ABSTRACT
The knowledge of sorption isotherms is important for establishing conditions of storage and of processes like drying. There are several models for fitting sorption isotherms. This work presents a study about the agreement of 40 mathematical models of sorption isotherms to experimental data of 53 food products. The quadratic residual sum and the standard error were the criteria of evaluation. For the major part of the products, the best agreement was obtained with equation of Jaafar and Michalowski, if temperature or saturation pressure were not considered as a variable. For cases where temperature or saturation pressure were considered, the equation of Strohman and Yoerger was the one with the best agreement for most of the products. Ross equation, based on thermodynamics aspects, was also tested for some products, but the agreement was just satisfactory.
Subject(s)
Food Preservation , Food Storage , Food Technology , Isotherm , ThermodynamicsABSTRACT
The influence of variables as temperature, solid shape, temperature, branching and cultivar on drying of bananas were studied. Bananas from cv. Prata and D'água, on disk and cylindrical shape, blanched or not, were dehydrated in a tray dryer in natural convection at 40 and 70ºC. Drying behavior was analyzed by using a mathematical model. The exponential model showed good agreement to experimental data (r² 0.93 - 0.99 and standard error: 0.01- 0.05). Temperature presented positive influence on drying rate in all the tested conditions. With respect to the sample shape, the disk shape carried out to significantly higher drying rates only for D'água cultivar without blanching. Blanching was significantly influent, with positive influence, on drying rate of banana cv. Prata at 40º C. The influence of the cultivar did not present a defined tendency.
No presente trabalho, estudou-se a influência de variáveis como temperatura, formato do sólido, branqueamento e cultivar na secagem de bananas. Bananas cultivares Prata e D'água, nos formatos disco e cilindro, branqueadas ou não, foram desidratadas em secador de bandejas com convecção natural nas temperaturas de 40 e 70ºC. O comportamento da secagem foi analisado utilizandose modelagem matemática. O modelo exponencial mostrou bom ajuste aos resultados experimentais (r²: 0,93 - 0,99 e erro de estimativa padrão: 0,01 - 0,04). A temperatura apresentou influência positiva na taxa de secagem em todas as condições testadas. Com relação ao formato das amostras, o formato disco conduziu a taxas de secagem significativamente maiores somente para o cultivar D'água e sem branqueamento. O branqueamento se mostrou significativamente influente, com influência positiva na taxa de secagem da banana Prata a 40º C. A influência da cultivar não apresentou uma tendência definida.
ABSTRACT
This work present's a study of tomato osmotic dehidration in a NaCl solution. Solution temperature and concentration, immersion time and agitation had their influences evaluated. Kinetics of moisture content and solid gain were obtained. After the osmotic treatment, the fruits were dried (tray dryer) in a range of 40 to 60ºC in 10 hours. It was observed that temperature and agitation increases moisture reduction, but those variables are more influential on solid gain, what is not interesting. Osmotic treatment was responsible for increasing drying rate in a subsequent convective tray drying. The mathematical model used here was statistically coherent.