Atividade aquosa

A atividade aquosa é considerada como parâmetro no estudo da química dos alimentos.

A atividade aquosa (denominada também como atividade da água) define-se como a relação que existe entre a pressão de vapor de um alimento dado em relação com a pressão do vapor de água pura à mesma temperatura e varia de 0 a 1.[1] Denomina-se pela regra geral como Aw (do inglês: Activity of Water). A atividade aquosa é um parâmetro inteiramente ligado à umidade do alimento o que permite determinar sua capacidade de conservação, de propagação microbiana, etc. A atividade aquosa de um alimento pode ser reduzida aumentando a concentração de solutos na fase aquosa dos alimentos mediante a extração da água (liofilização) ou mediante a adição de novos solutos. A atividade aquosa junto a temperatura, o pH e o oxigênio, são os fatores que mais influenciam na estabilidade dos produtos alimentícios.

Definição formal

Uma definição mais formal da atividade aquosa, representada por aw:[2]

onde p é a pressão do vapor de água na substância, e po é a pressão do vapor de água pura à mesma temperatura. Existem definições alternativas como expressada em:

onde lw é o coeficiente da atividade da água e xw é a fração molar da água na fração aquosa.

Umidade relativa:

Estimado em dias de vida a uma temperatura de 21°C:

Valores de aw mínimos para desenvolvimento de microorganismos

Microorganismos aw
Item 1 Bactérias deteriorantes 0,90
Item 2 Leveduras deteriorantes 0,88
Item 3 Bolores deteriorantes 0,80


Referências

  1. ↑ Seara.com. «Ambifood». www.ambifood.com. Consultado em 23 de março de 2018 
  2. ↑ Livro Herrera, et al. Química de Alimentos: Manual de Laboratorio


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