Mechanical stability of intermediate moisture starch-glycerol systems

There is conflicting information on the mechanical properties and ageing kinetics of starch-water-glycerol systems. This makes understanding the changes occurring on storage of edible products difficult to predict. The work described in this thesis looks at model systems consisting of thermomechanically extruded plasticized starches (waxy maize, rice and wheat) and commercial products. The objectives of the work were to evaluate how the presence of polyols effects glass transition temperature (Tg), sorption isotherms, diffusion rates and texture parameters and to create models that could be used to predict behaviour. Very similar results were obtained for the starch samples except that monolayer (ma) values were higher for the waxy maize starch than for the wheat and rice. The waxy maize also was more brittle at equivalent moisture content when compared to the other two starches. Glycerol had a major impact on the water absorption. For RHs > 70% more water absorbed up by samples containing glycerol while the opposite occurred at RHs <60%. Monolayer values for GAB and BET confirmed this finding. The behaviour could be predicted if an interaction factor <1 was used in weight fraction models. Tg of the samples was measured by DSC and also by using predictive models, where the ten-Brinke Karas equation was found to give the best predictions. A value that was found to be most beneficial for the prediction of retrogradation was (storage temperature minus Tg). Change in texture was associate with (T-Tg), although the brittle ductile transition occurred 40°C below T-Tg=O. Diffusivity values increased with plasticizer level up to 8*10 3 m'z/s. There was an apparent fall in values when the samples were above Tg. However, it is suggested that this is due to sample geometry change rather than a change in diffusion mechanism. The Tg values also were found to be a good predictor of the type of change occurring in the model systems and food products during storage. Below Tg physical aging (enthalpy relaxtion) could be seen in the samples and retrogradation of the starch occurred above Tg. The rates of retrogradation were not affected by glycerol content directly and knowledge of Tg and storage temperature were sufficient to predict the retrogradation. Products became stiffer on storage and this was associated with molecular reassociation of the starchy component, but control of the moisture was also critical as water still dominated product behaviour even in the presence of glycerol

Mechanical stability of intermediate moisture starch-glycerol systems

There is conflicting information on the mechanical properties and ageing kinetics of starch-water-glycerol systems. This makes understanding the changes occurring on storage of edible products difficult to predict. The work described in this thesis looks at model systems consisting of thermomechanically extruded plasticized starches (waxy maize, rice and wheat) and commercial products. The objectives of the work were to evaluate how the presence of polyols effects glass transition temperature (Tg), sorption isotherms, diffusion rates and texture parameters and to create models that could be used to predict behaviour. Very similar results were obtained for the starch samples except that monolayer (ma) values were higher for the waxy maize starch than for the wheat and rice. The waxy maize also was more brittle at equivalent moisture content when compared to the other two starches. Glycerol had a major impact on the water absorption. For RHs > 70% more water absorbed up by samples containing glycerol while the opposite occurred at RHs <60%. Monolayer values for GAB and BET confirmed this finding. The behaviour could be predicted if an interaction factor <1 was used in weight fraction models. Tg of the samples was measured by DSC and also by using predictive models, where the ten-Brinke Karas equation was found to give the best predictions. A value that was found to be most beneficial for the prediction of retrogradation was (storage temperature minus Tg). Change in texture was associate with (T-Tg), although the brittle ductile transition occurred 40°C below T-Tg=O. Diffusivity values increased with plasticizer level up to 8*10 3 m'z/s. There was an apparent fall in values when the samples were above Tg. However, it is suggested that this is due to sample geometry change rather than a change in diffusion mechanism. The Tg values also were found to be a good predictor of the type of change occurring in the model systems and food products during storage. Below Tg physical aging (enthalpy relaxtion) could be seen in the samples and retrogradation of the starch occurred above Tg. The rates of retrogradation were not affected by glycerol content directly and knowledge of Tg and storage temperature were sufficient to predict the retrogradation. Products became stiffer on storage and this was associated with molecular reassociation of the starchy component, but control of the moisture was also critical as water still dominated product behaviour even in the presence of glycerol

Mechanical stability of intermediate moisture starch-glycerol systems

There is conflicting information on the mechanical properties and ageing kinetics of starch-water-glycerol systems. This makes understanding the changes occurring on storage of edible products difficult to predict. The work described in this thesis looks at model systems consisting of thermomechanically extruded plasticized starches (waxy maize, rice and wheat) and commercial products. The objectives of the work were to evaluate how the presence of polyols effects glass transition temperature (Tg), sorption isotherms, diffusion rates and texture parameters and to create models that could be used to predict behaviour. Very similar results were obtained for the starch samples except that monolayer (ma) values were higher for the waxy maize starch than for the wheat and rice. The waxy maize also was more brittle at equivalent moisture content when compared to the other two starches. Glycerol had a major impact on the water absorption. For RHs > 70% more water absorbed up by samples containing glycerol while the opposite occurred at RHs <60%. Monolayer values for GAB and BET confirmed this finding. The behaviour could be predicted if an interaction factor <1 was used in weight fraction models. Tg of the samples was measured by DSC and also by using predictive models, where the ten-Brinke Karas equation was found to give the best predictions. A value that was found to be most beneficial for the prediction of retrogradation was (storage temperature minus Tg). Change in texture was associate with (T-Tg), although the brittle ductile transition occurred 40°C below T-Tg=O. Diffusivity values increased with plasticizer level up to 8*10 3 m'z/s. There was an apparent fall in values when the samples were above Tg. However, it is suggested that this is due to sample geometry change rather than a change in diffusion mechanism. The Tg values also were found to be a good predictor of the type of change occurring in the model systems and food products during storage. Below Tg physical aging (enthalpy relaxtion) could be seen in the samples and retrogradation of the starch occurred above Tg. The rates of retrogradation were not affected by glycerol content directly and knowledge of Tg and storage temperature were sufficient to predict the retrogradation. Products became stiffer on storage and this was associated with molecular reassociation of the starchy component, but control of the moisture was also critical as water still dominated product behaviour even in the presence of glycerol

Efeito do sorbitol em relaxação estrutural de filmes de gelatina em estado vítreo

The objective of this work was to study the effect of sorbitol on the kinetic of enthalpy relaxation of gelatin films stored at temperatures below the glass transition temperature (Tg). Bovine gelatin and sorbitol films were prepared by cold casting method. Sorbitol was added at weight fraction (Qs) of 0.0, 0.06 and 0.10. Films were equilibrated in environment of 44% relative humidity using a saturated salt solution of potassium carbonate, giving a moisture weight fraction in samples (Qw) of 0.18, 0.16 and 0.18 respectively. Enthalpy relaxation (∆H) was measured by differential scanning calorimetry (DSC). Tg&nbsp;values of the samples tested were observed at 48ºC (Qs=0.0), 35ºC (Qs=0.06) and 30ºC (Qs=0.10). After the thermal history deletion (30ºC above Tg, 15 minutes), samples were annealed from 2 to 80 hours at 10ºC below Tgonset. The addition of sorbitol showed a significant reduction (p&lt;0.05) in structural relaxation kinetic. The linearization of relaxation enthalpy (∆H) versus log of annealing time showed a reduction of the slope in samples plasticized with sorbitol. The reduction in structural relaxation kinetic could be related to the effect of molecular packing by the presence of polyol in polymer matrix as has been recently reported by Positron Annihilation Spectroscopy (PALS).O objetivo deste estudo foi avaliar o efeito do sorbitol sobre a cinética da relaxação estrutural de películas de gelatina armazenadas a temperatura inferior a temperatura de transição vítrea (Tg). Filmes de gelatina bovina e sorbitol foram preparados por moldagem a frio. O sorbitol foi adicionado em fracções de peso (QS), de 0,0, 0,06 e 0,10. Os filmes foram acondicionados em atmosfera de humidade relativa constante (44%), utilizando uma solução saturada de carbonato de potássio, obtendo-se de frações de teor de humidade de peso (Qw) de 0,18, 0,16 e 0,18, respectivamente. A entalpia de relaxação (DH) foi determinada por Calorimetria Diferencial de Varrimento (DSC). As amostras usadas neste estudo apresentaram valores de Tg de 48°C (Qs = 0,0), 35ºC (Qs = 0,06) e 30ºC (Qs = 0,10). Após eliminar historial térmico (30°C a Tg, 15 minutos), as amostras foram armazenadas isotermicamente a 10°C sob Tgonset entre 2 e 80 horas. A adição de sorbitol produziu uma redução significativa (p &lt;0,05) na cinética da relaxação estrutural. A linearização do valor de entalpia de relaxação (DH) versus o logaritmo do tempo de armazenamento apresentou uma redução do declive nas amostras plastificados com sorbitol. A redução da cinética de relaxamento poderia estar relacionada com o efeito de empaquetamiento molecular associado à presença de polióis em matrizes em estado vítreo recentemente relatado pela espectroscopia de positroês (PALS).El objetivo de este trabajo fue evaluar el efecto del sorbitol sobre la cinética de relajación estructural de películas de gelatina almacenadas bajo la temperatura de transición vítrea (Tg). Películas de gelatina de bovino y sorbitol fueron preparadas mediante casting en frío. El sorbitol fue agregado en fracciones en peso (Qs) de 0,0, 0,06 y 0,10. Las películas fueron acondicionadas en un ambiente de humedad relativa constante (44%) utilizando una solución saturada de carbonato de potasio, obteniéndose fracciones de contenido de humedad en peso (Qw) de 0,18, 0,16 y 0,18 respectivamente. La entalpía de relajación (∆H) fue determinada mediante Calorimetría Diferencial de Barrido (DSC). Las muestras utilizadas en este estudio presentaron valores de Tg de 48ºC (Qs=0,0), 35ºC (Qs=0,06) y 30ºC (Qs=0,10). Luego de eliminar el historial térmico (30ºC sobre Tg, 15min), las muestras fueron almacenadas isotérmicamente a 10ºC bajo Tgonset entre 2 y 80 horas. La adición de sorbitol produjo una reducción significativa (p&lt;0,05) en la cinética de relajación estructural. La linealización del valor de entalpía de relajación (∆H) en función del logaritmo del tiempo de almacenamiento mostró una reducción de la pendiente en las muestras plastificadas con sorbitol. La reducción en la cinética de relajación estaría relacionada con el efecto de empaquetamiento molecular asociado a la presencia de polioles en matrices en estado vítreo recientemente reportada mediante espectroscopía de positrones (PALS)

Natural food colorant from blackcurrant spray-dried powder obtained by enzymatic treatment: Characterization and acceptability

Blackcurrant juice extraction was optimized by enzymatic maceration. A Box–Behnken experimental design was used considering the effect of enzyme concentration, temperature, and treatment time over the total polyphenolic content (TPC), antioxidant capacity (AC), and juice yield. Under the obtained optimal conditions (200 ppm enzyme, 45°C and 60 min), a 2.4-fold increment for TPC, 2.8-fold for AC, and 2.7-fold for total monomeric anthocyanins (ACY) were observed, along with a 15% increase in juice yield. The juice was spray-dried and the powder was tested as an ingredient in a jelly dessert. An attractive color product was obtained, also containing blackcurrant bioactive compounds (0.56 ± 0.03 mg GA/g, 0.20 ± 0.02 mg cyd-3-glu/g and 0.16 ± 0.02 mg of GA/g for TPC, ACY, and AC, respectively). This jelly was stable regarding syneresis and antioxidant compounds for 15 days at 4°C. The developed blackcurrant powder could be useful as natural colorant and source of bioactive compounds for several food applications. Practical applications: An efficient extraction process of blackcurrant juice by enzymatic treatment of ground fruit was achieved. As a result of the process, it was possible to improve the extraction of bioactive compounds and also increasing antioxidant activity. A fruit juice powder was obtained from the enriched juice by spray-drying. The blackcurrant powder showed relatively good physical characteristics and potential functional properties. The use of this powder as a natural colorant in a jelly dessert showed promising results. The ingredient not only enriched the product with bioactive components, but also provided a stable and attractive color. Moreover, the gel properties were improved and the jelly showed very good acceptance in the consumer’s perception test. These results prove that this ingredient has good potential to be used as natural colorant and functional additive in food.Fil: Toscano Martínez, Hernando. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; ArgentinaFil: Gagneten, Maite. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Industrias. Instituto de Tecnología de Alimentos y Procesos Quimicos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Tecnología de Alimentos y Procesos Quimicos.; ArgentinaFil: Díaz Calderón, Paulo. Universidad de Los Andes, Chile; ChileFil: Enrione, Javier. Universidad de Los Andes, Chile; ChileFil: Salvatori, Daniela Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Schebor, Carolina Claudia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Industrias. Instituto de Tecnología de Alimentos y Procesos Quimicos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Tecnología de Alimentos y Procesos Quimicos.; ArgentinaFil: Leiva, Graciela Edith. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentin

Changes in gelatinisation and pasting properties of various starches (wheat, maize and waxy maize) by the addition of bacterial cellulose fibrils

The aim of this work was to analyse the effect of bacterial cellulose fibrils (BCF) on the gelatinization profile and pasting properties of starches from different sources (wheat, maize and waxy maize) and amylose contents. Blends of 8% starch with different BCF levels (0, 0.5, 2, 6 and 10% based on the dry weight of starch) were prepared and tested by Rapid Visco-Analysis (RVA), Differential Scanning Calorimetry (DSC) and both Optical and Polarized Light Microscopy. Results showed that BCF produce a significant modification of pasting properties. The pasting temperature was reduced but viscosities (peak, final, trough, breakdown and final) increased. The reduction in pasting temperature at the highest BCF addition was 200C higher for maize and wheat starches but only 20C higher for waxy maize starch. In contrast to the pasting temperature, the gelatinisation temperature by DSC for all three starches slightly varied upon BCF addition, but the gelatinisation enthalpy was reduced to a greater extent than values reported for the addition of other hydrocolloids to starch blends. Optical and polarized light microscopy showed the presence of domains rich in starch and highly aggregated BCF in all three starches evaluated. The increase in viscosity and decrease in pasting temperature are discussed in terms of changes in starch concentrations in the starch rich domain. These results open interesting perspectives in the use of bacterial cellulose and plant cell walls to design novel bio-composites to structure foods

Rheological and Structural Study of Salmon Gelatin with Controlled Molecular Weight

This study explores the molecular structuring of salmon gelatin (SG) with controlled molecular weight produced from salmon skin, and its relationship with its thermal and rheological properties. SG was produced under different pH conditions to produce samples with well-defined high (SGH), medium (SGM), and low (SGL) molecular weight. These samples were characterized in terms of their molecular weight (MW, capillary viscometry), molecular weight distribution (electrophoresis), amino acid profile, and Raman spectroscopy. These results were correlated with thermal (gelation energy) and rheological properties. SGH presented the higher MW (173 kDa) whereas SGL showed shorter gelatin polymer chains (MW &lt; 65 kDa). Raman spectra and gelation energy suggest that amount of helical structures in gelatin is dependent on the molecular weight, which was well reflected by the higher viscosity and G&prime; values for SGH. Interestingly, for all the molecular weight and molecular configuration tested, SG behaved as a strong gel (tan &delta; &lt; 1), despite its low viscosity and low gelation temperature (3&ndash;10 &deg;C). Hence, the molecular structuring of SG reflected directly on the thermal and viscosity properties, but not in terms of the viscoelastic strength of gelatin produced. These results give new insights about the relationship among structural features and macromolecular properties (thermal and rheological), which is relevant to design a low viscosity biomaterial with tailored properties for specific applications