The thermal denaturation of proteins has been extensively studied using several methods including differential scanning calorimetry (DSC). A custom-built optical system was used to study thermal effects on protein as an alternative method to DSC measurements. It was used to investigate the thermal stability of bovine serum albumin (BSA) with a focus on comparisons with published DSC data. In the first study, the effect of protein concentration on the thermal denaturation (Td) of BSA was determined and validated using published DSC data for bovine serum albumin (BSA). The optical rotation (OR) and transmitted light (TL) signals indicating protein conformational changes and gel formation, respectively, were collected during the heating of BSA solutions at ~6��C/min from room temperature to ~85��C. The experiments were performed on 1, 2.5 and 5% (w/v) BSA in 0.01 M phosphate buffer at pH 7 and ionic strength (IS) 0.08. BSA���s Td values obtained from this investigation were consistent with published values and had low experimental variability (CV<2.5%). In agreement with some but not all published data, increasing BSA concentration did not affect its thermal stability. Protein gel formation, however, increased with protein concentration. In the second study, changes in the OR and TL signal of BSA in 0.01 M phosphate buffer at pH 6.1, 7 and 7.9 with IS maintained at 0.04, 0.08 and 0.16 were recorded during the heating of BSA solutions at ~6��C/min from room temperature to ~85��C. BSA showed a maximum and minimum thermostability at pH 7 and 7.9, respectively, consistent with published values determined by DSC. BSA formed opaque gel at pH 6.1 approaching the BSA���s pI values. Increasing IS level did not have a significant effect on BSA���s Td value but promoted gel formation. In the third study, the optical method was applied to investigate the heat stability of BSA as affected by low concentrations of sucrose, trehalose or sorbitol. BSA solutions (2.5% w/v) in the presence of 0 5% sucrose, trehalose and sorbitol were heated at ~6��C/min from ambient temperature to ~85��C. In contrast with published work on the thermal stability of BSA in the presence of higher sugar concentrations, this study showed that increasing sugar concentration did not enhance the thermal stability of this protein. Also, the ability to promote protein stability among sucrose, trehalose and sorbitol were not significantly different. The significance of these studies is that they demonstrate that the custom-built optical methods here developed can be used to study heat-induced protein denaturation and the effect of environmental conditions. Future studies will examine other proteins such as ��-lactoglobulin or ��-lacactalbumin. A further advantage of optical systems is their ability to conduct real-time measurements which could be used for food processing control. / Graduation date: 2007

Content: Synchrotron small-angle X-ray scattering (SAXS) technique was applied to leather research to understand the changes in molecular-level collagen structure during tanning and denaturation (shrinkage), which can help reduce the environmental impact from the extensive chrome usage. Based on SAXS results from realtime denaturation experiments on leather samples, we established a mechanistic model of chrome tanning indicated by the structural changes of collagen. It suggests that only a low level of chromium species is effectively involved in the cross-linking with collagen, which highlights the overuse of chrome during conventional tanning processes. Any extra amount of chrome added, however, can support the stabilisation of collagen possibly via a non-covalent mechanism. Such mechanism points towards a more environment-friendly tanning method by using suitable supplementary reagents to benefit tanning effect non-covalently instead of chrome. By pre-treating with complexing agents such as sodium formate and disodium phthalate, as well as nanoclay (sodium montmorillonite), the uniformity through bovine hide collagen matrix were improved significantly. These pre-treatments effectively reduce the reactivity of chromium during its cross-linking reaction with collagen while retaining its bound water. However, collagen pre-treated with a covalent cross-linker (glutaraldehyde) results in a decrease in both chromium-collagen cross-linking and bound water while improving uniformity. These molecular-level insights can be developed into metrics to guide us towards a more sustainable future for the leather industry. The coating on collagen fibrils can provide a pseudo-stabilisation effect of increasing the heat resistance of collagen. A group of tanning experiments were also conducted in situ on the SAXS beamline to observe the different mechanisms of free-of-chrome alternative tannages as potential replacements. Overall, synchrotron SAXS provides valuable information about collagen structure changes that could lead to more efficient use of chrome (or other tanning agents) in the global leather tanning industry. Take-Away: 1. Kinetics of hydrothermal denaturation and collagen crosslinking mechanism proceed through different pathways 2. Alternative chemistries to enhance chrome uptake at low offers. 3. The role of collagen structure studies in understanding tanning mechanims

Orientadores: Rosiane Lopes da Cunha, Miriam Dupas Hubinger / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-10T19:31:23Z (GMT). No. of bitstreams: 1 Neves_EdmeiaSabadini_D.pdf: 3460318 bytes, checksum: 852074cc798cd99ff46cf910e7887c71 (MD5) Previous issue date: 2008 / Resumo: Foram estudadas as interações entre as proteínas do leite e a carragena em sistemas acidificados com glucona-delta-lactona (GDL) contendo ou não co-solutos, como açúcar (sacarose) e a mistura salina KCl/NaCl, na formação/obtenção de géis. Foi possível avaliar o efeito das variáveis de composição (concentrações de caseinato de sódio, concentrado protéico do soro, carragena, sacarose ou mistura salina KCl/NaCl) e condições de processo (temperatura de mistura dos componentes, tempo de aquecimento e velocidade de agitação) nas propriedades mecânicas e da capacidade de retenção de água dos géis protéicos acidificados, utilizando a metodologia de planejamento experimental fatorial. Essas análises foram complementadas com microscopia eletrônica de varredura e calorimetria diferencial de varredura. Nos géis obtidos com adição de sacarose verificou-se que a concentração de carragena foi a variável de maior contribuição ao aumento da dureza, deformabilidade e firmeza dos géis. Através dos ensaios de relaxação de tensões, verificou-se que o módulo elástico foi fortemente influenciado pelas interações entre a carragena e o caseinato de sódio, na presença do açúcar. O gel mais forte foi obtido em altas concentrações de biopolímeros, sendo o efeito da sacarose associado à diminuição das interações polissacarídeo-solvente. Na análise dos ensaios de ruptura e de relaxação de tensões constatou-se que os géis com a adição da mistura salina (KCl/NaCl), comportaram-se de maneira diferente dos com e sem sacarose. Foram estruturalmente muito mais frágeis e, em certas formulações, não se formou gel, sendo a força iônica e a temperatura de processo, as variáveis que definiram as características reológicas do sistema com sal. Pode-se observar o efeito negativo da concentração do concentrado protéico do soro (CPS) nas propriedades mecânicas do gel lácteo. Na avaliação da capacidade de retenção de água nos sistemas contendo sal, o comportamento foi totalmente diferente do da sacarose. A adição do açúcar promoveu o fortalecimento da rede do gel, com uma malha mais firme e coesa ao contrário do observado para os géis com adição da mistura salina KCL/NaCl / Abstract: Gel formation due to interactions between milk proteins and carrageenan in systems acidified by glucono-delta-lactona (GDL) with or without co-solutes like sugar (sucrose) and KCl/NaCl, were studied. A factorial experimental design was used to determine the effect of several variables, such as: the composition of the system (concentrations of sodium caseinate, whey protein concentrate, carrageenan and sucrose or a KCl/NaCl mixture); the process conditions (temperature of the mixture, heating time and stirring speed), on the mechanical properties of the acidified gels, as well as their water holding capacity. Scanning Electronic Microscopy and Differential Scanning Calorimetry were also used to complement the studies. In the gels containing sucrose, the concentration of carrageen was the more important variable with respect to the increase in hardness, rigidity and consistence of the gels. Using the stress relaxation experiments, it was observed that the elastic modulus was highly affected by the interactions between the carrageenan and sodium caseinate if sucrose was present. The strongest gel was obtained with the higher concentrations of the biopolymers, and this can be attributed to a decrease in the interactions between the polysaccharides and the water. In the presence of salts (KCl/NaCl) the stress relaxation and rupture experiments showed that the gels obtained were different from those obtained with the addition of sucrose or without a solute. The gels containing salts were much weaker and in some cases failed to form a gel. For these gels, the ionic strength and the temperature were the more important variables affecting the rheological properties of the gels. On the other hand, a negative effect of the concentration of whey protein concentrate on the mechanical properties of the lacteous gels could also be observed, due to strong interactions between the sodium caseinate and carrageenan. In terms of the water holding capacity, the behaviors of the gels containing salts and sucrose were again completely different. In the presence of sucrose, the molecular structure of the gel became stronger and cohesive, the opposite effect being observed in gels containing salts (KCl/NaCl) / Doutorado / Doutor em Engenharia de Alimentos