Pectin test protocol

Practical guidelines by Karien O'Kennedy - 05 Apr 2016

 What you need

  • See-through glass test tubes and test tube rack
  • 5 ml graduated glass pipette
  • Juice that is as clear as possible
  • Acidified alcohol

Method

  • Put 2.5 ml of juice in a test tube
  • Add 5 ml (or double the juice volume) of acidified alcohol
  • Mix gently and let it stand for 5 minutes

Interpretation of results

  • The presence of large flocs is an indication of incomplete depectinisation – not suitable for flotation
  • Small, evenly spread flocs is an indication that depectinisation is in process – not suitable for flotation
  • Clear juice indicates that depectinisation is complete – suitable for flotation
  • A very light, evenly spread haze that does not enlarge to flocs after 10 minutes is an indication of proteins also precipitating with the alcohol – suitable for flotation

 

Useful tips

If possible, obtain acidified alcohol from an analytical laboratory. Acidified alcohol is obtained by mixing hydrochloric acid (HCl) with 96% ethanol. This should preferably be done by a qualified laboratory technician. The final product is stable and the acid very diluted so it is not harmful if it accidently should come into contact with your skin during the mixing process.

Results must be read after exactly 5 minutes. Flocs will form immediately after alcohol addition if there is still a large concentration of long-chain pectin molecules. If the work of the enzyme is close to completion, flocs can take up to 5 minutes to form. Proteins can start to precipitate after 10 minutes, which can wrongly be interpreted as a positive pectin test.

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