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 Chernoff (57), and the calcium pectate by the Carré-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 
Composition 
Sodium 
7 2 Specific 
Pectin ee Blea a ea © A Meth- al rota- 
. tai : ) ectic| Calcium alac- | tion 
Ash | Acidity ape precipi-| acid | pectate eh = Araban tan 
hydrol- tate 
ysis 
Grams 
NaOH 
Per | per 100 Per 
cent | grams | Per cent|Per cent) cent | Per cent| Per cent | Per cent| Per cent | Degrees 
Apples — 2.4: 0. 70 3. 86 14.10 | 96.72 | 63.86 98. 00 10.90 | 39. 68 65. +210 
Lemon..-.-_- 5, 42 3. 86 13. 58 89.90 | 62. 76 96. 80 10. 26 39. 12 58.92 | +206. $ 
Orange--.-- . 90 1. 00 12.06 | 81.76 | 54.80 84. 60 8.85 | 34.96 56.08 | +175 
Calculated to aleohol-precipitate (pure pectin) basis 
Applesstten| is. 2s ea 3. 99 ANC ety jal |B eae 665 02(2-s 3 11.27 41. 02 67. 78 | +217.1 
hemon=2524)22 "| saws 4, 29 3 0) Neon 69a 42-54 aes 11. 41 43. 51 65. 54 | +229. 7 
Oranges 2ie eae: |e 1. 22 Ve Wee? (a | (eran Sa Gf 020) aoe oe 10. 82 42.76 68. 59 | +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 (44) 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 bemg made. Possibly the 
lack of acidity in the extracting solutions yielded a pectin of low 
