Dye Reduction Method to Classify Raw and Determine Shelf-Life of Pasteurized Milk

EXERCISE 3
Dye Reduction Method to Classify Raw and Determine Shelf-life of Pasteurized Milk

I. OBJECTIVES

By the end of the exercise, the student should be able to: a. To determine and test the quality of milk samples; b. To determine the grade of the raw milk sample; c. To know the shelf-life of the milk sample and the efficiency of pasteurization.

II. DATA

Table 3.1. Observations on the test of raw milk sample using Resazurin Reduction Test for 3-hours at 1- hour interval.

TIME OBSERVATION DISCOLORATION
1st hour
2nd hour
3rd hour

Table 3.2. Observations on the test of raw milk sample using Methylene Blue Reduction Test for 3- hours at 30-minute interval.

TIME OBSERVATIONS FOR 3 TUBES
2:30 Purple (no color change)
3:00 Purple (no color change)
3:30 Purple (no color change)
4:00 Purple (no color change)
4:30 Purple (no color change)
5:00 Purple (no color change)
5:30 Purple (no color change)
6:00 Purple (no color change)

Table 3.3. Observations on the color changes of pasteurized milk samples subjected to Resazurin Reduction Test incubated at 7.20C for 7 days.

DATE OBSERVATIONS COW HEAD MAGNOLIA FRESH MILK 1st tube 2nd tube 1st tube 2nd tube
December 15 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent
December 16 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent
December 17 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent
December 18 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent
December 19 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent
December 20 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent
December 21 Blue - Excellent Blue - Excellent Blue - Excellent Blue - Excellent

III. ANSWERS TO QUESTIONS

1. What is the function of resazurin in the reduction test and what type of chemical reaction is involved?

Resazurin is a blue crystalline dye C12H7NO4 that is an

References: Atherton, H.V. and Newlander, J.A. 1977. Chemistry and Testing of Dairy Products, 4th ed. AVI, Westport, CT. Schwartz (1929). Milch. Forch. 7, 558. Thornton and Hastings (1929). J, Bact. 18, 319.