APPLE JUICE EXTRACTION FOR .lEI.I.Y •221 



Color, taste, turbidity, and sediment were {riven ratings on a basis of organ- 

 oleptic tests only. Four classes were made in each case — for example, the 

 color or taste was considered excellent, good, fair, or poor. Likewise tiirhid- 

 ity and sediment were classified as much, moderate, slight, or none. 



Sugar in Jellies was determined by the Abl>e refractometer. In tlie case 

 of juices a'comjiarison was made of tiie results obtained by the Brix hydro- 

 meter, refractometer and chemical determination of soluble solids. These 

 results are discussed elsewhere in this bulletin. 



Centrifugal Method for Pectic Acid 



A centrifugal method was developed during the course of the work and 

 will be described more fully in a separate publication. In brief, it consisted 

 of measuring either 5 or 10 c. c. of juice, according to concentration, into 

 15 c. c. tapered, graduated, glass centrifuge tubes. When 5 c. c. were em- 

 ployed, the juice was always diluted to the 10 c. c. mark before the addition 

 of alkali. One c. c. of a 10 per cent sodium hydroxide solution was added 

 to each tube, the contents mixed by shaking and allowed to stand for 15 

 minutes. Two c. c. of a 10 per cent hj'drochloric acid solution were intro- 

 duced and thoroughly mixed. The tube was then placed in boiling water for 

 5 to 8 minutes (or until the gelatinous precipitate was entirely flocculated 

 and freed from air bubbles), removed, cooled to below 25°C. and whirled 

 in a centrifuge 15 minutes at 2600 revolutions per minute on a 14-inch 

 head. It was found within certain limits that the vohmie of the precipitate 

 could be correlated with the chemical determination of pectic acid. Tiie 

 precipitate was also centrifuged without previous heating, but the readings 

 were much higher than with the heated precipitate and less consistent. It 

 was found that the centrifugal method did not yield reliable results when 

 applied to the alcohol precipitate of juices or pectin extracts. 



For practical purposes, it was believed that the chemical determination 

 of pectic acid yielded more reliable results than the alcohol precipitate 

 (pectin). It has i)een proved recently by Nelson (11) that the pectic acid 

 obtained in this manner consisted of a definite stable substance, namely 

 digalacturonic acid. The composition and physical properties of the alcohol 

 precipitate w-ere foimd to be variable and it was difficult to obtain satis- 

 factory checks by using the method. The ratio of pectin (alcohol precipitate) 

 to pectic acid, A. O. A. C. method, was variable but averaged approximately 

 1.7:1 for Baldwin apples. Wichmann (19) estimated that this ratio for most 

 varieties of apples was about 2:1. 



Jelly Strength Determination 



Obviously the jelly strength test commonly employed, i. e., the resistance 

 of the jelly to the fingers, is inaccurate. Paine (12), Sucharipa (16), and 

 Tarr (18) have described the advantages of a suitable jelly-strength tester. 

 Sucharipa (16) devised a tester which would break a laj'er of jelly of definite 

 thickness by means of air pressure, the latter being registered on a mano- 

 meter. Later Tarr (18) and Baker (3) modified and simplified Sucharipa's 

 apparatus by using water pressure in place of air pressure. 



By substituting a light paper cup in place of the heavier metallic one 

 furnished with the Bloom gelometer (13), a standard instrument used in 

 gelatin and glue testing, the writer found this instrument gave very satis- 

 factory results in determining the jelly strength of fruit or pectin jellies, 

 jams or sauces. 



