Efeitos de modificações físicas sobre as propriedades de amido de tuberosas
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Data
2016-02-29
Autores
Santos, Thaís Paes Rodrigues dos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Amidos pré-gelatinizados podem ser usados em aplicações de produtos de conveniência pela indústria de alimentos, pois apresentam maior solubilidade em água fria e menor temperatura de gelatinização. As modificações físicas por spray drying e por extrusão são métodos que podem resultar em alterações na região cristalina, com mudanças nas propriedades térmicas e de pasta dos amidos. Objetivou-se neste trabalho verificar as alterações estruturais e funcionais provocadas, pelos métodos de modificações físicas citados, nos amidos de mandioca, mandioquinha-salsa e batata-doce. A modificação por spray drying foi realizada com aquecimento da suspensão à 57 °C e concentração de 8 % de amido, com temperatura de saída e vazão no spray dryer, respectivamente, de 105 °C e 0,5 L h-1. A modificação por extrusão foi realizada no amido a 20 % de umidade, temperaturas de 25, 50 e 75 ºC, respectivamente, na 1a zona, 2ª zona e 3ª zona do extrusor e rotação de 245 rpm. Após a finalização deste experimento, os resultados evidenciaram que a modificação por spray drying provocou alterações menos severas nas características dos amidos estudados. Sendo assim, foi realizado um segundo experimento com os amidos de mandioca e batata-doce a fim de determinar as melhores condições de processo da modificação por spray drying, seguindo planejamento experimental central composto rotacional nos dois ensaios experimentais. Os amidos modificados no primeiro experimento foram analisados em relação as características estruturais e propriedades de pasta e térmica. A modificação por spray drying não provocou alterações no teor de amilose, massa molecular e raio médio de giro, assim como na distribuição dos comprimentos das cadeias ramificadas de amilopectina, mostrando que não houve degradação das ligações glicosídicas. Houve redução dos picos do padrão de difração de Raios X dos amidos, refletindo na diminuição na cristalinidade relativa. A morfologia dos grânulos apresentou aglomerados para os amidos de mandioca e mandioquinha-salsa, indicando gelatinização parcial dos grânulos. O amido de mandioquinha-salsa modificado por spray drying apresentou aumento na viscosidade a frio e diminuição da viscosidade de pico e final. Para todos os amidos, houve aumento no setback (tendência a retrogradação). As temperaturas de gelatinização não sofreram alterações significativas, porém a variação da temperatura diminuiu, assim como a variação da entalpia. Os amidos modificados por extrusão não apresentaram alteração no teor de amilose e na distribuição dos comprimentos das cadeias ramificadas da amilopectina, no entanto, houve alteração na massa molecular e no raio médio de giro, indicando provável rompimento das ligações glicosídicas. Os amidos modificados por extrusão apresentaram redução total dos picos do padrão de difração dos amidos, indicando total gelatinização. Nas imagens de microscopia eletrônica de varredura não foram observados grânulos para todos os tratamentos, confirmando a gelatinização total do amido com perda da estrutura granular durante o processo de extrusão, o que também foi observado pela ausência de curva de gelatinização na análise de propriedade térmica. Tais alterações levaram a um aumento na viscosidade a frio. As modificações por spray drying e extrusão resultam em amidos com diferentes propriedades, sendo que o amido modificado por spray drying seria indicado para produtos que necessitem de consistência mais firme, enquanto o amido modificado por extrusão seria indicado para produtos com viscosidade a frio e com consistência mais fluída. Em relação aos amidos estudados, o amido de mandioquinha-salsa apresentou maior sensibilidade ao processo, devido sua temperatura de gelatinização ser próxima às temperaturas utilizadas, e também, pelo defeito na área cristalina. Os resultados obtidos no segundo experimento evidenciaram que as melhores condições de modificação dos amidos de mandioca e de batata-doce por spray drying são: alta temperatura (60 °C) e baixa concentração (5 %). Nas condições citadas, podem ser obtidos amidos modificados por spray drying com boas características de pasta e térmica, como leve viscosidade a frio, consistência no produto final e temperatura de gelatinização uniforme, refletindo em melhor utilização de energia no processo.
Pregelatinized starches can be used in applications of convenience products by the food industry, since they have greater solubility in cold water and low gelatinization temperature. The physical modification by spray drying and extrusion are methods which can result in changes in the crystalline region, with changes in the thermal and pasting properties of starch. The aim of this work was to verify the structural and functional changes caused by physical modification methods mentioned in starches from cassava, Peruvian carrot and sweet potato. The modification by spray drying was performed using temperature of 57 °C and concentration of 8 %, with outlet temperature and feed rate in spray dryer of 105 °c and 0.5 L h-1, respectively. The modification by extrusion was carried out with 20 % of starch moisture, with temperatures of 25 °C, 50 °C and 75 °C in the 1st zone, 2nd zone and 3rd zone respectively, and rotation 245 rpm. After completion of this experiment, the results show that the modification by spray drying caused less severe changes in the characteristics of the studied starches. Thus, it was conducted a second experiment with starches from cassava and sweet potato, in order to determine the best process conditions of modification by spray drying, following experimental design central composite rotational in both experimental tests. The modified starches of the first experiment were analyzed for structural characteristics and thermal and pasting properties. The modification by spray drying caused no changes in the amylose content, molecular weight and the average gyration radius, and distribution branch chains-length of amylopectin showing that there was no degradation of glycosides bonds. There was reduction of the peaks of the diffraction pattern of starches, reflecting in decrease of relative crystallinity. The morphology of the granules showed agglomerates for the starches of cassava and Peruvian carrot, indicating partial gelatinization of the granules. Modified starch of Peruvian carrot by spray drying showed increase in cold viscosity and decrease in peak and final viscosity. For all starches, there was increase in setback. The temperatures of gelatinization no showed significant changes, although the temperature range decrease, as well as the enthalpy change. Modified starches by extrusion no show change in the amylose content and the distribution of branch chains-length of amylopectin, however, changes were observed in the molecular weight and the average gyration radius, indicating likely breaking of glycosidic bonds. Modified starches by extrusion showed total reduction in peaks of the diffraction pattern of the starches, indicating complete gelatinization of starches. In scanning electron microscopy observed no granules, confirming complete gelatinization of the starch, with loss of granular structure during the extrusion process, which also were observed by absence of gelatinization curve in thermal analysis. These changes leaded to increase of cold viscosity. The modifications by spray drying and extrusion resulted in starches with different properties, being the modified starch by spray drying can be indicated to apply in products that need of firmness consistency, and the modified starch by extrusion may be indicated to apply in products with cold viscosity and less consistency. Among of studied starches, Peruvian carrot starch showed be more susceptible for both process, due to its gelatinization temperature to be near the temperatures used in these experiments, and due to its defect in crystalline area. The results obtained in the second experiment show that the best conditions for modification of starches of cassava and sweet potato by spray drying are: high temperature (60 °C) and low concentration (5%). In these conditions can be obtained modified starches by spray drying with good pasting and thermal properties, as the cold viscosity, consistency in final product and gelatinization temperature uniform between the granules, reflecting in better utilization of energy by process.
Pregelatinized starches can be used in applications of convenience products by the food industry, since they have greater solubility in cold water and low gelatinization temperature. The physical modification by spray drying and extrusion are methods which can result in changes in the crystalline region, with changes in the thermal and pasting properties of starch. The aim of this work was to verify the structural and functional changes caused by physical modification methods mentioned in starches from cassava, Peruvian carrot and sweet potato. The modification by spray drying was performed using temperature of 57 °C and concentration of 8 %, with outlet temperature and feed rate in spray dryer of 105 °c and 0.5 L h-1, respectively. The modification by extrusion was carried out with 20 % of starch moisture, with temperatures of 25 °C, 50 °C and 75 °C in the 1st zone, 2nd zone and 3rd zone respectively, and rotation 245 rpm. After completion of this experiment, the results show that the modification by spray drying caused less severe changes in the characteristics of the studied starches. Thus, it was conducted a second experiment with starches from cassava and sweet potato, in order to determine the best process conditions of modification by spray drying, following experimental design central composite rotational in both experimental tests. The modified starches of the first experiment were analyzed for structural characteristics and thermal and pasting properties. The modification by spray drying caused no changes in the amylose content, molecular weight and the average gyration radius, and distribution branch chains-length of amylopectin showing that there was no degradation of glycosides bonds. There was reduction of the peaks of the diffraction pattern of starches, reflecting in decrease of relative crystallinity. The morphology of the granules showed agglomerates for the starches of cassava and Peruvian carrot, indicating partial gelatinization of the granules. Modified starch of Peruvian carrot by spray drying showed increase in cold viscosity and decrease in peak and final viscosity. For all starches, there was increase in setback. The temperatures of gelatinization no showed significant changes, although the temperature range decrease, as well as the enthalpy change. Modified starches by extrusion no show change in the amylose content and the distribution of branch chains-length of amylopectin, however, changes were observed in the molecular weight and the average gyration radius, indicating likely breaking of glycosidic bonds. Modified starches by extrusion showed total reduction in peaks of the diffraction pattern of the starches, indicating complete gelatinization of starches. In scanning electron microscopy observed no granules, confirming complete gelatinization of the starch, with loss of granular structure during the extrusion process, which also were observed by absence of gelatinization curve in thermal analysis. These changes leaded to increase of cold viscosity. The modifications by spray drying and extrusion resulted in starches with different properties, being the modified starch by spray drying can be indicated to apply in products that need of firmness consistency, and the modified starch by extrusion may be indicated to apply in products with cold viscosity and less consistency. Among of studied starches, Peruvian carrot starch showed be more susceptible for both process, due to its gelatinization temperature to be near the temperatures used in these experiments, and due to its defect in crystalline area. The results obtained in the second experiment show that the best conditions for modification of starches of cassava and sweet potato by spray drying are: high temperature (60 °C) and low concentration (5%). In these conditions can be obtained modified starches by spray drying with good pasting and thermal properties, as the cold viscosity, consistency in final product and gelatinization temperature uniform between the granules, reflecting in better utilization of energy by process.
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Palavras-chave
Manihot esculenta, Arracacia xanthorrhiza, Ipoema batatas, Gelatinização, Extrusão, Spray dryer, Gelatinization, Extrusion