O medronho (Arbutus unedo L.) é uma árvore ornamental comum no Mediterrâneo que produz frutos comestíveis avermelhados e doces quando maduros. As propriedades bioativas destes frutos têm sido descritas e relacionadas com a sua composição em compostos fenólicos, principalmente flavan-3-óis, tais como catequinas e procianidinas, o que torna interessante explorar esta matriz como fonte alternativa para extrair estes compostos.
O presente estudo visou otimizar as técnicas de extração de catequina a partir de frutos de A. unedo por maceração, micro-ondas e ultrassons e avaliar a estabilidade desses compostos durante os processos de armazenagem e aplicação, simulando uma matriz alimentar. Para obter as condições de maximização do rendimento da extração de catequina, utilizou-se uma metodologia de superfície de resposta.
As técnicas de extração por maceração e micro-ondas foram consideradas mais eficazes, capazes de produzir 1,38±0,1 e 1,70±0,3 mg de catequina/g matéria seca (ms), respetivamente, nas condições ótimas de extração. Essas condições foram para a maceração 93,2±3,7 min, 79,6±5,2 ºC e 23,1±3,7 % de etanol, enquanto para o micro-ondas foram 42,2±4,1 min, 137,1±8,1 ºC e 12,1±1,1 % de etanol. O sistema de extração por micro-ondas ofereceu uma resposta ótima mais rápida e com rendimentos de extração de catequina ligeiramente mais elevados do que os da maceração, mas esta necessitou de temperaturas mais baixas para atingir rendimentos de extração semelhantes. O método de extração por ultrassons foi menos eficaz em termos de rendimento de extração de catequina (0,71±0,1 mg/g em 42,4±3,6 min, 314,9±21,2 W e 40,3±3,8 % de etanol).
Foi também testada a estabilidade do extrato enriquecido em catequina (60% flavan-3-óis e 22% de catequina), obtido nas melhores condições de maceração. Assim, os extratos enriquecidos em catequina foram submetidos a estudos de estabilidade química e física, considerando as principais variáveis que afetam os compostos (tempo, temperatura e pH): i) um estudo de estabilidade dos extratos durante o armazenamento do sistema em pó; e ii) um estudo de estabilidade dos extratos em ambiente que simula um alimento (sistema de solução aquosa). Os resultados foram determinados pelo conteúdo de flavan-3-óis e catequina, utilizando HPLC-DAD, e pela atividade antioxidante dos extratos avaliada por ensaios hidrofílicos. Utilizaram-se equações mecanicistas e fenomenológicas para descrever as condições ideais para garantir a
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estabilidade de flavan-3-óis (incluindo catequina). As condições de estabilidade adequadas para o extrato em pó durante um mês foram: pH=5,4 e T=-20ºC; enquanto a sua estabilidade em solução aquosa permaneceu durante as 24h de aplicação a um pH <4 e T <30ºC. Estes resultados fornecem informações úteis para: i) potencial utilização industrial dos frutos de A. unedo como fontes alternativas de flavan-3-óis e ii) cálculos de vida de prateleira e previsões de perda de catequina em condições específicas de temperatura e pH. Finalmente, os resultados obtidos estão de acordo com estudos de estabilidade de catequina em sistemas em pó ou em solução realizados anteriormente por outros autores, mas o presente estudo valida uma nova fonte alternativa: frutos de A. unedo.
The common Mediterranean ornamental strawberry-tree (Arbutus unedo L.) produces an edible reddish sweet berry that is found to be bland and tasteless unless it is consumed overripe, otherwise it is discarded or used as basic agricultural sub residue. The bioactive properties of this fruit have been reported and related with phenolic compounds, mainly flavan-3-ols, such as catechin and procyanidins, which has opened the opportunity to exploit their extraction from alternative sources.The common Mediterranean ornamental strawberry-tree (Arbutus unedo L.) produces an edible reddish sweet berry that is found to be bland and tasteless unless it is consumed overripe, otherwise it is discarded or used as basic agricultural sub residue. The bioactive properties of this fruit have been reported and related with phenolic compounds, mainly flavan-3-ols, such as catechin and procyanidins, which has opened the opportunity to exploit their extraction from alternative sources.
This study compares and optimizes the maceration, microwave and ultrasound extraction techniques in the recovery of a catechin extract from Arbutus unedo L. fruits and evaluate the stability of flavan-3-ols during storage and application processes. To obtain conditions that maximize the catechin extraction yield, a response surface methodology was used.
Maceration and microwave extractions were found to be the most effective methods, capable of yielding 1.38±0.1 and 1.70±0.3 mg of catechin/g dry weight (dw) in the corresponding optimal extraction conditions. The optimal conditions for maceration were 93.2±3.7 min, 79.6±5.2 ºC and 23.1±3.7 % of ethanol, while for the microwave extraction were 42.2±4.1 min, 137.1±8.1 ºC and 12.1±1.1 % of ethanol. The microwave system was a quicker solution, conducting to slightly higher yields of catechin than maceration, but this one needed lower temperatures to reach similar yields. The ultrasound method was the least effective solution in terms of catechin yield extraction (0.71±0.1 mg/g at 42.4±3.6 min, 314.9±21.2 W and 40.3±3.8 %. ethanol).
The stability was tested with of the catechin-enriched extract (60% flavan-3-ols and 22% catechin), obtained under the best maceration conditions, was tested. Therefore, catechin-enriched extracts were submitted to physical and chemical stability studies, considering the main affecting variables (time, temperature and pH): i) a stability study of the extracts during storage as powder system; and ii) a stability study of the extracts in simulated food environment (aqueous solution system). The measured responses were the flavan-3-ols and catechin contents, determined by HPLC-DAD, and the antioxidant activity of the extracts evaluated by hydrophilic assays. Mechanistic and phenomenological equations were used to describe the responses, and the optimal conditions for flavan-3-ols (including catechin) stability as powder extract during a month were pH= 5.4 and T= -20ºC; while its stability in aqueous solution remained during the 24 h of application at pH<4 and T<30ºC.
This study compares and optimizes the maceration, microwave and ultrasound extraction techniques in the recovery of a catechin extract from Arbutus unedo L. fruits and evaluate the stability of flavan-3-ols during storage and application processes. To obtain conditions that maximize the catechin extraction yield, a response surface methodology was used.
Maceration and microwave extractions were found to be the most effective methods, capable of yielding 1.38±0.1 and 1.70±0.3 mg of catechin/g dry weight (dw) in the corresponding optimal extraction conditions. The optimal conditions for maceration were 93.2±3.7 min, 79.6±5.2 ºC and 23.1±3.7 % of ethanol, while for the microwave extraction were 42.2±4.1 min, 137.1±8.1 ºC and 12.1±1.1 % of ethanol. The microwave system was a quicker solution, conducting to slightly higher yields of catechin than maceration, but this one needed lower temperatures to reach similar yields. The ultrasound method was the least effective solution in terms of catechin yield extraction (0.71±0.1 mg/g at 42.4±3.6 min, 314.9±21.2 W and 40.3±3.8 %. ethanol).
The stability was tested with of the catechin-enriched extract (60% flavan-3-ols and 22% catechin), obtained under the best maceration conditions, was tested. Therefore, catechin-enriched extracts were submitted to physical and chemical stability studies, considering the main affecting variables (time, temperature and pH): i) a stability study of the extracts during storage as powder system; and ii) a stability study of the extracts in simulated food environment (aqueous solution system). The measured responses were the flavan-3-ols and catechin contents, determined by HPLC-DAD, and the antioxidant activity of the extracts evaluated by hydrophilic assays. Mechanistic and phenomenological equations were used to describe the responses, and the optimal conditions for flavan-3-ols (including catechin) stability as powder extract during a month were pH= 5.4 and T= -20ºC; while its stability in aqueous solution remained during the 24 h of application at pH<4 and T<30ºC.
