Determination of organic acid content in fruits and vegetables
Organic acids are found in a wide range of plant organs and play an important role in metabolism. The content of organic acids varies in different parts of the plant. In fruits and berries, free acids are the most abundant, while in leaves the salts of organic acids are predominant, and their content varies according to cultivation conditions. The nature and content of organic acids change during ripening and storage of fruits and vegetables, and they are also an indicator of the flavor and quality of the fruit. Therefore, the determination of organic acid content in fruits and vegetables can identify changes in their quality.
Principle
The basic principle of the determination of organic acid content in fruits and vegetables is that organic acids are easily soluble in water, alcohols and oils, and these solvents can be used to extract the organic acids first, and then titrated with alkaline solution, which can determine the content of organic acids.
Operation method
Determination of organic acid content in fruits and vegetables
Principle
The basic principle of the determination of organic acid content in fruits and vegetables is that organic acids are easily soluble in water, alcohols and oils, and these solvents can be used to extract the organic acids first, and then titrated with alkaline solution, which can determine the content of organic acids.
Materials and Instruments
Material: apple, orange or other plant tissue. Move The basic procedure for the determination of organic acid content in fruits and vegetables can be divided into the following steps:1. Extraction: Weigh 5 g of fruits or vegetables into a mortar, add a little quartz sand to make a homogenous paste, rinse with a little distilled water into a 50 mL triangular flask, then add water to about 30 mL, and put it in a water bath at 80°C for 30 min, stirring every 5 min, take it out to cool down and then filter it, and the filtrate and the residue filtrate of the rinsing are combined, and then shaken well to make it available for the determination.2 . Determination: take 50 mL dry clean triangular flask 3, were filled with sample extract 10 mL, l% phenol 2 drops, with 0. 1 mol - L l NaOH solution titration until slightly red, shake for 1 min does not fade that is the end point of the titration, record the amount of consumed lye, the results of the experiment will be recorded in the Table 54-10 such as the color of the extract may interfere with the end point of the titration, for this reason can be in the extraction of liquid put a piece of litmus paper, according to the color changes in the titration. If the extract has color, it may interfere with the titration endpoint, so we can put a piece of litmus paper in the extract and determine the endpoint according to the color change.Table 54-1 Determination of Organic Acid Content in Samples Caveat During titration, air bubbles are removed from the lower end of the burette. For more product details, please visit Aladdin Scientific website.
Equipment: balance, thermostatic water bath, mortar, funnel, buret, pipette, volumetric flask, measuring cylinder, triangular flask.
Reagents:
①1% phenol reagent
②0.1 mol -L
②0.1 mol -L
NaOH solution
3. Calculation of results.Where: w - sample mass, g;c - NaOH concentration, 0.1 mol - L'1;K - conversion factor: 67 for malic acid and 75 for tartaric acid;K - conversion factor: 67 for malic acid, 75 for tartaric acid; - total amount of sample solution at extraction, mL;ro a measurement of the amount of sample solution, mL; is a consumption of NaOH solution volume, mL. SampleName Sample weight(W/g) Total Dilution(V/mL) Volume of sample liquid at the time of measurement( V2/mL ) Volume of NaOH solution consumed in titration (W/mL)NaOH solution volume (W/mL) Conversion factor and type of acid (K) Organic acid content/% Apple Orange