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33.2.44 AOAC Official Method 990.20 Solids (Total) in Milk By Direct Forced Air Oven Drying First Action 1990 Final Action 1993 IDF–ISO–AOAC Method

Results of the interlaboratory study supporting acceptance of the method: sr = 0.019; sR = 0.042; RSDr = 0.149%; RSDR = 0.327% A. Principle

Total solids are determined by weighing milk, drying milk, and weighing dried milk residue. Test portion is dried 4 h at 100° ± 1°C in forced air oven. Total solids content of milk is weight of dried milk residue expressed as % of original milk test portion weight. B. Apparatus

See 990.19B(a)–(d) and (f)–(h) (see 33.2.43). C. Determination

See 990.19C(a) and (b) (see 33.2.43), and in addition: (a) Ini tial weigh ing.—(Note: Sam ple and weigh milk at 38° ± 1°C. Record all weights to 4 decimal places.) Remove metal shelf from oven and place next to balance. Weigh predried weighing dish. Pipet ca 3 g of 38° ± 1°C prepared test portion to nearest 0.1 mg

directly into preweighed dish. Do not chase drift. Record test portion weight immediately after weight stabilizes and just before start of drift to lower numbers. Remove dish from balance and place on oven shelf for transport to oven. Check balance zero between weighings. (b) Blanks.—Weigh 2 empty, predried dishes. (c) Drying.—Preheat oven to 100° ± 1°C. Open hot air exhaust vent to let moisture be removed from oven. After test portions are weighed, turn off oven and place shelf plus all dishes (including blanks) into forced air oven. (Note: Do not place dishes on solid trays; this does not allow heat to circulate evenly around dishes. Do not place anything else in oven.) Immediately after loading all test portions in oven, close door and turn oven on again, and dry for 4 h at 100° ± 1°C. Do not open oven door until 4 h drying is completed. (d) Cooling.—Remove dishes from oven and let cool to room temperature in desiccator (³30 min). Weigh dish plus dry milk on same balance that was used for initial weighings. D. Calculations

See 990.19D (see 33.2.43). E. Repeatability and Reproducibility

Repeatability (r) and reproducibility (R) values established in the collaborative study were 0.054 and 0.118, respectively. Reference: JAOAC 72, 712(1989).

2006 AOAC INTERNATIONAL

ã 2005 AOAC INTERNATIONAL