2009_Book_FoodChemistry

18 Fruits and Fruit Products
18.1 Fruits
18.1.1 Foreword
Fruits include both true fruits and spurious fruits,
as well as seeds of cultivated and wild perennial
plants. Fruits are commonly classified as pomaceous
fruits, stone fruits, berries, tropical and subtropical
fruits, hard-shelled dry fruits and wild
fruits. The most important fruits are presented in
Table 18.1 with pertinent data on botanical classification
and use. Table 18.2 provides data about
fruit production.
18.1.2.1.1 Proteins, Enzymes
The protein fraction varies greatly with fruit variety
and ripeness. This fraction is primarily enzymes.
Besides those involved in carbohydrate
metabolism (e. g., pectinolytic enzymes, cellulases,
amylases, phosphorylases, saccharases,
enzymes of the pentose phosphate cycle, aldolases),
there are enzymes involved in lipid
18.1.2 Composition
Fruit composition can be strongly influenced
by the variety and ripeness, thus data given
should be used only as a guide. Table 18.3
shows that the dry matter content of fruits
(berries and pomme, stone, citrus and tropical
fruits) varies between 10–20%. The major
constituents are sugars, polysaccharides and
organic acids, while N-compounds and lipids
are present in lesser amounts. Minor constituents
include pigments and aroma substances of
importance to organoleptic quality, and vitamins
and minerals of nutritional importance.
Nuts are highly variable in composition (Table
18.4). Their moisture content is below 10%,
N-compounds are about 20% and lipids are as
high as 50%.
18.1.2.1 N-Containing Compounds
Fruits contain 0.1–1.5% N-compounds, of which
35–75% is protein. Free amino acids are also
widely distributed. Other nitrogen compounds
are only minor constituents. The special value of
nuts, with their high protein content, has already
been outlined.
Fig. 18.1. Protein patterns of various wine cultivars
obtained by isoelectric focussing (pH 3–10) using
Sephadex G-75 as a gel support medium. Staining was
done by Coomassie Blue. The figures show the electropherograms
and the corresponding densitograms.
Cultivation region South Palatinate; 1 Morio Muscat,
2 Mueller-Thurgau, 3 Rulaender, 4 Sylvaner (according
to Drawert and Mueller, 1973)
H.-D. Belitz · W. Grosch · P. Schieberle, Food Chemistry 807
© Springer 2009