CN102338749A

CN102338749A - Determination method of protein content in foodstuff

Info

Publication number: CN102338749A
Application number: CN2010102379279A
Authority: CN
Inventors: 郭景鹏; 沙飞翔; 丁国才
Original assignee: SHANGHAI HAIDI GARDENING CO Ltd
Current assignee: SHANGHAI HAIDI GARDENING CO Ltd
Priority date: 2010-07-27
Filing date: 2010-07-27
Publication date: 2012-02-01

Abstract

The invention relates to a determination method of the protein content in foodstuff in the technical field of food detection, comprising the following steps of: digesting a sample by using a digestive juice of hydrogen peroxide and concentrated sulfuric acid so as to obtain a mixed solution; taking the mixed solution, using methyl red as an indicator, and adding a NaOH aqueous solution; adding a formaldehyde solution, shaking, adding a phenolphtalein indicator, titrating by the use of a NaOH aqueous solution at the concentration of C until the mixed solution shows reddish and does not fade in color within half a minute, recoding the volume V of the consumed NaOH aqueous solution, and calculating the protein content by the use of a formula. The digestive juice used in the method can help accelerate the digestive speed of the sample, shorten the digestive time and accelerate the analysis speed; in addition, the formaldehyde method is adopted for titration so as to simplify the operation.

Description

The assay method of protein content in the food

Technical field

The present invention relates to the food inspection technical field, be specifically related to the assay method of protein content in a kind of food.

Background technology

Protein is the important component that constitutes biological cell, and the protein in the food is unique source of nitrogen in the human body, has the irreplaceable effects of biomacromolecule such as carbohydrate and fat.Nutrition and Metabolism in protein and the biosome, eucaryotic cell structure, enzyme, hormone, virus and immunity, substance transportation and heredity etc. are closely related, and it separates and qualitatively or quantitatively determines in Food Inspection significant.Measuring method for determination of protein in the food has a variety ofly, generally can be divided into indirect method and direct method, and indirect method is through the nitrogen content of protein in the working sample and then calculates protein content; Direct method is then directly measured Protein content according to the physics or the chemical property of protein.Kjeldahl also is a method the most frequently used in the protein determination as the official method of foodstuff product protein content determination, and it is stable, accurate to measure the result with it; At home and abroad obtained adopting widely; But this method complex operation, reagent consumption is big, the SO that discharges during digestion ₂Health is caused direct harm, and time-consuming, take the electricity, water wasting; Also all there is the shortcoming of complex operation in other such as methods such as AAS and titrimetrys; And it is too high to utilize kjeldahl apparatus to carry out the protein determination cost, and since instrument costliness itself be difficult to promote the use of.

Summary of the invention

It is loaded down with trivial details to the objective of the invention is to overcome in the prior art in the food assay method complicated operation of protein content, big to operating personnel's harmfulness, the technical matters that expense is too high.

The assay method of protein content comprises the steps: in the food of the present invention

Step 1, the digestive juice sample digestion with the oxydol and the concentrated sulphuric acid are formed gets mixed solution;

Step 2 is got mixed solution, as indicator, adds the WS of NaOH with methyl red;

Step 3 adds the formalin jolting, adds phenolphthalein indicator afterwards; Use concentration not fade in WS titration to the blush half a minute as the NaOH of C; The volume V of the WS of the NaOH that record consumes utilizes formula to calculate Protein content, and said formula is:

Protein content=CV * 14.01 * 6.25 * 100%/m, wherein, m is the sample quality that contains in the mixed solution of getting in the step 2.

Preferably, the concentration of said oxydol is 8.8mol/L.

Preferably, the volume ratio of the oxydol and the concentrated sulphuric acid is 4: 1 in the said digestive juice.

Preferably, said digestion comprises the steps: sample thief, adds the concentrated sulphuric acid, and heating drips digestive juice, and heating makes solution become colorless by black, heating, cooling, adding distil water constant volume.

Preferably, in the WS of said adding NaOH with digestive juice in acid-specific be: use the WS neutralisation of sulphuric acid of the NaOH of 2.5mol/L earlier, use WS titration to the red color disappeared yellowing of the NaOH of 0.1mol/L during near terminal point instead.

Preferably, the concentration of said formalin is 6.5mol/L.

Preferably, the concentration of the WS of said NaOH is 0.1mol/L.

The present invention has following beneficial effect:

(1) digestive juice of method use of the present invention can be accelerated the digestion rate of sample, shortens digestion time, makes analysis speed accelerate;

(2) method of the present invention adopts formaldehyde method to carry out titration, has simplified operation;

(3) method of the present invention has been eliminated air pollution, has reduced the harmfulness to operating personnel, and has practiced thrift reagent and water power;

(4) method of the present invention is suitable for carrying out the protein content determination of batch samples.

Embodiment

Below in conjunction with specific embodiment, the present invention is described further.Should be understood that following examples only are used to the present invention is described but not are used to limit scope of the present invention.

Embodiment

The slaking apparatus that uses in the present embodiment is: replace kjeldahl flask with 100ml pyriform three-necked bottle; Connect tap funnel, vacuum conditions pipe and bend pipe above respectively; Bend pipe links to each other with vacuum pump with the bottle,suction of interior Sheng dilute alkaline soln with conduit, and the flue gas that digestion is produced absorbs with alkali lye.

The reagent that uses among the embodiment is:

The concentrated sulphuric acid is purchased in Chemical Reagent Co., Ltd., Sinopharm Group;

8.8mol/L hydrogen peroxide is purchased the Group Co.,Ltd of becoming civilized in Kaifeng;

NaOH is purchased the chemical reagent factory in the Zibo City;

Formaldehyde is purchased the chemical reagent factory in the Zibo City;

Hexamethylenetetramine is purchased in Nat'l Pharmaceutical & Biological Products Control Institute;

Phenolphthalein indicator is purchased reagent three factories in Shanghai City;

Methyl red indicator is purchased reagent three factories in Shanghai City.

1, sample digestion gets mixed solution

Take by weighing the 0.5g sample and place slaking apparatus, add concentrated sulphuric acid 5ml; Open vacuum pump; Regulate the pressure in the three-necked bottle with screw clamp; The flue gas of generation is absorbed by alkali lye fully; Three-necked bottle is put and is heated 2～5min on the electric furnace, slowly drips the 15ml digestive juice with tap funnel then, and said digestive juice is to be that oxydol and the concentrated sulphuric acid of 8.8mol/L is that 4: 1 ratio is mixed and got by volume with concentration; Add continued heating 3min, sample is become colorless by black, heats 2min again, removes H ₂O ₂Slowly add distilled water 20ml after the cooling, shake up, quantitatively be transferred in the 100ml volumetric flask, with distilled water diluting to scale.

2, get mixed solution, add in the WS of NaOH with mixed solution in acid

Get mixed solution 10ml in the triangular flask of 100ml, add 2 of distilled water 20ml and methyl red indicators, use distilled water diluting earlier here, can prevent in the process of the follow-up NaOH of adding solution, to occur the local overrich of alkali, avoid producing the ammonia mistake of from solution, escaping; Earlier with in the NaOH solution of 2.5mol/L with superfluous sulfuric acid, the NaOH solution titration of using 0.1mol/L during near terminal point instead is to the red color disappeared yellowing, can avoid adding excessive alkali with the NaOH solution neutralizing acid with low concentration after the high concentration earlier.

3, titration

The formalin 10ml that adds 6.5mol/L, powerful jolting 0.5min places 1～2min, adds 2 of phenolphthalein indicators then, does not move back with NaOH standard solution titration to blush half a minute of 0.1mol/L, is terminal point, writes down the volume of quota of expenditure solution;

Said formula is: protein content=CV * 14.01 * 6.25 * 100%/m, and wherein, C is the concentration of NaOH standard solution, and V is the volume of the WS of the NaOH that consumes, and m is the quality of sample in the mixed solution in the step 2.

The result of implementation of present embodiment:

(1) determination of recovery rates

Get 3 duplicate samples (soybean), add a certain amount of hexamethylenetetramine respectively, press the method for embodiment and measure, the theoretical nitrogen content of this primary standard substance is 39.85%, and the result is as shown in table 1.The result shows that average recovery rate is 98.80%.

Table 1

Numbering	Nitrogen content (%)	The recovery (%)
			1	39.14	98.89
2	39.96	98.43
			3	39.21	99.07
On average	39.10	98.80

(2) protein content determination

With the protein content in the method working sample (soybean) of conventional Kjeldahl (seeing protein measuring method in the GB/T14771-93. food [S]) and present embodiment; The result is as shown in table 2; As shown in table 2; The result that the method for present embodiment is measured measures basically identical as a result with conventional Kjeldahl, has very high accuracy.

Table 2

In sum, of the present invention method is simple, and analysis speed is fast, and security is higher, and is with low cost, and the precision of sample determination is higher, measures result and conventional Kjeldahl and measure basically identical as a result, is convenient to apply on a large scale.

Claims

1. the assay method of protein content in the food is characterized in that, comprises the steps:

2. the assay method of protein content is characterized in that in the food as claimed in claim 1, and the concentration of said oxydol is 8.8mol/L.

3. the assay method of protein content in according to claim 1 or claim 2 the food is characterized in that in the step 1, the volume ratio of the oxydol and the concentrated sulphuric acid is 4: 1 in the said digestive juice.

4. the assay method of protein content is characterized in that in the food as claimed in claim 1, and in the step 1, said digestion comprises the steps: sample thief; Add the concentrated sulphuric acid, heating drips digestive juice, and heating makes solution become colorless by black; Heating, cooling, adding distil water constant volume.

5. the assay method of protein content in the food as claimed in claim 1; It is characterized in that; In the step 2; In the WS of said adding NaOH with digestive juice in acid-specific be: use the WS neutralisation of sulphuric acid of the NaOH of 2.5mol/L earlier, use WS titration to the red color disappeared yellowing of the NaOH of 0.1mol/L during near terminal point instead.

6. the assay method of protein content is characterized in that in the food as claimed in claim 1, and in the step 3, the concentration of said formalin is 6.5mol/L.

7. the assay method of protein content is characterized in that in the food as claimed in claim 1, and in the step 3, the concentration of the WS of said NaOH is 0.1mol/L.