Cryo-Scanning Electron Microscopy

Equipment: Hitachi S-570 scanning electron microscope, Emitech K1250X cryo-preparation unit.

Conventional scanning electron microscopy (SEM) requires that samples be dry and electron dense. Many foods are high in water and fat; microstructure is not well preserved by fixation and drying. These foods can be frozen to preserve their constituents. 

Cryo-SEM samples are frozen or kept frozen (ice cream), fractured and sublimated to remove surface water. Surfaces are imaged on a cold stage in the SEM (-140◦C). 

Images allow evaluation of changes in microstructure brought about by changes in formulation, source of ingredients or storage. This approach is useful for product development and quality control.

Cryo-Scanning electron micrographs

GoudaIce CreamCheese_Mite

Nitrogen Determination - Dumas method

Equipment: Leco-FP528

The Dumas combustion method for quantifying the amount of nitrogen in organic compounds was developed by Jean-Batiste Dumas in 1833.
The method (Simonne et al. J. Food Science and Agriculture, 1997. V. 73, 39-45): 

1.  Conversion of all forms of nitrogen into nitrogen oxides (NO x) by complete combustion in an induction furnace
2. Reduction of NO_x gases to N₂
3. Quantification of N₂ by thermal conductivity

The Dumas method is fast, reproducible and does not require wet chemistry. Both solid and liquid samples can be analyzed. The accuracy and repeatability of the method is reported to be better than Kjeldahl (Schmitter and Rihs, J. Agric. Food Chemistry, 1989. V. 37, 992-994).

Crude protein content is determined by multiplying the measured amino-nitrogen value by a protein conversion factor as listed in Table 1 (Simonne et al. J. Food Science and Agriculture, 1997. V. 73, 39-45). 

Table 1. Conversion factor to calculate protein from the nitrogen level determined by through the Dumas method using the Leco FP528

Scanning Electron Microscopy

Equipment: Hitachi S-570 scanning electron microscope.

Scanning electron microscopy (SEM) is a high resolution surface imaging technique.

Food microstructure can be examined, in the vacuum system, using an electron beam, on foods that are dry and electron dense. Therefore some samples can be imaged following minimal treatment, such as coating with gold, while others require fixation, dehydration and critical point drying to preserve their structure.

Images allow evaluation of changes in microstructure brought about by changes in formulation, source of ingredients or storage. This approach is useful for product development and quality control.
Microstructure correlates well with texture analysis.  

Scanning electron microscopy images

BacteriaStarch in beansNano-fibres