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Caraterização de bolotas de Quercus ilex subsp. rotundifolia ao longo de um gradiente climático no Alentejo
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Como consequência das alterações climáticas, é esperado um aumento de aridez nas zonas áridas da Bacia do Mediterrâneo. Em Portugal, estas zonas são dominadas por azinheira (Quercus ilex subsp. rotundifólia Lam.), quercínea que, a par com o sobreiro (Quercus suber L.), integram o sistema agrosilvopastoril designado de Montado (Dehesa em Espanha). Este sistema cobre a maior parte da região sul do país, o Alentejo, e providencia biodiversidade e uma diversidade de serviços de ecossistema. Contudo, nas últimas décadas tem-se vindo a assistir a um declínio do Montado, causado especialmente pelo uso insustentável do solo e agravado pelo aumento da aridez. A perda de indivíduos adultos e a falta de regeneração natural da azinheira suscitam preocupações, uma vez que esta espécie está melhor adaptada às condições mais extremas das zonas áridas. Desta forma, torna-se necessário encontrar estratégias que apoiem a regeneração da azinheira. Parte da solução passa pela sua valorização e dos seus frutos que, sendo nutricionalmente ricos, podem contribuir para uma dieta equilibrada. Atualmente, as bolotas são utilizadas principalmente para a alimentação dos porcos ibéricos, no entanto, foram usadas como parte da dieta humana durante séculos na Península Ibérica. Hoje em dia, novas receitas são criadas com bolota e esta começa novamente a usar-se como recurso alimentar para consumo humano. As bolotas de azinheira são descritas como as mais doces dentro do género Quercus em Portugal. Ainda assim, nem todas as azinheiras produzem bolota naturalmente agradável ao palato. Consta que o povo português designava de “castanholas” as bolotas que eram doces e que apresentavam uma forma mais arredondada. Neste sentido, surgiu a necessidade de compreender como reconhecer azinheiras produtoras de bolota “doce”, tendo em vista a possibilidade de aumentar o interesse no consumo deste fruto e, consequente, de aumentar a valorização da azinheira e do montado onde se insere. Os principais objetivos deste estudo visam compreender a variabilidade das bolotas no seu conteúdo em hidratos de carbono não estruturais e em fenóis totais ao longo de um gradiente de precipitação, e face a diferenças na sua forma. Isto é, perceber a tendência na perceção de doçura das bolotas num cenário de alterações climáticas. Foram recolhidas bolotas de cinco indivíduos, ao longo de um gradiente espacial macroclimático de precipitação média anual (30 anos) definido por seis locais de recolha no Alentejo (Portugal), de forma a mimetizar o aumento da aridez, consequência das alterações climáticas previstas para o nosso país. A caraterização das bolotas teve como base parâmetros morfométricos, tais como peso fresco, volume e rácio da forma. Foi também calculado para cada amostra o conteúdo hídrico médio. Os parâmetros bioquímicos determinados foram aqueles que se relacionavam mais com o sabor: os hidratos de carbono não estruturais (o amido, insolúvel, e hidratos de carbono solúveis: D-glucose, D-frutose e sacarose), responsáveis pela doçura; e os fenóis totais como forma indireta de testar o amargor das bolotas. Concluiu-se que concentrações médias mais elevadas de hidratos de carbono não estruturais, correspondem a locais com níveis de precipitação média anual inferiores. Esta tendência é devida ao decréscimo significativo das concentrações de amido e de hidratos de carbono solúveis, com o aumento da precipitação média anual, e é inversa ao que se determinou para concentrações fenólicas. Deste modo, num cenário em que a aridez se intensifique na zona sul do nosso país, os resultados obtidos sugerem que as bolotas terão maiores concentrações de amido, D-glucose e D-frutose e menores concentrações fenólicas na sua composição e, como tal, serão bolotas mais “doces”. Adicionalmente, concluiu-se que a forma das bolotas apresenta apenas, através do rácio entre o seu comprimento e diâmetro, uma ligeira tendência decrescente com a concentração fenólica total, não apresentando qualquer relação com a composição em hidratos de carbono não estruturais e, portanto, não sendo suficiente para se afirmar que bolotas mais redondas são mais “doces”, como o conhecimento empírico sugere.
As a consequence of climate change, an increase in aridity is expected in the arid areas of the Mediterranean Basin. In Portugal, these areas are dominated by holm oak (Quercus ilex subsp. rotundifolia Lam.), that together with the cork oak (Quercus suber L.), integrate the agrosilvopastoral system called Dehesa or Montado. This system covers most of the southern region of the country, Alentejo, and provides biodiversity and a diversity of ecosystem services. However, in the last decades there has been a decline of the Montado, specially caused by unsustainable land use and aggravated by the increase in aridity. The lack of natural regeneration of the holm oak raises concern, since this species is better adapted to the extreme conditions of arid areas. Therefore, it is necessary to find strategies that best support the regeneration of the holm oak. Part of the solution lies in the valorisation of this species, specially its fruits which are nutritionally rich, thus contributing to a balanced diet. Nowadays, acorns are mainly used to feed iberian pigs, however, they have been used as part of the human diet for centuries in the Iberian Peninsula. Currently, new recipes are being created and begin to support acorns as a food resource for human consumption. Holm oak acorns are described as the sweetest within the Quercus genus in Portugal. Nonetheless, not all holm oak trees produce acorns that are naturally palate-pleasing and, according to popular belief, the sweetest acorns are the roundest ones, also known as "castanholas". Therefore, it is advantageous to understand how to easily recognize which holm oak trees produce "sweet" acorns, to increase the interest in the consumption of this fruit and, consequently, increase the value of holm oak trees and the Montado. The main goals of this study were to understand the variability of the acorn content in non-structural carbohydrates and total phenols, along a precipitation gradient and, additionally, understand the variability of the acorn contents in relation to the acorns’ shape. That is, to understand the tendency of the sweetness perception for the acorns, in a scenario of climate change. Six sampling sites in Alentejo, Portugal, were defined along a macroclimatic spatial gradient of average annual precipitation (30 years) to mimic the increase in aridity. From each site, acorns from five trees were collected. The acorns characterization was based on morphometric parameters, such as fresh weight, volume, and shape ratio. The average water content was also calculated for each sample. The biochemical parameters measured were those most related to taste: non-structural carbohydrates (starch, insoluble and soluble carbohydrates: D-glucose, D-fructose and sucrose), responsible for sweetness, and total phenols as an indirect way of testing the acorns bitterness. It was concluded that higher average concentrations of non-structural carbohydrates correspond to lower average annual precipitation levels. This correlation is the same for starch and soluble carbohydrates concentrations, and is reversed for phenolic concentrations. Therefore, in a scenario of increased aridity, the results obtained suggest an increase in the concentrations of starch, D-glucose and D-fructose and a decrease in the phenolic concentrations, thus, "sweeter" acorns. Additionally, it was concluded that the acorns’ shape ratio shows a slight decreasing tendency with the increase in total phenolics, although not presenting any relation with their composition in non-structural carbohydrates and, therefore, it is not possible to state that rounder acorns are "sweeter".
As a consequence of climate change, an increase in aridity is expected in the arid areas of the Mediterranean Basin. In Portugal, these areas are dominated by holm oak (Quercus ilex subsp. rotundifolia Lam.), that together with the cork oak (Quercus suber L.), integrate the agrosilvopastoral system called Dehesa or Montado. This system covers most of the southern region of the country, Alentejo, and provides biodiversity and a diversity of ecosystem services. However, in the last decades there has been a decline of the Montado, specially caused by unsustainable land use and aggravated by the increase in aridity. The lack of natural regeneration of the holm oak raises concern, since this species is better adapted to the extreme conditions of arid areas. Therefore, it is necessary to find strategies that best support the regeneration of the holm oak. Part of the solution lies in the valorisation of this species, specially its fruits which are nutritionally rich, thus contributing to a balanced diet. Nowadays, acorns are mainly used to feed iberian pigs, however, they have been used as part of the human diet for centuries in the Iberian Peninsula. Currently, new recipes are being created and begin to support acorns as a food resource for human consumption. Holm oak acorns are described as the sweetest within the Quercus genus in Portugal. Nonetheless, not all holm oak trees produce acorns that are naturally palate-pleasing and, according to popular belief, the sweetest acorns are the roundest ones, also known as "castanholas". Therefore, it is advantageous to understand how to easily recognize which holm oak trees produce "sweet" acorns, to increase the interest in the consumption of this fruit and, consequently, increase the value of holm oak trees and the Montado. The main goals of this study were to understand the variability of the acorn content in non-structural carbohydrates and total phenols, along a precipitation gradient and, additionally, understand the variability of the acorn contents in relation to the acorns’ shape. That is, to understand the tendency of the sweetness perception for the acorns, in a scenario of climate change. Six sampling sites in Alentejo, Portugal, were defined along a macroclimatic spatial gradient of average annual precipitation (30 years) to mimic the increase in aridity. From each site, acorns from five trees were collected. The acorns characterization was based on morphometric parameters, such as fresh weight, volume, and shape ratio. The average water content was also calculated for each sample. The biochemical parameters measured were those most related to taste: non-structural carbohydrates (starch, insoluble and soluble carbohydrates: D-glucose, D-fructose and sucrose), responsible for sweetness, and total phenols as an indirect way of testing the acorns bitterness. It was concluded that higher average concentrations of non-structural carbohydrates correspond to lower average annual precipitation levels. This correlation is the same for starch and soluble carbohydrates concentrations, and is reversed for phenolic concentrations. Therefore, in a scenario of increased aridity, the results obtained suggest an increase in the concentrations of starch, D-glucose and D-fructose and a decrease in the phenolic concentrations, thus, "sweeter" acorns. Additionally, it was concluded that the acorns’ shape ratio shows a slight decreasing tendency with the increase in total phenolics, although not presenting any relation with their composition in non-structural carbohydrates and, therefore, it is not possible to state that rounder acorns are "sweeter".
Descrição
Tese de mestrado em Biologia dos Recursos Vegetais, Universidade de Lisboa, Faculdade de Ciências, 2020
Palavras-chave
Aridez Bolotas Fenóis Hidratos de Carbono Morfometria Teses de mestrado - 2020