LPT 321: Meat Science (1+1)

ESTIMATION OF TYROSINE VALUE

• In the presence of tyrosine, folin ciocalteu phenol reagent produces blue colour, the intensity of which is a measure of protein cleavage.
• Tyrosine value can effectively monitor the meat quality to indicate proteolysis and to measure the amino acid tyrosine and tryptophan present in a non polar extract of meat.
• Tyrosine value increases rapidly in meat stored at 7° C than at -10° C.

Apparatus required

• Blender
• Glass funnel
• Measuring cylinder
• Test tubes
• Volumetric flask
• Glass beakers
• Spectrophotometer
• Water bath
• Distilled water bottle
• Whatman No.1 filter paper (18.5 cm dia.)

Reagent

• Folin ciocalteu phenol reagent
• Tyrosine
• Trichloro acetic acid
• 0.5 N Sodium hydroxide
• Distilled water

Preparation of TCA extract

• As in estimation of TBA number.

Procedure

• 2.5 ml of TCA extract is diluted with equal quantity of distilled water in a test tube.
• To this 10 ml of 0.5 N sodium hydroxide is added followed by 3 ml of diluted folin ciocalteu phenol reagent (1 part of folin ciocalteu phenol reagent with 2 parts of distilled water).
• After mixing keep it for 15 minutes at room temperature.
• The developed blue colour is measured as absorbance value at 660 nm in a spectrophotometer using a blank (5 ml of 5% TCA) for comparison.
• With reference to the standard graph, the tyrosine value will be calculated and expressed as mg of tyrosine/ 100 gm of meat sample.

Preparation of standard graph for the estimation of tyrosine value

• 100 mg of pure tyrosine is dissolved in 500 ml 5% trichloroacetic acid in a volumetric flask.
• The following volume of tyrosine solution is transferred to a series of 100 ml volumetric flask: 0, 1 ml, 3 ml, 5 ml, 7 ml, 9 ml, 10 ml, 12 ml, 15 ml and 20 ml.
• The volume of each volumetric flask is made upto the mark with distilled water and mixed thoroughly.
• To 5 ml of each of this solution in a test tube add 10 ml 0.5 N sodium hydroxide and 3 ml of diluted folin ciocalteu phenol reagent and mix well.
• This is kept for 15 minutes at room temperature.
• The developed colour is measured as absorbance at 660 nm in a spectrophotometer as described earlier.
• The value of absorbance is recorded for various dilution of tyrosine and plotted on a graph sheet.