2- BULLETIN 1323, U. S. DEPARTMENT OF AGRICULTURE 
RESULTS OF PREVIOUS INVESTIGATIONS 
Pectin was discovered in 1825 by Braconnot (6). Since then the 
chemistry of pectin and its related compounds has been the subject 
of extended research. Czapek (18), von Lippmann (36), Grafe (1), 
Beilstein (4), and Toll ens (50) have summarized these investigations. 
Bigelow, Gore, and Howard (5) give a review, with an extended bibli- 
ography, of the work done up to 1905. More recently Ehrlich (20), 
Oden (39), and Fellenberg (2Jf) have published work on this subject. 
Confusion in designating substances of a pectinous nature has 
always existed. Fellenberg's exhaustive research helps to clarify the 
matter by giving the relations between the compounds. All pectinous 
materials are derived from pectose, or protopectin, an insoluble 
substance which forms the covering of the intercellular walls and 
middle lamella of unripe and some ripe, but no overripe, fruit. 
During the ripening of the fruit, pectose is converted into soluble 
Eectin by the action of enzymes. This action may be produced also 
y boiling the fruit with water, the change occurring more rapidly 
when a weak organic acid solution is used. According to Fellenberg, 
this reversible colloid should have the formula C 78 H 120 O 68 , not that of 
a true carbohydrate. Earlier investigators suggested formulas 
which also lack the number of hydrogen atoms requisite for a car- 
bohydrate. 
Pectin is closely related to starch and the plant gums and is usually 
classed as a polysaccharide. When mixed under certain conditions 
with sugar, acid, and water it produces a jelly and, with an excess of 
alcohol, precipitates from solution. As fruit rots, the pectin is 
changed to pectic acid by an enzyme (pectase), an action which also 
may be, produced by treating pectin in the cold with dilute sodium 
hydroxide. Fellenberg found that methyl alcohol was split off 
during this change and since then Tutin (51) has shown that acetone 
is produced. Fellenberg considers pectin to be the methyl ester of 
pectic acid, containing eight carboxyl groups. Pectic acid is only 
slightly soluble in water and will not form a jelly with acid and 
sugar. Upon treatment with acids it breaks down into arabinose, 
galactose, galacturonic acid, and other compounds. Gaertner (26) 
found that sugar-beet marc contained a large proportion of pectose, 
which was converted into pectin upon boiling with water. From 
the pectin he obtained pectic acid and from the pectic acid, galactose 
and galacturonic acid. Weisberg (56) and Wilhelmj (59) have also 
worked with pectin from sugar beets. Carre (12) has shown that 
pectin in apples reaches a maximum during the process of ripening 
and gradually decreases as the fruit becomes overripe. These results 
show that only good sound fruit, not too ripe, should be used for 
the commercial production of pectin; in fact, unripe fruit is better. 
METHODS FOR DETERMINATION OF PECTIN 
The method of the Association of Official Agricultural Chemists 
for alcohol precipitate in fruits and fruit products (2) was not satis- 
factory in working with solutions which contained a large proportion 
of pectin, because gums and other alcohol-insoluble substances were 
