APPLES AS FOOD 7 



There is some variation in the composition of apples according to variety and 

 other factors. Ordinarily more than four-fifths (80 to 86 percent) of the apple 

 consists of water. The total solids vary from approximately 14 to 19 percent, of 

 which 12 to 15.5 percent is soluble solids. Sugars make up a large proportion of 

 the solids (approximately 75 percent and approximately 12 percent of the total 

 weight of the apple). The chief organic acid of the apple is malic acid, which is 

 found to the extent of from 0.5 to 1.0 percent. Citric acid has been found in 

 only a few varieties. 



Carbohydrates 



From a nutritional standpoint carbohydrates can be divided into two groups: 

 the so-called available carbohydrates such as starches and sugars; and the un- 

 available or fiber fraction consisting of pectin, cellulose, and hemicellulose, usually 

 considered indigestible. 



The young apple contains a relatively large amount of starch (3 to 4 percent), 

 but as the fruit ripens the starch is converted into sugars. A fully ripe apple 

 contains little or no starch. 



The total available sugar content of the apple amounts to approximately 12 

 percent. The sugars consist of at least three distinct compounds; sucrose (from 

 to 6 percent), and a mixture of dextrose and levulose of which there may be 

 from 5 to 10 percent. The excess of levulose over dextrose is rather unusual in 

 fruits (Shaw, 1911). According to Manville (1936b) the excess of levulose in 

 apples may account for the greater tolerance of diabetics for this fruit. 



According to Sherman (1946) one good-sized apple will furnish 100 calories, 

 which is equivalent to the energy provided by one fair-sized potato, one thick 

 or two thin slices of bread, or two-thirds of a glass of milk (about five ounces). 

 Apples may be considered a food of moderate energy value, comparing favorably 

 in this respect with many of the other fruits such as apricots, blueberries, oranges, 

 peaches, pears, plums, raspberries, and strawberries. 



The caloric value of the apple is relatively well utilized in ihe body according 

 to Ullmann (1933), who found that 88.3 percent of the caloric value of ingested 

 apples was assimilated by the body. 



Pectin 



As a nutritive element in apples, pectin is particularly interesting. Pectin 

 was discovered in 1825 by Braconnot, a French scientist, who first suggested that 

 this material might be of value as an antidote for lead poisoning (Rooker, 1928). 

 However, pectin was only a laboratory curiosity until 1909, nearly 100 years 

 later. At that time investigators established the relationship between pectin, 

 sugar, and acid. In 1913 the first patent for the commercial production of pectin 

 was issued to Douglas. Since that time it has come into general use in jelly and 

 preserve making. 



The pectin content of fresh apples averages about 0.5 percent. Chemically, 

 pectin is a polygalacturonate, containing 8 molecules of galacturonic acid. It 

 was pointed out by Manville (1936b) that galacturonic acid plays a definite role 

 in mucin formation and in this respect has a vitamin A-sparing action. 



The uronic acid content of apples, as reported by Manville (1936b) and shown 

 in Table 4, appears to vary with the variety of apple; but in all cases apples were 

 considerably richer in this compound than such fruits as lemons, oranges, or 

 tomatoes. 



