Bromate-Bromide Mixture. To make a 0.1 A7 bromate-bromide solution, 2.780 grams of c.p. potassium brómate and 10.00 grams of c.p. potassium bromide is dissolved in about 500 ml. of distilled water and diluted to 1 liter in a volumetric flask.

No abstract

Z''1 ROWING interest in the role of pectic substances in controlling texture of fruits and vegetables during processing and storage has focused attention on simpler methods for their determination.Usually complete characterization of the pectic substances before and after a particular change is necessary. Occasionally, the problem may be resolved by determining the total quantity of pectic substances in solution.Methods that have been used include weight of alcohol precipitate (1), titration of acid carboxyls plus saponification of methyl esters (5), weight of calcium pectate (0), decarboxylation by heating in concentrated mineral acids (8), and optical rotation (7). Some of these methods require considerable purification of the

Fruit pectins consist primarily of polyanhydrogalacturonic acid units in unbranched chains with varying amounts of nongalacturonide carbohydrate materials such as araban and galactan probably in or closely associated with them. Usually 80% of the carboxyl groups are esterified with methyl alcohol, and the remaining 20% are free acids or salts. In some pectins a few of the secondary alcohol groups are esterified as acetyl esters. I n addition to these variables in composition, pectins vary in their molecular sizes. These variations in composition and average molecular size probably affect texture of fruits, consistency and gel strength of processed fruits, and rate of drying and subsequent rehydration of fruits.A study of the pectic substances in ripe and unripe fruits has been made, including characterizations of certain of the chemical and physical properties of pectins extracted from specific fruit tissues. Pectic enzymes are generally assumed to be the cause of changes in texture during ripening of fruits. Since the enzyme pectinesterase occurs almost universally in fruits (6), its activity was not determined. Polygalacturonase, not generally found in fruits (6, 7), was assayed to determine, if possible, whether its presence could be demonstrated in peaches, pears, and avocados. EXPERIMENTALSelection of samples. The fruits examined in the present study were obtained from a fruit grower. Thus they were orchard-run samples, picked from the same trees at the same times. About 60 pounds of Elberta peaches were selected for color and firmness. One lot of green-hard fruits was selected to represent unripe peaches. A lot of yellowsoft fruits was selected as the ripe sample. No pressure tests were made. Twenty-five pounds of Bartlett pears (all green and hard) were selected for uniform color and size, free from bruises or abrasions. The steins had been detached a t the absciss layer during picking and it was assumed that the fruits were of the same maturity. These unripe fruits were immediately subjected to analysis. The remaining fruits were stored at 25"C.(77"F.) and after 8 days they were uniformly colored yellow and had the softened texture of fully ripened pears. These were regarded as the ripe pears and were then subjected to analysis. One box of size 30 unripe-green-hard Fuerte avocados was divided into two portions. The unripe portion was analyzed immediately. The remaining fruits were stored a t 25"C.(77"F.) for 6 days. The fruits were then soft to the touch and the skin could be separated easily from the flesh. All of the fruits were superficially comparable in their degree of ripeness. These were considered to be ripe avocados and were then processed as described.Extraction procedures. Ripe and unripe fruits of the mine variety were extracted with boiling alcohol; the dried sugar-free material, referred t o herein as "marc," was then analyzed directly and the pectic substances extracted from the m a n by mild means. Pectic substances, assumed t o be representative of those present in the fruit,