Comportamento das isotermas de adsorção do pó da polpa de manga liofilizada

Abstract

RESUMOA qualidade e a vida útil dos pós de frutas dependem de seus teores de água e da maneira como esta se encontra ligada ao alimento. O comportamento higroscópico de alimentos em pó pode ser avaliado através de suas isotermas de sorção. O objetivo deste trabalho foi avaliar modelos matemáticos para representação da isoterma de sorção do pó de manga liofilizada e avaliar as características físico-químicas da polpa de manga in natura e seu pó liofilizado. Foram feitas as análises de umidade, pH, sólidos solúveis, acidez total titulável, ácido ascórbico e cor. Os modelos matemáticos ajustados aos dados experimentais foram BET, GAB, Henderson e Oswin nas temperaturas de 25, 30 e 35 ºC. O melhor ajuste aos dados experimentais foi obtido pelo modelo de GAB. O modelo de GAB apresentou erros médios de 4,092 a 5,175% e valores de R 2 entre 0,9986 a 0,9993 para as temperaturas estudadas. As isotermas do pó da polpa de manga liofilizada apresentaram formato característico do tipo III. Palavras-chave: higroscopicidade, secagem, pó de frutasBehavior of adsorption isotherms of freeze-dried mango pulp powder ABSTRACT The content of water and how it binds to food influence the quality and shelf life of fruit powder. The hygroscopic behavior of powder food can be evaluated by the study of moisture sorption isotherms. This study aimed to evaluate some mathematical models to represent the sorption isotherm of freeze-dried mango pulp powder and to evaluate physicochemically mango pulp and mango pulp powder. The analyses were moisture, pH, total soluble solids, total titratable acidity, ascorbic acid and color. The models adjusted to data were BET, GAB, Henderson and Oswin models at 25, 30 and 35 °C. The GAB model showed the best fit. The GAB model showed mean errors of 4.092 to 5.175% and R 2 values from 0.9986 to 0.9993 for the all temperatures. The isotherms of freeze-dried mango pulp showed characteristic shape of type III.

Hygroscopic behavior of lyophilized acerola pulp powder

“…Similarly, Oliveira et al (2011) observed higher moisture content in the molecular monolayer (Xm) for the model of BET, for the lyophilized sapodilla powder. Moreira et al (2013) also observed increase in temperature as a predominant factor for the increment of moisture contents in the monolayer (Xm) through the models of GAB and BET, similar to the result of the present study.…”

“…Moreira et al (2013) claim that this reduction in C values is expected and cite that low temperatures favor the force of interaction between adsorbate-adsorbent, favoring an increment in the values of the constant C. Figure 1 shows that the obtained isotherm is of type III, according to the classification of Braunauer (Andrade et al, 2011). The typical form of an isotherm reflects the form in which it connects to the system, so that the weaker interactions with water molecules generate higher water activity; thus, the product becomes more unstable (Andrade et al, 2011).…”

“…According to Moreira et al (2013), through the GAB and BET models adjusted for obtaining isotherms, it is possible to evaluate the moisture content of the monolayer (X m ) of foods, allowing a physical knowledge on the adsorption theory. The molecular monolayer is the primary layer of the food and its water content interferes with the hygroscopicity or affinity of the molecules to water.…”

“…(1), which was also used by Moreira et al (2013): Table 1. Saturated saline solution and water activity of the cell according to the temperature where:…”

Adsorption isotherms of the red mombin powder produced in spouted bed dryer

“…In the model of Oswin, the lowest value of the constant 'a' (17.5067) and highest value of 'b' (0.5943) were obtained at the temperature of 30 ºC, which was also observed by Moreira et al (2013), analyzing the hygroscopic behavior of mango powder obtained through lyophilization. According to Alcântara et al (2009), for a good representation of the adsorption isotherms of a food, the values of the parameter 'a' in the Oswin model must be higher than zero and those of 'b' must be between zero and 1.0; this model satisfactorily fitted to the experimental data.…”