228 INDUSTRIAL APPLICATIONS OF PHASE MICROSCOPY 



3. FOODS, DRUGS, AND PHARMACEUTICALS 



The phase microscope is useful in identifying foods, revealing im- 

 purities, and evaluating and controlling processing methods. Homo- 

 genization, which is important for milk and for salad dressings, may be 

 evaluated with a 0.2A+0.25X diffraction plate in a 4- or 1.8-mm ob- 

 jective. Emulsions for salad dressings usually show well with this or 

 with a IB— 0.25X or 0.14A — 0.25X diffraction plate. As pointed out 

 in Section 3.1 of Chapter V, it is usually not possible to identify a single 

 coccus bacterium or distinguish it from a fat globule of the same size. 

 Bacteria of other sizes and shapes or of different optical density may be 

 seen and the number present determined. Inorganic particles such as 

 undissolved crystals are made visible in mayonnaise and in similar 

 materials. 



Small changes resulting from processing foods may be seen, such as the 

 hydrolysis of starch, or the results of cooking. With a 0.14A+0.25X 

 diffraction plate, partially hydrolyzed starch shows the changes in the 

 grains when mounted in Crown Immersion Oil. Another specimen was 

 seen better in a water mount with a medium, rather than the low, dark 

 (A — ) contrast. Some experimentation is necessary to determine 

 the most appropriate procedures. The effect of digestion may be stud- 

 ied with a phase microscope by comparing the feed and the feces. 



Insect parts that are relatively transparent are readily revealed with 

 the phase microscope, which makes it valuable in discovering and identi- 

 fying such filth in dirty food. Transparentizing the specimen with a 

 suitable mounting medium will assist in finding the extraneous matter 

 (see Section 3.2 of Chapter IV). The problem of mold counting in 

 tomato products was discussed in Section 3.2 of Chapter V. 



Many applications of the phase microscope are possible in the drug 

 and pharmaceutical industry. The purity of cultures used in making 

 biologicals can be determined, the nature of emulsions and the degree of 

 inhomogenization can be seen, and impurities may be found and identi- 

 fied. The components of preparations containing paraffin oil, agar, 

 yeast, and similar materials and their relation to each other are easily 

 seen. The 0.14A+0.25X is the most useful single phase objective for 

 such a specimen, although the 2.5B— 0.25X is better for yeast and the 

 IB— 0.25X is better for smallest visible oil globules and agar plaques. 

 The dark-contrast (A — ) phase objectives are also useful for emulsions 

 (see Section 3.3 of Chapter IV and Section 1 of this chapter). The 

 8-mm objective will be helpful for many specimens which do not require 

 the highest resolution, because of its longer working distance and larger 

 field of view. 



