National Standard for the Determination of Organic Sulphides in Dehydrated Garlic in China

This standard is equivalent to the International Organisation for Standardisation (ISO) 5567-1982 "Determination of volatile organic sulphides in dehydrated garlic".

1 Summary of the method

The sample is soaked in water, ethanol is added, volatile organosulfur compounds are distilled, and the distillate in nitric acid medium is titrated by silver measurement method, and the content of volatile organosulfur compounds is calculated from the consumption of silver nitrate solution.

2 Reagents

2.1 Nitric acid (specific gravity 1.42)
2.2 Ethanol 95% (V/V)
2.3 Liquid paraffin
2.4 Nitric acid 10% (V/V)
2.5 Ammonium hydroxide 10% (V/V)
2.6 0.1000mol/L silver nitrate standard solution, preparation and calibration method according to GB 601-1977 "chemical reagent standard solution preparation method" operation.
2.7 0.1000mol/L ammonium thiocyanate standard solution, weighing ammonium thiocyanate 8g dissolved in 1L water. Calibration reference GB 601-1977 "chemical reagent standard solution preparation method" in the sodium thiocyanate calibration method.
2.8 Ferric ammonium sulfate indicator solution, saturated solution.

3 Instrumentation

During analysis, especially the distillation apparatus should be avoided contact with copper or rubber products, distillation apparatus are ground mouth glass connection.
3.1 The distillation apparatus (see diagram) is a 250mL long necked flask, capable of being used with a stopper and a gooseneck elbow, and the gooseneck elbow and straight tube condenser connections are either spherical or standard glass with ground ends.
3.2 250 mL ground-necked conical flasks, capable of being used in connection with a reflux condenser.
3.3 Constant temperature water bath, capable of controlling the temperature to 37±1°C.
3.4 G2 or G3 glass funnel.
3.5 Vacuum pump or water pump.
3.6 pH precision test paper, capable of indicating at pH = 7 ± 0.1. Allylated sulphur distillation unit.

4 Analytical Procedures

4.1 Sample pretreatment
Dehydrated Garlic Flakes were made into uniform particles and then sampled, Dehydrated garlic granules and garlic powder were sampled directly.
4.2 Sample size
Weigh about 10g sample, accurate to 0.01g.
4.3 Determination
4.3.1 Soaking
Put the weighed sample into a flask (3.1) with 100mL of 40°C water, stopper the flask with a ground glass stopper, and soak it in a constant temperature water bath (3.3) at a temperature of 37±1°C for 2h.
4.3.2 Distillation
After adding 20mL of ethanol (2.2) and 2mL of liquid paraffin (2.3) to the flask (3.1), quickly connect the flask to the distillation apparatus (see figure), and add 10mL of ammonium hydroxide (2.5) to the conical flask (3.2) so that the lower outlet of the condenser is submerged in the ammonium hydroxide solution.
Heat the flask (3.1) to stop distillation after obtaining 60 mL of distillate, wash the condenser with water, and collect the washings into a conical flask.
The temperature should be regulated during the distillation to avoid spillage of gas bubbles and to allow the appropriate rate of distillation to be obtained.
4.3.3 Titration
Neutralise the distillate (A) in the conical flask with nitric acid (2.4) and stabilise the pH at 7 ± 0.1 as measured with pH precision test paper (3.6). accurately add 20.00 mL of a standard solution of silver nitrate (2.6) to the distillate (A) and heat it in a water bath at reflux for 1 h. The distillate (A) is cooled to room temperature and filtered by pumping with a glass funnel, (3.4) a vacuum pump or a water pump (3.5) and the The precipitate was washed with hot water 4 times and the filtrate and washings (B) were collected. Add 5 mL of nitric acid (2.1) and a few drops of ferric ammonium sulphate indicator solution (2.8) to the filtrate and washing solution (B), titrate with 0.1000 mol/L ammonium thiocyanate standard solution (2.7) until the solution is light brown-red and keep it for 0.5 min.

5 Calculation of analysis results

5.1 Calculation method
The content of volatile organosulphur compounds in dehydrated garlic expressed as mass percentage of allylated sulphur is given by the following formula: mCVCX100057.0)20(21××××-=
Where: X--percentage content of volatile organosulfur compounds in dehydrated garlic, %;
C1 - concentration of silver nitrate standard solution (2.6), mol/L;
C2 - concentration of ammonium thiocyanate standard solution (2.7), mol/L;
V - volume of ammonium thiocyanate standard solution consumed, mL;
0.057 - grams of burnt propylated sulphur [(CH2CH=CH2)2S] equivalent to 1.00 mL of a standard solution of silver nitrate with C=1.000 mol/L;
m - mass of the specimen g. The results obtained shall be expressed to two decimal places.
5.2 Precision of the method
For the same operator, the difference between two consecutive results should not exceed 5 per cent of their mean value, otherwise repeat the determination.
5.3 Experimental report
Take the arithmetic mean of two determinations as the result.

Annotation:

This standard is proposed by the bureau of non-staple food of the ministry of commerce of the People's Republic of China.
This standard is responsible for drafting by Beijing food research institute.
The main drafter of this standard Shen Bing, Liu Zhenfang, Li Weidong, back to Jiuzhen.
Ministry of Commerce of the People's Republic of China 1988-02-29 approved 1988-07-01 implementation.