Page 229 - Natural Antioxidants, Applications in Foods of Animal Origin

208 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir where K is the distribution coefficient,

n = the number of extractions,
V = unit of measurement for solvent system (sp. gr. × volume),
s
V = unit of measurement for meat homogenate (g).
m
The equation shows that the lipid fraction (containing products of lipid
oxidation) extracted from the raw meat homogenate increases with serial
extractions, the amount of solvent(s) is minimized when the K is large.
For meat applications, serial extractions are not always practical. There-
fore, the meat sample is finely ground under controlled conditions (to mini-
mize further oxidation during preparation) to have the same efficiency as
serial extractions:

1. The secondary oxidation products extracted should not react with the
solvent system.
2. The secondary oxidation products extracted should be easily recov-
ered; low temperature roto-vaporization under vacuum is often used.
3. The solvent should have low toxicity.

6.2 ANALYTICAL METHODS FOR QUANTIFYING PRODUCTS OF
LIPID OXIDATION

6.2.1 PEROXIDES

Peroxides are the initial products formed during lipid oxidation (Fig. 6.1).
The peroxides formed are odorless and tasteless. Nonetheless they are
widely used as an indicator of the current status of lipid oxidation. As will be
discussed later in this chapter, peroxide values (PVs) can be mathematically
combined with para-anisidine values (p-AVs) for a more comprehensive
approach for determining the oxidative status of meat and meat by-prod-
ucts. Three different methods may be used to determine the PVs on solvent
extracted lipids from meat.

1. Iodometric titration (color indicators, stoichiometry).
2. Photo-spectroscopic (Beer’s law).
3. Electrochemical (Nernst equation).

The iodometric titration method is a common method for determining
PVs on solvent extracted fat from a meat sample. A sample of extracted fat
containing a starch indicator is titrated with standardized sodium thiosulfate.