Propriedades termodinâmicas de adsorção de água do amido de rizomas do lírio-do-brejo (Hedychium coronarium)

Abstract

GROTH, 1991;MACEDO, 1997).No Brasil, o lírio-do-brejo é considerado uma planta exótica invasora e atualmente vêm se estudando o manejo e o controle desta praga, uma vez que a conseqüência negativa sobre as espécies nativas torna esta planta daninha nos locais onde prolifera (SANTOS; PEDRALLI; MEYER, 2005).Apresenta uma ampla utilização, principalmente farmacológica e ornamental (AGAREZ; PEREIRA; ATIDIO, 1994), no entanto, apesar do teor de amido nos rizomas do lírio-do-brejo, não há na literatura estudos sobre este amido natural, tornando-se necessárias pesquisas sobre suas propriedades termodinâmicas de adsorção de água aplicadas ao processo de secagem do amido.As propriedades termodinâmicas de adsorção de água são fundamentais para a análise de projetos de equipamentos em AbstractThermodynamic properties where determined (differential enthalpy, of differential entropy, integral enthalpy, and integral entropy) of the starch of rhizomes of swamp lily through water adsorption isotherms. The isotherms were determined in water activities in the range of 0.11 to 0.84, in temperatures ranging from 30 to 50 °C. The GAB equation which fits well to the experimental isotherms was used to estimate the properties of thermodynamic adsorption. The slight reversal of the isotherms indicates damaged starch. The enthalpy and entropy differential gap increased with the decrease in moisture and correlated to each other confirming the chemical linear compensation. An exponential model type Y = b.e (a/X e ) described adequately the dependence of these properties differential on the moisture content of balance. The integral enthalpy and entropy increased continuously with the moisture content of balance but presented negative values for the integral entropy. These thermodynamic properties of water adsorption showed that the starch extracted from the rhizomes of swamp lily has low hygroscopicity despite the occurrence of damaged starch granules.

<b>Kinetic modeling of water sorption by roasted and ground coffee

“…Figure 3 shows an increase of integral isosteric heat of sorption with decrease of equilibrium moisture content, for roasted coffee at medium and coarse particle sizes. This trend was also reported for other agricultural products (Cano-Higuita, VillaVélez, Telis-Romero, Váquiro, & Telis, 2015;Ascheri, Moura, Ascheri, & Junior, 2009;Goula, Karapantsios, Achilias, & Adamoupolos, 2008). This is because, at the beginning of sorption, there are highly active polar sites of elevated interaction energy at the product surface, which are covered with water molecules, forming a monomolecular layer.…”

Pequi pulp (Caryocar brasiliense Cambess): Drying kinetics and thermodynamic properties

“…Table 4 shows the values of the enthalpy and entropy variation and the Gibbs free energy. The calculation of these energies is relevant, since entropy and enthalpy result in Gibbs free energy, which is a thermodynamic state function representing the maximum amount of energy released in a process occurring at constant temperature and pressure that is free to perform the useful work (Ascheri et al, 2009). This study shows lower enthalpy values for higher temperatures during the drying process, indicating a smaller amount of energy required for the drying to occur at higher temperatures, that is, enthalpy decreases with increasing temperature.…”

Modelagem e propriedades termodinâmicas na secagem de morangos

“…Os valores negativos de variação de entalpia diferencial representam uma transformação exotérmica, ou seja, processo com liberação de calor. Ascheri et al (2009) encontraram valores entre -6.990,00 e 21.000,00 J mol -1 para o processo de adsorção de água em rizomas de lírio-do-brejo. Rodríguez-Bernal et al (2015) encontraram valores de variação de entalpia entre -30.000,00 e -57.416,00 J mol -1 para a adsorção de água pela polpa de borojó.…”

“…O cultivo do morango também se adapta a regiões quentes, como o cerrado (ANTUNES; REISSER JUNIOR, 2007). No Distrito Federal, ele ocupa em torno de 200 hectares e no período de safra a produção chega a 6,7 toneladas/ano, sendo a principal fonte de renda agrícola da região administrativa de Brazlândia (EMATER, 2013).…”