Several physical techniques were used to study the extent of spoilage in apple juice deliberately inoculated with yeast (concentration of Saccharomyces cerevisiae ranged from 25 cells mL(-1) to 2.5 x 10(6) cells mL(-1), respectively) and their performance compared in terms of detection limit achieved. The optical methods used in this investigation rely on the measurement of either absorption [as is the case for classical spectrophotometry (SP) and the so called optothermal window (OW), a variant of a photothermal method], or scattering [examples are turbidimetry (TB), laser scattering (SC), and laser speckle fluctuation (SF)]. It is shown that the presence of yeast increases both optical absorption and scattering. The most favorable detection limit (25 cells mL(-1)) and a highest (nearly 10(4)) dynamic range, combined with a good linearity, were obtained with the experimental set-up for SC. In addition, the extent of correlation between different methods was determined using two markedly different reference substances, i.e., (i) the mixture of apple and blackcurrant juices, representing a strongly absorbing sample, and (ii) diluted (dilution factor of 103) milk as a strong scatterer. Finally, one has monitored the progress of a spontaneous spoilage process in the inoculated juices stored at 5degreesC under aerobic conditions.
Chirtoc, I., Chirtoc, M., Bicanic, D. D., Cozijnsen, J. L., & Breeuwer, P. (2003). Comparison of some physical techniques for detection of spoilage in apple juice inoculated with Saccharomyces cerevisiae: Optical and photothermal methods. Instrumentation Science and Technology, 31(3), 211-229. https://doi.org/10.1081/CI-120022650