Science Popularization | | The role and application of plant protein in hair care

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In daily life, the hair cuticle protective layer of our hair will be damaged and shed over time due to the influence of nature (such as ultraviolet radiation, sunlight) and daily life (such as combing, hot air blowing) or hairdressing (dyeing, perming).

Due to the impact of natural and human factors on hair damage such as decreased moisture content, protein loss, and changes in hair structure, our hair becomes frizzy and dry, prone to splitting and breakage, and reduced glossiness. Therefore, hair care is particularly important. Through hair care, we can reduce hair damage or further repair damaged hair, allowing our damaged hair to return to a "healthy" and "shiny" beautiful state.

Hair care is a long-lasting and systematic process. Understanding the structural composition, physiological functions, and factors causing hair damage, as well as the role of plant proteins in hair care, can provide consumers with a deeper and clearer scientific understanding when selecting hair care products. For researchers, they can develop more effective care products that meet consumer needs based on the characteristics of hair.

一,Composition and damage factors of hair

1.1  Composition of hair

The main component of hair is keratin, which accounts for approximately 65% to 95% and is composed of two parts: the hair shaft and hair follicles. Among them, the hair shaft is composed of the cortex, cuticle, and medulla, and their composition and function are shown in Table 1. The recognized nutrients for skin and hair include histidine, arginine, glutamic acid, aspartic acid, serine, and lysine. Keratin is composed of over 20 alpha amino acids connected by peptide bonds, and the content and arrangement of alpha amino acids affect the physicochemical properties of hair fibers. Therefore, hair has dual properties of amino acids and keratin, and both proteins and amino acids can be used for hair care.

Sheet 1 Hair structure and function

1.2 Factors causing hair damage

Due to the different environments in which hair is located, many external factors can cause damage to the hair, such as light exposure, chemical treatment, environmental pollution, mechanical damage, etc. These factors can cause the hair scales on the surface of the hair to curl up and most of the keratin to be lost. Macroscopically, this is manifested as rough and unsmooth hair, easy breakage, and reduced tensile strength.

According to external factors, hair damage can be attributed to the following reasons

(1) Physical damage

Physical damage generally refers to the pressure exerted on hair by the external environment, such as during daily hair combing. If the hair is rough, not smooth enough, and difficult to comb, it is easy to generate pulling and frictional forces between the comb teeth, resulting in hair damage and shedding, stretching and deforming the hair fibers, and damaging the alpha helix in keratin; If the hair is combed against the direction of the small skin covering, it is easy to cause the small skin to curl and break, and even fall off, further damaging the stratum corneum.

(2) Chemical damage

Chemical damage generally refers to the damage suffered by hair when it comes into contact with chemical reagents such as perm agents, hair dyes, and bleaching agents, causing changes in the structure of the stratum corneum. These chemical reagents can penetrate through the stratum corneum and enter the cortex, thereby breaking the disulfide bonds of keratin in the hair, causing changes in the fibrous structure of the hair, resulting in protein loss and changes in the composition of amino acids, leading to hollowing out of the internal structure of the hair.

(3) Thermal damage

Thermal damage refers to the damage to hair caused by high temperatures, such as excessive temperature or time during hot blowing or perming, which can cause the moisture in the hair to quickly evaporate, resulting in dry and frizzy hair. Generally speaking, the moisture content in hair is around 15%. If it is lower than 10%, the hair will experience static electricity, hair loss, cracked ends, and be relatively fragile.

(4) Sunlight damage

The accumulation of ultraviolet radiation in sunlight to a certain intensity can cause changes in hair structure and photodegradation of proteins. The melanin in hair fibers is prone to oxidation and fading under sunlight, and tryptophan, cysteine, and tyrosine in keratin structures can also undergo photodegradation. In addition, hair is exposed to the external environment all day long, and various weather phenomena can cause damage to hair and accelerate hair aging.

Hair damage is inevitable in our daily lives, so it is crucial for us to take care of and repair the damaged hair. Due to the similarity in composition between plant proteins and our skin and hair, as well as their good film-forming and moisturizing properties, they are widely added to hair care products. They can penetrate through the skin and hair surface to further protect and repair our damaged hair.

二,

The role and mechanism of plant proteins

Plant proteins used for hair care are generally divided into two types: hydrolyzed plant proteins; Another type is the derivative of hydrolyzed plant protein, which is prepared by chemical modification by introducing other functional groups into the protein side chain or end.

2.1

Hydrolyzed plant protein

Hydrolyzed plant protein is made by hydrolyzing various plant proteins with acids, alkalis, or enzymes, all of which are composed of amino acids. Therefore, it has good affinity with the skin and hair and has mild and non irritating properties. It can penetrate the surface of the skin and hair, form a film on the skin or hair surface, and lock in moisture to achieve moisturizing effect. When hydrolyzed plant protein is used for hair care, it can improve the processability, texture, combing ability, luster, and organization of hair, and can reduce the damage to hair caused by various treatments, as well as repair cracked ends.

Sheet 2 Types of hydrolyzed plant proteins

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2.2

Derivatives of hydrolyzed plant protein

--Quaternized hydrolyzed plant protein

Quaternary ammonium hydrolysis of plant protein is synthesized from plant protein or plant protein powder through two steps: enzymatic hydrolysis and quaternization. The quaternized hydrolyzed plant protein used in hair care products has both protein conditioning properties and quaternized adsorption properties. The positively charged quaternized hydrolyzed plant protein strongly interacts with negatively charged hair, and the hydrophilic group can firmly adhere to the surface of the hair. The hydrophobic group moves away from the hair surface and is oriented and arranged throughout the hair surface, forming a relatively strong protective film that gives the hair luster, smoothness, and easy combing properties.

The keratin that makes up hair has an isoelectric point of pH 4, while the hydrolyzed proteins used in most cosmetics have an isoelectric point of 4.0~6.0. They only exhibit cationic properties below their isoelectric point, so hydrolyzed proteins do not have true cationic properties in practical use. Only when the concentration of hydrolyzed plant protein reaches a certain level, can it have strong adsorption. However, many times due to cost limitations, the concentration of hydrolyzed plant protein is generally low, which limits the adsorption capacity of hydrolyzed plant protein. Therefore, if limited by cost, quaternized hydrolyzed proteins can be selected.

The advantages of quaternized hydrolyzed protein compared to general hydrolyzed protein include stronger conditioning, better luster, improved electrostatic accumulation, stronger adsorption, and better compatibility with anions.

Sheet 3 Types of quaternized hydrolyzed plant proteins

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