Determination of Vitamin B1 in Food

Vitamin B 1 is also known as thiamine .
Natural vitamin B _{1 is} mostly found in bran and germ; in foods such as cereals, beans, nuts, lean pork, etc.
, it usually exists in nature in free form or in the form of pyrophosphate.

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Quantitative analysis of vitamin B ₁ in foods can be performed spectrophotometrically by using free vitamin B ₁ which can be coupled with a variety of diazonium salts to show various colors

1.
Principle

After the sample is treated with hot dilute acid, vitamin B _{1 is} extracted
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If vitamin B contained in the sample ₁ are in free form, it may be in an alkaline potassium ferricyanide direct oxidation of thiamine ethyl thiazole dye solution, under UV irradiation, ethyl thiazole dye fluoresce

Where x——the content of thiamine in the sample, mg/100g

U-sample fluorescence intensity

U _b —— sample blank fluorescence intensity

S-standard fluorescence intensity

S _b ——Standard blank fluorescence intensity

p——The concentration of thiamine standard solution, ug/mL

V——Volume of standard thiamine used for purification, mL

V ₁ ——The constant volume volume of the sample after hydrolysis, mL

V ₂ ——The volume of extraction liquid used by the sample for purification, mL

m——sample mass, g
——sample content is converted from micrograms per gram (ug/g) to milligrams per hundred grams (mg/100g) coefficient

The calculation result retains two significant digits
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The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean

2.

Tips

(1) the sample generally vitamin B ₁ of free type, there are bound to, and enzymatic hydrolysis with acid, so bound into free type, and then applied to the determination
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If the sample contains too much impurities, it should be treated with an ion exchanger to separate thiamine from the impurities, and then use the resulting solution for determination

(2) Artificial pumice is required for sample purification, and its dosage depends on the sampling volume
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Generally, each gram of artificial pumice can absorb 30ug of thiamine .

If the amount of thiamine is too large, the recovery rate will decrease

(3) After the sample is mixed with potassium ferricyanide solution, the yellow color should be maintained for at least 15s to prove that the amount of potassium ferricyanide is sufficient, otherwise 1 to 2 drops of potassium ferricyanide should be added dropwise
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Because the sample contains reducing substances and the amount of potassium ferricyanide is insufficient, the oxidation of thiamine is incomplete, making the measurement result low

(4) Ultraviolet rays destroy sulfur pigments, so after the formation of sulfur pigments, it is necessary to measure quickly, and try to avoid light operation
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(5) Thiochrome is soluble in n-butanol , and it is more stable in n-butanol than in water, so the sulfur pigment is extracted with n-butanol
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Shaking should not be too strong during extraction to avoid emulsification and stratification

Related Links: Determination of Vitamin A in Food