Vegetable protein drink is a complex protein colloid system, is also a thermodynamically unstable system, the system includes a suspension formed by proteins, emulsions formed by fats, as well as the formation of sugar, salt and other real solutions.

Therefore, during the production and storage of plant protein beverages, protein denaturation, precipitation, fat floating and other phenomena are likely to occur, resulting in the system to produce stratification, flocculation, agglomeration, etc., which will significantly reduce the quality of the product. The stability of plant protein beverages is affected by a variety of factors, but in general, the main factors include chemical, physical and microbiological factors.

Physical factors

1.1 Temperature

Temperature is a common factor that leads to protein denaturation, which in turn affects the stability of plant protein beverages, and both low and high temperatures can lead to protein denaturation. When the raw materials are stored at temperatures below 0℃, the proteins will be denatured, which may be related to the hydrophobic interactions of proteins, causing the dissociation and rearrangement of some functional groups.

At high temperatures, the molecules will produce violent movement, stabilize the protein high-level structure of the bond (such as hydrophobic interactions, electrostatic interactions) is easy to interrupt, the hydrophobic groups of proteins from the internal exposure, protein and water molecules weakened interactions, protein solubility decreased.

Therefore, in order to meet the production requirements, the production process should try to shorten the heating time, rapid cooling after sterilization, as well as to improve the interaction between proteins and lipids, which is conducive to reducing the degree of denaturation of proteins, in order to improve the stability of the product.

1.2 Particle size
The stability of vegetable protein drinks is closely related to the particle size of the dispersed phase. Stokes’ law shows that the rate of particle sinking or floating is proportional to the square of the particle radius.

The larger the particle size, the easier it is to precipitate due to gravity. However, when the particle diameter is less than 0.2μm, the particles produce Brownian motion in the solution, which is conducive to the stabilization of the solution.

According to Stokes’ law, for specific plant protein drinks, particle density is a constant; medium density and viscosity change is small, can also be regarded as a constant.

Therefore, the larger the particle size of the plant protein drink, the greater the settling speed. Most of the non-failure precipitation stratification in plant protein drinks is caused by the large particle diameter, accelerated settling speed and disruption of the settling equilibrium.

Microbiological factors

Microorganisms are usually one of the most important factors affecting the stability of vegetable protein drinks. In non-fermented vegetable protein drinks, if not sterilized, microorganisms are very easy to cause product spoilage, and the common bacteria that cause the spoilage of vegetable protein drinks are Pseudomonas, Aspergillus, Clostridium, and so on.

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

In commercial production, if the sterilization of plant protein drinks is not complete, under the appropriate temperature conditions, microorganisms will grow and multiply, 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 viscosity, poor stability, and color darkening of the product.

In order to ensure the safety of the product, have to sacrifice its color and other sensory qualities, at the same time, in order to ensure the stability of the product, usually need to add sodium carboxymethyl cellulose and other stabilizers.

At present, the common fermented vegetable protein drinks are lactic acid bacteria fermentation products. Lactobacillus microorganisms mainly ferment carbohydrates to produce lactic acid.

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

On the other hand, the production of lactic acid leads to a decrease in the pH of the product, which may lead to a change in the protein structure and precipitation.

Conclusion and Outlook

Vegetable protein beverages are becoming more and more popular among consumers because they are rich in protein and amino acids, moderate amount of unsaturated fatty acids, no or low cholesterol, and comprehensive and reasonable nutrient composition.

In recent years, China’s plant protein drinks have made great progress. However, in the whole beverage market plant protein drinks its share is still insufficient, and the overall market capacity is low, far behind the fruit juice, tea, carbonated drinks; in addition, the current plant protein drinks market is almost completely occupied by soy milk, walnut milk, almond milk, coconut milk, peanut milk and other five types of possession, and make great efforts to develop other types of plant protein beverages, such as corn protein drinks, potato protein drinks, etc., to enrich the product range, and to develop other types of plant protein drinks, such as corn protein drinks, potato protein drinks, etc., to enrich the product range, and to develop other types of plant protein drinks, such as potato protein drinks. It is imperative to enrich product varieties and expand the scope and market capacity of plant protein drinks.

The development of many kinds of plant protein drinks is conducive to improving the level of deep processing and added value of agricultural products, which not only can satisfy the demand of people’s tastes and preferences, but also has practical significance in improving the income of farmers and solving the problems of the three rural areas.