Sistemas complexos de baixo teor de lipídeos estabilizados pela interação eletrostática entre biopolímeros com aplicação de ultrassom ou alta pressão
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2017-08-25
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Universidade Estadual Paulista (Unesp)
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Sistemas de partículas coloidais a base de biopolímeros naturais vêm sendo cada vez mais usados como sistemas de encapsulação ou de veiculação de ingredientes ativos, ou ainda para modular as propriedades sensoriais dos alimentos. A maior parte dessas aplicações envolve uma etapa de emulsificação durante o processamento. A heteroagregação de gotículas de lipídeos com proteínas e polissacarídeos pode ser usada para criar emulsões altamente viscosas ou similares a géis, mas com um conteúdo de óleo menor que as emulsões convencionais. Essa agregação é induzida pela mistura de uma emulsão primária - na qual as gotículas de óleo são estabilizadas por uma proteína - com uma solução de polissacarídeo em pH no qual os biopolímeros apresentam cargas opostas. A aplicação de ultrassom (US) de alta intensidade e de homogeneizador a alta pressão com o objetivo de alterar propriedades funcionais dos biopolímeros vem sendo bastante estudada e, além disso, são métodos que possibilitam a preparação de emulsões com tamanhos de gotas reduzidos. Inicialmente, foi determinado o potencial zeta das proteínas (concentrado proteico de soro de leite, WPC, isolado proteico de soja, SPI) e polissacarídeos (pectina e alginato de sódio) puros, buscando identificar o pH de maior potencial de interação, constatando ocorrer no pH 3,5. Em seguida, foi investigada a interação entre os pares de proteína-polissacarídeo (WPC/Pectina, WPC/Alginato, SPI/Pectina e SPI/Alginato) no pH 3,5 em função da razão proteína:polissacarídeo (1:1, 2:1, 3:1, 4:1 e 5:1), com e sem a aplicação de ultrassom. Foram feitos ensaios de turbidimetria, avaliação visual, microscopia ótica, bem como de reologia em cisalhamento constante com ajuste de modelos reológicos e em cisalhamento oscilatório, ambos a 25 ºC. Após essa avaliação, devido às características físicas apresentadas sistemas com e sem aplicação de US na razão proteína:polissacarídeo 1:1 (sem forte separação de fases) e 4:1 (com forte separação de fases) foram selecionados para análise de FT-IR e preparo das emulsões. A turbidimetria indicou que a aplicação de ultrassom ocasionou a diminuição de tamanho das partículas complexadas dispersas no meio, gerando uma solução menos turva, o que consequentemente diminuiu a leitura de absorbância, exceto para o par SPI:PEC. Para os pares contendo alginato, a avaliação visual permitiu observar a formação de complexos coacervados que sedimentaram, indicando a forte interação eletrostática entre os polímeros. Os pares com pectina não apresentaram sedimentação, mas complexos também foram formados, porém solúveis o que pode indicar a miscibilidade dos polímeros. Os modelos reológicos Lei da Potência, Sisko e Newton ajustaram-se bem aos dados (R2 > 0,9) de acordo com as características das amostras. Os pares WPC:ALG e SPI:ALG apresentaram comportamento pseudoplástico (n < 1), o índice de consistência (K) aumentou com o aumento da proporção de proteína, e houve leve tixotropia. No entanto, a aplicação de ultrassom reduziu a tixotropia do par SPI:ALG por reduzir o tamanho dos complexos minimizando os efeitos da taxa de deformação aplicada. O comportamento dos pares WPC:PEC e SPI:PEC mostraram que a pectina interage com as proteínas de forma diferente que o alginato; apresentando comportamento predominantemente newtoniano. Nos ensaios de cisalhamento oscilatório, com os pares de alginato G’ foi maior que G’’ em toda faixa de frequência aplicada, indicando um material estruturado e viscoelástico. A microscopia ótica confirmou as imagens obtidas na avaliação visual e ajudou a explicar com mais clareza os dados obtidos nos ensaios de reologia. O FTIR indicou os grupos estruturais das aminas, estiramento C-H, amidas I e II presentes nas proteínas e as hidroxilas, a estrutura do sacarídeo e ácidos carboxílicos I e II encontrados nos polissacarídeos. A reologia das emulsões sonicadas foi investigada em cisalhamento constante e oscilatório e os resultados indicaram que as emulsões preparadas com proteínas e pectina, apresentaram comportamento newtoniano. Essas emulsões foram formadas por pequenas gotas e se mostraram estáveis, exceto em algumas proporções de SPI, onde houve instabilidade. Emulsões preparadas com proteínas e alginato apresentaram comportamento pseudoplástico e embora com separação de fases, o creme permaneceu estável no decorrer de 7 dias; houve formação de gotas maiores e o índice de cremeação diminuiu com o aumento de óleo, tendendo a uma emulsão estável para proporção 1:1. A influência dos componentes na instabilidade das emulsões foi comprovada pela análise de composição química. Cremes das emulsões com alginato apresentaram G’ > G’’ em toda faixa de frequência aplicada, indicando ser um material estruturado. Na sequência do trabalho foram realizadas análises do comportamento reológico das emulsões em função de rampas de aquecimento/resfriamento que permitiram identificar o efeito da temperatura nas emulsões e a influência do biopolímero predominante. A microscopia confocal de varredura a laser permitiu identificar a forma física e a distribuição das gotas para cada sistema, que foi comprovada pela análise de distribuição de tamanho de gotas, que apresentou pequenas gotículas para sistemas com pectina e maiores gotas nos sistemas com alginato. Por fim, foi aplicado um homogeneizador de alta pressão de dois estágios nas emulsões com alginato na proporção 1:1 que propiciou a estabilização das emulsões com significativa redução do tamanho de gotículas em relação às emulsões preparadas com ultrassom, diagnosticado por análise visual, microscopia ótica e análise de distribuição de tamanho de gotas, além da redução da viscosidade aparente em ambos sistemas e a permanência de um material estruturado com G’ > G’’ em toda frequência aplicada. Conclui-se que os biopolímeros e os processos de homogeneização utilizados no preparo das emulsões tiveram forte influência na estabilização de emulsões. As emulsões estáveis obtidas sugerem sua aplicação como possíveis substitutos de gordura devido ao baixo teor de lipídeos assim como os cremes são uma alternativa na melhoria de atributos sensoriais de produtos alimentícios devido às características reológicas apresentadas.
Systems based on colloidal particles of natural biopolymers are being increasingly used as encapsulation systems, for delivering active ingredients, or to modulate the sensory properties of food. Most of these applications involve a step of emulsification during processing. The hyper-aggregation of the lipid droplets with proteins and polysaccharide can be used to create highly viscous emulsions or gels similar to, but with lower oil content than conventional emulsions. This aggregation is induced by mixing a primary emulsion - with oil droplets stabilized by a protein - and a polysaccharide solution at a pH at which the biopolymers have opposite charges. The application of high intensity ultrasound with the aim of changing functional properties of biopolymers has been widely studied and, in addition, the use of ultrasound is one of methods that allow the preparation of emulsions with reduced droplet sizes. The zeta potential of pure proteins (whey protein concentrate, WPC, soy protein isolate, SPI) and pure polysaccharides (pectin and sodium alginate), was determined searching for the pH value at which the potential for electrostatic interactions are maximum, occuring at pH 3.5. The interaction between polysaccharideprotein pairs (WPC/Pectin, WPC/Alginate, SPI/Pectin e SPI/Alginate) was investigated at pH 3.5 as a function of the protein:polysaccharide ratio (1:1, 2:1, 3:1, 4:1 and 5:1), with and without ultrasound application. The systems were analyzed by turbidimetry, visual evaluation, optical microscopy, and rheological measurements under steady shear, with adjustment of rheological models, and under oscillatory shear, at 25 °C. After this evaluation, due to the physical characteristics presented systems with and without US application in the protein:polysaccharide ratios 1:1 (without strong phase separation) and 4:1 (with strong phase separation), were selected for FTIR analysis and emulsions preparation. Turbidity values indicated that the application of ultrasound decreased the size of complexes dispersed in the medium, generating a less turbid solution which, consequently, resulted in lower absorbance reading, except for the pair SPI:PEC. Visual assessment showed formation of complex coacervates that sedimented in the pairs containing alginate, indicating an strong electrostatic interaction between biopolymers. The pairs with pectin did not show sediment formation, but complexes were also formed, however soluble which could indicate miscibility of the biopolymers. The rheological models Law of Power, Sisko and Newton fitted well to the data (R2 > 0.9) according to the characteristics of the samples. The pairs WPC: ALG and SPI:ALG exhibited pseudoplastic behavior (n < 1), the consistency index (K) increased with the increase of the proportion of protein, and there was a slight thixotropy. However, the application of ultrasound reduced thixotropy of the pair SPI: ALG because reduced the size of the complexes by minimizing the effects of the applied strain rate. The rheology of the pairs WPC:PEC and SPI:PEC showed that pectin has a different behavior than alginate, presenting predominantly Newtonian behavior. In oscillatory shear tests, with alginate pairs G’ was greater than G’’ to all pairs along the frequency range applied, indicating a structured viscoelastic material. Optical microscopy confirmed the images obtained in the visual assessment and helps explaining more clearly the data obtained in the rheological tests. FTIR indicated the structural groups of amines, C-H stretch, amides I and II present in proteins, and hydroxyls, saccharide structure and carboxylic acids I and II found in polysaccharides. Rheological testing of sonicated emulsions in steady and oscillatory shear were also performed. Emulsions prepared with proteins and pectin, showed Newtonian behavior and were stable, with small droplets, and no phase separation, except for SPI, in which some proportions showed instability. Emulsions made with proteins and alginate exhibited pseudoplastic behavior and although with phase separation, the cream reimaned stable over 7 days. There was formation of larger droplets and creaming rate decreased with increasing oil content, tending to a stable emulsion in the proportion 1:1. The components influence on the emulsion instability was confirmed by the chemical composition analysis. Creams from emulsions with alginate showed G’ > G’’ across the frequency range applied, indicating a structured, viscoelastic system. Following work rheological analyzes were performed on the emulsions in function heating /cooling ramp which allowed to identify the temperature effect on the emulsions and the influence of the predominant biopolymer. The confocal microscopy allowed to identify the physical form and the droplets size distribution for each system that was proven by the droplet size analysis that showed small droplets for pectin systems and larger droplets in alginate systems. Finally, a two-stage high-pressure homogenizer was applied in 1:1 emulsions with alginate, which allowed the emulsions stabilization with significant reduction of droplets size distribution in relation to emulsions prepared with ultrasound, diagnosed by visual analysis, optical microscopy and droplet size analysis, in addition to the apparent viscosity reduction in both systems and the permanence of a structured material (G '> G') at applied frequency. It is concluded that the biopolymers and the homogenization processes used in the emulsions preparation had a strong influence on the emulsions stabilization. The stable emulsions obtained suggest their application as possible fat substitutes due to the lipids content low, as well as the creams are a alternative in the improvement of sensory attributes of food products and in the bioactive compounds microencapsulantion due to its presented rheological characteristics.
Systems based on colloidal particles of natural biopolymers are being increasingly used as encapsulation systems, for delivering active ingredients, or to modulate the sensory properties of food. Most of these applications involve a step of emulsification during processing. The hyper-aggregation of the lipid droplets with proteins and polysaccharide can be used to create highly viscous emulsions or gels similar to, but with lower oil content than conventional emulsions. This aggregation is induced by mixing a primary emulsion - with oil droplets stabilized by a protein - and a polysaccharide solution at a pH at which the biopolymers have opposite charges. The application of high intensity ultrasound with the aim of changing functional properties of biopolymers has been widely studied and, in addition, the use of ultrasound is one of methods that allow the preparation of emulsions with reduced droplet sizes. The zeta potential of pure proteins (whey protein concentrate, WPC, soy protein isolate, SPI) and pure polysaccharides (pectin and sodium alginate), was determined searching for the pH value at which the potential for electrostatic interactions are maximum, occuring at pH 3.5. The interaction between polysaccharideprotein pairs (WPC/Pectin, WPC/Alginate, SPI/Pectin e SPI/Alginate) was investigated at pH 3.5 as a function of the protein:polysaccharide ratio (1:1, 2:1, 3:1, 4:1 and 5:1), with and without ultrasound application. The systems were analyzed by turbidimetry, visual evaluation, optical microscopy, and rheological measurements under steady shear, with adjustment of rheological models, and under oscillatory shear, at 25 °C. After this evaluation, due to the physical characteristics presented systems with and without US application in the protein:polysaccharide ratios 1:1 (without strong phase separation) and 4:1 (with strong phase separation), were selected for FTIR analysis and emulsions preparation. Turbidity values indicated that the application of ultrasound decreased the size of complexes dispersed in the medium, generating a less turbid solution which, consequently, resulted in lower absorbance reading, except for the pair SPI:PEC. Visual assessment showed formation of complex coacervates that sedimented in the pairs containing alginate, indicating an strong electrostatic interaction between biopolymers. The pairs with pectin did not show sediment formation, but complexes were also formed, however soluble which could indicate miscibility of the biopolymers. The rheological models Law of Power, Sisko and Newton fitted well to the data (R2 > 0.9) according to the characteristics of the samples. The pairs WPC: ALG and SPI:ALG exhibited pseudoplastic behavior (n < 1), the consistency index (K) increased with the increase of the proportion of protein, and there was a slight thixotropy. However, the application of ultrasound reduced thixotropy of the pair SPI: ALG because reduced the size of the complexes by minimizing the effects of the applied strain rate. The rheology of the pairs WPC:PEC and SPI:PEC showed that pectin has a different behavior than alginate, presenting predominantly Newtonian behavior. In oscillatory shear tests, with alginate pairs G’ was greater than G’’ to all pairs along the frequency range applied, indicating a structured viscoelastic material. Optical microscopy confirmed the images obtained in the visual assessment and helps explaining more clearly the data obtained in the rheological tests. FTIR indicated the structural groups of amines, C-H stretch, amides I and II present in proteins, and hydroxyls, saccharide structure and carboxylic acids I and II found in polysaccharides. Rheological testing of sonicated emulsions in steady and oscillatory shear were also performed. Emulsions prepared with proteins and pectin, showed Newtonian behavior and were stable, with small droplets, and no phase separation, except for SPI, in which some proportions showed instability. Emulsions made with proteins and alginate exhibited pseudoplastic behavior and although with phase separation, the cream reimaned stable over 7 days. There was formation of larger droplets and creaming rate decreased with increasing oil content, tending to a stable emulsion in the proportion 1:1. The components influence on the emulsion instability was confirmed by the chemical composition analysis. Creams from emulsions with alginate showed G’ > G’’ across the frequency range applied, indicating a structured, viscoelastic system. Following work rheological analyzes were performed on the emulsions in function heating /cooling ramp which allowed to identify the temperature effect on the emulsions and the influence of the predominant biopolymer. The confocal microscopy allowed to identify the physical form and the droplets size distribution for each system that was proven by the droplet size analysis that showed small droplets for pectin systems and larger droplets in alginate systems. Finally, a two-stage high-pressure homogenizer was applied in 1:1 emulsions with alginate, which allowed the emulsions stabilization with significant reduction of droplets size distribution in relation to emulsions prepared with ultrasound, diagnosed by visual analysis, optical microscopy and droplet size analysis, in addition to the apparent viscosity reduction in both systems and the permanence of a structured material (G '> G') at applied frequency. It is concluded that the biopolymers and the homogenization processes used in the emulsions preparation had a strong influence on the emulsions stabilization. The stable emulsions obtained suggest their application as possible fat substitutes due to the lipids content low, as well as the creams are a alternative in the improvement of sensory attributes of food products and in the bioactive compounds microencapsulantion due to its presented rheological characteristics.
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Emulsões O/W, Sistemas coloidais, Comportamento reológico, Métodos de homogeneização, Proteínas de soro e soja, Polissacarídeos pectina e alginato, O/W emulsions, Colloidal systems, Rheological behavior, Homogenization methods, Whey and soy proteins, Pectin and alginate polysaccharides