Isolamento e caracterização do amido de castanha
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2014-01-28
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Neste trabalho foi desenvolvido um método suave de isolamento do amido de castanha envolvendo o descasque da castanha, a despelagem, o corte e a liofilização dos frutos de forma a diminuir o seu conteúdo de água e aumentar a sua estabilidade em termos de transformações físico-químicas e bioquímicas. Após liofilização as castanhas foram moídas, embebidas na solução de extracção (solução aquosa contendo 25 mM de bissulfito de sódio) e maceradas durante 1h à temperatura ambiente. Após este período, a mistura foi homogeneizada num homogeneizador Waring durante 3 min à potência máxima. O amido foi purificado por sedimentação, sendo o sobrenadante separado do depósito de amido e a mucilagem castanha presente na superfície removida. Este procedimento foi repetido oito vezes até não se observar a formação da camada mucilaginosa na superfície. O rendimento da purificação foi dependente da variedade de castanha e variou entre 50 a 70%, tendo sido obtido com elevado grau de pureza dado o seu elevado teor de amido, 80 a 93%, baixo teor em proteína (0,4 a 0,6%) e baixo teor de amido danificado (11 a 30%). O amido isolado das quatro variedades de castanha apresentou uma cristalinidade do tipo B. O grau de cristalinidade é dependente da percentagem de humidade dos amidos, variando entre ~50% para um teor de humidade de ~30% e ~10% para um teor de humidade de ~5%. Os grânulos de amido isolados da castanha apresentavam uma forma arredondada e oval irregular. A análise por ATR-FTIR mostram que os amidos de castanha isolados das variedades Judia e Martaínha apresentam um nível superior de organização da sua região mais exterior quando comparado com os amidos isolados das variedades Longal e especialmente da variedade Lada. O tamanho dos grânulos de amido isolados a partir das diferentes variedades de castanha apresentou um valor médio de 11 m, tendo-se observado diâmetro de grânulos de amido desde 4 m até 21 m.
A percentagem de amilose aparente dos amidos de castanha isolados das diferentes variedades de castanha variou entre 21,0 e 24,8%, com os amidos isolados das variedades Longal e Martaínha com um conteúdo de amilose aparente significativamente superior às outras variedades, sendo o amido isolado da variedade Judia aquele que apresentou um conteúdo de amilose aparente inferior. Para os amidos isolados das variedades Longal e Lada, o conteúdo de amilose e de amilose aparente não apresentaram diferenças significativas. No entanto para os amidos isolados das variedades Martaínha e Judia estes contem amilose complexada com lípidos (em média
~4g/100g de amido). A temperatura inicial de gelatinização variou de 56 a 58ºC, apresenta um máximo entre os 62 e 64ºC e um final de gelatinização de 66-70ºC. O amido isolado das variedades Longal e Lada apresentaram um poder de inchamento significativamente superior ao observado para as variedades Martainha e Judia. Este menor poder de inchamento destas duas últimas variedades pode ser o reflexo do seu conteúdo em amilose complexada com lípidos.
A amilopectina presente no amido isolado da variedade Longal foi a que apresentou um peso molecular superior ao das outras variedades (>4 MDa e <2MDa), apresentando-se como um único pico na região de elevado peso molecular do cromatograma. A amilopectina da variedade Lada apresentou-se também com um peso molecular homogéneo na região de elevado peso molecular, embora o seu peso molecular seja inferior ao observado para a amilopectina presente no amido isolado da variedade Longal. A amilopectina isolada da variedade Martaína apresenta uma distribuição de pesos moleculares na região de elevado peso molecular, uma população de amilopectinas com peso molecular semelhante à amilopectina da variedade Longal, e uma população mais abundante de amilopectina com peso molecular inferior a 2MDa. O mesmo acontece para a amilopectina isolada da variedade Judia, embora em termos médios a população de amilopectina de menor peso molecular é superior ao observado para a variedade Martaínha, e menor que a amilopectina isolada da variedade Lada.
Os amidos isolados das diferentes variedades de castanha apresentaram diferentes perfis viscomialográficos durante o processo de formação de pastas de amido. A temperatura de gelatinização (temperatura do início do aumento brusco da viscosidade) foi de 56,1 ºC para o amido de castanha isolado da variedade Longal, 57,4ºC para as variedades Martaínha e Lada e de 58,6ºC para o amido isolado da variedade Judia. As temperaturas de gelatinização inferiores do amido de castanha isolados da variedade Longal, mostram uma menor resistência do amido desta variedade para a gelatinização. A temperatura do máximo de viscosidade também variou significativamente entre os amidos isolados das diferentes variedades de castanha, sendo superior para o amido isolado da variedade Martaínha (85ºC), seguido das variedades Judia e Longal (78,6 e 80 ºC, respectivamente), tendo o amido isolado da variedade Lada aquele que apresentou uma menor temperatura de máximo de viscosidade (72,3ºC). A viscosidade máxima dos amidos de castanha variou entre 0,527 Pa.s para o amido de castanha isolado da variedade Judia, e 1,127 Pa.s para o amido de castanha isolado da variedade Longal. A quebra de viscosidade (uma medida da
desintegração do amido gelatinizado) foi também superior para o amido de castanha isolado da variedade Longal (0,576) e menor para o amido isolado da variedade Judia (0.159). A viscosidade final (indicativo da capacidade do amido para formar pastas viscosas) para os amidos isolados das castanhas provenientes das diferentes variedades variou entre 0,798 e 1,167, para os amidos isolados das variedades Judia e Longal, respectivamente.
Os amidos isolados das diferentes variedades de castanha apresentam diferenças na sua composição química, nomeadamente na quantidade de amilose total e presença de amilose complexada com lípidos, peso molecular da amilopectina e amilose que explicam o seu diferente comportamento quer em termos de grau de inchamento, temperaturas de gelatinização e comportamento de formação de pastas. Estas diferenças nas propriedades reológicas podem ter um impacto significativo na qualidade das castanhas após processamento térmico (assamento e cozedura), bem como no seu comportamento durante os processos tecnológicos de transformação da farinha da castanha e farinha de castanha como por exemplo na produção de marron glacé, doces e outros produtos de pastelaria.
In this work it was developed a soft method for isolation of chestnut starch involving the freeze-drying of fruits in order to reduce its water content and increase its stability in terms of physical, chemical, biochemical transformations. After freeze-drying the fruits were crushed, soaked in the extraction solution (aqueous solution containing 25 mM sodium bisulfite) and macerated for 1 h at room temperature. After this period, the mixture was homogenized in a Waring blender for 3 min at full power. Starch was purified by sedimentation, and the supernatant is separated from the deposit and the mucilage present in the top of starch sediment was removed. This procedure was repeated eight times until no more formation of the mucilaginous layer on the surface was observed. The yield of the purification was dependent on the variety of chestnut and ranged from 50 to 70%, and starch was obtained with high purity because of their high starch, 80 to 93% low protein content (0.4 to 0, 6%) and low damaged starch (11-30%). The starch isolated from four varieties of chestnut showed a type B crystallinity. The degree of crystallinity is dependent on the moisture content of the starch, ranging from ~ 50% to a moisture content of ~ 30% and ~ 10% to a moisture content of ~ 5%. The starch granules isolated from chestnut had an irregular rounded and oval shape. The analysis by ATR-FTIR show that the starches isolated from chestnut varieties Judia and Martaínha have a higher level of organization of the outermost region as compared to starch isolated from Longal varieties and especially the Lada variety. The size of the starch granules isolated from different varieties of nuts had a mean value of 11 m, and it was observed diameter of starch granules from 4 to 21 m. The percentage of apparent amylose of the starches isolated from chestnut from different varieties ranged between 21.0 and 24.8%, with varieties of starches isolated Longal and Martaínha with apparent amylose content significantly higher than other varieties, and the starch variety of isolated from Judia was variety the one that showed a lower apparent amylose content. The starch isolated from Longal and Lada varieties, didn‟t contain amylose complexed with lipids. However for starches isolated from the Martaínha and Judia varieties contains amylose complexed with lipids (average ~ 4g/100g starch). The initial temperature of gelatinization ranged from 56 to 58 º C, has a maximum between 62 and 64 º C and a final gelatinization of 66-70 º C. The isolated starch from Longal and Lada varieties showed a swelling power significantly higher than that observed for the varieties Martainha and Judia. This lower swelling power of these last two varieties may be a reflection of its content in amylose complexed with lipids. The amylopectin from the Longal variety starch showed the highest molecular weight of all the varieties studied (> 4 MDa and <2MDa), presenting himself as a single peak in the high molecular weight region of the chromatogram. The amylopectin of the Lada variety was also present as a single homogeneous peak in the high molecular weight region, though its molecular weight is lower than that observed for the amylopectin present in the starch isolated from Longal variety. The amylopectin from Martaínha variety presented a molecular weight distribution in high molecular weight region, a population of amylopectins with molecular weight similar to the Longal variety, and a more abundant population of amylopectins with a molecular weight below 2MDa. The same was observed for the amylopectin isolated from Judia variety, although in average the amylopectin population with a lower molecular weight was higher than that observed for the Martaínha variety, and less than amylopectin isolated from Lada variety. The starches isolated from different chestnut varieties showed different viscoamylographic profiles during the formation of starch pastes. The gelatinization temperature (temperature at the beginning of the sharp increase in viscosity) was 56.1 °C for the starch isolated from Longal variety, 57.4 °C for the Martaínha and Lada varieties and 58.6 °C for the starch isolated from Judia variety. The lower gelatinization temperatures of the starch isolated from Longal chestnut variety shows the lower resistance of the starch from this variety to gelatinization. The temperature of maximum viscosity also varied significantly among the starches isolated from different varieties of chestnuts, being higher for the starch isolated from the Martaínha variety (85 ºC), followed by Judia and Longal varieties (78.6 and 80 °C, respectively), and the starch isolated from Lada variety who had a lower maximum temperature viscosity (72.3 °C). The maximum viscosity of the starches pasted ranged from 0.527 Pa.s for the starch isolated from the Judia variety, and 1.127 Pa.s for the starch isolated Longal variety. The fall of viscosity (a measure of disintegration of gelatinized starch) was also higher than for starch isolated from the Longal chestnut (0.576) than for starch isolated from Judia variety (0159). The final viscosity (indicative of the ability of starch to form viscous pastes) for starches isolated from the chestnuts of the different varieties ranged from 0.798 and 1.167, for the starches isolated from Judia and Longal varieties, respectively. The starches isolated from different chestnut varieties differ in their chemical composition, notably in the total amount of amylose and presence of amylose complexed with lipids, molecular weight of amylopectin and amylose which explain their different behavior in terms of swelling index, gelatinization temperature, gelatinization behavior. These differences in rheological properties may have a significant impact on the quality of the chestnuts after thermal processing (baking and cooking), as well as their behavior during the technological processes of chestnut transformation either of chestnuts and chestnut flours, such as in the production of marron glacé , and other sweet pastries.
In this work it was developed a soft method for isolation of chestnut starch involving the freeze-drying of fruits in order to reduce its water content and increase its stability in terms of physical, chemical, biochemical transformations. After freeze-drying the fruits were crushed, soaked in the extraction solution (aqueous solution containing 25 mM sodium bisulfite) and macerated for 1 h at room temperature. After this period, the mixture was homogenized in a Waring blender for 3 min at full power. Starch was purified by sedimentation, and the supernatant is separated from the deposit and the mucilage present in the top of starch sediment was removed. This procedure was repeated eight times until no more formation of the mucilaginous layer on the surface was observed. The yield of the purification was dependent on the variety of chestnut and ranged from 50 to 70%, and starch was obtained with high purity because of their high starch, 80 to 93% low protein content (0.4 to 0, 6%) and low damaged starch (11-30%). The starch isolated from four varieties of chestnut showed a type B crystallinity. The degree of crystallinity is dependent on the moisture content of the starch, ranging from ~ 50% to a moisture content of ~ 30% and ~ 10% to a moisture content of ~ 5%. The starch granules isolated from chestnut had an irregular rounded and oval shape. The analysis by ATR-FTIR show that the starches isolated from chestnut varieties Judia and Martaínha have a higher level of organization of the outermost region as compared to starch isolated from Longal varieties and especially the Lada variety. The size of the starch granules isolated from different varieties of nuts had a mean value of 11 m, and it was observed diameter of starch granules from 4 to 21 m. The percentage of apparent amylose of the starches isolated from chestnut from different varieties ranged between 21.0 and 24.8%, with varieties of starches isolated Longal and Martaínha with apparent amylose content significantly higher than other varieties, and the starch variety of isolated from Judia was variety the one that showed a lower apparent amylose content. The starch isolated from Longal and Lada varieties, didn‟t contain amylose complexed with lipids. However for starches isolated from the Martaínha and Judia varieties contains amylose complexed with lipids (average ~ 4g/100g starch). The initial temperature of gelatinization ranged from 56 to 58 º C, has a maximum between 62 and 64 º C and a final gelatinization of 66-70 º C. The isolated starch from Longal and Lada varieties showed a swelling power significantly higher than that observed for the varieties Martainha and Judia. This lower swelling power of these last two varieties may be a reflection of its content in amylose complexed with lipids. The amylopectin from the Longal variety starch showed the highest molecular weight of all the varieties studied (> 4 MDa and <2MDa), presenting himself as a single peak in the high molecular weight region of the chromatogram. The amylopectin of the Lada variety was also present as a single homogeneous peak in the high molecular weight region, though its molecular weight is lower than that observed for the amylopectin present in the starch isolated from Longal variety. The amylopectin from Martaínha variety presented a molecular weight distribution in high molecular weight region, a population of amylopectins with molecular weight similar to the Longal variety, and a more abundant population of amylopectins with a molecular weight below 2MDa. The same was observed for the amylopectin isolated from Judia variety, although in average the amylopectin population with a lower molecular weight was higher than that observed for the Martaínha variety, and less than amylopectin isolated from Lada variety. The starches isolated from different chestnut varieties showed different viscoamylographic profiles during the formation of starch pastes. The gelatinization temperature (temperature at the beginning of the sharp increase in viscosity) was 56.1 °C for the starch isolated from Longal variety, 57.4 °C for the Martaínha and Lada varieties and 58.6 °C for the starch isolated from Judia variety. The lower gelatinization temperatures of the starch isolated from Longal chestnut variety shows the lower resistance of the starch from this variety to gelatinization. The temperature of maximum viscosity also varied significantly among the starches isolated from different varieties of chestnuts, being higher for the starch isolated from the Martaínha variety (85 ºC), followed by Judia and Longal varieties (78.6 and 80 °C, respectively), and the starch isolated from Lada variety who had a lower maximum temperature viscosity (72.3 °C). The maximum viscosity of the starches pasted ranged from 0.527 Pa.s for the starch isolated from the Judia variety, and 1.127 Pa.s for the starch isolated Longal variety. The fall of viscosity (a measure of disintegration of gelatinized starch) was also higher than for starch isolated from the Longal chestnut (0.576) than for starch isolated from Judia variety (0159). The final viscosity (indicative of the ability of starch to form viscous pastes) for starches isolated from the chestnuts of the different varieties ranged from 0.798 and 1.167, for the starches isolated from Judia and Longal varieties, respectively. The starches isolated from different chestnut varieties differ in their chemical composition, notably in the total amount of amylose and presence of amylose complexed with lipids, molecular weight of amylopectin and amylose which explain their different behavior in terms of swelling index, gelatinization temperature, gelatinization behavior. These differences in rheological properties may have a significant impact on the quality of the chestnuts after thermal processing (baking and cooking), as well as their behavior during the technological processes of chestnut transformation either of chestnuts and chestnut flours, such as in the production of marron glacé , and other sweet pastries.
Descrição
Dissertação de Mestrado em Biotecnologia e Qualidade Alimentar
Palavras-chave
Castanha , Amido