Page 230 - Natural Antioxidants, Applications in Foods of Animal Origin

Methods and Their Applications for Measuring 209
VetBooks.ir RH + O ROOH

(lipid) 2 (lipid hydroperoxide)

ROOH + 2KI + CH COOH I + K CH3 COO + 2H O
–
+
2
3
2

(purple solution)
I + 2Na S O Na S O + 2 NaI
6
2
2 4
3
2 2
(yellow translucent solution)
Because volume and normality of the standardized sodium thiosul-
fate solution are known, the PV is derived stoichiometrically (normality 1
× volume = normality × volume ). This relationship between the reactants
2
1
2
and products is shown the Equation 6.3.
×
×

×
(mL Na S O ) (N Na S O ) 0.127 meq. 1000 = Meq O (from hydro peroxides) (6.3)
3
2 2
2 2
2
4
wt. (g) of sample (solvent extracted fat or oil) Kg oil
PV may also be expressed based on the weight of the sample as long as
the exact fat content is known.
Calculation for PVs is based on “equivalents,” not equivalent weight.
Higher numerical values are indicative of a more oxidized sample. PVs that
distinguish rancid foods from non-rancid foods are based on experience and
science based historical data. As a guide, specifications for acceptable PVs
should be based on the following points:
1. Stage of processing (finished or raw material).
2. Product type (pepperoni, cooked beef roast, fresh sausage, etc.).
3. Required shelf life.
4. Sensory evaluation (aroma, flavor).
The data in Figure 6.3 show that PVs can be used to assess the oxida-
tive quality of freshly rendered lard. PV data provide information about the
storage stability of the rendered lard and the effectiveness of natural oxida-
tion inhibitors.
Interpretation of PV data in Figure 6.3 can be used to improve or imple-
ment GOMPs by incorporating natural oxidation in combination with a
nitrogen (N ) sparge and/or blanket as well as decreasing the turn over time
2
of the stored lard.
From our experience, the level of quantification (LOQ) has been ± 2 meq
kg fat or oil. The LOQ for the titrimetric measurement of PVs is based on
-1
the precision inherent in the method, the amount of the sample collected for
fat extraction, and the efficiency of the fat extraction procedure. Advances