VEGETABLE AND FRUIT DEHYDRATION 153 



being analyzed, 5 to 10 gm. of sample is sufficient, in accordance with this same 

 classification. These may require a half hour of soaking in the acid before 

 blending. 



Centrifuge or filter the extract through fluted filter paper. Moderate turbidi- 

 ties do not interfere, since the instrument is calibrated with proper blanks. Ex- 

 tracts of starchy vegetables, such as potatoes, should be centrifuged or suction- 

 filtered, if difficulty is encountered with the ordinary filter. 



Pipette 1-ml. portions of the filtrate into three matched tubes from the photo- 

 electric colorimeter. A)dd 9 ml. of distilled water to one tube and adjust the 

 colorimeter to read 100 with this tube. 



To each of the other tubes add 9 ml. of a previously standardized indophenol 

 dye solution from a calibrated rapid-delivery pipette. Take a reading in the 

 colorimeter 15 seconds after the beginning' of the addition of dye. This read- 

 ing is G 2 , from which the corresponding L 2 value is obtained from the calibra- 

 tion table provided with the instrument or calculated from the following formula : 

 L=2— log G or log 1/T. 



Ascorbic acid, mg. per 100 ml. of filtrate=ir (Li— Ls). 



K must be determined for each colorimeter by preparation of a curve with 

 pure ascorbic acid. 



K=C/D. 



C=concentration of ascorbic acid in mg. per 100 ml. 



Z)=density= (Li— Ln) . 



The equation for fruit and vegetable tissue becomes : 



Ascorbic acid, mg. per 100 gm. tissue= 



-rr lT T v ml. acid extractant-fml. water in sample 



-fi- (-^l — -^2) 7 ; 



gm. of sample 



With dehydrated vegetables, the moisture content (if below 5 percent) can 

 usually be neglected. The formula then becomes : 



ml. acid added 



Ascorbic acid, mg. per 100 gm. product=IT (Li — L 2 ) 



gm. sample 



Add the dye to the tube outside the colorimeter and agitate the tube slightly 

 before putting it into the instrument. If an automatic 9-ml. pipette is used, 

 it must extend to near the surface of the liquid in the tube to avoid splash- 

 ing and must be calibrated to drain uniformly in less than 5 seconds. 



The dye is standardized by noting the 15-second reading given by a tube 

 containing 1 ml. of 1-percent metaphosphoric acid and 9 ml. of the dye solution. 

 This value is Gi, from which I* is obtained on the calibration table or from the 

 formula above. This standardization is very much easier and faster than 

 titrimetric procedures. 



THIAMINE AND RIBOFLAVIN 



Because of the relatively infrequent determination of thiamine 

 and riboflavin in dehydrated fruits and vegetables, details are not 

 presented here. It has been found that the method of Conner and 

 Straub (12) is useful for both fresh and dehydrated products. This 

 is a fluorometric method in which the vitamins are extracted by dilute 

 acid and separated from one another by adsorption procedures. 



Determination of Sugar (Vegetables) 



Determination of sugar content is valuable in examinations of raw 

 products for maturity or loss of quality in storage. It is often used 

 on dehydrated products, such as carrots, sweet corn, and potatoes, to 

 indicate quality, loss of solubles in blanching and washing, and causes 

 of difficulty in drying, and also to obtain information useful in the 

 compression of the dried materials. The method described here 16 



lfl Essentially as developed by J. P. Nielsen of the Western Regional Research Laboratory 

 by modification of the method of W. Z. Hassid {19, 20). 



