Assessment of milk fermentation process at three temperatures using laser speckle technique

Abstract

This research work contains information on speckle activity at different stages of the milk fermentation process at temperatures of 24 °C, 32 °C and 40 °C, using the dynamic laser speckle technique for the first time, to the best of our knowledge. Image processing algorithms such as inertia moment (IM), the absolute value of differences, the probability mass function of regular difference, spatial-temporal speckle correlation and 3D graphs of spectral images have been applied to show the speckle activity of the samples. All the methods show that the speckle activity of the sample is higher at the semisolid stage than at the liquid stage of the sample. Also, higher speckle activity of the curd has been observed at 40 °C (11 576.18 using IM) than at 32 °C (8550.92 using IM), followed by that at 24 °C (4855.88 using IM). At 40 °C, the thermal motion of curd particles is higher than that of the curd particles at the other two temperatures, and are responsible for the higher speckle activity. The preparation time for curd at 40 °C (5 h) is lower in comparison to the curds at 24 °C (10 h) and 32 °C (6 h). The lowest value for the titratable acidity of the curd prepared at 24 °C shows a lower % lactic acid than the curd at 32 °C and that at 40 °C. The lowest value of susceptibility to syneresis of the curd at 40 °C (30.00) represents a more compact curd than the curds at 32 °C (37.50) and 24 °C (45.00). The horizontal speckle grain size of the curd has been calculated using an autocovariance function; the highest is for curd fermented at 40 °C (12.34 μm), followed by that at 32 °C (11.59 μm), then that at 24 °C (10.96 μm).