Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

Browse

Filters

2013 - 20186

Settings

Author: search.filters.author.Harsa, Hayriye ŞebnemDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Food Engineering

Search Results

Now showing 1 - 6 of 6
  • Doctoral Thesis
    Preparation, Production and Industrial Application of Cheese Protective Cultures
    (Izmir Institute of Technology, 2018) Şatana, Elçin; Harsa, Hayriye Şebnem
    Cheese industry is always under the risk of microbiological contaminations. These contaminants can be either bacteria or fungal species; both affect the final product quality and acceptance. Globally, 20% of the cheese produced industrially is lost due to microbial contaminations. Fungal contaminations can be overcome by the usage of chemicals; sorbate, benzoate, natamycine, propionate, etc. or by natural biopreservatives such as protective cultures or some metabolites of antifungal cultures. Chemical preservatives have a legal limit for their usage and these limits are generally not effective to prevent the product from fungal growth. Also consumers demand goes toward the clean-labeled products and force the manufacturers to use bioprotectants if necessary. There are many types of bioprotectants commercially available with defined lactic acid bacteria combinations which are not so effective for some fungal species due to the species that they include. In this study, several lactic acid bacteria (LAB) strain has been selected to prepare efficient protective culture combinations e.g. Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus paracasei spp. paracasei. The maximum antifungal effect was determined by using mixed culture combination of lactic acid bacteria strains with equal volume. In cheese applications, 3x108 cfu/ml antifungal bacteria mixture including; Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus paracasei spp. paracasei, was inoculated into the curd before fermentation and found more effective than surface applications to the final products. In yoghurt production, same antifungal lactic acid bacteria mixture was found to be effective when applied before fermentation with 106 cfu/ml initial cell counts.
  • Doctoral Thesis
    Development of Gluten-Free Bread Formulations Based on Chickpea Flour: Optimization of Formulation, Evaluation of Dough Properties and Bread Quality
    (01. Izmir Institute of Technology, 2016) 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.
  • Doctoral Thesis
    Polysaccharide Based Packaging Film for Fresh Cut Produce
    (Izmir Institute of Technology, 2017) Şamlı, Merve; Harsa, Hayriye Şebnem; Büyükkileci, Ali Oğuz
    In this thesis, agro industrial wastes such as bracts and leaves of artichoke were used to develop biodegradable packaging materials for fresh-cut artichokes. As flim forming materials; cellulose, hemicellulose, lignin and wax fractions were extracted by using mild alkaline treatment applied to artichoke wastes. Carboxy methyl cellulose was chemically synthesized from extracted cellulose fiber. A mechanical process (Masuko Supermasscolloider, at-100 um grind size via 5 times feeding) with minimum environmental impact was selected to obtain cellulose micro fibrils with micro sized dimensions (50-200 um in length and 10-30 um in width).These fractions used as polysaccharide sources in film forming solutions. Different combinations of these polysaccharide based film materials were optimized using General Factorial Design and four film combinations were selected among the films produced.elected films were MFC and CMC based having good elasticity (16 % strain), tensile strength and low gas permeability properties (150mlO2/m2.day).Different concentrations of additives such as wax, stearic acid, chitosan were used with the glycerol addition of plasticizer. SEM analyses of selected films showed films showed films having smooth surface and dense structure by looking their cross sectional area. Thermal analyses proved sealabilitiy of films obtained by extracted fractions from artichoke at 200-250 oC temperature intervals. But, presence of MFC in films hindered the heat sealing ability. Therefore, MFC and CMC based films successfully showed optimal properties when they were combined with glycerol, stearic acid and wax.
  • Doctoral Thesis
    Isolation, Characterization, and Screening Probiotic Properties of Artisanal Yoghurt Starter Strains From Urla Region
    (Izmir Institute of Technology, 2014) Okuklu, Burcu; Harsa, Hayriye Şebnem; Yenidünya, A.Fazıl
    Probiotics are bacteria that help to maintain the natural balance of microflora in the intestine. The largest group of probiotic bacteria in the intestine is lactic acid bacteria, found in yoghurt with live culture. In this study, 13 different artisanal yoghurt samples were collected from Urla region to isolate artisanal starter strains. These isolated strains were firstly identified and characterized by using basic biochemical, physiological and probiotic characterization methods. Among 453 LAB strains in total, 5 Streptecoccus thermophilus and 26 Lactobacillus delbrueckii ssp. bulgaricus isolates resulted as probiotic candidates. PCR-RFLP and PFGE-RFLP methods were used for the differentiation of probiotic candidates. Probiotic features of strains were screened by using bile salt tolerance, bile salt deconjugation, and cholesterol assimilation, transit tolerance to gastrointestinal tract, antibiotic resistances, autoaggregation, cell surface hydrophobicity, antimicrobial activities, adhesion abilities, and growth capacity with prebiotics. The results showed that, the isolated strains gave different properties against these tests; but all of them were acid and bile resistant, had ability to adhesion Caco-2 cell lines, and grown very well with prebiotic sources. They had also antimicrobial activity against Escherichia coli and Listeria innocua. Further studies were conducted; probiotic yoghurts were produced by using probiotic candidates. Sixteen starter combinations were made using the two cocci and eight bacilli isolates, and thus these yoghurt products were characterized by using physical, chemical, rheological, and organoleptic methods. Acetaldehyde content of yoghurt samples varied between 5.61 and 15.38 mg/L and apparent viscosity values ranged from 261 and 608 m Pa.s. Hardness value of samples ranged from 3.81 and 6.71 N. Yoghurt starter having probiotic features is an advantage for dairy industry to produce large amount of functional yoghurt. In this study, a good number of cocci and bacilli were paired as probiotic/starter strain combinations that could perfectly be used for the production of functional yoghurt for dairy industry.
  • Doctoral Thesis
    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) 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.
  • Doctoral Thesis
    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.