Calor específico e densidade da polpa de cajá (Spondias lutea L.) com diferentes concentrações de sólidos solúveis sob baixas temperaturas
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Data
2005-08-01
Autores
Mata, Mario E. R. M. Cavalcanti
Duarte
Zanini, Helen L. H. T. [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Associação Brasileira de Engenharia Agrícola (SBEA)
Resumo
A polpa de cajá tem sido exportada da região Nordeste para todo o Brasil, e uma das maneiras de conservá-la é processando-a e armazenado-a na forma congelada. Durante o processamento, existem dois fatores que favorecem a qualidade do produto a ser armazenado: a rapidez com que o produto é congelado e a adição de açúcar como forma de dificultar a ação microbiológica. Na linha de processo, algumas propriedades termofísicas, como o calor específico e a densidade, se alteram com as temperaturas negativas e com o teor de sólidos solúveis totais; dessa forma, para o dimensionamento adequado de máquinas e equipamentos, torna-se necessário conhecer essas propriedades, principalmente quando se operam equipamentos criogênicos, onde as temperaturas podem chegar a -196 ºC. Neste trabalho, determinaram-se a densidade e o calor específico da polpa do cajá com quatro diferentes níveis de sólidos solúveis totais (natural da polpa; 20; 40 e 60%) e temperaturas entre -196 ºC e -18 ºC. A densidade foi obtida pela razão entre a massa da polpa e o seu volume. O volume foi determinado pelo método do deslocamento de massa (água) e o calor específico por meio de balanço de calor entre a massa da polpa, a massa do cilindro que contém a polpa e a massa do gelo. Conclui-se que a densidade da polpa de cajá aumenta em função da redução da temperatura e do aumento do teor de sólidos solúveis totais de 9 para 60 °Brix e que o calor específico da polpa diminui com a diminuição de temperatura e aumenta com a concentração de sólidos solúveis totais.
The cajá pulp has been exported from the Northeast area to all parts of Brazil, and one of the ways of conserving it is processing and storing it in the frozen form. During the processing, there are two factors that favor the quality of the product to be stored; the speed that the product is frozen and the addition of sugar as a form of hindering the microbiologic action. In the process line, some thermo-physics properties like the specific heat and the density change themselves according to the negative temperatures and the total soluble solids content. Then, it's necessary to know those properties mainly when cryogenic equipments are operated, where the temperatures can be -196 ºC to have the appropriate dimension of machines and equipment. Therefore, in this work, it was determined the cajá pulp density and the specific heat for 4 different levels of total soluble solids (natural of the pulp; 20; 40 and 60%) and temperatures from -196 to -18 ºC. The density was obtained by the rate between mass of the pulp and its volume. The volume was determined by the displacement of mass (water) and the specific heat was determined by the balance of heating among the mass of the pulp, the mass of the cylinder that contains the pulp and the mass of the ice. The results allow to conclude that: a) the cajá pulp density increases in function of the variation of the temperature from -18 to -196 °C, and also as a function of the increase of the total soluble solids content from 9 to 60 °Brix; b) the cajá pulp specific heat decreases according to the decrease of the temperature and it increases according to the concentration of total soluble solids.
The cajá pulp has been exported from the Northeast area to all parts of Brazil, and one of the ways of conserving it is processing and storing it in the frozen form. During the processing, there are two factors that favor the quality of the product to be stored; the speed that the product is frozen and the addition of sugar as a form of hindering the microbiologic action. In the process line, some thermo-physics properties like the specific heat and the density change themselves according to the negative temperatures and the total soluble solids content. Then, it's necessary to know those properties mainly when cryogenic equipments are operated, where the temperatures can be -196 ºC to have the appropriate dimension of machines and equipment. Therefore, in this work, it was determined the cajá pulp density and the specific heat for 4 different levels of total soluble solids (natural of the pulp; 20; 40 and 60%) and temperatures from -196 to -18 ºC. The density was obtained by the rate between mass of the pulp and its volume. The volume was determined by the displacement of mass (water) and the specific heat was determined by the balance of heating among the mass of the pulp, the mass of the cylinder that contains the pulp and the mass of the ice. The results allow to conclude that: a) the cajá pulp density increases in function of the variation of the temperature from -18 to -196 °C, and also as a function of the increase of the total soluble solids content from 9 to 60 °Brix; b) the cajá pulp specific heat decreases according to the decrease of the temperature and it increases according to the concentration of total soluble solids.
Descrição
Palavras-chave
propriedades termofísicas, criogenia, congelamento, thermo-physics properties, cryogenics, freezing
Como citar
Engenharia Agrícola. Associação Brasileira de Engenharia Agrícola, v. 25, n. 2, p. 488-498, 2005.