Plant protein drinks are a complex protein colloidal system and a thermodynamically unstable system that includes a suspension formed by proteins, an emulsion formed by fat, and a true solution formed by sugars, salts, etc.
Therefore, during the production and storage of plant protein beverages, protein denaturation, precipitation, fat floating and other phenomena are prone to occur, resulting in system stratification, flocculation, agglomeration, etc., which will significantly reduce product quality. The stability of plant protein drinks is affected by a variety of factors, but in general, it mainly includes chemical, physical and microbiological factors.
Chemical factors
01PART
Protein concentration
In plant protein drinks, there are simultaneous protein-protein interactions and protein-lipid interactions, the former is easy to lead to flocculation and precipitation, while the latter is conducive to the stability of the system. Protein concentrations have an effect on both of these interactions.
In addition, these 2 interactions are also affected by the physicochemical properties of proteins. The types of plant proteins and lipids are complex, and their physicochemical properties are directly related to their composition and structure, and at present, there is a lack of research on the interaction between specific types of proteins and between proteins and lipids in the field of plant beverages.
02PART
PH
The hydration of the protein is obviously affected by the pH of the system, because the protein molecule contains amino and carboxyl groups, which have acid-base amphoteric and isoelectric points.
Plant proteins from different sources have significant differences in their isoelectric points. Even the same plant protein, due to its structure and environment, its isoelectric point is also different.
The isoelectric point of common plant proteins is between pH4 and pH6, such as the isoelectric point of soybean protein is around pH 4.5. Under these conditions, the net charge of the protein is close to zero, and the electrostatic repulsion between the protein molecules is lacking, and its hydration effect is the weakest, the solubility is the smallest, and it is easy to produce flocculation precipitation. In order to ensure the stability of plant protein drinks, it is necessary to promote the dissociation of proteins to improve the hydration capacity and solubility of plant protein molecules.
Therefore, under the premise of satisfying the taste and flavor, the pH of the plant protein beverage should be kept away from the isoelectric point of the plant protein. Under extremely acidic and alkaline conditions, the quality of plant protein drinks decreases, which is not conducive to drinking, so the optimal pH of plant protein drinks is generally controlled at 7 to 8.
03PART
Salt ions
In general, salt ions have a "salt-soluble effect" and a "salt-precipitation effect" on proteins. Low Na+ concentration promotes protein lysis, and when its concentration reaches more than 0.5 mol/L, it will lead to protein precipitation, in particular, Ca2+, Mg2+ and other divalent salt ions and other polyvalent ions can easily lead to protein precipitation.
Therefore, during the production and storage of plant protein drinks, the presence of high concentrations of salt ions should be avoided.
04PART
Ingredient ingredients
The effect of ingredients in plant-based protein beverages on the stability of their systems is complex. The main ones are sugars, emulsifiers and thickeners.
In general, carbohydrates are easy to form a sugar film on the surface of protein molecules, and thus improve the affinity of proteins and water, in addition, carbohydrates can also improve the viscosity and density of dispersion media, thus improving the stability of plant protein drinks to a certain extent.
The emulsifier can reduce the tension of the two-phase interface, reduce the interface energy of the dispersion system, improve the uniformity of fat distribution in the emulsion and the stability of the solution. The charged emulsifier molecules can make the surface of the droplet charged to form a double layer, enhance the electrostatic repulsion between the droplets, and reduce the chance of droplet collision and coalescence.
Emulsifiers commonly used in plant protein drinks are mono and diglyceryl stearates, polyglyceryl fatty acid esters, and sucrose fatty acid esters. According to the provisions of the national standard GB 2760-2014, in protein drinks, mono and diglyceride stearate can be used in an appropriate amount, and there is no clear limit requirement, the maximum use of polyglyceride fatty acid esters is 10g/kg, and the maximum use of sucrose fatty acids is 1.5 g/kg.
The relationship between the specific emulsifier and the stabilization effect of protein and fat in the beverage system is not only related to the type of emulsifier, but also related to the physicochemical properties of protein and fat, in general, the higher the emulsifier concentration, the more conducive to the stability of the beverage system.
Stokes' law shows that an increase in viscosity reduces the rate of particle settling in an emulsion system, thereby improving the stability of the system. Thickeners can increase the viscosity of plant protein drinks, so that the beverage remains in a uniform and stable state. Thickeners commonly used in the production of plant protein drinks are xanthan gum, pectin, carrageenan, guar gum, sodium carboxymethyl cellulose and so on.
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