Moisture adsorption isotherms of the borojó fruit (Borojoa patinoi. Cuatrecasas) and gum arabic powders

Moisture Adsorption potentials and energy models of Gongronema latifolium leaves dried in separate environments

Moisture adsorption isotherm potentials and energy models of Gongronema latifolium leaf grits were investigated. Fresh leaves were dried in sun; passive solar dryer and hot air oven, while proximate composition of the dried and fresh leaves were determined using standard laboratory procedure. Equilibrium moisture content (EMC) of the leaf grits was measured using gravimetric static method. Selected mathematical and statistical models were applied on the experimental data to evaluate data fitting. Energy calculations were done based on the mathematical models. The EMCs of the leaf grits directly increased with water activity (aW) at specific temperatures. Adsorption data was better represented by GAB model than others while differential enthalpy decreased as the EMC of the oven sample increased. Differential entropy of all the samples decreased as the EMC increased. The safest monolayer moisture content varied between 7.1036 and 8.0164 gH2O/100 g solid, below 40°C, within relative humidity of 10%-50%. Sun and oven leaf grits adsorbed more moisture than solar sample. Proximate contents of the dried leaves showed higher values for protein and ash. Overall results indicated that the leaf grits when properly packaged could be used as spice or tea powder to manage household nutrient security in addition to the use as therapeutic foods.

Application of Different Compositions of Apple Puree Gels and Drying Methods to Fabricate Snacks of Modified Structure, Storage Stability and Hygroscopicity

The aim of this study was to determine the effect of incorporation of apple puree and maltodextrin to agar sol on the sorption properties and structure of the dried gel. The effect of different drying methods on the sorption behaviour of aerated apple puree gels was also observed. The gels with the addition of 25% and 40% concentration of apple puree and with or without maltodextrin were prepared and dried. The foamed agar gel was subjected to freeze-drying, air-drying and vacuum-drying. The sorption properties of dried gels (adsorption isotherms, water uptake in time) were investigated. The relations between the glass transition temperature, water activity and water content were also obtained for some apple snacks. The increase in apple puree in freeze-dried gels increased the hygroscopicity and decreased the glass transition temperature (Tg). The water content at given activity and hygroscopicity were reduced by the addition of maltodextrin, which also caused the increase in Tg. The application of different drying methods enabled obtaining different structures of material. The open-pore, fragile materials were obtained by freeze-drying, the expanded matrix with big holes was characteristic for vacuum-dried gels, but the closed pores with thick walls were created during the air-drying.

Modelagem e propriedades termodinâmicas na secagem de morangos

Resumo A secagem de produtos agrícolas é largamente utilizada no mundo para diminuir o teor de água do produto, dificultando o crescimento microbiano e a ocorrência de reações químicas e bioquímicas e possibilitando a armazenagem segura por períodos longos, além de reduzir o volume e a massa a ser transportada. O objetivo do presente trabalho foi avaliar e modelar a etapa de secagem de morangos (Fragaria L.), bem como obter parâmetros termodinâmicos em três diferentes temperaturas (40 °C, 50 °C e 60 °C). Foram utilizados frutos obtidos na CEASA-DF, com teor de água inicial de 93,0% (b.u.). Os dados experimentais foram ajustados a seis modelos matemáticos usualmente utilizados para a representação da etapa de secagem. A energia de ativação para a secagem dos morangos, a entropia, a entalpia e a energia livre de Gibbs foram obtidas. O modelo Logaritmo foi o que melhor representou a secagem de frutos de morangueiro, apresentando valores de erro médio relativo entre 7,59% e 8,48%, desvio-padrão da estimativa entre 0,03 e 0,06 e coeficiente de determinação entre 99,93% e 99,95%. A entalpia do processo de secagem diminuiu com o aumento da temperatura de secagem, com valores de –481,21, –564,35 e –647,49 J mol–1 para as temperaturas 40, 50 e 60 °C, respectivamente. O mesmo comportamento ocorreu com a entropia, com valores -238,35, -238,61 e –238,86 J mol–1 K–1, para temperaturas 40, 50 e 60 °C, respectivamente. A energia livre de Gibbs aumentou com o aumento da temperatura, atingindo valores de 74.159,75, 76.544,54 e 78.931,90 J mol–1 para as temperaturas 40, 50 e 60 °C, respectivamente.