Vegetable protein drink is a complex protein colloid system, and it is also a thermodynamically unstable system, which includes a suspension formed by protein, an emulsion formed by fat, and a true solution formed by sugar, salt, etc. .

Therefore, during the production and storage of vegetable protein beverages, protein denaturation, precipitation, and fat floating are prone to occur, resulting in stratification, flocculation, and agglomeration of the system, which will significantly reduce product quality. The stability of plant protein beverages is affected by many factors, but in general, it mainly includes three factors: chemical, physical and microbial.

01 Physical factors

1.1 Temperature

Temperature is a common factor leading to protein denaturation, which affects the stability of vegetable protein beverages, and both low and high temperatures can lead to protein denaturation. When the raw material is stored at a temperature below 0 °C, the protein is denatured, which may be related to the hydrophobic interaction of the protein, causing the dissociation and rearrangement of some functional groups.

At high temperature, there will be violent movement between molecules, the bonds that stabilize the higher structure of the protein (such as hydrophobic interaction, electrostatic interaction) are easily broken, the hydrophobic group of the protein is exposed from the inside, and the interaction between the protein and the water molecule is weakened. Protein solubility decreases.

Therefore, if the production requirements are met, the heating time should be shortened as much as possible, the rapid cooling after sterilization, and the improvement of the interaction between proteins and lipids will help reduce the degree of protein denaturation and improve the stability of the product.

1.2 Grain size

The stability of vegetable protein beverages is closely related to the particle size of the dispersed phase. Stokes' law shows that the speed at which a particle settles or floats is proportional to the square of the particle radius.

The larger the particle size, the easier it is to precipitate out due to the action of gravity. But when the particle diameter is less than 0.2μm, the particles produce Brownian motion in the solution, which is beneficial to the stability of the solution.

According to Stokes' law, for a specific vegetable protein beverage, the particle density is constant; the medium density and viscosity change little and can also be regarded as constant.

Therefore, the larger the particle size of vegetable protein beverages, the higher the sedimentation velocity. Most of the non-rancid precipitation stratification in vegetable protein beverages is caused by the large particle diameter, the accelerated sedimentation speed, and the destruction of the sedimentation balance.

02 Microbial factors

Microorganisms are usually one of the important factors affecting the stability of vegetable protein beverages. In non-fermented vegetable protein beverages, if not sterilized, microorganisms can easily lead to spoilage of products. Common bacteria that cause spoilage of vegetable protein beverages include Pseudomonas, Proteus, Clostridium, etc.

In order to avoid the damage caused by microorganisms, the measures that can be taken are to strengthen the quality control and sanitation management in the production process of vegetable protein beverages, and to standardize the sterilization process.

In commercial production, if the sterilization is not complete in the production of vegetable protein beverages, under suitable temperature conditions, microorganisms will grow and reproduce, resulting in product spoilage; if the sterilization temperature is too high or the sterilization time is too long, it may lead to protein denaturation, Fat oxidation, resulting in decreased product viscosity, poor stability, and darker color.

In order to ensure the safety of the product, sensory qualities such as color and luster have to be sacrificed. At the same time, in order to ensure the stability of the product, it is usually necessary to add stabilizers such as sodium carboxymethyl cellulose.

At present, the common fermented vegetable protein beverages are lactic acid bacteria fermented products. Lactic acid bacteria mainly ferment carbohydrates to produce lactic acid.

Since the presence of starch and insoluble carbohydrates will reduce the stability of the product, from this aspect, the fermentation of lactic acid bacteria is beneficial to the stability of vegetable protein beverages.

On the other hand, the formation of lactic acid leads to a decrease in the pH of the product, which may lead to changes in the protein structure, which can lead to precipitation.

03 Conclusion and Outlook

Plant protein drinks are more and more popular among consumers because of their rich protein and amino acids, moderate amount of unsaturated fatty acids, no or less cholesterol, and comprehensive and reasonable nutrients.

In recent years, my country's plant protein beverages have made great progress. However, the market share of vegetable protein beverages in the entire beverage market is still insufficient, and the overall market capacity is relatively low, far behind fruit juice, tea and carbonated beverages; in addition, the current vegetable protein beverage market is almost completely dominated by soy milk and walnut milk. , almond milk, coconut milk, peanut milk and other 5 types, vigorously develop other types of plant protein drinks, such as corn protein drinks, potato protein drinks, etc., to enrich product categories, and expand the scope of plant protein drinks and expand market capacity potential Must do.

The development of various types of vegetable protein beverages is conducive to improving the level of intensive processing and added value of agricultural products.