GB/T 10742-2008Raw fiber material - Determination of pectin content (English PDF)

3.2.5 Ammonia water, NH3H2O, aqueous solution of ammonia, rho =

0.90 g/mL.

3.2.6 Ethanol solution containing hydrochloric acid. Measure 1 000 mL of ethanol; add 11 mL of hydrochloric acid (rho

1.19 g/ mL); mix well.

3.2.7 Ethanol washing solution containing hydrochloric acid. Measure 1 000 mL of ethanol, 11 mL of hydrochloric acid (rho

1.19 g/mL) and 250 mL of water; mix well. 3.2.8

0.1 mol/L sodium hydroxide solution. Weigh 4 g of sodium hydroxide and dissolve it in water; then, add water to fix the volume to 1 000 mL. 3.2.9 1 mol/L acetic acid solution. Measure 29 mL of glacial acetic acid (99% ~ 100%); add water to adjust the volume to 500 mL. 3.2.10 1 mol/L calcium chloride solution. Weigh 110 g of anhydrous calcium chloride and dissolve it in water; add water to adjust the volume to 1000 mL.

3.3 Apparatus Commonly used apparatus in the laboratory and the following apparatus.

3.3.1 Electronic balance, sensitivity

0.001 g.

3.3.2 Soxhlet extractor. 3.3.3 500 mL conical flask with reflux condenser.

3.3.4 Thermostatically controlled hot plate.

3.3.5 Oven, adjustable at 105 °C ± 2 °C.

3.4 Test procedure

3.4.1 Sample collection and processing Follow the provisions of GB/T 2677.1.

3.4.2 Weighing of samples Accurately weigh 1 g ~ 3 g (accurate to

0.001

g) of the sample and prepare two parallel samples. If the pectin content of the sample is high, adjust the sample amount according to the test value, where the minimum shall not be less than 1 g. At the same time, weigh another sample and determine the moisture content according to GB/T 2677.2.

3.4.3 Purification of sample Use qualitative filter paper to wrap the sample; tie it with thread; put it into the Soxhlet extractor (3.3.2). Add 100 mL of benzene alcohol mixture (3.2.2); place it in a boiling water bath for extraction for 3 h to remove interfering impurities; take out the sample and spread it out to air dry.

Note. The test shall be carried out in a fume hood. The used benzene-alcohol mixture can be distilled and purified before reuse.

3.4.4 Extraction of pectin Transfer the air-dried sample (3.4.3) to a 500 mL conical flask (3.3.3); add 100 mL of 1% ammonium oxalate solution (3.2.3); install a reflux condenser; heat in a boiling water bath for 3 h. Filter out the extract by pouring; try to keep the residue in the conical flask; do not let it flow into the filter paper. Add 100 mL of 0.5% ammonium oxalate solution (3.2.4) to the conical flask; install a reflux condenser; put it back in a boiling water bath; heat for 2 h to fully extract the pectin. Use the filter paper used last time to filter out the extract. Use hot water to wash the residue and filter paper three times; combine the filtrate obtained twice and the washing liquid in a 500 mL beaker.

3.4.5 Precipitation of pectin Place the filtrate on a thermostatically controlled hot plate; place an asbestos net on it; control the temperature so that the filtrate does not boil; evaporate and concentrate to 70 mL ~ 80 mL; cool it down and transfer it to a 100 mL volumetric flask; add water to the mark; shake it well. Transfer 25 mL of this solution to a 500 mL beaker; then slowly add 90 mL of ethanol solution containing hydrochloric acid (3.2.6) under constant stirring; let it stand overnight; filter. Use about 30 mL of ethanol washing solution containing hydrochloric acid (3.2.7) to wash the precipitated pectin substance three times.

3.4.6 Dissolution of pectin additional sample shall be tested. After excluding abnormal values, take the average of the three test values as the reported value.

4.2.4 Ammonia water, NH3H2O, aqueous solution of ammonia, rho =

0.90 g/mL.

4.2.5 Ethanol solution containing hydrochloric acid. Measure 1 000 mL of ethanol; add 11 mL of hydrochloric acid (rho =

1.19 g/mL); mix well.

4.2.6 Ethanol washing solution containing hydrochloric acid. Measure 1 000 mL of ethanol, 11 mL of hydrochloric acid (rho =

1.19 g/mL) and 250 mL of water; mix well. 4.2.7 1000 mg/L galacturonic acid standard solution. Weigh

0.1 g (accurate to 0.000 1

g) of galacturonic acid; dissolve it in water; add water to adjust the volume to 100 mL. 4.2.8 0.15% carbazole anhydrous ethanol. Weigh

0.075 g of carbazole; dissolve it in anhydrous ethanol; use anhydrous ethanol to adjust the volume to 50 mL.

4.2.9 Concentrated sulfuric acid, H2SO4, rho =

1.84 g/mL, mass fraction 95% ~ 98%.

4.3 Apparatus Commonly used apparatus in the laboratory and the following apparatus.

4.3.1 Electronic balance, sensitivity 0.000 1 g. 4.3.2 500 mL conical flask with reflux condenser.

4.3.3 Thermostatically controlled hot plate.

4.3.4 Ultraviolet-visible spectrophotometer.

4.4 Test procedure

4.4.1 Collection and processing of samples Follow the provisions of GB/T 2677.1.

4.4.2 Weighing of samples Weigh 1 g (accurate to

0.001

g) of the sample accurately and prepare two parallel samples. If the pectin content of the sample is high, adjust the sample amount according to the test value and reduce the sample amount to

0.2 g. At the same time, weigh another sample and determine the moisture content according to GB/T 2677.2.

4.4.3 Extraction of pectin Place the sample in a 500 mL conical flask (4.3.2); add 100 mL of 1% ammonium oxalate solution (4.2.2); install a reflux condenser; heat in a boiling water bath for 3 h. Filter out the extract by pouring; try to keep the residue in the conical flask; do not let it flow into the filter paper. Add 100 mL of 0.5% ammonium oxalate solution (4.2.3) to the conical flask; install a reflux condenser; put it back in a boiling water bath; heat for 2 h to fully extract the pectin. Use the filter paper used last time to filter out the extract. Use hot water to wash the residue and filter paper three times; combine the filtrate obtained twice and the washing liquid in a 500 mL beaker.

4.4.4 Precipitation of pectin Place the filtrate on a thermostatically controlled hot plate; place an asbestos net on it; control the temperature so that the filtrate does not boil; evaporate and concentrate to about 70 mL ~ 80 mL; cool it down and transfer it to a 100 mL volumetric flask; add water to the mark; shake it well. Transfer 25 mL of this solution to a 500 mL beaker; then slowly add 90 mL of ethanol solution containing hydrochloric acid (4.2.5) under constant stirring; let it stand overnight; filter. Use about 30 mL of ethanol washing solution containing hydrochloric acid (4.2.6) to wash the precipitated pectin substance three times.

4.4.5 Dissolution of pectin Put the precipitate obtained after filtration together with the filter paper into another small beaker; pour 75 mL of hot ammonia solution [mixed from 75 mL of boiling water and