AOAC 905_02

33.2.25

AOAC Official Method905.02

Fat in Milk

Roese-Gottlieb Method

First Action1905

Final Action

Reference Method1973

IDF–ISO–AOAC Method

Codex-Adopted–AOAC Method*

Prepare as in925.21(see33.2.02)and weigh,to nearest mg,ca

10g test portion into fat-extraction flask or tube.Add1.25mL

NH4OH(2mL if test sample is sour)and mix thoroughly.Add

10mL alcohol and mix well.Add25mL ether(all ether must be per-

oxide-free),stopper with cork or stopper(synthetic rubber)unaf-

fected by usual fat solvents,and shake very vigorously1min.Cool,

if necessary;add25mL petroleum ether(boiling range30–60°C)

and repeat vigorous shaking.Centrifuge flask at ca600rpm or let it

stand until upper liquid is practically clear.Decant ether solution

into suitable flask or metal dish.Wash lip and stopper of extraction

flask or tube with mixture of equal parts of the2ethers and add

washings to weighing flask or dish.Repeat extraction of liquid re-

maining in flask or tube twice,using15mL of each solvent each time

and adding H2O if necessary,but omitting rinsing with mixed sol-

vents after final extraction.(Third extraction is not necessary with

skim milk.)

Evaporate solvents completely on steam bath at temperature that

does not cause spattering or bumping(boiling chips may be added).

Dry fat to constant weight in oven at102±2°C or vacuum oven at

70–75°C under pressure<50mm Hg(6.7kPa).Weigh cooled flask

or dish,without wiping immediately before weighing.Remove fat

completely from container with15–25mL warm petroleum ether,

dry,and weigh as before.Loss in weight=weight fat.Correct weight

fat by blank determination on reagents used.If blank is>0.5mg,pu-

rify or replace reagents.Difference between duplicate determina-

tions obtained simultaneously by same analyst should be≤0.03g

fat/100g product.

References:Z.Nahr.Genussm.9,531(1905).

JAOAC34,237(1951);52,235(1969).

Revised:March1996

*Adopted as a Codex Reference Method(Type II)for gravimetry of fat in

milk.

?2000AOAC INTERNATIONAL