CN103529034B - Differentiate the method for milk freshness - Google Patents
Differentiate the method for milk freshness Download PDFInfo
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- CN103529034B CN103529034B CN201310476834.5A CN201310476834A CN103529034B CN 103529034 B CN103529034 B CN 103529034B CN 201310476834 A CN201310476834 A CN 201310476834A CN 103529034 B CN103529034 B CN 103529034B
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Abstract
The invention provides a kind of method of differentiating milk freshness, relate to field of food, described method comprises milk is mixed with to milk sample to be measured; The pH meter of calibration is inserted in milk sample to be measured, record pH value; By pH value with preset pH scope and compare, when pH value is during in default pH scope, milk is fresh, otherwise, stale; Default pH scope is: 6.54-6.80. The present invention has avoided the experimental error causing because of subjective factor in traditional acidity titration process, the method only needs operator that pH meter is inserted in milk sample to be measured, and reading, artificial property of participation is little, and manual operation is less on the impact of pH value result accuracy, thereby makes its measurement result more accurately and reliably.
Description
Technical field
The present invention relates to field of food, in particular to the method for differentiating milk freshness.
Background technology
The acidity of milk is an important measurement index of milk freshness. Measure at present oxThe method of milk acidity all adopts the method for acid base titration, reflects by titratable acidity (° T)The freshness of milk.
The mensuration of milk acidity generally adopts titration. This method is because reviewer is to used moltenConcentration, consumption, rate of titration and the titration end-point judgements etc. of liquid are all difficult to control, and therefore existAffect to a certain extent the accuracy of measurement result.
Summary of the invention
The object of the present invention is to provide the method for differentiating milk freshness, above-mentioned to solveProblem.
The method of differentiating milk freshness is provided in embodiments of the present invention, as Fig. 1, instituteShow, comprising:
Step 101, is mixed with milk sample to be measured by milk;
Step 102, inserts the pH meter of calibration in described milk sample to be measured, records pHValue;
Step 103, by described pH value with preset pH scope and compare, as described pHValue is in the time of described default pH scope, and described milk is fresh, otherwise, stale;
Described default pH scope is: 6.54-6.80.
The method of the discriminating milk freshness providing in the embodiment of the present invention, with existing skillTitratable acidity in art is compared, and it has following beneficial effect:
By the pH value of direct test milk sample to be measured, by this pH value with preset pH modelEnclose and compare, if dropped in scope, illustrate that milk is fresh, otherwise, stale. ThisThe experimental error causing because of subjective factor in traditional acidity titration process, the party have been avoided in inventionMethod only needs operator that pH meter is inserted in milk sample to be measured, and reading, artificialProperty of participation is little, and manual operation is less on the impact of pH value result accuracy, thereby makes itMeasurement result more accurately and reliably.
Brief description of the drawings
Fig. 1 is the step schematic diagram of differentiating milk freshness in one embodiment of the invention;
Fig. 2 is titratable acidity in one embodiment of the invention (° T)--pH corresponding diagram.
Detailed description of the invention
Also by reference to the accompanying drawings the present invention is done further in detail below by specific embodimentThin description.
The embodiment of the present invention provides a kind of method of differentiating milk freshness, as Fig. 1, and instituteShow, comprising:
Step 101, is mixed with milk sample to be measured by milk;
Step 102, inserts the pH meter of calibration in described milk sample to be measured, records pHValue;
Step 103, by described pH value with preset pH scope and compare, as described pHValue is in the time of described default pH scope, and described milk is fresh, otherwise, stale;
Described default pH scope is: 6.54-6.80.
By the pH value of direct test milk sample to be measured, by this pH value with preset pH modelEnclose and compare, if dropped in scope, illustrate that milk is fresh, otherwise, stale. Keep awayExempt from traditional acidity titration process artificial property of participation excessive, inaccurate the asking of result of causingTopic, the method only needs operator that pH meter is inserted to milk sample to be measured, and reading,Artificial property of participation is little, and manual operation do not exert an influence to the result of pH value, therefore,Result is accurate, and identification method is fast, easy to operate.
Next,, by some specific embodiments, describe this in detail and differentiate that fast milk is newThe method of freshness:
A method of differentiating milk freshness, comprising:
Step 201, prepares instrument, reagent;
ZD-2A automatical potentiometric titrimeter, accuracy is 0.01, for acidity titration;
Universal buret, adopts tetrafluoroethene cock, and scale division is 0.1mL, forAcidity titration;
PH meter, glass electrode, is soaked in saturated kCl solution, for the survey of pH valueExamination;
Balance, sensibility reciprocal is 1 milligram, for weighing;
Standard solution of sodium hydroxide, 0.0861mol/L, for acidity titration;
PH titer: pH6.86(mixed phosphate salting liquid, 25 DEG C), the adjacent benzene of pH4.01(Diformazan potassium hydrogen phthalate, 25 DEG C), calibrate for pH meter;
Water, adopts distilled water, cleans for solution preparation and instrument.
Step 202, calibration pH meter;
Adopt 2 calibration methods, the method is comparatively general calibrating mode.
Select in certain embodiments following calibration condition: calibration temperature is 25 DEG C; Calibration markAccurate liquid comprises: the mixed phosphate salting liquid of pH6.86, the Potassium Hydrogen Phthalate of pH4.01Solution.
Concrete operation step:
Open instrument power source, preheating half an hour, after parameters is stable, calibrate. AdoptIt is calibrated with 2 calibration methods. Take out pH meter glass electrode, carry out with distilled waterRinse, and cleaned. Regulate the temperature adjustment knob to 25 DEG C of instrument. First, by pH meterGlass electrode is inserted in the standard liquid of pH6.86, regulates positioning knob, makes its registrationBe shown as 6.86; Then, take out pH meter glass electrode, after being cleaned up, be inserted intoIn the pH standard liquid of pH4.01, now regulate slope knob, make it be shown as 4.01.In these two kinds of pH standard liquids, calibration repeatedly, overregulates slope knob instrument until obstructedTill just can accurately demonstrating the registration of pH titer, now, instrument calibration is complete.
Step 203, prepares milk sample to be measured;
Mixing match is: by 10 grams of described milk (preferably mixing) and 20 milliliters of steamingsHeating up in a steamer water mixes.
Wherein, in certain embodiments, milk is accurate to 0.001 gram.
Concrete operation step is: take the milk that 10 grams (being accurate to 0.001 gram) have mixedSample, is placed in 150 milliliters of conical flasks, adds 20 ml distilled waters to it, mixes.
Step 204, inserts the pH meter of calibration in milk sample to be measured, records pH value;
The pH meter of calibration is inserted in milk sample to be measured, after its registration is stable, recordPH reading.
Step 205, by pH value with preset pH scope and compare;
Default pH scope is: 6.54-6.80, this scope be by titratable acidity (° T) andBetween pH value, set up that regression equation calculation gets. How rear extended meeting is to setting up recurrence sideJourney, and how to be converted into pH value by titratable acidity and to describe.
Wherein, default pH method of determining range, comprising:
Step 301, utilizes some parts of milk samples to be measured of aforesaid way preparation;
Step 302, carries out respectively acidity titration by milk sample to be measured every portion and drips to determineDetermine acidity (° T);
With standard solution of sodium hydroxide rinse buret 2-3 time, in buret, add hydrogen-oxygenChange sodium standard solution, make the concave meniscus of standard solution of sodium hydroxide higher than zero groove of buret(being preferably controlled at zero groove a little more than buret), gets rid of in buret and tube connectorThe bubble of portion, is down to below zero groove the concave meniscus of standard solution of sodium hydroxide, records thisTime the scale value corresponding to concave meniscus of standard solution of sodium hydroxide, and be defined as NaOHThe initial volume V of standard liquidInitial NaOH；
In titration process, carry out continuous stirring to milk sample to be measured, ensure whole mistakeCheng Dangzhong solution can mix rapidly, and concrete mode can adopt and use continuously stirring rodThe mode stirring, or in conical flask, add magneton.
Milk sample to be measured is carried out to titration with the standard solution of sodium hydroxide in buret, andAnd the pH meter of calibration is measured the pH of milk sample to be measured in titration process at any time;
In the time that the pH meter of calibration shows 8.3, stop titration;
Record the concave meniscus that titration finishes standard solution of sodium hydroxide in rear buret correspondingScale value, and be defined as the terminal volume V of standard solution of sodium hydroxideTerminal NaOH；
Utilize VInitial NaOHAnd VTerminal NaOHThe NaOH standard of calculating titration use is moltenThe amount of liquid, then utilizes acidity computing formula to calculate titratable acidity.
The computational methods of titratable acidity (° T) are with reference to standard GB/T 5413.34-2010 " foodThe mensuration of the safe national standard-milk and milk products of product acidity " carry out.
Step 303, and utilize the method for above-mentioned discriminating milk freshness to carry out pH mensuration;
Step 304, sets up titratable acidity--the corresponding relation of pH of milk sample;
This corresponding relation, sees the following form:
Table 1: the corresponding data of titratable acidity and pH
Step 305, according to the titratable acidity of all umbers (° T)--the corresponding relation of pH,Determine equation of linear regression;
Map according to table 1, as shown in Figure 2, by the figure doing, known, pH withBetween ° T, exist stronger linear relationship.
According to table 1 and Fig. 2, and by can be calculated accordingly linearity side between the twoCheng Wei:
pH=7.3091-0.0425°T
r=-0.8571
Step 306, according to equation of linear regression, calculating titratable acidity is 12 ° of T and 18 ° of TTime corresponding pH, obtain default pH scope.
In the time that titratable acidity is 12 ° of T, now pH=6.80;
In the time that titratable acidity is 18 ° of T, now pH=6.54.
Therefore default pH scope is 6.54-6.80.
The freshness of milk is weighed by acidity, mainly for full-cream, half degreasing,Corresponding pasteurization milk and sterile milk in the milk of degreasing are measured, national standard requirementThe acidity of pasteurization milk and sterile milk is 12-18 ° of T, namely pH 6.54-6.80 itBetween. Therefore we can, directly by measuring the pH of sample milk, just can come fastJudge the freshness of milk. The method is easy, fast and have stronger scientific basis andReliability.
The present invention mainly for milk comprise pasteurization milk (full-cream, degreasing and part be de-Fat) and sterile milk (full-cream, degreasing and partially skimmed). According to standard GB/T19645-2010 " national food safety standard-pasteurization milk ", GB25190-2010 " foodSafe national standard-the sterile milk of product " known, acidity requires as 12-18 ° of T. Mark according to countryAccurate GB5413.34-2010 " mensuration of national food safety standard-milk and milk products acidity "Requirement formulate milk sample, we find initial pH and the titratable acidity (° T) of sampleBetween exist stronger linear regression relation. We pass through a large amount of experimental data of statistics,Finally establish the regression equation between initial pH and the titratable acidity (° T) of sample. LogicalCross regression equation, can be easy to draw corresponding relation between the two, also just can calculateGo out 12 ° of T and the 18 ° of T pH of milk in corresponding initial sample respectively, also just drawn newThe scope of the pH that fresh milk sample is corresponding.
By the pH value of direct test milk sample to be measured, by this pH value with preset pH modelEnclose and compare, if dropped in scope, illustrate that milk is fresh, otherwise, stale. ThisThe experimental error causing because of subjective factor in traditional acidity titration process, the party have been avoided in inventionMethod only needs operator that pH meter is inserted in milk sample to be measured, and reading, artificialProperty of participation is little, and manual operation is less on the impact of pH value result accuracy, thereby makes itMore accurately and reliably, and discrimination method is simple, easy to operate for measurement result, comparatively quickObtain result accurately.
The foregoing is only the preferred embodiments of the present invention, be not limited to thisBright, for a person skilled in the art, the present invention can have various modifications and variations.Within the spirit and principles in the present invention all, any amendment of doing, be equal to replacement, improveDeng, within all should being included in protection scope of the present invention.
Claims (5)
1. a method of differentiating milk freshness, is characterized in that, comprising:
(1), 10 grams of milk and 20 ml distilled waters are mixed, described milk is mixed withMilk sample to be measured;
(2), the pH meter of calibration is inserted in described milk sample to be measured, record pH value;
(3), by described pH value with preset pH scope and compare, when described pH value existsWhen described default pH scope, described milk is fresh, otherwise, stale;
Described default pH scope is: 6.54-6.80;
Described default pH method of determining range comprises:
Choose some parts of described milk samples to be measured;
Described every portion milk sample to be measured is carried out respectively to acidity titration to determine Titrable acidDegree, utilizes above-mentioned steps (1) and step (2) to carry out pH mensuration;
Set up the titratable acidity of the described milk sample to be measured of every portion--the corresponding relation of pH, rootAccording to the described titratable acidity of all umbers--the corresponding relation of pH, determine that equation of linear regression is:pH＝7.3091-0.0425°T，r＝-0.8571；
According to described equation of linear regression, correspondence when calculating titratable acidity is 12 ° of T and 18 ° of TPH, obtain described default pH scope;
Wherein, the method for described acidity titration is:
With standard solution of sodium hydroxide rinse buret 2-3 time, in described buret, addDescribed standard solution of sodium hydroxide, makes the concave meniscus of described standard solution of sodium hydroxide higher than instituteState zero groove of buret, get rid of the bubble of described buret and tube connector inside, make instituteState the concave meniscus of standard solution of sodium hydroxide and be down to below described zero groove, record institute nowState the scale value corresponding to concave meniscus of standard solution of sodium hydroxide, and be defined as NaOH markThe initial NaOH of initial volume V of accurate solution;
With the described standard solution of sodium hydroxide in described buret to described milk sample to be measuredCarry out titration, and the pH meter of calibration is measured milk examination to be measured described in titration process at any timeThe pH value of sample;
In the time that the pH meter of described calibration shows 8.3, stop titration;
Record the concave meniscus that titration finishes standard solution of sodium hydroxide described in rear described buretCorresponding scale value, and be defined as the terminal volume V terminal hydrogen-oxygen of standard solution of sodium hydroxideChange sodium;
Utilize the initial NaOH of described V and V terminal NaOH and acidity computing formula meterCalculation obtains described titratable acidity;
Wherein, the concentration of described standard solution of sodium hydroxide is 0.0861mol/L.
2. the method for discriminating milk freshness according to claim 1, its feature existsIn, the calibrating mode of described pH meter is: 2 calibration methods.
3. the method for discriminating milk freshness according to claim 2, its feature existsIn, calibration temperature is 25 DEG C; Calibration criterion liquid comprises: the mixed phosphate salting liquid of pH6.86,The Potassium Hydrogen Phthalate solution of pH4.01.
4. the method for discriminating milk freshness according to claim 1, its feature existsIn, at the described standard solution of sodium hydroxide with in described buret, described milk to be measured is triedSample carries out in the process of titration, and described method also comprises: described milk sample to be measured is carried outContinuous stirring.
5. according to the method for the discriminating milk freshness described in claim 1-4 any one,It is characterized in that, described method is for described ox full-cream and/or degreasing and/or half degreasingPasteurization milk in milk and sterile milk.
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Non-Patent Citations (4)
| Title |
|---|
| 《IDF奶粉酸度测定标准的验证实验及对国标方法的修改意见》;黄敏等;《中国乳品工业》;19970831;第25卷(第4期);第41页 * |
| 《以鲜牛奶新鲜度检测为案例的研究性学习设计》;李献文;《化学教与学》;20120531(第5期);第55页第1栏 * |
| 《牛奶的检验》;方培生;《中国奶牛》;19930831(第4期);第50页第2栏 * |
| 《酸度计测试原理及实际使用中的问题解析》;刘传海;《中国造纸学会薄型纸专业委员会第十二届学术交流会论文集》;20051231;第2、4页 * |
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Effective date of registration: 20160307 Address after: 200082 Shanghai city Yangpu District State Road 1688 Lane 68, room 201012 Applicant after: Food (Shanghai) Biotechnology Co., Ltd. Address before: 200092, room 32, 407-5 Tieling Road, Shanghai, Yangpu District Applicant before: Fortune Trading (Shanghai) Trading Co., Ltd. |
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