Microscale to Macroscale Measurement of Bubbles in Frozen Materials with Cryogenic Microtome Spectral Imaging System

Abstract

The internal structures of frozen materials and the formation of bubbles significantly affect the physical properties of such materials as ice cream. Various measurement techniques including optical and scanning electron microscopies, and X-ray microcomputed tomography have been employed to obser ve bubbles and the internal structures of frozen samples. However, these measurement techniques revealed only a limited measurement range and low resolution. The objectives of this work were to develop a cr yogenic microtome spectral imaging system (CMtSIS) to measure microscale to macroscale with respect to bubbles and internal structures formed in some frozen materials. The CMtSIS, which consisted of a microtome, automatic high-precision XY stage and a near-infrared (NIR) spectral imaging system, enable the capture of consecutive cross-sectional images of a frozen sample exposed by multi-slicing with a minimum thickness of 0.001 mm and a maximum area of 60× 60 mm. Bubbles in an ice cream sample were identified as defocused spots in two-dimensional (2D) CMtSIS images due to the difference in the focal distance created by the vacant spaces. NIR images of ice crystals in the frozen sample appeared darker than the other components at 1500 nm due to weak reflected light at this peak wavelength. Milk solids were also observed by the flux differences in light reflected from the different interfaces in the ice cream.

Three-dimensional measurement of internal structure in frozen food materials by cryogenic microtome spectral imaging system

“…The sample, OCT compound, and the ring of dry ice fixed on the heat exchanger were sliced together, and cross-sectional images were then captured by the CCD camera through a microscope. Bubbles, ice crystals and milk solids in the ice cream sample were identified from the CMtSIS iamges by the microscale to macroscale measurement method previously reported by Do et al [6].…”

“…The CMtSIS [6] consists of a microtome unit, an automatic high-precision XY stage, an image acquisition unit (visible, fluorescence and spectroscopic), and a 3-D image processor (Fig. 1).…”