UNITED STATES DEPARTMENT OF AGRICULTURE 
Issued March 9, 1925 
Revised October, 1926 
Washington, D. C. 
CITRUS PECTIN 
By Homer D. Poors, Assistant Chemist, Laboratory of Fruit and Vegetable 
Chemistry, Bureau of Chemistry } 
CONTENTS 
Page Page 
Purpose of investigation.________-------------- 1 | Composition of apple, lemon, and orange 
Results of previous investigations_--__-------_- 2 Pectims--_-__--- a fee 12 
Methods for determination of pectin.........-- 2 | Proportions of acid, sugar, and citrus pectin 
Preliminary experiments ----..---------------- 3 necessary to produce jellies__-----_--________ 12 
Meme extraction 5 9 5 | How to'make citrus jellies and marmalades___ 15 
Preparation of concentrated solutions and | Summary- ------_-_-______-_----- 16 
powdered i “Sa SE ON a aa Ae eS ee ae 16 
PURPOSE OF INVESTIGATION 
Lemon, orange, and grapefruit residue, thousands of tons of which 
are discarded each year at citrus by-product factories, consists 
principally of peel, pulp, and seeds. From 1.5 to 3 per cent of such 
residue, depending upon the ripeness of the fruit, is pectin, which 
occurs largely as pectose, an insoluble material, in the covering of 
the intercellular walls of the peel. 
Pectin is a necessary constituent of jellies and marmalades. When 
any fruit lacks enough pectin to form a jelly, the quantity re- 
quired to supply the natural deficiency may be added to the jelly 
stock. The principal source of commercial pectin used in this way 
has been apple pomace from vinegar factories, but, according to Will 
(60)? and Zoller (61), the possibilities of producing pectin from _ 
citrus fruit by-products are great. The simple method used in 
making apple pectin, which consists in dissolving out the pectin 
from the apple pomace with hot acidulated water and then concen- 
trating it to a viscous sirup, can not be satisfactorily applied to citrus 
residues. The oils and bitter principle in citrus peel impart a dis- 
agreeable bitter taste to the product, making it necessary to either 
remove them or precipitate the pectin from the solution. 
The properties of citrus pectin were studied in the Bureau of 
Chemistry and methods for its production on a commercial scale 
were evolved. The results of this work are reported in the following 
pages. 
15. M. Chace, chemist in charge, laboratory of fruit and vegetable chemistry, supervised the work here 
reported. 
7 Italic numbers in parentheses refer to the bibliography on p. 16. Not all of the articles there listed, 
however, are referred to in the text; several were published after the work here reported was completed. 
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