Food color is an important sensory index to identify food quality. The causes of food color mainly come from two aspects: one is the original natural pigment in food, and the other is the synthetic pigment used in food processing.

1. food pigments-food pigments can be divided into natural pigments and synthetic pigments according to their sources.

(1) Natural pigment-Edible natural pigment is extracted from animal tissues and is a natural component of food. There are two forms of its existence, one is a colored substance visible to the naked eye in fresh raw materials, and the other is a colorless food that presents color due to chemical reaction during the processing of food raw materials.

Edible natural pigments mainly include chlorophyll,&; Szlig- carotene, curcumin, beet red, monascus pigment, shellac pigment, caramel pigment. Edible natural pigments are safe to use and not limited by dosage, which is the development direction of coloring materials.

(2) Synthetic pigments-Synthetic pigments are widely used in modern food production. Compared with natural pigments, synthetic pigments have bright colors, high fastness, stable performance, strong coloring power and can be adjusted at will. However, synthetic pigments are mostly made from coal tar by chemical synthesis, which has different degrees of toxicity. Therefore, in the food hygiene standards, there are strict requirements for the use of synthetic pigments, and only five pigments are allowed, namely amaranth, carmine, tartrazine, indigo and sunset yellow.

2. Color change of food during processing and cooking-The color change of food during cooking is extremely complicated, which is closely related to the ingredients of food, the nature of heating medium, temperature and other factors.

(1) Browning-Browning is a common discoloration phenomenon in food. When food raw materials are processed, stored and mechanically damaged, they tend to darken or turn brown, which is called browning. In the process of food processing, some foods need to take advantage of browning, such as golden brown produced in the baking process of bread and cake. However, some food raw materials, such as fruits and vegetables, will brown during processing, which will not only affect the appearance, but also reduce the nutritional value.

Browning can be divided into enzymatic browning and non-enzymatic browning according to its mechanism.

Enzymatic browning mainly occurs in lighter fruits and vegetables, such as apples, bananas and potatoes. When their tissues are scratched, cut and peeled, they become ill or are in an enzymatic browning state. In practical work, heat treatment, acid treatment and air isolation can be used to prevent food browning. Because the enzyme content is above 45% and the pH value is below 3.0, the processed raw materials can be soaked in clear water, sugar water or salt water to prevent the formation of enzymatic browning.

Non-enzymatic browning is a browning effect that can be produced without the action of enzymes, mainly including caramelization reaction and Maillard reaction.

Caramel reaction is the coking of sugary food due to high temperature during processing, thus coloring the food. Therefore, in the process of food processing, adding appropriate amount of sugar according to technological requirements is beneficial to the coloring of products.

Maillard reaction is the main cause of food browning after heating or long-term storage, and the reaction process is very complicated. In practical work, if it is necessary to control non-enzymatic browning, we can control non-enzymatic browning by cooling, sulfurous acid treatment, lowering pH value, reducing the concentration of finished products or using sugars that are not easy to brown.

(2) Starch hydrolysis-Starch is easy to hydrolyze, and when heated in water, some molecules can be cracked. In the process of incomplete hydrolysis of starch, a large amount of dextrin will be produced. At high temperature, dextrin will produce pyrodextrin due to coking, and food will produce yellow or brownish red during baking or frying.

(3) Food itself contains natural pigments, such as carrot pigments, anthocyanins, vegetable tannins, etc., which can make food produce or change color under certain conditions.

(4) Adding proper amount of pigment during food processing or cooking to change or highlight the color of some products.

Second, the aroma in food.

Aroma is an important part of food flavor. Aroma is composed of a variety of volatile aroma substances, and the production of various aromas is closely related to some genes of volatile substances in food.

The aroma in food includes: fruit, meat, baking, frankincense, fragrance and sweetness.

1. Ways of flavor formation-Some of the flavors in food are contained in the food itself, and some are produced by biological or chemical means or degraded into odorous substances. The pathway of formation can be roughly divided into biosynthesis, direct enzymatic action, indirect enzymatic action and pyrolysis.

(1) Biosynthesis-refers to the aroma in food, which is naturally synthesized by natural raw materials in the process of growth and maturity, or formed in the process of post-ripening. Bananas, for example, do not show aroma during the growth period or harvest, but gradually show it in the later stage.

(2) Direct enzymatic action refers to the activation of enzymes contained in food raw materials or added enzymes, so that odor precursors in food raw materials directly form aroma substances and produce aroma, such as onions and garlic, which belongs to this mechanism.

(3) Indirect enzyme action-In food processing, some intermediate products are formed due to the action of enzymes, which act on aroma precursors to form aroma. For example, the formation of strong aroma of black tea is a typical example of indirect enzyme.

(4) the role of pyrolysis-most foods will produce attractive aroma when heated, which is mainly caused by carbonyl ammonia reaction, such as peanuts, sesame seeds, bread and so on. Here, the pyrolysis reaction of oil can also produce various unique flavors.

2. Important aroma substances in food-In the process of food processing and cooking, important aroma substances include fruit aroma, milk aroma, cream aroma, sesame aroma, bread aroma and so on.

Third, the taste of food.

1. The concept of taste-the taste in food is an important basis for judging the quality of food. Taste in a broad sense is a series of senses from seeing food to food entering the digestive tract from the mouth, including psychological taste, physical taste and chemical taste.

Psychological taste refers to all kinds of psychological feelings about food before and during eating, including the feelings about the environment and the color, luster and shape of food to diners.

Physical taste refers to the stimulation of the physical properties of food to the oral tactile organs, which is usually called "taste". For example, the mouth feels the softness, hardness, hot and cold, viscosity and so on of food are all physical tastes.

Chemical taste refers to the feeling that chemicals in food stimulate the taste organs. The salty, sweet, sour and bitter taste of food are all chemical.

The food is rich in flavor. In China, it is customary to divide tastes into five categories: sweet, bitter, sour, salty and spicy. In fact, there are far more than five flavors, and only the taste nerves can obviously feel umami, cool and astringent.

2. the formation of taste in food-the taste in food is produced by the dissolution of soluble substances in saliva or liquid food to stimulate the taste buds on the tongue. Different foods don't taste exactly the same. Even if they have the same taste, the substances that make up this taste are not exactly the same. However, in either case, only when various flavor-presenting substances reach a certain concentration can taste be produced. Usually, the standard to measure taste sensitivity is called threshold. The lower the threshold, the higher the sensitivity.

People's perception of taste will be influenced by many factors, including concentration, temperature, solubility, physiological phenomena and so on. For example, people feel different degrees of taste due to different food temperatures. The temperature that can stimulate the taste most is between10 and 40℃, of which 30℃ is the most intense, and many tastes will weaken below 10℃ or above 40℃. For another example, the higher the solubility of various flavor substances in food, the fuller the taste, otherwise it will affect the taste feeling of food.

Fourth, the shape in food.

The shape in food is also an important part of the sensory quality of food. Only when the four beauties of color, fragrance, taste and shape coexist can food be called quality food.

There are two ways to form the shape of food: one is in the process of processing, including mold molding, manual molding, mechanical molding and so on; The other is to shape the finished product through artistic conception after the food matures. This molding method can form food with different shapes such as patterns, geometries, images and decorations according to the needs of food.