Identification and quantification and antioxidant activity of flavonoids in different strains of silk cocoon, Bombyx mori

Study of the Antioxidative Effects of Bombyx mori Silk Sericin in Cultures of Murine Retinal Photoreceptor Cells

The availability of natural substances able to fulfill the role of antioxidants in a physiologic environment is important for the development of therapies against diseases associated with excessive production of reactive oxygen species and ensuing oxidative stress. Antioxidant properties have been reported episodically for sericin, a proteinaceous constituent of the silk thread in the cocoons generated by the larvae of the Lepidoptera order. We investigated the sericin fractions isolated from the cocoons spun by the domesticated (Bombyx mori) silkworm. Three fractions were isolated and evaluated, including two peptidoid fractions, the crude sericin and the purified (dialyzed) sericin, and the non-peptidoid methanolic extract of the crude fraction. When subjected to Trolox equivalent antioxidant capacity (TEAC) assay, the extract showed much higher antioxidant capacity as compared to the crude or purified sericin fractions. The three fractions were also evaluated in cultures of murine retinal photoreceptor cells (661 W), a cell line that is highly susceptible to oxidants and is crucially involved in the retinopathies primarily caused by oxidative stress. The extract displayed a significant dose-dependent protective effect on the cultured cells exposed to hydrogen peroxide. In identical conditions, the crude sericin showed a certain level of antioxidative activity at a higher concentration, while the purified sericin did not show any activity. We concluded that the non-peptidoid components accompanying sericin were chiefly responsible for the previously reported antioxidant capacity associated with sericin fractions, a conclusion supported by the qualitative detection of flavonoids in the extract but not in the purified sericin fraction.

Functionality of Silk Cocoon (Bombyx mori L.) Sericin Extracts Obtained through High-Temperature Hydrothermal Method

Sericin, a textile waste, can be used for antioxidant and skin-whitening purposes. The hydrothermal method of extracting sericin is more eco-friendly than are chemical and enzymatic methods. In this study, silk cocoons were cut into pieces and then subjected to hydrothermal extraction at three temperatures (160, 200, and 220 °C) to obtain sericin extracts (Sericin160, Sericin200, and Sericin220, respectively). Antioxidant activity and tyrosinase inhibition were measured to determine the extracts' effectiveness. Sericin220 was the strongest antioxidant, with total phenol content, total flavonoid content, and ferric reducing power of 62.19 ± 0.04 mg gallic acid equivalents/g dry weight, 0.07 ± 0.01 mg quercetin equivalent/g dry weight, and 181.49 ± 0.024 mg vitamin C equivalent/g dry weight, respectively. The half-maximal inhibitory concentrations for DPPH and ABTS free-radical scavenging ability were 6.41 ± 0.05 and 0.79 ± 0.37 mg/mL, respectively. Sericin220 also exhibited the highest tyrosinase inhibition activity (70.82 ± 4.1 mg vitamin C equivalent/g), indicating its whitening potential.

Changes in Amino Acid Profiles and Bioactive Compounds of Thai Silk Cocoons as Affected by Water Extraction

Silk proteins have many advantageous components including proteins and pigments. The proteins-sericin and fibroin-have been widely studied for medical applications due to their good physiochemical properties and biological activities. Various strains of cocoon display different compositions such as amino-acid profiles and levels of antioxidant activity. Therefore, the objectives of this study were to find a suitable silk protein extraction method to obtain products with chemical and biological properties suitable as functional foods in two strains of Bombyx mori silk cocoon (Nangsew strains; yellow cocoon) and Samia ricini silk cocoon (Eri strains; white cocoon) extracted by water at 100 °C for 2, 4, 6 and 8 h. The results showed that Nangsew strains extracted for 6 h contained the highest amounts of protein, amino acids, total phenolics (TPC) and total flavonoids (TFC), plus DPPH radical-scavenging activity, ABTS radical scavenging capacity, and ferric reducing antioxidant power (FRAP), anti-glycation, α-amylase and α-glucosidase inhibition. The longer extraction time produced higher concentrations of amino acids, contributing to sweet and umami tastes in both silk strains. It seemed that the bitterness decreased as the extraction time increased, resulting in improvements in the sweetness and umami of silk-protein extracts.

Extraction and antioxidant activity of sericin, a protein from silk

Abstract Sericin is a globular protein that represents 20% to 30% of the silk fiber from Bombyx mori silkworm cocoon. This protein is usually removed from the raw fiber and discarded by silk producers, a process known as degumming. However, sericin possesses significant biological properties that allows its application in various fields. The antioxidant activity is one of its most relevant benefits. Several authors have reported its anti-tyrosinase activity, lipid peroxidation inhibition and free radical neutralization. The antioxidant potential of sericin protein varies according to the extraction method used. Even though a wide variety of extraction techniques have been studied, simple technics including water at high temperature have exhibited efficient results. Furthermore, this method does not interfere with the safety of sericin for subsequent applications in food.

Protective effect of Thai silk extracts on drug-induced phototoxicity in human epidermal A431 cells and a reconstructed human epidermis model

Bombyx mori silk extracts, derived from the cocoon degumming process of draw and dye silk in the textile industry, are mainly composed of sericin protein. To add value to the Thai silk extracts, and hence the silk industry, a simple enrichment process was recently developed and the enriched silk extracts were then applied in nano-cosmeceutical products and nano-delivery systems. In this study, the protective effect of Thai silk extracts from three different strains of Bombyx mori on the drug-induced phototoxicity was evaluated in vitro using chlorpromazine (CPZ), a commonly used antipsychotic drug, as a representative phototoxic drug. The human epidermal A431 cell line and reconstructed human epidermis (RhE) model were used as the in vitro skin model. The silk extracts significantly improved the viability of A431 cells after CPZ exposure and ultraviolet A (UVA) irradiation, as shown by the significantly increased CPZ and UVA IC₅₀ values and the decreased proportion of apoptotic cells. The protective effect of these silk extracts against the CPZ-induced UVA-phototoxicity in A431 cells was associated with the attenuation of intracellular oxidative stress via an increased intracellular glutathione level. Likewise, the silk extracts exhibited a protective effect on the CPZ-induced UVA-phototoxicity in the RhE model, in terms of an improved tissue viability and attenuation of the released inflammatory cytokine, interleukin-1α. These findings support the potential usefulness of silk extracts in novel applications, especially in the protection of drug-induced phototoxicity.