12 
BULLETIN 1323, U. S. DEPARTMENT OF AGRICULTURE 
COMPOSITION OF APPLE, LEMON, AND ORANGE PECTINS 
• Samples of lemon and orange pectins, obtained by double alcoholic 
precipitation, and a sample of apple pectin, obtained by washing apple 
pomace three times with boiling alcohol and precipitating the water 
extract with alcohol containing hydrochloric acid, were analyzed 
by E. K. Nelson, of the Bureau of Chemistry. The alcohol precipi- 
tate and pectic acid were determined by the method of Wichmann 
and ChernofT {57), and the calcium pectate by the Carre-Haynes 
method (13), while the Zeisel method was employed for the methoxy 
number. The methods of the Association of Official Agricultural 
Chemists were used for determining the araban and galactan. The 
results are given in Table 14. 
Table 14. — Composition of pectins 
Pectin 
Apple.. 
Lemon. 
Orange . 
Mois- 
Per 
cent 
1.12 
3.64 
8.14 
Composition 
Ash 
Per 
cent 
0.70 
5.42 
5.90 
Acidity 
Grams 
NaOH 
per 100 
grams 
3.86 
3.86 
1.00 
Sodium 
hydrox- 
ide re- 
quired 
for cold 
hydrol- 
ysis 
Per cent 
14.10 
13.58 
12.06 
Alco- 
hol 
precipi- 
tate 
Per cent 
89.90 
81.76 
Pectic 
acid 
Per 
cent 
DZ. 10 
54. SO 
Calcium 
pectate 
Per cent 
98.00 
96.80 
84.60 
Meth- 
oxy 
number 
Per cent 
10.90 
10.26 
8.85 
Calculated to alcohol-precipitate (pure pectin) basis 
Araban 
Galac- 
tan 
Per cent Per cent 
39.68 
39. 12 I 
34.96 ! 
65.56 
58.92 
56.08 
Specific 
rota- 
tion 
Degrees 
+210 
+206. 5 
+175 
Apple 


3.99 
4.29 
1.22 
14.57 
15.10 
14.75 
66.02 I 
___| 11.27 1 
41.02 
43. 51 
42. 76 
67.78 
65.54 
68.59 
+217. 1 
69.81 | 
67.02 
... 11.41 
... 10.82 
+229.7 
+214 
The apple pectin is much purer than the citrus pectins. When 
calculated back to the pure pectin basis, however, no great differences 
were noted in the chemical composition, and no hope of being able 
to distinguish between them chemically is indicated. 
PROPORTIONS OF ACID, SUGAR, AND CITRUS PECTIN NECESSARY 
TO PRODUCE JELLIES 
Goldthwaite (27) studied the proportions of sugar and acid and 
the quantities of invert sugar produced in making fruit juice jellies, 
but paid little attention to the percentages of pectin actually present. 
Cruess and McNair (16) found that, with a 1 per cent solution of 
orange pectin, a concentration of 0.3 per cent acid is necessary to 
give a firm jelly. Singh (4-4) studied the relations of pure citrus 
pectin, pure citric acid, and sugar in detail, but evidently used a 
pectin of poor jellying power, as a minimum of 0.9 per cent was 
required to jelly. He states that to prepare the pectin solution 
commercial powdered citrus fruit pectin was leached in boiling water 
and filtered through felt, four extractions being made. Possibly the 
lack of acidity in the extracting solutions yielded a pectin of low 
