AOAC Official Method 935.61 Gums in Salad Dressing Qualitative Tests

(Applicable in presence of starch.)
A. Reagents
(a) Calcium chloride solution.—Specific gravity 1.2 at 20°C. If cloudy, let solution stand so insoluble matter may precipitate, and then filter.
(b) Iodine solution.—See 940.30A(c) (see 43.1.24).
(c) Basic lead acetate solution.—Activate litharge by heating 2.5–3 h at 650–670°C in furnace (cooled product should be lemon color). Boil 430 g neutral Pb(CH3COO)2×3H2O, 130 g freshly activated litharge, and1LH2O30 min. Let mixture cool and settle; then dilute supernate to specific gravity of 1.25 with recently boiledH2O. [Solid basic Pb(CH3COO)2 may be substituted for the normal salt and litharge in preparation of solution. Because of error caused by volume of precipitate, this reagent is not recommended for clarifying products of low purity.]

B. Separation of Gums from Starch
Defat 50 g salad dressing by heating on steam bath in 250 mL beaker until fat separates, cool, and extract with petroleum ether until last ether extract is colorless. Make alkaline with MgCO3 (2–2.5 g), testing with pH test paper. Heat mixture in H2O bath at 80°C until residual ether and CO2 are expelled. Add 100 mL CaCl2 solution and heat in boiling H2O bath 30 min, stirring occasionally.

Pour into 250 mL Pyrex centrifuge bottle, centrifuge, and decant as much of supernate as possible into 250 mL separator. Add 10 mL CaCl2 solution to residue in bottle and shake well. Centrifuge and decant supernate as before into separator. Swirl funnel gently and let oil separate. Drain all material below oil into another 250 mL Pyrex centrifuge bottle. Centrifuge and filter supernate through 11 cm Büchner fitted with Whatman No. 1, or equivalent, paper precoated with layer of Celite filter-aid, or equivalent. Collect filtrate in beaker within bell jar or in large test tube in suction flask. Add 10 mL CaCl2 solution to residue in centrifuge bottle, shake well, centrifuge, and decant supernate onto filter in Büchner. Wash filter with enough
CaCl2 solution to make total volume filtrate ca 110 mL. Add slowly, with stirring, 20mLI2 solution to clear extract