Study on the Application of Sericin in Cosmetics

Abstract

The high purity silk peptide powder can be obtained by the method of atomizing drying after the boiled silk (sericin) is decolorized, enzymatic dissolved, ion exchange purificated and concentrated. It can be used as the additive of high-grade cosmetics. The amino acid components of sericin provide excellent moisture absorption and retention on the skin. The molecular weight size of sericin will directly affect the types of cosmetic application. The results show that the sericin can inhibit the activity of tyrosine and the formation of melanochrome effectively. Through the experiment and SEM observation, we discovered that the sericin on the hair provides excellent hair care and repair effect. The application of sericin in cosmetics will provide parameter value of experimental evidence for developing new varieties of sericin in cosmetics.

Full text

Study on the application of sericin in cosmetics
Jia-yong Sheng
1,2,a
, Jie Xu
1,2,b
, Yu Zhuang
3,c
, Dao-quan Sun
3,d
,
Tie-ling Xing
1,2,e
, Guo-qiang Chen
1,2,f
1
National Engineering Laboratory of Modern Silk, Suzhou, 215123, China
2
College of Textile and Clothing Engineering, Soochow University, Suzhou, 215021, China
3
Xinyuan Cocoon Silk Group CO., LTD, Haian , 226600, China
a
sjy39@163.com,
b
xujiemeabcd@163.com,
c
hazhuangyu@sina.com,
d
937503850@163.com,
e
xingtieling@suda.edu.cn ,
f
chenguojiang@suda.edu.cn
Keywords: high purity silk peptide powder; cosmetics; application
Abstract. The high purity silk peptide powder can be obtained by the method of atomizing drying
after the boiled silk (sericin) is decolorized, enzymatic dissolved, ion exchange purificated and
concentrated. It can be used as the additive of high-grade cosmetics. The amino acid components of
sericin provide excellent moisture absorption and retention on the skin. The molecular weight size
of sericin will directly affect the types of cosmetic application. The results show that the sericin can
inhibit the activity of tyrosine and the formation of melanochrome effectively. Through the
experiment and SEM observation, we discovered that the sericin on the hair provides excellent hair
care and repair effect. The application of sericin in cosmetics will provide parameter value of
experimental evidence for developing new varieties of sericin in cosmetics.
Introduction
Over the years, a good impression of cocoon silk has existed in people’s mind because of its
“cool in summer and warm in winter, won’t hurt the skin”. The cosmetics made of silk have a long
history. In the early 1960s, the cosmetics containing silk were used to produce silk cream. And a
certain amount of fibroin powder is added to this kind of cosmetics. What’s more, silk cream has a
certain effect for skin care and beauty. The products have still been sold on the market so far. The
second generation of cosmetics containing silk – fibroin peptide first appeared in Japan in the early
1980s. Fibroin hydrolysate is added to this kind of cosmetics and its average molecular weight is
500~10000D. It is water-soluble silk multiple peptides. The fibroin peptide cosmetics are still
popular in the domestic and international markets until now. And they are also widely applied to all
kinds of high-grade cosmetics.
Collagen (hydrolyzed gelatin, bone glue) plays significantly on the skin, and it is always the main
raw material of the skin care cosmetics. However, in recent years, Western countries had occurred
Mad Cow Disease. And collagen is made from bovine bone, so we should take more caution in this
kind of materials when used in cosmetics. The property of sericin is similar to the animal glue, but it
was derived from the outer layer of collagen of the cocoon, so its security has got an absolute
guarantee. The sericin is the silk fibroin in cocoon sheath at the periphery of the fibroin and it is
globular protein. Through bleaching, enzymatic, ion exchange purification, concentration, spray
drying and other processes in the silk degumming solution we can obtain high purity of the soluble
silk crumb.
The soluble silk crumb can dissolve easily in cold water and the silk protein owns high purity,
uniform particle, fineness, white appearance and other excellent properties. The sericin contains
eighteen kinds of amino acids and the content of essential up to 18% or more. The molecular
Advanced Materials Research Vol. 796 (2013) pp 416-423
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conformation of the soluble sericin is mainly of coil structure and the aggregation structure of the
polymer is amorphous structure [1].
The sericin added to the cosmetics can show the unique effectiveness of moisturizing, whitening,
anti-oxidation as one feature. So it gets special attention from people. In this paper, we conduct a
detail study in sericin applied on cosmetics and can provide necessary experimental basis for further
exploring the series of cosmetics which is made of sericin.
Materials and Characterization
Materials. The preparation of high purity of the soluble silk crumb: Taking cocoon as raw
materials, and using pure water to clean cocoon coat 3 to 4 times. Then degumming the cocoon coat
with the pure water at 98~100℃. The silk glue decolorized with activated charcoal, degradation
with protease, ion exchange purification, concentrated by vacuum thin film, spray drying, and then,
the end product can be got. In detail, the invention patent [2] can be referred.
Characterization
Amino acid analysis. Putting the sample of silk crumb in the hydrolysis tube, adding 6M HCL,
vacuum sealing and hydrolyzing at 110±2℃ for 24 hours. After then, removing hydrochloric acid,
filtering and fixing volume. At last, we can measure it on a Hitachi L-8800 high-speed amino acid
analyzer.
Hygroscopic test. Weighing different concentrations of sericin and glycerol each for 10g, then
placing each in a 50 ml beaker, and then doing hygroscopic test in the temperature and humidity
regulator. The temperature of the test is set of 27℃, and the relative humidity of 86% RH. After 12
hours, we can weigh them and calculate the moisture absorption rate of each solution, and each test
was repeated three times on average.
Determination of the molecular weight of sericin. Preinstalled controlled with Superdex75
10/300 made by GE Healthcare, USA, and conducting in the system of AKTA Explore 100. The
injection volume of the samples of the standard protein and sericin is both 100ul. Then eluted with
PBS, and the flow rate is 0.5ml/min. After that, it will be detected with UV
280.
At first, we can
obtain the standard curve of the molecular weight of protein according to the elution volume of
standard proteins. Then we can calculate the average molecular weight of the various samples of the
sericin according to the outflow volume of the samples of sericin which can refer the formula of the
molecular weight of the polymer average protein.
Testing of inhibiting melanin production. The samples of sericin which has been tested can
refer the methods of the silk peptide which can inhibit melanin production [3].
Testing of elasticity and tensile for hair. Taking each for 10 hairs of various concentrations of
the sericin solution. After impregnating in the sericin solution, taking them out and airing. To
measure the percentage of elastic, we use the type of Y391 yarn elastic instrument. In addition, the
strength of the sample of hair can be tested in the electronics strength and elongation instrument.
And each sample was measured 10 times; the last measurement data is the average of 10 times.
SEM images of the hair. Drying the untreated hair (control samples), the hair which
impregnated by perm fine and the hair which was first impregnated by sericin solution out. Then,
spraying the three groups of the hair samples which were handled by perm agents with gold in a
high vacuum. The three groups of different samples were observed under the type of S-570 SEM.
Advanced Materials Research Vol. 796 417

Results and Discussion
The amino acid composition of the sericin. The silk fibers are similar to the structures of the
skin of human body and keratin of hair and the silk fabric is considered as a “third skin”. In the
middle of the last century, the silk fibroin cream was sold well both at home and abroad. And in this
cosmetic, the powder of fibroin fine was added. The fibroin cream can play a certain skin care, but
the inadequacy is the powder of the fibroin fine is water-insoluble. So it is difficult to be absorbed
by the skin. The powder of silk fibroin fine in the silk fibroin cream was treated by concentrated
alkali. After that the original composition of amino acid for fibroin will be changed. At the same
time, the original luster of silk fiber will disappear. The process of preparation of soluble silk crumb
is under mild conditions and these defects weren’t existed. The amino acid composition of the
soluble silk crumb is in the Table 1:
Table 1 The amino acid composition of the soluble silk crumb (%)
Amino acids Content (%) Amino
acids Content (%) Amino acids Content (%)
Asparticacid 18.70 Alanine 3.88 Tyrosine 1.60
Threonine 7.08 Cystine 0.35 Phenylalanine
0.18
Serine 29.34 Valine 2.24 Lysine 5.85
Glutamicacid
12.16 Isoleucine 0.42 Histidine 0.88
Glycine 8.98 Leucine 0.73 Arginine 3.46
Proline 0.23
The sericin contains 10 kinds of amino acids, and it almost covers the essential amino acids
which human needs. The content is over 16.5% of the total amino acids and is much higher than the
silk fibroin. The sericin which made of globular protein is water-soluble, so it can easily be
absorbed by the skin. In particular, the amino acid composition of the sericin contains rich serine,
asparticacid, glutamicacid, lysine, arginine which are all nutrients of skin. These nutrients can be
absorbed through the gap and glands of the epidermal, thus enriching the nutrition of the skin and
enhancing the vitality and elasticity of the skin cells. In addition, it can promote the metabolism of
the epidermal cells. So the long-term use of cosmetics which were added sericin can provide the
necessary nutrients for maintaining the beauty of skin.
The efficacy of moisturizing and hygroscopic for sericin. The stratum corneum of the skin
should be kept 10 to 20% of water which can make the skin plump and elastic, however, when was
the water in the stratum corneum of the skin less than 10% the skin performed dry and cracking.
Why did the stratum corneum contain a certain amount of moisture in the skin, on the one hand,
sebum the membrane prevents the evaporation of moisture, on the other hand, the stratum corneum
contains a natural moisturizing factor (the Natural Moisturizing Factor, NMF), it plays an important
role in skin moisturizing which can maintain appropriate moisture content in the skin and made the
skin more elastic and smooth and soft. However, due to the existence of the external environment,
only
relying on the skin contained NMF; it cannot play humidity on the skin and moisturizing effect.
Therefore, it continued to supply NMF from outside. Composition of the NMF in stratum corneum
of the skin was measured by Striance and other person; they were respectively amino acids,
pyrrolidone carboxylic acid, lactate, urea, sugars, organic acids, peptides and other substances [4].
Yet, the sericin protein in outer layer of the silk is an ideal natural moisturizing factor substance.
418 Silk, Protective Clothing and Eco-Textiles

The amino acid composition of sericin is very close to skin’s NMF and many polar groups of
polypeptide chains of the sericin were on the surface. The water in the body can be transferred to
the stratum corneum of the skin binding and thereby maintaining certain moisture on the skin.
Table 2 The comparison of amino acid composition between sericin and NMF for human skin
Amino acid composition
(%)
Serine Tyrosine
Alanine
Threonine
Aspartic acid
The natural
moisturizing
factor of human
skin （NMF）
30 18 9 7 5
Sericin 29.34 8.98 3.88 7.08 18.7
Fibroin
[5]
14.7 42.8 32.4 1.2 1.7
Bone glue
[6]
3.0 32.0 11.0 4.0 5.0
Table 2 shows that the amino acid composition of sericin and the natural moisturizing factor of
human skin are very close. However, the difference between fibroin and bone glue is very poor.
To research the efficacy of moisturizing and hygroscopic for sericin, taking glycerol as a control
and putting them in a temperature and humidity regulator while the temperature of 27℃ and
humidity of 86% RH. After 12 hours, the comparison of the moisture absorption rate between
sericin and glycerol. And the results are shown in Table 3:
Table 3 The comparison of the hygroscopic rate between sericin and glycerol
Sericin Hygroscopic Glycerol Hygroscopic
Concentration (%) rate (%) Concentration (%)
rate (%)
10.0 13.8 100 11.7
8.0 10.2 90 8.5
6.0 8.6 80 6.1
4.0 5.4 70 5.3
3.0 4.1 60 4.1
2.0 3.1 40 3.5
Table 3 shows that when the sericin concentration is 3%, the hygroscopic rate is equal to the
glycerol concentration of 60%. In other words, even if the concentration of sericin is 20 times lower
than the concentration of glycerol, it still has the same hygroscopic rate. This fully shows that we
can get good efficacy of moisturizing and hygroscopic for skin simply by adding a small amount of
sericin in the cosmetics. The sericin has good efficacy of moisturizing and hygroscopic is
determined by the molecular structure of the sericin. The molecular conformation of the soluble
sericin is mainly of coil structure and its polypeptide chain was loose and disordered state. And this
makes many hydrophilic group of its polypeptide chain on the surface of the spatial structure of the
molecule. However, these hydrophilic groups can combine the water of body which can be
transferred to the stratum corneum and can maintain the content of moisture in the skin properly.
Thus it can also make the skin elastic, smooth and soft. Although polios like glycerol also owe good
Advanced Materials Research Vol. 796 419

efficacy of hygroscopic, when using an excessive consumption or a long-term, it will be a slight
irritation on the skin. And it is easy to block the pores of the skin while these defects weren’t existed
of sericin.
The molecular weight of the soluble sericin. Cocoon coat was boiled with pure water under the
condition of high temperature to attain sericin solution. The range of molecular weight of sericin
solution is wide from 10000~150000D and it had poor solubility in cold water. The unglued sericin
solution of sericin which applied to the cosmetics must be degraded with protease. According to the
length of enzymatic hydrolysis time and the amount of sericin of protease, controlling different
production processes of sericin. Then the sericin of different specifications of molecular weight can
be produced. The specification of sericin molecular weight didn’t explicitly require both in the
industry standards and corporate standards for existing sericin. However, the molecular weight of
sericin will directly affect the effect of the application of cosmetics species. So the sericin molecular
weight must be measured was advised and as one of the quality inspection indicators applied to
cosmetics products. If the molecular weight of sericin is 30000~150000D, as the molecular weight
of sericin is too much larger and can not penetrate the cell membrane of human epidermal. Thus it
can not easily be absorbed by the skin. So if the molecular weight of sericin is more than 30000
which added to the cosmetics is not appropriate. Actually, the sericin polypeptides obtained from
soluble silk crumb through enzymatic. The solubility in cold water(8℃）is 18.05g of 100g water, but
the solubility of the sericin without enzymatic in cold water is only 1.8g of 100g water. The addition
amount of sericin in the cosmetics is generally 1~5%, so the soluble silk crumb can completely
meet people’s requirements. The smaller the molecular weight of sericin is, the better the
water-soluble is. To determine the molecular weight of different specifications of soluble crumb by
Gel chromatography, the results are listed in the following:
Table 4 The average molecular weight of soluble silk crumb measured by Gel chromatography
Soluble silk crumb samples Average molecular weight
（KD）
Peak corresponding to the
molecular weight（KD）
Sample A 15.48±1.42 14.83
Sample B 12.35±1.38 11.88
Sample C 6.45±0.43 6.130
Sample D 5.13±0.24 5.242
Table 4 shows that the molecular weight of soluble silk crumb sample A and sample B wide
from 12000~17000D. This specification of molecular weight of sericin is suitable for applying to
the cosmetics for hair care. While the molecular weight of soluble silk crumb sample C and sample
D wide from 5000~7000D, and this specification of molecular weight of sericin is suitable for
applying to the cosmetics for skin care. It is good for sericin protein to penetrate the cell membrane
and then fully absorbed by the skin because of the small molecular weight of sericin. And it also
plays a certain effect on reducing the appearance of local fine wrinkles for skin.
The sericin can inhibit the production of melanin in the skin effective. The formation of the
melanocytes in the cortical layer can affect the whitening of human skin, but the melanocytes can
produce melanin to make skin darken. The mechanism of the formation of melanin in the skin is
considered that the melanocytes contain tyrosine and it can make the tyrosine in the fraction of
keratin protein in the skin oxidize to melanin. However, UV can promote this oxidation reaction, so
it is easy to become dark when exposed to sunlight frequently in the summer.
420 Silk, Protective Clothing and Eco-Textiles

Table5.The inhibition of the production of melanin by sericin protein
Sericin concentration（%） Absorbance(A
640
nm) Inhibition ratio（%）
Distilled water
（comparison） 2.094 0
0.1 1.877 10.36
0.5 1.598 23.69
1.0 0.997 52.39
5.0 0.562 63.16
10.0 0.490 76.60
Table 5 shows that the activity of tyrosine reduced by more than half when added 1% sericin
and the inhibition rate of melanin would reach 52.39%. The sericin contains hydroxyl amino acids
(serine, threonine) and trace elements (copper, iron, etc.) and they will complex. Thereby it will
affect the normal play of the activity of tyrosine. The sericin can inhibit the activity of tyrosine
which is very effectively in inhibiting the formation of melanin in the skin. So the cosmetics of skin
care which added sericin can keep the skin white and flawless.
The efficacy of conditioner and repairing hair of sericin. The chemical property of the hair
protein is inactive and stable, but it is sensitive to hot acids, alkalis and chemicals (such as chemical
perm fine). When perm lotion used frequently in the hairdressing process, the hair will be damaged
and destructed in varying degrees. The main ingredient of common perm agents is ammonium
thioglycolate. When the hair handled by perm agents, the double-mercapto key in hair keratin
would be destroyed. But under the conditions of alkaline and hot air, after a short interval, the
double-mercapto key in hair keratin may be re-bonded. And this would force the arrangement of the
hair cell to change, thus shaping a variety of curls and beautiful hair. However, the elasticity and
strength of the hair and the water storage would reduce when the perm agents were often used. And
the hair would be easy to be dried; the tips of the hair bifurcation would increase, as well as the hair
shine would be poor.
The structure of sericin and the angle prion whitening protein is very similar, so sericin has a
good affinity with the hair. The adsorption amount of hair by sericin is also large [7], and Table 6
shows that when the sericin solution dipped and adsorbed by the hair, the elasticity and strength of
the hair would be increased.
Table 6 The changes between the elasticity and strength of hair after dipping the sericin solution
Samples Sericin concentration
（%） Elasticity（%） Strength（CN/dtex）
Normal hair（comparison）
0 54.83 7.98
A 0.2 63.45 8.14
B 0.4 72.12 8.35
C 0.6 79.54 8.65
D 0.8 83.56 8.70
E 1.0 86.79 8.72
Advanced Materials Research Vol. 796 421

Table 6 shows that when the sericin solution dipped and adsorbed by the hair, the elasticity of the
hair would increase. Even when the sericin concentration was lower than 0.2% (A), its elasticity
(63.45%) was 15.7% higher than the control samples. When the sericin concentration was high of
1.0% (A), its elasticity (86.79%) was 58.3% higher than the control samples. When the sericin was
adsorbed by the hair, its strength would also be increased. But the low sericin concentration
couldn’t improve the strength of the hair obviously. As the sericin concentration increasing, the
strength of the hair would increase obviously.
I II III
Figure1. SEM micrographs of
untreated hair (Ⅰ), the hair impregnated by perm fine (Ⅱ) and the
hair which was first smeared by sericin and handled by perm agent after drying (Ⅲ)
To further illustrate the efficacy of hair care of the sericin, under different conditions, observing
SEM images of the hair, Figure 1-Ⅰis SEM image of untreated hair, we can find that the outermost
layer of the nuclear-free clear cell of hair consisted of cuticle, ichthyoids ribbon of the hair which
was imbricate arrangement, clear texture, neat and regular and close to the cortex of the hair.
Therefore, the surface of the hair relatively flat, smooth feel, better gloss, under the action of Hair
perm agents, the hair cuticle suffered injury or even peeled, from Figure 1-Ⅱof the SEM of hair
treated with perm agents, we can see that scales strip of cuticle disorderly arranged, fuzzy hair
surface texture, rough and the reflection of light is reduced which affected the hair shine, but hair
impregnated with sericin solution firstly ,because of sericin had good absorption on hair, a layer of
transparent film was formed on the hair surface after sericin dried, which played a very good
protection against chemicals and thermal that directly contacted with the hair and damage and
greatly reduced the extent of the damage of the hair. Firstly sericin smeared hair, then perm agents
treated hair, according to Figure 1-Ⅲ, we can easily observed that ichthyoids ribbon of the hair was
imbricate arrangement, clear texture and hair surface structure was nearly similar to normal hair
undamaged. As a result, in the process of hair care sericin can have a very good effect on hair care
and repair.
Conclusion
The sericin contains more than 10 kinds of amino acids. The sericin which is water-soluble can
easily be absorbed by the skin. So these components of nutrient amino acid can enrich the nutrition
of skin and enhance the vitality and elasticity of the skin cells. Thus they can promote the
metabolism of the epidermal cells.
The amino acid composition of sericin is very close to skin’s NMF and it is an ideal substance of
natural moisturizing factor. It can maintain appropriate moisture content in the skin and make the
skin more elastic and smooth and soft. The sericin had high function of hygroscopic and we can get
422 Silk, Protective Clothing and Eco-Textiles

good efficacy of moisturizing and hygroscopic for skin simply by adding a small amount of sericin
in the cosmetics.
The molecular weight of sericin would directly affect the effect of the application of cosmetics
species. While the molecular weight of the sericin wide from 12000~17000D, and this specification
of molecular weight of sericin is suitable for applying to the cosmetics for hair care. While the
molecular weight of the sericin wide from 5000~7000D, and this specification of molecular weight
of sericin is suitable for applying to the cosmetics for skin care.
The experimental results show that the sericin can inhibit the activity of tyrosine which is very
effectively in inhibiting the formation of melanin in the skin. So the cosmetics of skin care which
added sericin can keep the skin white and flawless.
The experimental results show that the sericin had a good function of adsorption in hair and it can
enhance the flexibility of the hair. As the sericin had good affinity interaction on the hair and the
transparent film can be formed on the surface of hair, it can prevent the damage of hair and repair
the damaged hair effectively.
References
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[2] Li Min-Xu, Sheng Jia-Yong, Chinese Patent 200810195777.2 (2011)
[3] Sheng Jia-Yong: Suzhou Silk Institute of Technology Vol. 4 (1990), p. 47-55
[4] Liu Lan-Bing: Cosmetic technology, (Light Industry Press, Beijing 1987).
[5] Suzhou Silk Institute of Technology, Zhejiang Institute of Silk, Manufacture of chemical
(Textile Industry Press, Beijing 1992).
[6] Zhou Yong-Yuan: The slurry chemistry with physics (Textile Industry Press, Beijing 1985).
[7] Yao Yan-Qin, Shen Zhi-Quan: Journal of Textile Research Vol. 1 (2004), p. 10~12
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