Food acids

Lecture 11 Food acids

1. Characteristics of acids food
2. Food acid and their influence on the quality of products

Food contains various organic acids, which are combined into a group of food acids. Food acids accumulate in plant raw materials as a result of biochemical transformations at the stage of plant development, and acids can accumulate due to biochemical changes during the technological process of food preparation (alcohol fermentation, lactic fermentation). Food acids can be introduced into the food system during the process to adjust the pH, impart a certain taste (drinks), to form a certain consistency (dairy products, confectionery).

The introduced food acids in the process of production of products are referred to the group of food additives. Their use is not limited in terms of hygiene, but is regulated by technological instructions for specific food products. The fumaric acid possesses increased toxicity, for which the level of an acceptable daily dose of 6 mg / kg of human body weight is established.

Acetic acid is used in the form of essences 70 - 80% concentration and in the form of table vinegar 9% concentration. Also used are salts of acetic acid - acetates. The main area of ​​application of acetic acid is the preparation of canned vegetables.

Lactic acid is used as a 40% solution and a concentrate of 70% solution. Salts of lactic acid are called lactates. Lactic acid is used in the production of beer (acidification of mash), nonalcoholic beverages, confectionery products, fermented milk products.

Citric acid is used in the form of white crystals obtained by biochemical synthesis from the mold fungus Aspergillus niger. Citric acid salts are called citrates. Citric acid has a mild taste, less irritating the mucous membrane of the gastrointestinal tract. In high concentrations, citric acid is contained in citrus fruits. It is used in the production of beverages, juices, confectionery, canned fish.

Apple acid is used in the form of crystals of white or yellowish color. The salts of malic acid are called malates. Apple acid has a mild taste, it does not irritate the mucous membrane of the gastrointestinal tract. In high concentrations, malic acid is contained in fruits. It is used in the production of beverages, confectionery.

Tartaric acid is used in the form of crystals of white or yellowish color. Obtained during processing of winemaking waste. Tartaric acid salts are called tartrates. Tartaric acid has a mild taste, less irritating to the mucous membrane of the gastrointestinal tract. Contained in grapes. It is used in the production of beverages, confectionery.

Less often in the production of food products, acids are used: adipic, amber, fumaric.

Phosphoric acid is a representative of mineral acids, but it is widely represented in food raw materials and food products, especially phosphoric acid salts - phosphates. Phosphoric acid is a component of complex organic compounds: phospholipids, nucleic acids, ATP (adenosine triphosphate). In high concentrations, phosphates are contained in dairy, meat products, in nuts. It is used in the production of beverages, confectionery.

Food products contain various amino acids: alanine, valine, serine, lysine, methionine, etc., which are part of proteins. Food contains various lipids, which include fatty acids: palmitic, stearic, oleic, linoleic, linoleic and others. Aromatic acid - benzoic acid is a natural preservative, it is found in some berries.

Food acids in the composition of food raw materials and products perform various functions related to the quality of food objects.

As part of a complex of flavoring substances, they participate in the formation of taste and aroma, which are among the main indicators of the quality of the food product. It is the taste, along with the smell and appearance, to this day has a more significant impact on the consumer's choice of a product compared to such indicators as composition and nutritional value. Changes in taste and aroma are often signs of a spoiling food product or the presence of foreign substances in its composition.

The main taste sensation, caused by the presence of acids in the product, is an acidic taste, which in general is proportional to the concentration of H + ions (taking into account the differences in the activity of substances that cause the same taste perception). For example, the threshold concentration (the minimum concentration of the taste substance, perceived by the senses), which makes it possible to sense an acid taste, is 0.017% for citric acid, 0.03% for acetic acid.

In the case of organic acids, the anion of the molecule also influences the perception of acid taste. Depending on the nature of the latter, there may be combined taste sensations, for example, citric acid has a sweet and sour taste, and picric acid is sour-bitter. Change in taste sensations occurs in the presence of salts of organic acids. So, ammonium salts give the product a salty taste.

Naturally, the presence of several organic acids in the product composition in combination with the organic flavoring substances of other classes determines the formation of original gustatory sensations, often characteristic of only one particular type of food.

The composition of the aroma-forming complex of fermented milk products includes lactic, citric, acetic, propionic and formic acids.

The quality of the food product is an integral value that includes, in addition to the organoleptic properties (taste, color, aroma), indicators that characterize its colloidal, chemical and microbiological stability.

Formation of product quality is carried out at all stages of the technological process of its production. At the same time, many technological indicators ensuring the creation of a high-quality product depend on the active acidity (pH) of the food system.

In general, the pH value affects the following process parameters:

- the formation of taste and aroma components, characteristic for a particular type of product;

- colloidal stability of a polydisperse food system (for example, the colloidal state of milk proteins or a complex of protein-tannic compounds in beer);

- the thermal stability of the food system (for example, the thermal stability of milk protein products, depending on the equilibrium between ionized and colloidally dispersed calcium phosphate);

- biological stability (for example, beer and juices);

- activity of enzymes;

- Conditions for the growth of useful microflora and its effect on maturation processes (for example, beer or cheeses).

Пищевые кислоты в составе продовольственного сырья и продуктов выполняют различные функции, связанные с качеством пищевых объектов.
В составе комплекса вкусоароматических веществ они участвуют в формировании вкуса и аромата, принадлежащих к числу основных показателей качества пищевого продукта. Именно вкус, наряду с запахом и внешним видом, по сей день оказывает более существенное влияние на выбор потребителем того или иного продукта по сравнению с такими показателями, как состав и пищевая ценность. Изменения вкуса и аромата часто оказываются признаками начинающейся порчи пищевого продукта или наличия в его составе посторонних веществ.
Главное вкусовое ощущение, вызываемое присутствием кислот в составе продукта, — кислый вкус, который в общем случае пропорционален концентрации ионов Н+ (с учетом различий в активности веществ, вызывающих одинаковое вкусовое восприятие). Например, пороговая концентрация (минимальная концентрация вкусового вещества, воспринимаемая органами чувств), позволяющая ощутить кислый вкус, составляет для лимонной кислоты 0,017%, для уксусной — 0,03%.
В случае органических кислот на восприятие кислого вкуса оказывает  влияние и анион молекулы. В зависимости от природы последнего могут возникать комбинированные вкусовые ощущения, например, лимонная кислота имеет кисло-сладкий вкус, а пикриновая — кисло-горький. Изменение вкусовых ощущений происходит и в присутствии солей органических кислот. Так, соли аммония придают продукту соленый вкус.
Естественно, что наличие  в составе продукта нескольких органических кислот в сочетании с вкусовыми  органическими веществами других классов обусловливают формирование оригинальных вкусовых ощущений, часто присущих исключительно одному, конкретному виду пищевых продуктов.
В состав ароматообразующего комплекса кисломолочных продуктов  входят молочная, лимонная, уксусная, пропионовая  и муравьиная кислоты.
Качество пищевого продукта представляет собой интегральную величину, включающую, помимо органолептических свойств (вкуса, цвета, аромата), показатели, характеризующие его коллоидную, химическую и микробиологическую стабильность.
Формирование качества продукта осуществляется на всех этапах технологического процесса его получения. При этом многие технологические показатели, обеспечивающие создание высококачественного продукта, зависят от активной кислотности (рН) пищевой системы.
В общем случае величина рН оказывает влияние на следующие  технологические параметры:
— образование компонентов вкуса и аромата, характерных для конкретного вида продукта;
— коллоидную стабильность полидисперсной пищевой системы (например, коллоидное состояние белков молока или комплекса белково-дубильных соединений в пиве);
— термическую стабильность пищевой системы (например, термоустойчивость белковых веществ молочных продуктов, зависящую от состояния равновесия между ионизированным и коллоидно распределенным фосфатом кальция);
— биологическую стойкость (например, пива и соков);
— активность ферментов;
— условия роста полезной микрофлоры и ее влияние на процессы созревания (например, пива или сыров).