Determination of acids in food

1.
The concept of acidity

1.
Total acidity

Total acidity refers to the total amount of all acidic components in food, including the concentration of dissociated acid and the concentration of undissociated acid
.

Because the standard alkali solution is used for titration, the total acidity is also called titratable acidity, which is generally expressed by the mass fraction of the main acid (such as citric acid , malic acid , tartaric acid , etc.

2.
Effective acidity

Effective acidity refers to the concentration of hydrogen ions in a free state in the sample, refers to the concentration of H ⁺ in the test solution (to be precise, it should be activity), and reflects the concentration of dissociated acid, which is usually expressed by pH
.

3.
Volatile acidity

Volatile acidity refers to volatile organic acids in food, such as acetic acid , formic acid and butyric acid and other low-carbon straight-chain fatty acids
.

4.
Bovine lactate

Cow milk has two kinds of acidity, namely, external acidity and true acidity
.

Also known as intrinsic acidity outer acidity (acidity potential), refers to freshly extruded fresh milk itself has acidity, is phosphoric acid , casein , albumin , citric acid , and CO.
'S ₂ and the like caused
.

The external acidity accounts for 0.

The true acidity is also called the fermentation acidity, which refers to the part of the acidity that is increased by the fermentation of lactose to produce lactic acid under the action of lactic acid bacteria during the storage of the milk
.

If the acid content of the milk exceeds 0.

The acidity of milk is generally expressed by the volume (mL) of 0.
1000mol/L NaOH consumed to titrate a 100mL milk sample, called T, which is the titer acidity, or acidity for short
.

It can also be expressed as the mass fraction of lactic acid, which is the same as the calculation method of total acidity, and lactic acid is used to express bovine lactic acid

2.
Types and functions of acids in food

The sour ingredients in food are mainly organic acids and inorganic acids
.

Most organic acids have a refreshing sour taste, while inorganic acids generally have an unpleasant bitter and astringent taste, so most people do not use inorganic acids as food sour agents

The organic acids in foods are partly in the free state and partly in the acid salt state
.

Common organic acids are citric acid , malic acid , tartaric acid, oxalic acid, succinic acid, lactic acid and acetic acid

The role of acids in food is reflected in many aspects
.

One is to affect the smell and taste of food.

3.
The meaning and method of measuring the acidity of food

Acidity measurement can evaluate the quality of food raw materials and products
.

For example, by measuring the sugar and acid content of fruits and vegetables, the maturity of fruits and vegetables can be judged

The acidity determination provides an important basis for food coloring, flavoring, and food stability control, and has guiding significance for the food processing and production process
.
For example, the browning of food can be controlled by controlling pH; products with better flavor can be obtained by adjusting the ratio of sugar to acid
.
The quality standards of fermented products such as liquor, beer, soy sauce and vinegar all have clear requirements for acidity
.

The indicator method is commonly used for the determination of total acid in various light-colored foods such as fruit and vegetable products, beverages, and the potentiometric titration method for foods with too dark or turbid color
.
The methods for measuring effective acidity include test paper method, colorimetric method and potentiometric method.
Among them, the pH potentiometric method (pH meter method) is the most commonly used method, which is easy to operate and accurate
.
The determination of volatile acid generally adopts the steam distillation method
.
The degree of bovine lactate can be determined by standard alkali titration
.

Related link: Selection of graying conditions