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An optical system for the measurement of pH value of foods during its high-pressure treatment was developed. The principle is an absorption measurement using indicator dyes. An indicator mix of 16 different pH-sensitive substances is used to cover the pH range of food. To manage the difficult spectra, a multivariate approach is used. The calibration of the system is performed by taking five different buffer solutions with known pressure behavior (TRIS, CAPS, citric, phosphoric, and acetic acid buffers). The corresponding spectra of the indicator mix are measured and fed to a multivariate data model together with calculated pH values. Some chemometric models have been tested to estimate the pH value based upon the spectra of the indicator mix. The calibration device covers a pH range from 2 to 8 at ambient pressure. After calibration, the system is able to determine the pH value at pressures of up to 450 MPa with an accuracy of 0.24 pH units using eight different test media. Industrial relevance : pH is an important factor in nearly every sector of food industry. During high-pressure treatment of food both the pH and its influence of pH sensitive reactions changes. Therefore, the development of an in-situ measuring device is necessary for scientific examination and monitoring in the food industry. |
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