The necessary pasteurization temperature, F and z values for pectinesterase inactivation were developed for three varieties of orange juices and one grapefruit juice. Since common commercial practice involves blending various orange varieties, the recommended conditions are those for the most heat resistant variety. For an FT = 1.0 min, the recommended processes are T = 194°F with z = 12.2 for orange juice and T = 186°F with z = 9.3 for grapefruit juice.

Citrus processors are becoming increasingly aware of the importance of pectic substances in frozen citrus juices. Pectic substances are naturally occurring colloidal stabilizers that give citrus juices a viscosity or consistency often termed "body" by the fruit juice industry. When a citrus juice lacks these colloidal pectic substances the suspended cellular material settles rapidly and the juice is clear rather than cloudy. These thin-bodied jnices are commonly termed ((watery."Recently pectic substances became of vital interest to producers of frozen citrus concentrates when the problems of gelation and clarification were found by Rouse (9) to be related to the low-methoxyl pectin content. Gelation and clarification of frozen citrus concentrate are 2 related defects resulting from demethylation of pectin by the enzyme, pectinesterase.The importance of pectic substances to the quality of frozen citrus concentrates made it desirable to develop a rapid method f o r determining the type and quantity of pectic substances in these products. Basic investigational work on pectic substances and laboratory control procedures in concentrating plants have been hampered previously by the tedious nature of standard pectin analyses. The Carre and Haynes ( 3 ) calcium pectate method and the A.O.A.C. (1) pectic acid method are long analyses that require careful attention t o technique. The acetone precipitate method of Hinton (6) and the pectic acid precipitate method of Fellers and Rice (5) are simplified methods that give comparative values for samples within a series, but are not sufficiently accurate for determining the pectic content of citrus juices.Recently pectic substances in citrus have been determined by optical rotation (8) and the pectic substances in cotton have been determined by a colorimetric reaction with carbazole (10). The latter method was applied by Averill (2) to frozen citrus concentrate. Further modification of the colorimetric procedure led t o the development of the following method. The new method is rapid and well suited for routine laboratory analyses.The colorimetric determination of pectic substances is based on Dische's ( 4 ) carbazole-hexuronic acid-sulfuric acid reaction. Depending upon the type of standard, results may be expressed as anhydrogalacturonic acid, pectic acid, o r in terms of a stated pectin o r calcium pectate. It is desirable that the results be reported as anhydrogalact~~roiiic acid, since this is the basic structural unit of the pectin molecule.

SUMMARY Pectinesterase activity, 3 pectic fractions, and other characteristics were determined periodically on 5 component parts of Valencia oranges during a 7‐month maturation cycle for 2 seasons. Usually, PE activity for peel, membrane, and juice sacs was least in December, when the Brix/acid ratio was low, and highest in June, when this ratio was greatest. The order of component parts for PE in most cases, from highest to lowest activity, was juice sacs, membrane, peel, seeds, and juice. Water‐soluble pectin generally remained constant in peel and juice sacs, increased slightly and then remained constant in the membrane, and was irregular throughout the cycle in the seeds. The trend of ammonium‐oxalate‐soluble pectin in the components was to increase during maturation. Protopectin in the component parts usually increased to a peak and then gradually decreased for the remainder of the season, except that protopectin in the juice sacs decreased throughout the sampling period. In this component, protopectin evidently was at its maximum by the first picking in December. Total pectin remained constant in the juice and seeds, and slowly declined in the other 3 components with maturation. Membrane contained the highest source of protopectin and total pectin throughout the season.

Samples of approximately 3.50 kg of commercially leached lime and lemon peel were dried in a pilot plant direct fired rotary dryer with inlet air temperatures of 370, 425 and 535°C yielding dried pectin pomace with a final moisture content of 15-20, 8-12 and 3-7%, respectively. Pectin was extracted from laboratory leached, undried peel, each of the above dried samples, and commercially leached and dried samples. From fresh peel leached in the laboratory, we found a 65.6 and 55.9% yield of 150 grade pectin on a dry weight basis for lime and lemon, respectively. Drying lemon peel to final moistures of 15-20, 8-12 and 3-7% resulted in yields of 41.1, 41.1 and 25%, respectively. Dehydration of lime peel to 3-7% moisture decreased the yield to 37%. Similar losses were found in commercially dried pectin pomace. A separate experiment was conducted to evaluate the effect of drying on pectin yield from fresh, unleached lemon peel. Unleached peel was successfully dried by mixing 1 part unleached peel with 2.5 parts.of dry leached peel. There was a slight loss in the percentage yield of pectin 23.3 and 21.8, but not much change in the jelly grade 230 and 232 between the dry leached and dry unleached peel, respectively.