VEGETABLE AND FRUIT DEHYDRATION 149 



comparing the color intensity developed in tests run on boiled and 

 unboiled samples. 



Regeneration of peroxidase may be responsible for some of the 

 variable results reported by the industry. In laboratory studies this 

 phenomenon has not been observed in the dehydrated material but 

 has been observed in blanched rutabagas, potatoes, cabbage, and 

 others before dehydration. Frequently the inactivation of peroxidase 

 during drying will exceed the regeneration, with the result that a 

 lower activity will be obtained on dry material than on that freshly 

 blanched. Drying conditions and time of holding between blancher 

 and drier and between blancher and enzyme test will, however, affect 

 results. It is important in comparing results on wet blanched samples 

 with those on corresponding dried samples to make sure that the 

 different results are not due to differences in test procedure. For 

 example, allowance must be made for the water taken up during 

 dehydration, or a considerable difference in final reagent concentration 

 may exist. Also, as indicated above, the time of holding should be 

 standardized to avoid variable amounts of regeneration. 



The test that the processor uses at the end of his blancher may vary 

 not only with the vegetable but also with the consumer or purchaser. 

 Vegetables to be purchased by Government agencies should be tested at 

 the end of the blancher by a procedure that will correlate with the 

 inspection test on the dried material. The tolerance permissible at 

 the blancher can best be determined by the plant chemist, since the 

 regeneration and inactivation that occur during drying will vary 

 with plant practice. When possible, the product should, of course, be 

 blanched appreciably more than the minimum. On material pre- 

 pared for the general public it may be desirable to use a different 

 blanching treatment and hence an enzyme test having a different 

 tolerance, since a wide margin of safety has been required on vegeta- 

 bles dehydrated for the armed forces because of the severe storage and 

 transportation conditions that they may encounter. 



In general the catalase test is not recommended, because catalase 

 is too easily destroyed in most vegetables and would therefore indicate 

 only gross underblanching. Complete and permanent destruction of 

 peroxidase, on the other hand, would correspond to overblanching of 

 many vegetables. The use of peroxidase in these cases therefore 

 requires a tolerance. Although the peroxidase test is not entirely sat- 

 isfactory because of the many factors that affect it, the following 

 procedure is presented for illustrative purposes and will doubtless be 

 improved or replaced as research proceeds. 



The procedure employs guaiacol, one of the most suitable peroxidase 

 substrates, and higher concentrations of reagents to avoid the effect 

 of small variations in reagent concentration. Further, it can be 

 made essentially objective by the use of color standards. Use of color 

 standards permits the adoption of tolerances that can be varied to suit 

 any particular purpose. Processors must, of course, use the current 

 test that the product must pass. 



PEROXIDASE TESTS 



Peroxidase catalyses the oxidation by hydrogen peroxide (or certain 

 other peroxides) of a number of compounds such as pyrogallol, 

 guaiacol, benzidine, catechol, etc. to give colored compounds, Most 



