Team:Paris Bettencourt/Protocols/titration-acid-phytic

Titration of phytic acid using Megazyme© Kit
  • Preparation of reagent solutions (not supllied) :
    • Trichloroacetic acid (50% w/v) : 100mL
      • Add 50g of thrichloroacetic to 60mL of distilled water and dissolve. Make to volume (100mL) with distilled water. (Stable for > 6 moths at 4°C)
    • Hydrochloric acid (0.66M) : 1L
      • Add 54.5mL of hydrochloric acid to 945.5mL of distilled wtaer an mix. (Store at room temperature)
    • Sodium hydroxide (0.75M) : 200mL
      • Add 6g of sodium hydroxide pellets to 180mL of distilled water and dissolve. Make to volume (200mL) with distilled water. (Store at room temperature)
    • Phytic acid :
      • Pure phytic acid control sample may be required.
  • Sample extraction :
    • Weigh 1g of sample material.
    • Add 20mL of hydrochloric acid (0.66M).
    • Cover with foil and incubate for a minimum of 3 hours at room temperature.
    • Transfer 1mL of extract to a 1.5mL microcentrifuge tube.
    • Centrifuge 10 minutes at 13,000rpm.
    • Transfer 0.5mL of the resulting extract supernatant to a fresh 1.5mL microfuge tube.
    • Add 0.5mL of sodium hydroxide solution (0.75M) to neutralise.
  • Enzymatic dephosphorylation reaction :
  • Colourimetric determination of phosphorous :
  • Preparation of phosphorous calibration curve :
  • Calculation :
    • Phosphorous calibration curve :
      • Determine the absorbance of each phosphorous standard. Substract the absorbance of STD0 from the absorbance of the others STD, therby obtaining ΔA(phosphorous). Calculate M as follows, for each standard: \[ \begin{align} M = \frac{P(\mu g)}{\Delta A (phosphorous)} \end{align} \] Use "Mean M" to calculate the phosphorous content of test samples.
    • Phosphorous / phytic acid content :
      • Determine the absorbance of the both "Free Phosphorous" and "Total Phosphorous". Substract the absorbance of the "Free Phosphorous" sample from the absorbance of the "Total Phosphorous" sample. Obtaining ΔA(phosphorous). \[ \begin{align} C^{o} = \frac{mean(M)\times 20 \times F}{10000 \times 1.0 \times \nu} \times \Delta A(phosphorous) \end{align} \]
      Where :
      \(20\) = original sample extract volume
      \(F\) = dilution factor
      \(10000\) = conversion from µg/g to g/100g
      \(1.0\) = wigh of original sample material
      \(\nu\) = sample volume

      It follows for phosphorous :
      \[ \begin{align} C^{o} ~= \frac{mean(M)\times 20 \times 55.6}{10000 \times 1.0 \times \nu} \times \Delta A(phosphorous)\\ ~= mean(M) \times 0.1112 \times \Delta A(phosphorous) \end{align} \] It follows for phytic acid :
      \[ \begin{align} C^{o} = \frac{phosphorus}{0.282} \end{align} \]