150 MISC. PUBLICATION 5 4 0. U. S. DEPT. OF AGRICULTURE 



of the procedures for estimating peroxidase are based on the observa- 

 tion of the color formed after various periods of time. 



The followincr procedure depends on the observation of guaiaeol 

 oxidation product color in solution and disregards the color of the 

 solid pieces. This procedure has been used experimentally on white 

 potatoes and may require some change in regard to observation time, 

 size of sample, or other factors if used on other vegetables. 



Reagents : Use A. C. $.. U. S. P.. N. F.. or equivalent grade chemicals : 10 per- 

 cent gnaiacol in 95 percent alcohol. 30 percent hydrogen peroxide. 5M ammonium 

 acetate • 193 gm. of (NELJCyHsOa dissolved in sufficient water to make 500 ml. of 

 solution ) . 



Procedure : The test should be made in triplicate. To each 25-gm. portion in a 

 400 ml. beaker add 5 ml. of 5M ammonium acetate and 270 ml. of distilled water. 

 Stir thoroughly wirh a stirring rod, without breaking pieces, and allow to rehy- 

 ttrare for one hour. After the hour of rehydration add 5 ml. of 10 percent guaia- 

 col. stir, and acid 3 drops (0.15 ml.'* of 30 percent hydrogen peroxide (equivalent 

 amounts of each concentrations may be usedi. Again stir thoroughly and allow 

 to react for just one hour without agitation. After the addition of the hydrogen 

 peroxide the samples must be protected from direct sunlight and shielded from 

 intense artificial illumination. I Covering with a towel is a convenient method 

 of protecting samples from light. ) At the end of the hour of reaction time stir 

 thoroughly, filter a portion of the sample through fairly fast paper into a test 

 tube (18 x 150 mm.) and compare the color of the filtrate with a color standard 

 or determine the extent of coloration with a colorimeter* 



A stable color standard may be made from Coi XO ? ) 2 .6H 2 and 

 KCi\0 : . For freshly dehydrated white potatoes that are to be used 

 domestically the color in the filtrate should be less than that 

 of a standard containing 0.01 percent K 2 Cr 2 : and 0.65 percent 

 Co(XO ; U.6ELO. If the potatoes are not seriously damaged by addi- 

 tional blanching it would be consistent with the principle of the 

 safest practical margin to use a standard having one-half or one- 

 third the above concentrations of salts. As mentioned before, the 

 test procedure used at the end of the blancher would need to be 

 correlated in the plant with the test to be used on the dehydrated 

 material. 



Vitamin Determinations 



The principal vitamins contained in dehydrated fruits and vege- 

 tables are ascorbic acid (vitamin C). carotene (provitamin A), and 

 certain members of the B group, such as thiamine and riboflavin. Of 

 these the B vitamins are comparatively stable and. though suffering 

 some loss hi dehydration, are retained well in storage. Thiamine and 

 riboflavin occur in many vegetables but are present in noteworthy 

 amounts principally in the greens and legumes. 



Ascorbic acid occurs widely in citrus fruits, berries, tomatoes, cab- 

 bage, greens, carrots, potatoes, and others, but it is difficult to preserve 

 and frequently undergoes destruction to the extent of 50 to 7~> percent 

 in the course of processing. Retention in storage is aided by low mois- 

 ture content, low oxygen content of storage atmosphere, and low- 

 storage temperatures. Adequate blanching and rapid drying also 

 favor its retention during dehydration and storage, although sub- 

 stantial losses may be encountered in the blanching operation. With 

 uitrarapid drying, such as spray drying, retention of as high as 90 

 percent can be attained without difficulty. Ascorbic acid is of con- 



