AOAC Official Method 974.23 Bacterial Population of Maple Sap
First Action 1974
Final Action 1975
A. Principle
Resazurin is reduced to resorufin in direct proportion to bacterial action, with color change from purple to pink. Method permits rapid estimation of bacterial populations >1 ´ 106 cells/mL in maple sap.
B. Apparatus
(a) Serological pipets.—To deliver 1 and 10 mL, with 1.0 mL graduations; sterilized.
(b) Test tubes.—150 ´ 16 mm, screw-top with molded plastic caps; sterilized.
(c) Incubator or water bath with opaque cover.—Constant temperature, capable of maintaining 37.5 ± 0.5°C.
(d) Bottles.—200 mL amber, glass-stoppered.
C. Reagents
(a) Nonfat milk solution.—Dissolve 100 g instant nonfat dry milk in 500 mL H2O. Autoclave 15 min at 121°C.
(b) Resazurin dye.—Autoclave 200 mL H2O in amber glass bottle 15 min at 121°C. Using sterile forceps, add 1 standard (certified by Biological Stain Commission) resazurin dye tablet (Aldrich Chemical Co., No. 19, 930-3) and shake to completely dissolve dye before H2O cools. Store in cool, dark place. Prepare weekly.
(c) Sterile maple sap control.—Place 10 mL raw sap in test tube and autoclave 15 min at 121°C.
