Food Lipids: Chemistry, Nutrition, and Biotechnology

Table 3 Membrane Deterioration in Animal and Plant Tissues
Tissue Description of deterioration Manifestations of deterioration
Animal Loss of membrane integrity
Oxidative degradation of membrane
lipids
Plant Loss of membrane integrity
Chilling injury
Senescence/aging
Dehydration
V. EMULSIFYING PROPERTIES OF PHOSPHOLIPIDS
Drip
Generation of off-flavors: rancid,
warmed-over
Loss of crispness
Surface pitting; discoloration
Premature yellowing
Failure to rehydrate
When one of two immiscible liquid phases is dispersed in the other as droplets, the
resulting mixture is referred to as an emulsion. To aid in the stabilization of mainly
oil/water emulsions, phospholipids may act as an emulsifier by adsorbing at the
interface of the two phases, their amphipathic character contributing to the lowering
of interfacial tension. To characterize this process more specifically, a sequence of
phase or pseudophase transitions was described near the phase boundary between
immiscible liquids upon hydration of an adsorbed phospholipid in n-decane [20].
These transitions were spherical reverse micelles → three-dimensional network from
entangled wormlike micelles → organogel separation into a diluted solution and a
compact gel or solid mass precipitating on the interfacial boundary. When prepared
in the presence of electrolytes, however, these phospholipid emulsions have a poor
stability due to the ability of electrolytes to enhance the vibration of the phospholipid
groups at the interface [21]. To circumvent the destabilizing effect of electrolytes,
steric surfactants at low concentrations (0.025–0.05%) may be added [22].
Both soybean lecithin and egg yolk are used commercially as emulsifying
agents. Egg yolk contains 10% phospholipid and has been used to help form and
stabilize emulsions in mayonnaise, salad dressing, and cakes. Commercial soybean
lecithin, containing equal amounts of phosphatidylcholine (PC) and inositol, has also
been used as an emulsifying agent in ice cream, cakes, candies, and margarine. To
expand the range of food grade emulsifiers having different hydrophilic and lipophilic
properties, lecithins have been modified physically and enzymatically.
VI. HYDROLYSIS OF PHOSPHOLIPIDS
Several types of ester functionality, all capable of hydrolysis, are present in the
component parts of glycerophospholipids (Fig. 1). These may be hydrolyzed totally
by chemical methods or selectively by either chemical or enzymatic methods.
A. Chemical Hydrolysis
Mild acid hydrolysis (trichloroacetic acid, acetic acid, HCl, and a little HgCl2) results
in the complete cleavage of alk-1-enyl bonds of plasmalogens, producing long chain
aldehydes. With increasing strength of acid and heating (e.g., 2 N HCl or glacial
acetic acid at 100�C), diacylglycerol and inositol phosphate are formed from phos-
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