Melanoidinas das infusões de café arábica vs robusta. Caracterização química
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2017-08-30
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A natureza química das melanoidinas embora não totalmente conhecida inclui polissacarídeos, proteínas e compostos fenólicos. Trabalhos anteriores demonstraram que os compostos fenólicos incorporados nas melanoidinas do café estão numa forma condensada e esterificada, com uma grande abundância de compostos fenólicos numa forma condensada, sendo a quantidade de compostos fenólicos incorporados dependente da quantidade de compostos fenólicos presentes no café. Tipicamente os cafés robusta apresentam uma quantidade de ácidos clorogénicos superiores aos cafés arábica e um menor conteúdo de sacarose. Neste trabalho foram selecionados dois cafés, um arábica e um robusta apresentando níveis de ácidos clorogénicos e de sacarose diferentes, e a incorporação de compostos fenólicos na melanoidinas dos dois cafés foi avaliada. Após a preparação das infusões de café, o material de alto peso molecular (HMWM) foi isolado por diálise. Os principais componentes presentes no HMWM foram os polissacarídeos, presentes em maior quantidade no café robusta (46.2g/100g) quando comparado com o café arábica (37.2g/100g), seguido pelo conteúdo de proteína (12%) não havendo diferenças significativas entre as duas espécies de café, e os compostos fenólicos incorporados no HMWM do café robusta foi significativamente superior ao incorporado no café arábica (8.9% e ~5.8%, respectivamente). A quantidade de ácido quínico recuperado por metanólise correspondeu a 2.27% para o café robusta e 0.92% para o café arábica. O café arábica apresentou um valor superior de material desconhecido (51,5%) quando comparado com o café robusta (41,5%), sendo que a cor recuperada no HMWM correspondeu a 45% e 56% da cor presente nos sólidos totais, apresentado um “melanoidin brwoning índex” inferior (-31%) ao do café robusta. Os resultados obtidos suportam os resultados obtidos anteriormente de que quanto maior o conteúdo de ácidos clorogénicos presentes no café verde maior a quantidade de compostos fenólicos incorporados nas melanoidinas.
De forma a aprofundar a estrutura dos compostos fenólicos presentes nas melanoidinas de café foi aplicado a metanólise, método este capaz de hidrolisar ligações ester e glicosídicas. Os resultados obtidos permitiram demonstrar pela primeira vez a presença de quantidades significativas de compostos fenólicos ligados glicosidicamente às melanoidinas dos cafés (34% dos compostos fenólicos libertados por fusão alcalina), sendo estes libertados como ácido cafeico e acido ferúlico intactos, confirmando os resultados previamente obtidos em estudos modelo. A quantidade de ácido quínico
libertado por metanólise é maior no café robusta quando comparada com o café arábica correspondente a 0,65 mol / mol em relação aos compostos fenólicos recuperados por metanólise para o café Robusta e 0,35 mol / mol para o café Arábica. Esta diferença de compostos fenólicos incorporados nas melanoidinas do café de ambas as espécies estão de acordo com a atividade antioxidante das melanoidinas de ambos os cafés e também com o seu valor de Kmix a 280 e 325 nm.
Os resultados obtidos neste trabalho são uma contribuição significativa para o entendimento do mecanismo de formação das melanoidinas do café e o seu possível impacto em termos de saúde do consumidor, dada a importância das melanoidinas para a actividade antioxidante das bebidas de café.
The chemical nature of melanoidins although not fully known include polysaccharides, proteins and phenolic compounds. Previous work has shown that phenolic compounds incorporated into a coffee melanoidins are present in condensed and esterified forms, with a higher abundance of phenolic compounds in condensed form, and that the amount of phenolic compounds incorporated depend upon the amount of phenolic compounds present in coffee. Robusta coffees typically have a higher amount of chlorogenic acids when compared to Arabica coffees and a lower sucrose content. In this work we selected two coffees an arabica and a robusta coffee having typical levels of chlorogenic acids and of sucrose, and the incorporation of phenolic compounds into coffee melanoidins for the two coffees was evaluated. After preparation of coffee infusions, the high molecular weight material (HMWM) was isolated by dialysis. The major components present in the HMWM were polysaccharides, present in higher amounts in the robusta coffee (46.2g / 100g) when compared to Arabica coffee (37.2g / 100g), followed by protein (12%) with no significant differences between the two coffee species, and the amount of phenolic compounds incorporated into the robusta coffee HMWM was significantly higher when compared to arabica coffee (~ 8.9% and 5.8%, respectively). The amount of quinic acid recovered by methanolysis corresponded to 2.27% for robusta and 0.92% for Arabica coffees. Arabica coffee showed a higher amount of unknown material (51.5%) compared with the robusta coffee (41.5%), and the color recovered in the HMWM corresponded to 45% and 56% of the color of the total solids, presenting a “melanoidin browning index " lower (-31%) than that of robusta coffee. These results support the previous results that the higher the content of chlorogenic acids present in green coffee the greater the amount of phenolic compound incorporated into melanoidins. In order to deepen our understanding on the structure of phenolic compounds present in coffee melanoidins, methanolysis was applied to melanoidins. This method is capable of hydrolysing ester bonds and glyosidic bonds. The results allowed to demonstrate for the first time the presence of significant amounts of phenolic compounds glycosidically linked to coffee melanoidins (34% of phenolic compounds released by alkaline fusion), which are released as intact caffeic and ferulic acids, confirming the results previously obtained in model studies. The amount of quinic acid released by methanolysis in robusta coffee is greater compared with the corresponding arabica coffee corresponding to 0.65 mol / mol with respect to the phenolic compounds recovered by methanolysis for Robusta coffee and 0.35 mol / mol to Arabica. This difference of phenolic compounds incorporated in coffee melanoidins for both species are in accordance with their antioxidant activity, and also the value of KMIX 280 and 325 nm. The results of this work are a significant contribution to the understanding of the formation mechanism of the coffee melanoidins and their possible impact on consumer health, given the importance of melanoidins to the antioxidant activity of coffee drinks.
The chemical nature of melanoidins although not fully known include polysaccharides, proteins and phenolic compounds. Previous work has shown that phenolic compounds incorporated into a coffee melanoidins are present in condensed and esterified forms, with a higher abundance of phenolic compounds in condensed form, and that the amount of phenolic compounds incorporated depend upon the amount of phenolic compounds present in coffee. Robusta coffees typically have a higher amount of chlorogenic acids when compared to Arabica coffees and a lower sucrose content. In this work we selected two coffees an arabica and a robusta coffee having typical levels of chlorogenic acids and of sucrose, and the incorporation of phenolic compounds into coffee melanoidins for the two coffees was evaluated. After preparation of coffee infusions, the high molecular weight material (HMWM) was isolated by dialysis. The major components present in the HMWM were polysaccharides, present in higher amounts in the robusta coffee (46.2g / 100g) when compared to Arabica coffee (37.2g / 100g), followed by protein (12%) with no significant differences between the two coffee species, and the amount of phenolic compounds incorporated into the robusta coffee HMWM was significantly higher when compared to arabica coffee (~ 8.9% and 5.8%, respectively). The amount of quinic acid recovered by methanolysis corresponded to 2.27% for robusta and 0.92% for Arabica coffees. Arabica coffee showed a higher amount of unknown material (51.5%) compared with the robusta coffee (41.5%), and the color recovered in the HMWM corresponded to 45% and 56% of the color of the total solids, presenting a “melanoidin browning index " lower (-31%) than that of robusta coffee. These results support the previous results that the higher the content of chlorogenic acids present in green coffee the greater the amount of phenolic compound incorporated into melanoidins. In order to deepen our understanding on the structure of phenolic compounds present in coffee melanoidins, methanolysis was applied to melanoidins. This method is capable of hydrolysing ester bonds and glyosidic bonds. The results allowed to demonstrate for the first time the presence of significant amounts of phenolic compounds glycosidically linked to coffee melanoidins (34% of phenolic compounds released by alkaline fusion), which are released as intact caffeic and ferulic acids, confirming the results previously obtained in model studies. The amount of quinic acid released by methanolysis in robusta coffee is greater compared with the corresponding arabica coffee corresponding to 0.65 mol / mol with respect to the phenolic compounds recovered by methanolysis for Robusta coffee and 0.35 mol / mol to Arabica. This difference of phenolic compounds incorporated in coffee melanoidins for both species are in accordance with their antioxidant activity, and also the value of KMIX 280 and 325 nm. The results of this work are a significant contribution to the understanding of the formation mechanism of the coffee melanoidins and their possible impact on consumer health, given the importance of melanoidins to the antioxidant activity of coffee drinks.
Descrição
Dissertação de Mestrado em Biotecnologia e Qualidade Alimentar
Palavras-chave
Café , Composto fenólico , Melanoidinas