JP3169717B2 - Method and apparatus for measuring juice acidity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the acidity of juice used mainly for quality control of fruits for agriculture. More specifically, the present invention relates to a method for measuring the pH of juice and determining it in advance. The present invention relates to a method for measuring the acidity from the relationship between the pH and the acidity of the fruit juice and an apparatus capable of directly reading the measured acidity.

[0002]

2. Description of the Related Art The acidity of fruit juice has been conventionally measured by titration analysis using a sodium hydroxide solution. However, this method is a manual analysis method using a general chemical analysis instrument, and the operation is complicated and requires skill. Therefore, on-site measurement is difficult.

[0003] As another simple measuring method, a method of indirectly obtaining acidity by diluting fruit juice with water and measuring its electric conductivity has been devised. However, this method cannot avoid the influence of electrolytes other than the acid contained in the juice, and is easily affected by measurement errors due to the high dilution ratio of several tens of times. It could only be used for a simple preliminary test.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for measuring juice acidity which can measure the juice acidity even in the field such as outdoors, and which can be measured accurately with a simple operation requiring no skill. Is what you do.

[0005]

According to the present invention, in order to achieve the above object, the relationship between the acidity of fruit juice and the pH is determined in advance by using a buffer solution prepared so as to conform to the acidity of predetermined fruit juice. There is provided a method for measuring juice acidity, comprising measuring the pH of the juice to be measured and measuring the acidity of the juice from the above relationship. Furthermore, according to the present invention, a means for measuring the pH of a mixed solution of a buffer solution and a juice prepared so as to be compatible with the acidity of a predetermined juice, and the pH and the acidity of the juice mixture obtained in advance are determined. There is also provided an apparatus for measuring juice acidity comprising means for converting the measured pH value of the juice into acidity based on the relationship and displaying the acidity.

[0006]

Function and Aspect of the Invention The acidity of the juice according to the present invention is determined by mixing a predetermined amount of a buffer solution and juice prepared in accordance with the acidity of the juice (acidity or amount of acid) to be measured. By measuring the pH of the solution, it is automatically converted to an acidity based on a previously determined relationship between the pH and the acidity and displayed.

Hereinafter, the structure and operation of the present invention will be described with reference to the drawings. FIG. 1 is a graph in which a fixed amount of an acid component contained in fruit juice is added to sodium hydroxide and a buffer solution having the same specified amount, and the respective pH changes are plotted. The point indicated by EP is the end point in the titration method, but in the case of the buffer, a relatively gentle curve is drawn before and after the buffer, and this curve can be adjusted by adjusting the composition. Traverse this graph in reverse, p
In order to estimate the amount of acid added (and thus the acidity of the solution) by knowing H, in the case of sodium hydroxide, the end point (E
P) Estimation can be made with high accuracy only in a narrow range in the vicinity. That is, in the range of the amount of acid other than the vicinity of the end point, the curve is nearly horizontal, so that even a slight difference in pH, such as a measurement error, greatly changes the amount of acid, so that accurate measurement cannot be performed. On the other hand, in the case of using a buffer solution, a wider range can be estimated, and the formulation of the buffer solution can be arbitrarily designed depending on the required accuracy and measurement range.

Focusing on one kind of fruit juice, a mixture of fruit juice and a prepared buffer at a certain ratio shows a certain pH depending on the amount of acid contained therein. That is, if the pH of a specific fruit juice is measured while changing the amount of the acid contained therein, a curve (calibration curve) showing the relationship between the pH and the amount of the acid as shown in FIG. 1 is obtained. Therefore, by measuring the pH of the juice whose acidity is to be measured, the amount of acid in the juice can be known. Specifically, a previously prepared buffer solution and a known concentration of fruit juice are mixed to prepare a calibration curve,
This value is stored in a computer as data such as a table, and the acidity is calculated and displayed from the pH of the fruit juice actually measured by an inverse operation. Alternatively, a corresponding scale of acidity is also written on the display scale of the pH meter based on the calibration curve prepared in advance, so that the acidity can be read directly with a pH meter together with the pH of the fruit juice actually measured in an analog manner. Appropriate acidity indicating means can be employed.

In this manner, a buffer is formulated so as to have a calibration curve having an appropriate slope for various juices, and a means for displaying the juice acidity corresponding to the measured pH based on the calibration curve is provided. What is necessary is just to incorporate in a measuring device.
Since the range of the acidity contained in each kind of fruit is kept at a certain value, if the buffer is designed for each kind of fruit and supplied to the consumer, there is no need for the customer to make this design.

[0010]

EXAMPLES Hereinafter, an example in which the acidity meter according to the present invention is actually applied to mandarin juice will be described, and the present invention will be described in more detail. However, it goes without saying that the present invention is not limited to the following examples. FIG. 2 is a configuration diagram of the measuring unit of the acidity meter according to the present invention. A pH electrode 1 and a temperature electrode 2 are provided in a measurement cell 3. This output is converted into a digital quantity by an AD converter 4 with an amplification circuit and is converted into a computer unit (CPU).
5 is input. Here, the above-described inverse operation is performed, and the acidity is directly indicated on the display 6.

In this example, NaOH, Na ₂ HPO ₄ , and Na ₂ B ₄ O are used in such a manner that the amount of acid contained in the juice is converted into the amount of citric acid and the acidity of the juice is measured at 1 ± 0.2%. ₇ and NaHCO ₃ was formulated buffer. This solution 10c
FIG. 3 shows a calibration curve prepared by mixing m ³ and 0.5 cm ³ of fruit juice having a known acidity in the measurement cell. The calibration curve had an appropriate slope, indicating that the acidity could be easily obtained from the pH. The actual measurement was performed in the same manner as for buffer 10c.
It is only necessary to mix m ³ and 0.5 cm ³ of fruit juice of unknown concentration in the measuring cell 3 and read the numerical value output on the display 6. 10 cm ^3, for the amount of 0.5 cm ^3, are both graduated cylinder, weighing the use of the pipette suitable instrument easily and accurately perform weight was shown that procedure also simple.

[0012]

According to the present invention, since the acidity of the juice can be easily and accurately measured by anyone anywhere, the accurate acidity of the fruit juice which had to be removed and transported to a laboratory or the like to request a specialist in the past. The measurement can be carried out on site such as in a field. As a result, it is possible to know exactly when to harvest the fruit, and to ship it with high quality and high market value. In addition, the collection company and the sales company can also measure at the collection place and the store, so that the quality can be guaranteed and the added price can be increased.

[Brief description of the drawings]

FIG. 1 shows the pH when acid components contained in fruit juice are added to sodium hydroxide and a buffer solution having the same specified amount, respectively.
6 is a graph showing a change in the graph.

FIG. 2 is a schematic configuration diagram of a measuring unit of the juice acidity measuring device according to one embodiment of the present invention.

FIG. 3 shows the p measured for mandarin orange juice in the examples.
It is a graph which shows the relationship (calibration curve) between H and the amount of juice acidity conversion in citric acid.

[Explanation of symbols]

1 pH electrode, 2 Temperature electrode, 3 Measurement cell, 4
AD converter with amplifying circuit, 5 Computer unit (CPU), 6 Display.

Claims (2)

(57) [Claims] 1. The relationship between the acidity of juice and the pH is determined in advance using a buffer solution prepared so as to be compatible with the acidity of predetermined juice, and the pH of the juice to be measured is measured. A method for measuring juice acidity, comprising determining the acidity of the juice. 2. A means for measuring the pH of a mixture of a buffer solution and a juice prepared so as to conform to the acidity of a predetermined fruit juice, and a means for measuring the relationship between the previously determined pH and acidity of the juice mixture. And a means for converting the measured pH value of the fruit juice into an acidity and displaying the acidity based on the measured acidity.