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Authors
Abstract(s)
Os hidrogéis são materiais com elevada capacidade de absorção de água, formados por redes
tridimensionais capazes de reter água sem dissolução. Esta característica confere aos hidrogéis
a possibilidade de variadas aplicações na indústria alimentar, farmacêutica e cosmética,
apresentando capacidade gelificante e espessante. A microalga Spirulina platensis é uma
cianobactéria amplamente estudada devido ao seu alto teor proteico, bem como às suas
características nutracêuticas, considerando os compostos bioativos presentes na sua biomassa,
como ficobiliproteínas, vitaminas, minerais e compostos com capacidade antioxidante.
Este trabalho teve como objetivo o estudar da capacidade de gelificação e formação de hidrogel
da biomassa integral de S. platensis. Inicialmente foi aplicado um Planeamento Fatorial
Fracionado (PFF) para a avaliação dos efeitos de seis variáveis do processo (concentração de
biomassa, temperatura, pH, tempo de aquecimento, tempo e velocidade de agitação) nas
seguintes respostas do hidrogel formado: firmeza, consistência, coesividade e trabalho de
coesão. Seguidamente aplicou-se um Delineamento Composto Central Rotacional (DCCR)
usando apenas as variáveis significativas (pH e concentração de biomassa).
A partir das análises estatísticas dos planeamentos experimentais, foi possível maximizar o
processo de formação do hidrogel de acordo com suas características de textura, e a análise de
sinérese realizada demonstrou que os géis formados com maiores concentrações de biomassa
apresentaram uma menor perda de água devido à presença de uma maior concentração de
proteínas. Com a análise de infravermelho com transformada de Fourier (FTIR) para a amostra
com os fatores maximizados no planeamento, foi possível identificar as principais bandas dos
grupos funcionais presentes na biomassa e no hidrogel, demonstrando que os grupos presentes
na biomassa podem influenciar na formação do gel e na capacidade de absorção de água, devido
às interações estabelecidas entre os mesmos.
A análise por microscopia eletrónica de varrimento (MEV) e estabilidade térmica
demonstraram que o gel é, possivelmente, formado por agregados de moléculas de biomassa de
S. platensis gerando o que é designado por hidrogel particulado. As análises de reologia e
viscosidade foram realizadas visando comparar as propriedades mecânicas dos géis, um
preparado com 22% de biomassa e pH 5,6 (ponto ótimo nos planeamentos) e outro com 12%
de biomassa e pH 5,6. Os géis analisados apresentaram módulo de carga superior ao módulo de
perda para o teste de varrimento de frequência, apresentando propriedade elásticas. O teste de
recuperação realizado nas amostras, aplicando ciclos de baixa e alta taxa de cisalhamento,
demonstram uma recuperação de aproximadamente 30% para a amostra de maior concentração de biomassa (22%), contudo superior à obtida para a amostra com 12% de biomassa que foi de
25%, demonstrando uma baixa resistência da estrutura da amostra.
Testes preliminares de impressão 3D foram realizados para determinar a viabilidade de
impressão, demonstrando-se que o sistema desenvolvido tem características promissoras para
ser processado por esta tecnologia. Porém, são necessários ainda mais estudos para melhorar as
propriedades mecânicas, principalmente no que respeita à recuperação do material.
Hydrogels are water-absorbent polymers structured in three-dimensional networks capable of retaining water without dissolving. This characteristic gives hydrogels vast applications in the food, pharmaceutical and cosmetics industries, as they have gelling and thickening capabilities. The microalga Spirulina platensis is a widely studied cyanobacterium due to its high protein content, as well as its nutraceutical characteristics, considering the bioactive compounds present in its biomass, such as phycobiliproteins, vitamins, minerals and compounds with antioxidant capacity. The aim of this work was to study the gelling capacity and hydrogel formation of whole S. platensis biomass. Initially, a Fractional Factorial Design (FFD) was applied to assess the effects of six process variables (biomass concentration, temperature, pH, heating time, stirring time and speed) on the responses of firmness, consistency, cohesiveness and work of cohesion for the formation of gels; subsequently, a Rotational Central Composite Design (RCCD) was applied with the significant variables (pH and biomass concentration). From the statistics analyses of the experimental plans, it was possible to maximise the hydrogel formation process according to its textural characteristics, and the analysis of syneresis showed that the gels formed with higher concentrations of biomass showed less water loss due to the higher concentration of proteins. With the Fourier transform infrared analysis (FTIR) for the sample with the maximised planning factors, it was possible to identify the main bands of the functional groups present in the biomass and the hydrogel, demonstrating the groups that can influence gel formation and water absorption capacity, due to their interactions. Scanning electron microscopy and thermal stability analyses showed that the gel is possibly formed by aggregates of S. platensis biomass molecules generating the so called particulate hydrogel. Rheology and viscosity analyses were carried to compare the mechanical properties of two gels, namely a first one with a concentration of biomass of 22% and pH 5.6 (the optimal point in the plans) and the second with a concentration of biomass of 12% and pH 5.6. The analysed gels showed a load modulus higher than the loss modulus for the frequency sweep test, corroborating their elastic properties. The recovery test carried out on the samples, applying low and high shear rate cycles, showed a low recovery, namely of approximately 30 % for the sample with the highest concentration (22%) and 25% for the sample with the lowest concentration (12%), demonstrating low resistance of the formed gel structure. Preliminary 3D printing tests were carried out to determine the feasibility of printing, showing that the developed system has promising characteristics to be processed by this technology. However, studies are still needed to improve the mechanical properties, especially in what concerns the recovery of the material.
Hydrogels are water-absorbent polymers structured in three-dimensional networks capable of retaining water without dissolving. This characteristic gives hydrogels vast applications in the food, pharmaceutical and cosmetics industries, as they have gelling and thickening capabilities. The microalga Spirulina platensis is a widely studied cyanobacterium due to its high protein content, as well as its nutraceutical characteristics, considering the bioactive compounds present in its biomass, such as phycobiliproteins, vitamins, minerals and compounds with antioxidant capacity. The aim of this work was to study the gelling capacity and hydrogel formation of whole S. platensis biomass. Initially, a Fractional Factorial Design (FFD) was applied to assess the effects of six process variables (biomass concentration, temperature, pH, heating time, stirring time and speed) on the responses of firmness, consistency, cohesiveness and work of cohesion for the formation of gels; subsequently, a Rotational Central Composite Design (RCCD) was applied with the significant variables (pH and biomass concentration). From the statistics analyses of the experimental plans, it was possible to maximise the hydrogel formation process according to its textural characteristics, and the analysis of syneresis showed that the gels formed with higher concentrations of biomass showed less water loss due to the higher concentration of proteins. With the Fourier transform infrared analysis (FTIR) for the sample with the maximised planning factors, it was possible to identify the main bands of the functional groups present in the biomass and the hydrogel, demonstrating the groups that can influence gel formation and water absorption capacity, due to their interactions. Scanning electron microscopy and thermal stability analyses showed that the gel is possibly formed by aggregates of S. platensis biomass molecules generating the so called particulate hydrogel. Rheology and viscosity analyses were carried to compare the mechanical properties of two gels, namely a first one with a concentration of biomass of 22% and pH 5.6 (the optimal point in the plans) and the second with a concentration of biomass of 12% and pH 5.6. The analysed gels showed a load modulus higher than the loss modulus for the frequency sweep test, corroborating their elastic properties. The recovery test carried out on the samples, applying low and high shear rate cycles, showed a low recovery, namely of approximately 30 % for the sample with the highest concentration (22%) and 25% for the sample with the lowest concentration (12%), demonstrating low resistance of the formed gel structure. Preliminary 3D printing tests were carried out to determine the feasibility of printing, showing that the developed system has promising characteristics to be processed by this technology. However, studies are still needed to improve the mechanical properties, especially in what concerns the recovery of the material.
Description
Keywords
Biopolímeros Proteínas microbianas Compostos bioativos Propriedades tecnológicas