Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Gıda Mühendisliği Bölümü, Türkiye
Tezin Onay Tarihi: 2017
Tezin Dili: İngilizce
Öğrenci: Sezen Sevdin
Danışman: HAMİ ALPAS
Özet:Lipid crystal structures (polymorphs) are the determinant factors for sensorial, textural properties and the stability of the emulsions. Therefore, controlled crystallization gains importance during the production of foods such as margarine, confectionery, chocolate, etc. In literature, studies on the effect of high hydrostatic pressure (HHP) on lipid crystallization have contradictory results. To inspect the crystallization characteristics and response to the HHP treatment, palm stearinwater emulsions were prepared with two different emulsifiers (sodium caseinate and hydrogenated soy lecithin-xanthan gum mixture) and pressurized at 100 and 500 MPa, at 10, 20 and 40°C for 15 minutes. Particle size analysis, differential scanning calorimetry (DSC), transverse relaxation time (T2) and self-diffusion coefficient (SDC) determinations and small angle x-ray scattering (SAXS) were conducted to investigate the changes induced by HHP treatment. According to the results, HHP did not affect droplet size of sodium caseinate (SC) emulsions so it vi was observed that mean particle size was affected only by the types of emulsifiers and storage time. In addition, sodium caseinate has the capability to produce smaller particles than 80H_XG emulsion. HHP has no significant effect on the melting temperature of polymorphs; but pressure and storage time have significant effect on crystal polymorphs’ content in emulsions. HHP induced formation of more stable β crystals in both sodium caseinate and soy lecithin-xanthan gum mixture emulsions. In addition to this, HHP also induced solid wall formation in soy lecithin-xanthan gum mixture emulsions. Changes in α and β contents with respect to pressure and storage time were detected by T2 and SDC measurements. These findings suggested that the beginning of emulsions’ destabilization can be detected by NMR measurements. The pressure effect may easily be seen in the ab-initio structural model with SAXS measurements. The pressure application caused a structural change from spherical form to cylindrical form in sodium caseinate (SC) solution and SC emulsion droplets reached more compact spherical like aggregations.