GB 5009.230-2016National Food Safety Standard -- Determination of carbonyl value (English PDF)

3.1 Reagents

3.1.1 Ethanol (C2H6O). analytical purity.

3.1.2 Benzene (C6H6). spectral purity or chromatographic purity.

3.1.3 2,4-dinitrophenylhydrazine (C6H6N4O4). analytical purity.

3.1.4 Trichloroacetic acid (C2H6Cl3O2). analytical purity.

3.1.5 Potassium hydroxide (KOH). analytical purity.

3.1.6 Petroleum ether (C5H12O2). analytical purity, boiling range. 30 °C~60 °C.

3.1.7 Aluminum powder (Al). analytical purity.

3.2 Preparation of Reagents

3.2.1 Refined ethanol. take 1,000 mL of ethanol and place it in 2,000 mL round-bottom flask; add 5 g of aluminum powder, zeolite and 10 g of potassium hydroxide; connect with the reflux condenser of standard grinding mouth; start heating and reflux for 1 h in water bath, then, adopt all-glass distillation unit to distill and gather the distillate.

3.2.2 Trichloroacetic acid solution. weigh-take 4.3 g of solid trichloroacetic acid, add

100 mL of benzene to dissolve it.

evaporator under the room temperature; decompress and recover the reagent; use air-blowing drying oven to volatilize petroleum ether for 1 h under 50 °C, then, obtain grease for later determination. Store it in the refrigerator under 4 °C before usage.

5.2.3 Samples with low content of grease, such as bread and biscuit. weigh-take 250 g~300 g of mixed sample and place it in 500 mL wide-mouth bottle with a lid; add an appropriate amount of petroleum ether to soak the sample and place it for 14 h~18 h.

Take quick filter paper to filter it; start rotary evaporation for 15 min with a rotary evaporator under the room temperature; decompress and recover the reagent; use air-blowing drying oven to volatilize petroleum ether for 1 h under 50 °C, then, obtain grease for later determination. Store it in the refrigerator under 4 °C before usage.

5.2.4 Samples with high content of water. add an appropriate amount of anhydrous

sodium sulfate to make the sample granular; easily agglomerated sample. add 4 times~6 times of sea sand, mix it up, then, extract grease.

5.3 Determination

Weigh-take 0.025 g~0.5 g (accurate to 0.1 mg) of grease sample. weigh-take 0.1 g of grease sample with carbonyl value < 30 meq/kg; weigh-take 0.05 g of grease sample with carbonyl value 30 meq/kg~60 meq/kg; weigh-take 0.025 g of grease sample with carbonyl value >60 meq/kg; place it in 25 mL tube with a plug, then, add 5 mL of benzene to dissolve the grease sample; add 3 mL of trichloroacetic acid solution and

5 mL of 2,4-dinitrophenylhydrazine solution; meticulously shake it and mix it up.

Heat it up for 30 min in water bath at 60 °C; after reaction, take it out and use running water to cool it down to the room temperature. Slowly add 10 mL of potassium hydroxide-ethanol solution along the tube wall to turn it into two-liquid layer. Start vortex oscillation and mix it up, then, place it evenly for 10 min.

Take 1 cm colorimetric cup and adjust the zero point with reagent blank; measure absorbance at the wavelength of 440 nm.