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Os frutos constituem uma parte essencial de uma dieta saudável e são uma fonte única de inúmeros fitoquímicos importantes para a saúde.
Os frutos são muito perecíveis, e como tal necessitam de técnicas de preservação tanto para os frutos no seu estado fresco como previamente processados. É cada vez mais importante, do ponto de vista nutricional e funcional, compreender as consequências do processamento de forma a estabelecer as melhores condições tecnológicas necessárias à preservação dos fitoquímicos.
O objectivo geral deste programa de doutoramento passa pela compreensão do efeito das variáveis de processo e armazenamento nas propriedades funcionais de frutos como o morango (rico em compostos fenólicos, em particular antocianinas) e o pêssego (rico em carotenóides e alguns fenólicos). Esta informação seria coordenada de forma a possibilitar, no futuro, maximizar o conteúdo de compostos antioxidantes com o objectivo de desenvolver um alimento funcional com propriedades específicas.
O trabalho foi desenvolvido envolvendo o estudo sobre o efeito da pasteurização, modificação dos valores de pH da matriz, atmosfera modificada, congelação de longa duração e pasteurização após a congelação em diferentes tempos de armazenamento.
Foi observado que os compostos fenólicos do morango foram mais susceptíveis de serem degradados através da pasteurização, nomeadamente antocianinas, do que os fitoquímicos do pêssego.
Armazenamento de matrizes a baixos valores de pH (2,5) permitiram obter uma maior estabilidade nas antocianinas no morango, enquanto os carotenóides do pêssego foram melhor preservados a valores de pH intermédios (3,0 e 3,5). No pêssego, elevados valores de pH como 4,5 permitiram obter maior concentração dos ácidos neoclorogénico e clorogénico.
Relativamente às atmosferas modificadas testadas, baixa concentração de oxigénio foi a melhor condição para a preservação dos fitoquímicos de ambos os frutos testados, nomeadamente, 100 kPa N2, permitiu obter maior concentração de antocianinas no morango e carotenóides no pêssego.
Longos períodos de armazenamento (90 dias a 4 e 23 ºC) e temperaturas mais elevadas (23 ºC) tiveram impacto negativo na concentração dos fitoquímicos.
Frutos utilizados no processamento industrial são geralmente armazenados em condições de congelação, chegando a atingir períodos de 360 dias. O processo de congelação permitiu obter um maior extratibilidade de alguns fitoquímicos que por sua vez ficaram mais expostos à degradação através do tratamento térmico que se segue ao processo de congelação.
Quando analisado todo o processo industrial como um todo, as alterações no conteúdo de fitoquímicos foram mais reduzidas do que aquelas observadas para cada variável analisada individualmente. A adição de ingredientes na fase de formulação pode aumentar o potencial fitoquímico e o tempo de armazenamento que se segue aos tratamentos sequenciais afectaram de forma mais intensa os compostos fenólicos do morango ((+)-catequina, pelargonidina-3-glucósido e pelargonidina-3-rutenósido) e nos carotenóides do pêssego.
A fase final do processamento industrial passa pela incorporação dos preparados de frutos em matrizes alimentares. Os compostos fenólicos quando incorporados em produtos lácteos como o iogurte interagem com as proteínas do leite nomeadamente, β-lactoglobulina (β-LG) e polissacáridos normalmente adicionados aos preparados de fruta como estabilizantes. Para melhor compreender como esta interacção entre os componentes pode afectar a biodisponibilidade e o potencial dos compostos antioxidantes, sistema modelo de misturas de polifenól-proteína-polissacárido ((+)-catequina/cianidina-3-glucósido-β-LG-pectina/quitosano) foram estudados. A pectina demonstrou ter um impacto crucial na diminuição da concentração de fenólico livre e no seu potencial antioxidante.
No entanto, quando as misturas modelo e os iogurtes de fruta foram submetidos ao sistema gastrointestinal in vitro, uma maior bioacessibilidade dos compostos fenólicos foi observada na presença de proteínas e polissacáridos. Isto significa que os componentes alimentares podem formar complexos com os polifenóis dos frutos conferindo protecção da degradação através do processo digestivo tornando os polifenóis mais biodisponíveis.
Baseado nestes resultados a indústria dos processados de fruta pode prever e melhorar o impacto das variáveis de processo nas propriedades funcionais de morango e pêssego processado.
Fruits are an essential part of a healthy diet and carrier of a number of unique health promoting phytochemicals. Being very perishable, fruit require preservation, both as fresh or processed foods. From nutritional and functional point of view is important to understand the consequences of processing in food composition in order to select the best technological conditions required for the preservation of fruit health benefits. The general objective of this Ph.D. programme was to understand the effect of factors related to fruit processing and storage on the nutritive and functional properties of fruits — strawberry (rich in phenolic compounds, in particular anthocyanins) and peach (rich in carotenoids with some phenolic compounds). This information was integrated to in future optimize processing conditions that maximize the content of beneficial antioxidants compounds aiming the development of functional food with specific properties. The work was performed involving the study of pasteurization, matrix pH modification, modified atmosphere, long term storage after freezing and pasteurization of frozen fruit at different points of storage. It was possible to observe that strawberry polyphenols were more susceptible to degradation by pasteurization than peach phytochemicals, mainly due to anthocyanins. Storage under low conditions of pH (2.5) allowed to obtain higher stability of strawberries anthocyanins, while intermediate pH of about 3.0 and 3.5 were the best conditions for peach carotenoids stability and higher pH values of 4.5 led to higher content of neochlorogenic and chlorogenic acid on peach. In general, the low content of oxygen was the best condition for phytochemicals preservation, mainly 100 kPa N2 for anthocyanins and carotenoids. Long storage periods (90 d at 4 ºC and 23 ºC) showed a decrease on the content of all phytochemicals, at higher rate when temperatures where higher (23 ºC) as expected. Fruit used in processing can be stored under frozen conditions, reaching periods of 360 d. This process permited easier extractability for some phytochemicals increasing them, but became more susceptible to degradation by pasteurization. When looking to the industrial process as a whole, the phytochemicals content changes observed were lower than variables analysed independently. The addition of non-fruit food ingredients may enhance in general the phytochemical content and the storage time after the sequential treatments affected more strongly strawberry phenolics ((+)-catechin, pelargondin-3-glucoside and pelargonidin-3-rutinoside) and peach carotenoids. The final step of processing encompasses the incorporation of fruit preparates in dairy matrices. Fruit polyphenols when incorporated in yoghurt interacted with milk proteins namely β-lactoglobulin (β-LG) and with polysaccharides typically added to fruit formulations as stabilisers. To understand how their interaction limits the polyphenol bioacessibility and their potential as antioxidant compounds the model mixtures of polyphenol-protein-polyssacharide ((+)-catechin/cyanidin-3-glucoside-β-LG-pectin/chitosan) were studied. Pectin was proved to have a detrimental impact in decreasing significantly the phenolic content and consequently its antioxidant activity. However, when the model mixtures and fruit yoghurt where subjected to simulated gastrointestinal system, polyphenols revealed a higher bioaccessibility when in the presence of protein and polyssacharide. This means that food components may form complexes with polyphenols that allow protection from degradation trough the digestive process making them more bioavailable. Based on these results the industries can predict and improve the impact of these factors on the functional properties of processed strawberries and peaches.
Fruits are an essential part of a healthy diet and carrier of a number of unique health promoting phytochemicals. Being very perishable, fruit require preservation, both as fresh or processed foods. From nutritional and functional point of view is important to understand the consequences of processing in food composition in order to select the best technological conditions required for the preservation of fruit health benefits. The general objective of this Ph.D. programme was to understand the effect of factors related to fruit processing and storage on the nutritive and functional properties of fruits — strawberry (rich in phenolic compounds, in particular anthocyanins) and peach (rich in carotenoids with some phenolic compounds). This information was integrated to in future optimize processing conditions that maximize the content of beneficial antioxidants compounds aiming the development of functional food with specific properties. The work was performed involving the study of pasteurization, matrix pH modification, modified atmosphere, long term storage after freezing and pasteurization of frozen fruit at different points of storage. It was possible to observe that strawberry polyphenols were more susceptible to degradation by pasteurization than peach phytochemicals, mainly due to anthocyanins. Storage under low conditions of pH (2.5) allowed to obtain higher stability of strawberries anthocyanins, while intermediate pH of about 3.0 and 3.5 were the best conditions for peach carotenoids stability and higher pH values of 4.5 led to higher content of neochlorogenic and chlorogenic acid on peach. In general, the low content of oxygen was the best condition for phytochemicals preservation, mainly 100 kPa N2 for anthocyanins and carotenoids. Long storage periods (90 d at 4 ºC and 23 ºC) showed a decrease on the content of all phytochemicals, at higher rate when temperatures where higher (23 ºC) as expected. Fruit used in processing can be stored under frozen conditions, reaching periods of 360 d. This process permited easier extractability for some phytochemicals increasing them, but became more susceptible to degradation by pasteurization. When looking to the industrial process as a whole, the phytochemicals content changes observed were lower than variables analysed independently. The addition of non-fruit food ingredients may enhance in general the phytochemical content and the storage time after the sequential treatments affected more strongly strawberry phenolics ((+)-catechin, pelargondin-3-glucoside and pelargonidin-3-rutinoside) and peach carotenoids. The final step of processing encompasses the incorporation of fruit preparates in dairy matrices. Fruit polyphenols when incorporated in yoghurt interacted with milk proteins namely β-lactoglobulin (β-LG) and with polysaccharides typically added to fruit formulations as stabilisers. To understand how their interaction limits the polyphenol bioacessibility and their potential as antioxidant compounds the model mixtures of polyphenol-protein-polyssacharide ((+)-catechin/cyanidin-3-glucoside-β-LG-pectin/chitosan) were studied. Pectin was proved to have a detrimental impact in decreasing significantly the phenolic content and consequently its antioxidant activity. However, when the model mixtures and fruit yoghurt where subjected to simulated gastrointestinal system, polyphenols revealed a higher bioaccessibility when in the presence of protein and polyssacharide. This means that food components may form complexes with polyphenols that allow protection from degradation trough the digestive process making them more bioavailable. Based on these results the industries can predict and improve the impact of these factors on the functional properties of processed strawberries and peaches.