In recent years, sour foods such as Greek yogurt, Korean kimchi, and fruit juice liqueur (vinegar) have become more and more popular with consumers, and even sour beer has become highly sought after.

Why are sour foods so popular with consumers?
According to Ann Butler of EdibleEducation, a culinary company, “Sour flavors are more continuous and lingering than many other food flavors, and it’s a trend in food flavors, like an afterburn. Once you’re hooked, it’s hard to go back to bland flavors.”

Sourness also imparts a fullness of flavor to food, and the strong fullness of flavor that sourness imparts is what foodies and chefs are looking for”.

The Principle of Sourness

Sourness is caused by the stimulation of the tongue membrane by hydrogen ions. Therefore, any compound that can free H+ in solution has a sour taste. However, the concentration of sour taste and the intensity of sour taste is not a simple correlation between the various acids have a different sense of sourness, the sourness caused in the mouth and the type of acid root pH titratable acidity, buffering effects and other substances, especially with the presence of sugar.

At the same pH, organic acids are more acidic, and the most common edible acids have different acidic flavors at the same concentration. In addition, acidity is different in aqueous solutions than in actual food. Acidity is related to buffering, with weak acids being more acidic than mineral acids at equal pH. Saliva has a buffering effect with many components of food.

The anions of acidic substances have an effect on the flavor of food. While most organic acids have a brisk acidic flavor, most inorganic acids (e.g., hydrochloric acid) have a bitter taste that can degrade food. This is mainly the effect of anions. Because of the anion of the acidic substance, it often gives the food another flavor, which is a secondary flavor. Ethanol and sugar can attenuate sour flavors. The composition of sweet and sour flavors is an important factor in the flavor of fruit drinks.

Types of food acidulants

At present, there are about 20 kinds of acidulants used in the world, and the annual growth rate of demand is 3%~5%. Food acidulants are divided into organic acidulants and inorganic acidulants, as well as some related organic and inorganic salts, which can also be used as acidulants.

Common acidulants are generally organic acids, such as citric acid, malic acid, lactic acid, tartaric acid, and acetic acid, which are widely used in the modern food industry.

Among them, citric acid is the most used acidulant in the food industry, with a market share of more than 70% of all organic acid markets. Inorganic acidulants used more are generally phosphoric acid.

Acidic substances in food, mainly organic and inorganic acids that are soluble in water. In fruits and vegetables and their products, malic acid, citric acid, tartaric acid, succinic acid and acetic acid-based; in meat, fish food to lactic acid-based.

In addition, there are some inorganic acids, like hydrochloric acid and phosphoric acid. Some of these acidic substances are natural ingredients in food, such as tartaric acid in grapes and malic acid in apples; some of them are added artificially, such as citric acid added to formulated beverages; and some of them are produced in fermentation, such as lactic acid in sour milk.

Role of Food Acidulants

3.1 Flavor Developing Agent
No matter which way the acidic substances are obtained, they are important flavor developers of food and have a great influence on the flavor of food. Most of the organic acids have a strong fruity flavor, which can stimulate appetite, promote digestion, and play an important role in maintaining the acid-base balance of human body fluids.

3.2 Keep the color stable
The presence of acidic substances in food, i.e. the pH value, also plays a certain role in maintaining the stability of the color of food. In the process of fruit processing, if you add acid to reduce the PH value of the medium, can inhibit the enzymatic browning of fruits; selection of PH6.5-7.2 boiling water hot blanching vegetables, can be very good to maintain the unique fresh green green vegetables.

3.3 Preservative effect
Acid substances in food can also play a certain role in preservation. When the PH of the food is less than 2.5, generally in addition to mold, most of the growth of microorganisms are inhibited; if the concentration of acetic acid is controlled at 6%, it can effectively inhibit the growth of spoilage bacteria.

Some commonly used acidulants in food applications

Food acidulants in the beverage and fermentation industries have a wide range of applications, acidulants can not only enhance the flavor of beverages, but also play a preservative role, is a very important raw material in the production of beverages.

The use of acidulants in the fermentation industry includes fermented chili peppers, lactic acid beverages and so on. Some acidulants also have a variety of functional roles, such as food acidulants in the malic acid has a health role, is currently the world’s largest food industry, one of the better prospects for the development of organic acids.

4.1 Citric acid in food applications
Citric acid is the most widely distributed organic acid in fruits and vegetables, and it is also the most widely used acidifier in the food industry, named because it was originally discovered and produced from lemons.

According to statistics, 99% of the world’s citric acid comes from microbial fermentation. Citric acid is a triclinic crystal with rhombohedral crystal system containing 1 molecule of water of crystallization, soluble in water and ethanol, insoluble in ether. It is 100% soluble in water at 20℃ and has a strong acidic odor. Containing 1 molecule of water of crystallization, melting point 10 ℃ ~ 133 ℃, in the atmosphere for a long time is weathering. Does not contain water of crystallization of citric acid melting point of 153 ° C, in the wet air is hygroscopic and fork can form crystals.

It is characterized by its solubility in cold water than in hot water. Citric acid in citrus and berry fruits in the most content, and most of the coexistence with malic acid. In the citric acid can be up to 6% to 8% of the dry weight of citric acid acid acid flavor is crisp and delicious, rounded, nourishing, after the mouth that is to reach the highest acidity. But the continuation of the aftertaste is short, the amount usually used is 0.1% to 1.0%.

Citric acid is also commonly used in the production of pastry acidifier, which enhances the flavor at the same time, can prevent the pastry from rotting. The role of citric acid in food processing can generally be used as sucrose converting agent, fruit and vegetable color protection agent, antioxidant synergist and so on.

In addition, citric acid has a wider range of roles, Liao Lan et al. through the test showed that citric acid can effectively stretch the structure of wheat protein, is a kind of effective acid raw material that can replace the deamidation of hydrochloric acid, which can help to broaden the scope of application of wheat gluten protein.

4.2 Malic acid in food applications
Malic acid is white needle-like crystals generally dense into a globule, easy to loose in the air, soluble in water and ethanol. The solubility in water at 20℃ is 55.2%. Malic acid naturally occurring are L-type, almost all fruits contain it, with the most content of nuts and fruits.

The acidity of malic acid is stronger than that of citric acid, and the acidity is crisp, slightly astringent and bitter, and the aftertaste time in the mouth is significantly longer than that of citric acid. If combined with citric acid, it is very effective in enhancing the sour flavor. The malic acid used in industry is produced by synthetic method, and the usual usage is 0.05%~0.5%.

In addition, malic acid also has some utilization value in the fermentation industry. Malic acid is mainly used in the secondary fermentation of wine, and some studies have shown that L-malic acid promotes an increase in the biomass of wine wine cellulolytic bacteria, which contributes to the production of high-quality wines.

4.3 Application of lactic acid in foodstuffs
Lactic acid, as an important organic acidifier, occupies an important position in the food industry. Lactic acid is able to give food a unique sour flavor, has the function of regulating PH value, preventing food from rotting, and prolonging the shelf life of food in many aspects. Lactic acid is mainly used in the manufacture of beverages, fermented foods, food processing and some flavorings. Lactobacillus fermentation produces lactic acid in large quantities, which is helpful for human health.

The results of a study conducted by a research group of the Ministry of Health, Labor and Welfare of Japan show that if people eat lactic acid bacteria food every day, they can relieve certain allergic rhinitis symptoms to a certain extent. In addition, lactic acid is recognized by the U.S. FDA as a safe (GRAS) excellent preservative and and marinade, and can be used in the production of refreshing beverages, candies, and pastries.

At the same time, the aqueous solution of lactic acid can also be used to extend the shelf life of meat, and its application prospects are immeasurable. In beer production, the United States banned the use of phosphoric acid and other inorganic acids to regulate PH, and all changed to lactic acid. Lactic acid can change the structure and properties of rice starch to a certain extent, as a kind of edible acid, can be applied to the anti-aging of glutinous rice flour 1%. In addition, it has some value in baked food processing.

4.4 Vinegar
Vinegar is a common sour seasoning in China. In addition to 3% to 5% acetic acid, common vinegar also contains other organic acids, amino acids, sugar, alcohols, lipids and so on.

Vinegar is made from raw materials containing starch or sugar by fermentation. Because vinegar contains acidity and is mild, in cooking, it is used as seasoning and also has the function of removing fishy odor. Such as burning fish with vinegar in addition to fishy odor, burning beef, mutton with a little vinegar meat is easy to cook and so on. In addition, in daily life, our country folk has accumulated a lot of experience in using vinegar.

4.5 Acetic acid
Acetic acid, also known as acetic acid, is a colorless irritating liquid. Boiling point 118.2 ℃, melting point 16 ℃, concentration of more than 98% of the acid can be frozen into ice-like solid, so it is usually called anhydrous acetic acid for glacial acetic acid.

It can be mixed with water, alcohol, ether, glycerol in any proportion, can corrode the skin and has sterilization effect. Cool acid can be used to formulate synthetic vinegar, which is applied to the preservation and flavoring of food.

4.6 Compound application of food acidulants
Compound use of acidulants is divided into different acidulants compound use and acidulants and a variety of other food additives with the use.

Zhang Yusong use of acidulants fermented chili pepper test will be a variety of commonly used acidulants compound use, to a certain extent, to increase the flavor of chili. The test showed that it is generally difficult to use a single acidulant to achieve the sourness of fermented products, and it is necessary to use a variety of acidulants in conjunction with each other.

Food acidifier mixed with other food additives in the food industry is also widely used, not only to make the sensory characteristics of the food more prominent, but also to achieve better antibacterial and antiseptic effect.

Acidulants and sweeteners have an antagonistic effect, in the production and processing of beverages, confectionery and other food products, often acidulants and sweeteners with the use of good control of a certain sweet and sour ratio, you can get a better flavor of the product.

According to Dr. Withers, it is more challenging to reconcile acidity with other flavors in food or beverages. She pointed out that although consumers are open to challenging flavors, it is important for companies to create softer flavors that are more palatable to consumers, and Withers believes that consumer preference for sour flavors is not a foregone conclusion, and that in the future consumers will be more interested in blending sour flavors with other flavors.

Determination of Acidity in Foods and Precautions

5.1 The significance of determining acidity in foods
(1) Determination of acidity can determine the degree of ripeness of fruits and vegetables.
For example, if the organic acid contained in grapes is determined to be higher in malic acid than tartaric acid, it means that the grapes are not yet ripe, because ripe grapes contain a large amount of tartaric acid. The acid content of different kinds of fruits and vegetables varies according to the degree of maturity and growth conditions, and generally the higher the degree of maturity, the lower the acid content.

Such as tomatoes in the ripening process, the total acidity from the green ripe period of 0.94% down to the complete ripening period of 0.64%, while the sugar content had added, the sugar-acid ratio increased, with a good taste, so through the determination of the acidity of the raw materials can be judged by the degree of ripeness.

(2) can judge the freshness of food
For example: the lactic acid content in fresh milk is too high, indicating that the milk has been corrupted and spoiled fruit products have free galacturonic acid, indicating that the contamination of moldy fruit.

(3) acidity reflects the quality of food indicators
The amount of organic acid content in food directly affects the flavor, color, stability and quality of food. Acid determination of microbial fermentation process has a certain significance of guidance.
For example, in the production of wine and alcohol, there are certain requirements for the acidity of wort, fermentation broth, and wine curd. Acid in fermented products such as liquor, beer and soy sauce, vinegar, etc. is also an important quality indicator.

In addition, acid plays a significant role in maintaining the acid-base balance of human body fluids. Each of us also has certain requirements for the PH value of body fluids, and the PH value of human body fluids is 7.3~7.4, if the PH value of human body fluids is too large, we have to cramp, and if it is too small, it will be acidic poisoning again.

5.2 Principle of Measurement
Acidity in food is usually expressed as total acidity (titratable acidity), effective acidity, and volatile acidity.

Total acidity refers to the total amount of all acids in the food, including the concentration of dissociated and undissociated acids, and is titrated using a standard alkaline solution and expressed as the percentage of the main representative acid in the sample.

Effective acidity refers to the concentration of hydrogen ions in the sample that are in the ionic state (strictly speaking, the activity) is measured by a PH meter and expressed as pH value.

Volatile acidity refers to the organic acids in the volatile portion of the food. Such as acetic acid, formic acid, etc., can be measured by direct or indirect method.

For example: Determination of total acidity (titration method)
Organic acids (weak acids) in foodstuffs are neutralized to produce salts when titrated with a standard base. Phenolphthalein is used as an indicator, when the titration to the end point (pH = 8.2, the indicator shows red), according to the volume of standard lye consumed, the total acid content of the sample is calculated. The equation is as follows: RCOOH + NaOH – NaRCOO + H20

5.3 Sample handling and preparation
(1) Solid sample. The sample is moderately crushed through a sieve, mixed well, take the appropriate amount of sample, add a small amount of carbon dioxide-free distilled water, dissolve the sample into a 250ml volumetric flask, heated on a water bath at 75-80 ℃ C for 0.5 hours (in the case of preserved fruits, it is heated in boiling water for 1 hour), cooled, fixed, filtered through dry filter paper, discarding the initial liquid, and collect the filtrate for backup.

(2) Beverages and alcohol containing carbon dioxide. Heat the sample at 45 ℃ water bath for 30min, remove carbon dioxide, cool and prepare.

(3) Flavoring and non-carbon dioxide-containing beverages and alcohol. The sample is mixed well and then sampled directly, if necessary, can also be diluted with an appropriate amount of water, if turbid, then need to be filtered.

(4) Coffee samples. Crush the sample through a 40-mesh sieve, take 10g of sample in a triangular bottle, add 75ml of 80% ethanol, stoppered and placed for 16 hours, and from time to time shaking, filtering.

(5) Solid beverage. Weigh 5g of sample in a mortar, add a small amount of CO2-free distilled water, grinding into a paste, with CO2-free distilled water transferred to a 250ml volumetric flask to be fixed, shaking and filtering.

5.4 Sample titration
Accurately aspirate 50ml of the prepared filtrate, add 2~3 drops of phenolphthalein indicator, titrate with 0.1 mol/L standard alkaline solution until slightly red for 30 seconds without fading, record the dosage, and do the blank experiment at the same time. The following formula was used to calculate the acid content of the sample.

Where: C – concentration of standard sodium hydroxide solution molL;
V1–volume ml of standard lye solution consumed for titration;
V2 – volume ml of standard lye consumed for blank;
V3 – total volume of sample dilution ml;
V4 – volume ml of the sample solution taken up for titration;
M – mass or volume of the sample (g or ml);
K – coefficient of conversion to the appropriate acid, i.e. 1 mol of sodium hydroxide is equivalent to grams of the major acid.

Because food products contain a variety of organic acids, the results of total acidity determinations are usually expressed in terms of the kind of acid that is most abundant in the sample. For example, when analyzing grapes and their products in general, it is expressed as tartaric acid with K=0.075; when measuring citrus fruits and their products, it is expressed as citric acid with K=0.064 When analyzing apples and their products, it is expressed as malic acid with K=0.067: when analyzing dairy products, meats, aquatic products and their products, it is expressed as lactic acid with K=0.090; and when analyzing wines and spices, it is expressed as acetic acid with K=0.060.

5.5 Precautions
(1) sample soaking, dilution with distilled water can not contain CO2, because it dissolves in water to form acidic H2CO3, affecting the end of the titration phenolphthalein color change, the general practice is to analyze the distilled water before the boil and quickly cooled to remove the CO2 in the water, the sample if it contains CO2 also has an impact on the samples, so the samples of beverages that contain CO2, in the determination of the pre-completion of the CO2 must be removed.

(2) Sample in the dilution of water should be based on the acid content in the sample, in order to make the error within the allowable range, the general requirements of the titration consumption of 0.1 mol / LNaOH is not less than 5 ml, the best should be about 10-15 ml.

(3) Since the acid contained in the food is a weak acid, its titration endpoint is alkaline when titrated with a strong base, and the general pH is about 8.2, so phenolphthalein is used as the endpoint indicator.

(4) If the sample is colored (such as fruit juice) can be decolorized or potentiometric titration can also increase the dilution ratio, according to 100ml of sample liquid plus 0.3ml phenolphthalein determination.

The acidity of various types of food to the main acid, but some foods (such as milk, bread, etc.) can also be used to neutralize 100g (ml) of the sample required 0.1mol / L (dairy) or 1mol / L (bread) NaOH solution of the ml number of the expression, the symbol ° T. The acidity of fresh milk for 16-18 ° T, bread acidity for 3-9 ° T.