulation was decided to be kept at 10.00 log CFU/g since increasing initial load resulted in decreasing microencapsulation efficiency. The incorporation of pullulan into whey protein wall matrix created spherical microcapsules with denser and smoother surface structure. Microcapsules with varying pullulan concentrations in the wall matrix obtained the mean diameters between 68 μm to 80μm. The survival rates of Lactobacillus acidophilus NRRL-B 4495 under in vitro gastrointestinal conditions were significantly (p<0.05) improved by the presence of pullulan. WPI-pullulan wall matrix resulted in a 87.18% survival rate as compared to 73.19 % for free cells after 3h incubation in simulated gastric solution. Protein-polysaccharide gel network formed in the microcapsules restricted diffusion of bile salts, as well. During spray drying experiments with high concentration of pullulan, fibrous structure formation was observed. Optimal conditions for spray drying of probiotic cells were decided to have 145 ºC as an outlet temperature in the presence of WPI-pullulan wall matrix with 4.5:1 protein:pullulan ratio. Moreover pullulan incorporation in contributed to release properties of microcapsules by altering the dissolution and porosity properties. On the other hand, encapsulation into developed polymer wall matrix in wet and spray dried forms did not provide any positive advantage for the responses of probiotic microorganism against heat stress.
Effect of harvest time, malaxation tempetature and olive variety on the chemical characteristics of olive oils
(Izmir Institute of Technology, 2016-12) Jolayemi, Olusola Samuel; Tokatlı, Figen; Özen, Fatma Banu
Changes in chemical and quality characteristics of olive oils were evaluated with respect to pre and post-harvest factors such as: olive type, harvest time, malaxation temperature, and storage at room temperature. Additionally, discriminative and predictive capacities of UV-vis, near infrared (NIR), mid infrared (MIR) spectra and electronic nose data on olive oils by using multivariate statistical tools were studied. Varietal and harvest time differences were the most significant factors influencing the quality and chemical properties of Ayvalik and Memecik olive oils. Malaxation temperature was significant on a number of phenolic compounds such as tyrosol, hydroxytyrosol and pinoresinol, and peroxide value. Olive oils of early and mid-harvest were higher in phenolic alcohols, and pigments content, whereas peroxide values, linoleic and stearic acids characterized late harvest oils. Storage for 15 months at room temperature in dark facilitated evolution of some important phenols, while increasing the content of ethyl and methyl esters at varying degrees among varieties. There were no significant changes in fatty acids and acidity contents of the oils. However, total phenol content and oxidative stability declined and a significant depletion of colors and pigments contents occurred. Multivariate regression analysis indicated that lipid-based variables are the most consistent contributors (positive or negative) to olive oil oxidative stability. UV-vis, MIR, NIR spectroscopies and e-nose data were excellent varietal and harvest season discriminating tools. Pigments were well predicted by UV-vis, while MIR performs better in the prediction of fatty acids, alkyl esters, oxidative stability and free fatty acid.
Exploring lysozyme-nisin antimicrobial synergy at different conditions for novel food applications
(Izmir Institute of Technology, 2019-12) Sözbilen, Gözde Seval; Yemenicioğlu, Ahmet
The main objective of this thesis is to explore lysozyme-nisin antimicrobial synergy in combination with refrigeration, mild heating or edible packaging for novel food applications. The thesis is based on the following four chapters: (1) Characterization of biochemical properties of lysozyme at different conditions; (2) Lysozyme-nisin synergy in combination with mild heating against Listeria innocua: test of findings in inoculated raw-milk (3) Lysozyme-nisin synergy in combination with chitosan coating against Listeria innocua: test of findings on coated inoculated sprouting seeds; (4) Lysozyme-nisin synergy in combination with refrigeration against lactic acid bacteria (LAB): test of findings in boza, a traditional fermented beverage. The results of this thesis clearly showed that the use of lysozyme-nisin synergy in combination with mild heating at 50 ºC or in combination with edible chitosan coating could be employed to reduce risk of listeriosis from raw-milk and sprouted seeds, respectively. It is also clearly demonstrated that the lysozyme-nisin synergy in combination with refrigeration could be used to delay acidic spoilage of boza without reducing LAB below 106 CFU/mL. This thesis clearly showed the high potential of using lysozyme-nisin synergy against pathogenic or spoilage bacteria as an effective hurdle.
Exploring the factors modulating the solubilization of ß-carotene in dietary mixed micelles through computer simulations
(Izmir Institute of Technology, 2018-12) Tunçer, Esra; Bayramoğlu, Beste
β-carotene is one of the major carotenoids beneficial to human health in the prevention of a variety of diseases. However, due to its hydrophobic nature, the bioavailability of β-carotene is very low. The solubilization of β-carotene in the duodenal mixed micelles is considered as a key step in their bioavailability. Therefore, understanding the factors and the molecular mechanisms behind their solubilization within the dietary mixed micelles are of great importance. Based on this motivation, the aim of this dissertation was to systematically investigate this phenomenon via extensive coarse-grained molecular dynamics simulations in three steps: (i) the characterization of the self-assembly and structure of the mixed micelles of bile salts and phospholipids at fasted and fed state conditions, (ii) determination of the effects of addition of the fatty acids with different chain lengths and degrees of unsaturation ,(iii) solubilization of different amounts of β-carotene in the selected mixed micelles. As it would be computationally too expensive to equilibrate the systems with full atomistic resolution, the MARTINI force field, which is a well-established model for lipid systems, was used. All the simulations were carried out using the GROMACS simulation package. Validations of results were made by comparison of the micellar properties with experimental data in the literature when available. The knowledge gained by this study provides important information to be utilized in the design of effective nutraceutical delivery systems that optimize the bioaccessibility of β-carotene.
Feasibility of eugenol encapsulated poly (lactic acid) (PLA) films via electrospinning as a novel delivery system for volatile compounds in food packaging systems
(Izmir Institute of Technology, 2017-07) Arserim Uçar, Dilhun Keriman; Korel, Figen; Yam, Kit L.
Food safety and quality are important issues in food industry. The aim of this research was to evaluate the feasibility of delivering eugenol via poly(lactic) acid (PLA) emulsion fibers-grafted PLA films with bacterial cellulose into the package headspace. For this purpose, first, bacterial cellulose crystals as a natural carrier for eugenol were produced. The influence of hydrolysis temperature, time, and acid to cellulose ratio, acid concentration and type with the addition of the neutralization step on the structure, and the properties of bacterial cellulose crystals were studied. Nanocrystals, which had high thermal stability and high crystallinity bacterial cellulose, were produced. Bacterial cellulose stabilized oil-in-water Pickering emulsions were produced as carriers for eugenol. The emulsion formulations consisting of cellulose fibers and crystals, eugenol, and surfactants were characterized for food packaging applications. PLA films were produced with obtained eugenol emulsions and poly(lactic) acid which were obtained via the electrospinning method. The produced films revealed a significant antibacterial effect on L. innocua, and E. coli inoculated tomato stem scars as real food model. The fabricated films also had significant antifungal activity on B.cinerea inoculated table grapes. Developed novel biodegradable-PLA cellulose composite films had a great potential for delivering bioactive volatile compounds for intelligent food packaging applications. The findings of this research supports the technical feasibility of delivering eugenol for antimicrobial active packaging applications via electrospun fibers.

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