Produção e caracterização estrutural, molecular e morfológica de nanocristais a partir de diferentes amidos e sua aplicação em biofilmes
Carregando...
Arquivos
Data
2017-06-07
Autores
Costa, Mariana Souza [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
O efeito do padrão cristalino do amido na obtenção e na morfologia, características estruturais, moleculares e físico-químicas de nanocristais de amido (NCA) e sua aplicação em biofilmes foram estudados. Amidos de mandioca, milho e batata foram isolados e caracterizados. Suspensões de amido (14,7% p/v) em 3,16 M H2SO4 foram hidrolisadas durante 1, 3, 5 e 7 dias a 40 °C. As amilodextrinas obtidas foram caracterizadas quanto ao teor de amilose (titulação potenciométrica), espectroscopia vibracional por refletância total atenuada (FTIR-ATR), padrão cristalino e cristalinidade relativa (difração de raios-X), propriedades térmicas (DSC), análise termogravimétrica, distribuição das cadeias de amilodextrinas por cromatografia de troca aniônica de alta eficiência com detecção amperométrica pulsada (HPAEC-PAD), morfologia (MEV e MET) e tamanho (zetasizer). O amido de mandioca foi o mais suscetível à hidrólise devido às imperfeições na sua estrutura cristalina. Os padrões cristalinos das amilodextrinas mantiveram-se inalterados e a cristalinidade e as temperaturas de pico aumentaram com o tempo de hidrólise, enquanto a temperatura de degradação térmica diminuiu, independentemente do tempo de tratamento e da fonte de amido. As amilodextrinas (amidos de mandioca e milho) com padrão tipo A foram estrutural e termicamente mais estáveis que aquelas com padrão B (amido de batata), mas suas partículas tiveram maior tendência para aglomeração. NCA foram observados em MET a partir do terceiro dia de hidrólise nas amilodextrinas de mandioca, enquanto naquelas de milho e batata a partir do quinto dia. As amilodextrinas eram constituídas de duas estruturas com escalas micro- (partículas cristalinas) e nano- (organização das duplas hélices). Os NCA tipo A tiveram formato de plaquetas, enquanto os NCA tipo B eram redondos. NCA foram fracionados em coluna Bio-Gel P6 e frações de alto e baixo peso molecular foram coletadas. As frações I e III foram tratadas enzimaticamente (a: β-amilase seguido de isoamilase e pululanase; b: enzimas desramificantes seguido de β-amilase) e analisadas por HPAEC-PAD. Os NCA eram formados por duas populações de dextrinas compostas por cadeias lineares (grau de polimerização - GP 11-15) e uniramificadas (GP 22-25). NCA tipo A continham cadeias internas mais longas ligadas aos pontos de ramificação, as quais ficaram protegidas durante a hidrolise. NCA, independente do padrão cristalino, eram constituídos de duplas hélices estáveis formadas por cadeias com GP 10-15, porém com características distintas: enquanto NCA tipo A continham maior quantidade de ramificações localizadas principalmente na extremidade redutora de sua estrutura, os NCA tipo B tinham menos ramificações que estavam localizadas na extremidade não-redutora. A localização dos pontos de ramificação na estrutura cristalina influenciou o formato dos NCA. NCA de batata obtidos após 5 e 7 dias (BA5 e BA7) e NCA de mandioca e milho obtidos após 3 (MA3 e MI3), 5 (MA5 e MI5) e 7 (MA7 e MI7) dias de hidrólise foram adicionados em biofilmes de amido de mandioca em diferentes proporções (0, 1, 3 e 5%) que foram caracterizados. Os filmes adicionados de NCA tiveram menor teor de umidade e maior solubilidade, independente do tipo cristalino e concentração de NCA, com exceção daqueles com NCA de MI3. A adição de NCA de BA5, BA7, MA3, MA5, MI3 e MI5, independente da concentração, reduziu a permeabilidade ao vapor d’água (PVA) dos biofilmes melhorando as propriedades de barreira, enquanto NCA de MA7 e MI7 provocaram aumento na PVA devido aglomeração das partículas. A análise de componentes principais permitiu agrupar as amostras em quatro grupos de acordo com as propriedades mecânicas. Filmes adicionados de NCA 3%BA5, 5%BA7, 3%MA5, 1%MI3 e 5%MI3 se destacaram dos demais por apresentar melhores propriedades de barreira e mecânicas. A morfologia dos NCA não influenciou as propriedades mecânicas, mas a dispersão das partículas na matriz polimérica e a estabilidade das superfícies dos cristais melhoraram as forças de tensão. NCA de MI3 na concentração de 1% foi o mais adequado para serem aplicados em filmes à base de amido.
The effect of the crystalline pattern of starch on the obtainment and on the morphology, structural, molecular and physicochemical characteristics of starch nanocrystals (SNC) and their application in biofilms have been studied. The cassava, corn and potato starches were isolated and characterized. Suspensions of starch (14.7% w/v) in 3.16 M H2SO4 were hydrolyzed for 1, 3, 5 and 7 days at 40 °C. The amylodextrins obtained were characterized regarding amylose content (potentiometric titration), attenuated total reflectance vibration spectroscopy (FTIR-ATR), crystalline pattern and relative crystallinity (X-ray diffraction), thermal properties (DSC), thermogravimetric analysis, distribution of amylodextrins chains in high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), morphology (SEM and TEM) and size (zetasizer). Cassava starch was the most susceptible to hydrolysis due to imperfections in its crystalline structure. The crystalline patterns of amylodextrins kept unchanged and crystallinity and peak temperature increased with hydrolysis time, while thermal degradation temperature decreased, independently of treatment time and starch source. A-type amylodextrins (cassava and corn starches) were structurally and thermally more stable than B-amylodextrins (potato starch), but their particles had a greater tendency to agglomeration. SNC were observed by TEM from the third day of hydrolysis in cassava amylodextrins, while corn and potato amylodextrins displayed SNC only on the fifth day. The amylodextrins were formed by two structures: micro- (crystalline particles) and nano- (organization of double helices). A-type SNC displayed platelet shapes, while B-type SNC were rounded. SNC were fractionated in column of Bio-Gel P6 and the fractions of the high and low molecular weight were collected. Fractions I and III were treated enzymatically (a: β-amylase followed by isoamylase and pullulanase; b: debranching enzymes followed by β-amylase) and analyzed by HPAEC-PAD. SNC were formed by two populations of dextrins compound by linear chains (degree of polymerization - DP 11-15) and single branched (DP 22-25). A-type SNC contained inner longer chains linked to the branching points, which were protected during acid action. SNC, regardless the crystalline pattern, were compound by stable double helices formed by chains with DP 10-15, but with distinct characteristics: while SNC A-type contained a greater amount of branches located mainly in the reducing end of their structure, SNC B-type had fewer branches, which were located at the non-reducing end. The location of the branching points in the crystalline structure influenced the shape of the SNC. Potato SNC obtained after 5 and 7 days (PO5 and PO7) and cassava and corn SNC obtained after 3 (CA3 and CO3), 5 (CA5 and CO5) and 7 (CA7 and CO7) days of hydrolysis were added in biofilms of cassava starch in different proportions (0, 1, 3 and 5%) and were characterized. The films added of the SNC had lower moisture content and higher solubility, regardless the crystalline type and concentration of SNC, except for those added with CO3 SNC. The addition of SNC of PO5, PO7, CA3, CA5, CO3 and CO5, regardless concentration, reduced the water vapour permeability (WPV) of the biofilms by improving the barrier properties, while the CA7 and CO7 SNC caused increase in the WPV due to particle agglomeration. Principal component analysis allowed to group the samples into four groups according to the mechanical properties. Films added by SNC 3%PO5, 5%PO7, 3%CA5, 1%CO3 and 5%CO3 were distinguished the other SNC for presenting better barrier and mechanical properties. The morphology of the SNC did not influence the mechanical properties, but the dispersion of the particles in the polymer matrix and the stability of the crystal surfaces improved the tensile forces. The CO3 SNC at 1% concentration was the most suitable to be applied in starch-based films.
The effect of the crystalline pattern of starch on the obtainment and on the morphology, structural, molecular and physicochemical characteristics of starch nanocrystals (SNC) and their application in biofilms have been studied. The cassava, corn and potato starches were isolated and characterized. Suspensions of starch (14.7% w/v) in 3.16 M H2SO4 were hydrolyzed for 1, 3, 5 and 7 days at 40 °C. The amylodextrins obtained were characterized regarding amylose content (potentiometric titration), attenuated total reflectance vibration spectroscopy (FTIR-ATR), crystalline pattern and relative crystallinity (X-ray diffraction), thermal properties (DSC), thermogravimetric analysis, distribution of amylodextrins chains in high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), morphology (SEM and TEM) and size (zetasizer). Cassava starch was the most susceptible to hydrolysis due to imperfections in its crystalline structure. The crystalline patterns of amylodextrins kept unchanged and crystallinity and peak temperature increased with hydrolysis time, while thermal degradation temperature decreased, independently of treatment time and starch source. A-type amylodextrins (cassava and corn starches) were structurally and thermally more stable than B-amylodextrins (potato starch), but their particles had a greater tendency to agglomeration. SNC were observed by TEM from the third day of hydrolysis in cassava amylodextrins, while corn and potato amylodextrins displayed SNC only on the fifth day. The amylodextrins were formed by two structures: micro- (crystalline particles) and nano- (organization of double helices). A-type SNC displayed platelet shapes, while B-type SNC were rounded. SNC were fractionated in column of Bio-Gel P6 and the fractions of the high and low molecular weight were collected. Fractions I and III were treated enzymatically (a: β-amylase followed by isoamylase and pullulanase; b: debranching enzymes followed by β-amylase) and analyzed by HPAEC-PAD. SNC were formed by two populations of dextrins compound by linear chains (degree of polymerization - DP 11-15) and single branched (DP 22-25). A-type SNC contained inner longer chains linked to the branching points, which were protected during acid action. SNC, regardless the crystalline pattern, were compound by stable double helices formed by chains with DP 10-15, but with distinct characteristics: while SNC A-type contained a greater amount of branches located mainly in the reducing end of their structure, SNC B-type had fewer branches, which were located at the non-reducing end. The location of the branching points in the crystalline structure influenced the shape of the SNC. Potato SNC obtained after 5 and 7 days (PO5 and PO7) and cassava and corn SNC obtained after 3 (CA3 and CO3), 5 (CA5 and CO5) and 7 (CA7 and CO7) days of hydrolysis were added in biofilms of cassava starch in different proportions (0, 1, 3 and 5%) and were characterized. The films added of the SNC had lower moisture content and higher solubility, regardless the crystalline type and concentration of SNC, except for those added with CO3 SNC. The addition of SNC of PO5, PO7, CA3, CA5, CO3 and CO5, regardless concentration, reduced the water vapour permeability (WPV) of the biofilms by improving the barrier properties, while the CA7 and CO7 SNC caused increase in the WPV due to particle agglomeration. Principal component analysis allowed to group the samples into four groups according to the mechanical properties. Films added by SNC 3%PO5, 5%PO7, 3%CA5, 1%CO3 and 5%CO3 were distinguished the other SNC for presenting better barrier and mechanical properties. The morphology of the SNC did not influence the mechanical properties, but the dispersion of the particles in the polymer matrix and the stability of the crystal surfaces improved the tensile forces. The CO3 SNC at 1% concentration was the most suitable to be applied in starch-based films.
Descrição
Palavras-chave
Nanopartículas, Amido, Estrutura, Morfologia, Biofilme, Nanoparticles, Starch, Structure, Morphology, Biofilm