Vegetable protein beverage is a complex protein colloidal 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 plant protein beverages, protein denaturation, precipitation, and fat floating are prone to occur, resulting in stratification, flocculation, and coalescence 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: chemistry, physics and microorganisms.

1. Temperature

Temperature is a common factor leading to protein denaturation, which in turn affects the stability of vegetable protein beverages, and both low temperature and high temperature can lead to protein denaturation. When the raw material is stored at a temperature below 0°C, the protein will be 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 the molecules, and the bonds (such as hydrophobic interactions and electrostatic interactions) that stabilize the high-level structure of the protein are easily broken, the hydrophobic groups of the protein are exposed from the inside, and the interaction between the protein and the water molecule is weakened. Decreased protein solubility.
Therefore, in order to meet the production requirements, the heating time should be shortened as much as possible during the production process, the rapid cooling after sterilization, and the interaction between protein and lipid should be improved, which is beneficial to reduce the degree of protein denaturation and improve the stability of the product.

2. Particle 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 sinks or rises is proportional to the square of the particle’s radius.

The larger the particle size, the easier it is to precipitate due to the action of gravity. But when the particle diameter is less than 0.2μm, the particles will 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 density and viscosity of the medium vary little, and can also be regarded as constant.

Therefore, the larger the particle size of the vegetable protein beverage, the greater its sedimentation velocity. The non-rancid sedimentation and stratification in vegetable protein beverages is mostly caused by the large diameter of the particles, the acceleration of the sedimentation speed, and the destruction of the sedimentation balance.

3. Microbial factors

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

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 vegetable protein beverages, and standardize the sterilization process.

In commercial production, if the sterilization of plant protein beverages is not thorough, microorganisms will grow and multiply under suitable temperature conditions, resulting in product spoilage; if the temperature is too high or the sterilization time is too long, it may lead to protein denaturation, Oxidation of fat results in a decrease in product viscosity, poor stability, and darkening of color.

In order to ensure the safety of the product, it has to sacrifice its sensory qualities such as color and luster. 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 beverage is the product fermented by lactic acid bacteria. 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 perspective, lactic acid bacteria fermentation is beneficial to the stability of vegetable protein beverages.

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