Measurement of water activities of foods at different temperatures using biospeckle laser
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Water is one of the main components of food and its presence is related to the rate of deterioration of foods. Thus, control of the water activity (aw) is a fundamental feature of food technology. The methods currently used for determining aw of foods mostly use the relative vapor pressure of the product to quantify the aw at constant temperature. This last factor limits evaluation of the aw because the instrument used is not capable of determining the aw at temperatures lower than 25 °C and/or at negative temperatures. In this study, the potential of the biospeckle laser for aw measurement was evaluated. Contrast analysis using the biospeckle laser technique provided statistically significant differences in the concentrations and aw for lithium chloride solutions and model solutions of pectin and sucrose at temperatures of 0, 5, 10, 15, 20, and 25 °C, as well as at freezing temperatures. After calibration of the biospeckle laser with the lithium chloride solutions, aw of corn starch, oatmeal, and wheat flour was determined at different temperatures, with errors lower than 20%. This achievement provides a platform for developing protocols to measure the aw of foods at different temperatures using the biospeckle laser.
KeywordsOptical methods Saline solution Temporal contrast Water activity Biospeckle laser
The authors wish to thank the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG - Brazil), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Brazil), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES - Brazil) for financial support for this research.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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