2009_Book_FoodChemistry

3.7 Changes in Acyl Lipids of Food 187
The role of waxes is to protect the surface of
plant leaves, stems and seeds from dehydration
and infections by microorganisms. Waxes are removed
together with oils by solvent extraction of
nondehulled seeds. Waxes are oil-soluble at elevated
temperatures but crystallize at room temperature,
causing undesired oil turbidity. Ceryl
cerotate (ceryl alcohol esterified with cerotic acid,
C 25 H 51 COOH)
(3.47)
is removed from seed hulls during extraction
of sunflower oil. Waxes are removed by an oil
refining winterization step during the production
of clear edible oil.
Waxes are also components of the mass used to
cover fruit to protect it from drying out.
Waxes are present in fish oils, especially in sperm
whale blubber and whale head oil, which contain
a “reservoir” of spermaceti wax.
3.6.2.2 Alkoxy Lipids
The higher alcohols, 16:0, 18:0 and 18:1 (9), form
mono- and diethers with glycerol. Such alkoxylipids
are widely distributed in small amounts
in mammals and sea animals. Examples of confirmed
structures are shown in Formula 3.48.
The elucidation of ether lipid structure is usually
accomplished by cleavage by concentrated HI at
elevated temperatures.
Batyl alcohol (3.50)
Selachyl alcohol (3.51)
3.6.3 Cutin
Plant epidermal cells are protected by a suberized
or waxy cuticle. An additional layer of epicuticular
waxes is deposited above the cuticle in many
plants. The waxy cuticle consists of cutin. This
is a complex, high molecular weight polyester
which is readily solubilized in alkali. The structural
units of the polymer are hydroxy fatty acids.
The latter are similar in structure to the compounds
given in 3.7.2.4.1. A segment of the postulated
structure of cutin is presented in Fig. 3.16.
3.7 Changes in Acyl Lipids of Food
3.7.1 Enzymatic Hydrolysis
Hydrolases, which cleave acyl lipids, are present
in food and microorganisms. The release of
short-chain fatty acids (<C 14 ), e. g., in the
hydrolysis of milk fat, has a direct effect on food
aroma. Lipolysis is undesirable in fresh milk
(3.48)
Common names of some deacylated alkoxy lipids
(1-O-alkylglycerol) are the following:
Chimyl alcohol (3.49)
Fig. 3.16. A structural segment of cutin (according to
Hitchcock and Nichols, 1971)