s 
BULLETIN 1323, U. S. DEPARTMENT OF AGRICULTURE 
Two 200-gram samples from 1.300 grams of grapefruit peel were 
extracted twice at 98° C. for an hour, varying the acidity. The results 
are shown in Table 10. 
Table 10. — Results of two 1-hour extractions of grapefruit peel at 98° C, varying 
the acidity 
Sample 
No. 
Acidity 
(citric 
acid) 
Pectin 
in peel 
Pectin 
for a 
good 
jelly 
1 
2 
Per cent 
0.02 
.34 
Per cent 
1.17 
1.95 
Per cent 
0.86 
.41 
Although a good yield of pectin is obtained in two extractions with 
0.02 per cent acid, the jellying quality of such pectin is poor. Pectins 
of much higher jellying quality are obtained when at least 0.1 per 
cent of acid is present in the solution, and the quantity extracted 
increases with the increase of acid. After two extractions, the pectin 
is of inferior jellying quality. A third extraction yields enough pectin 
to warrant the extra cost if it were not of a poorer quality, but the 
fourth and fifth extractions are not of economic value. It is believed 
that 0.3 to 0.6 per cent acid is enough to produce pectin of good 
quality in two extractions of one hour each, and that possibly tartaric 
acid and other organic acids can be used. Although a little more 
pectin is obtained by heating for one and one-half hours, the quality 
of the product is not quite so good. 
PREPARATION OF CONCENTRATED SOLUTIONS AND POWDERED 
PECTIN 
The concentrated extracts are bitter, and jellies made from them, 
containing as little as 0.25 per cent pectin, although of good consist- 
ency, have a slightly bitter taste. The concentration of pectin extract 
for the production of a satisfactory solid product was studied. 
One hundred and sixty kilograms of pectin solution was obtained 
from 91 kilograms of lemon residue by two extractions. Bakers' 
yeast was added, and the mixture was allowed to ferment for four 
days at about 30° C. It was than clarified by adding 3 per cent by 
weight of kieselguhr. boiling, and filtering. As kieselguhr removes 
little pectin, if any, and is the best clarifying medium of those tried, 
it was used throughout the work. 
Although the pectin was not destroyed by the fermentation, its 
jellying quality was impaired Thirty kilograms of the fermented 
extract was concentrated to 5.5 kilograms by freezing and centri- 
fuging three times. After experimenting with a 40-gallon silver- 
fined vacuum pan and a small medicinal type atomizer, a spraying 
apparatus that produced about 50 grams of a very fine, light-colored 
powder at a temperature in the pan of 54° C. was arranged. The 
product thus obtained was very bitter; but, after extraction in a 
Soxhlet apparatus with 95 per cent alcohol, a lighter-colored powder 
without a trace of bitter taste was obtained. The composition of 
the solutions and the powder is given in Table 11* 
