Journal of Medicine, Radiology, Pathology & Surgery (2017), 4, 13–17 REVIEW ARTICLE Sericin, a dietary additive: Mini review Snehashish Ghosh, Roopa S. Rao, K. Shwetha Nambiar, Vanishri C. Haragannavar, Dominic Augustine, S. V. Sowmya Department of Oral Pathology and Microbiology, Faculty of Dental Sciences, M. S. Ramaiah University of Applied Sciences, Bengaluru, Karnataka, India Keywords Abstract Food, nutrition, sericin Realization of the nutritive value of silk and silk protein sericin is essential to exploit its compatibility and value added potential. Sericin, a globular protein, obtained from Correspondence: Dr. K. Shwetha Nambiar, Department of Oral cocoons, as a part of the refining process. It has a wide array of applications in food Pathology and Microbiology, industry, pharmaceuticals, molecular biology, cosmetics, and textile industry. Dietary Faculty of Dental Sciences, M. S. Ramaiah intake of sericin reduces the levels of serum cholesterols and triglyceride. Furthermore, University of Applied Sciences, exhibits antioxidant activity by inhibiting tyrosinase enzyme. The nutritive value of Bengaluru - 560 054, Karnataka, India. sericin is explored in countries such as Japan and China. Although sericin is exploited E-mail: [email protected] in India in cosmetic industry, textiles, and pharmaceutical industry, it has not been explored in the food industry. Sericin is a unique protein; its rate of production is high, Received: 01 February 2017; as enormous amount of silk is generated in India and most goes for waste. Instead, it Accepted: 18 March 2017 can be utilized into a dietary additive in the food industry. The aim of this review article is to highlight the nutritional benefits of sericin and how best it can be utilized in food doi: 10.15713/ins.jmrps.89 industry as a dietary additive for the health benefits. Introduction high serine content. Different amino acids present in sericin are serine (30-39%), glycine (14-16%), asparagine acid 6 (11-15%), The word sericin is derived from a Latin word “sericum” and threonine (8-10%). The total content of amino acids with meaning silk.[1] Silk is obtained from silkworm Bombyx mori, [2] a hydroxyl groups (-OH), including serine and threonine comprising two proteins sericin and fibroin. In Sanskrit, comprises about 40%. The acidic amino acids having carboxyl silk is popularly known as “Kitta-Sutram.” The word “kitta” groups (-COOH) and basic amino acids having amino groups means worm, and “sutram” means thread.[3] About 1 million (-NH2) are also high. The polar side chain amino acid content is tons of fresh weight cocoons produced worldwide and over 80%. Most of the chemical structure of sericin is still unclear, approximately 4,00,000 tons of dry cocoons are generated, but sericin is likely to have many hydrophilic groups (with a high that produce around 50,000 tons of recoverable sericin. India polarity) as side chains.[6] produces around 1600 tons of silk every year, leaving behind approximately 250-300 tons of sericin.[2,4] The glue-like protein secreted from the mid-region of the silk gland, functions as a Forms of Sericin[7] binder of the fiber. Presently, sericin is underutilized and mostly Sericin can be classified into three forms based on their solubility discarded as a degumming solution causing environmental as Sericin A, Sericin B, and Sericin C. hazard due to its soaring oxygen demand for degeneration of [5,6] microorganisms. Sericin A It has been reported that sericin if utilized properly has wide range of functions varying from useful food element, Consists of the outermost layer and insoluble in hot water. It applications in cosmetic industry and in medical field.[2,5,7] contains 17.2% nitrogen and amino acids such as threonine, Various applications of sericin have been listed in Table 1. glycine, serine, and aspartic acid. Sericin B Sericin-structure Consists of the middle layer, which on hydrolysis with acid yields Sericin consists of polypeptides with molecular weight of 400, the same amino acid of Sericin A, and tryptophan. It contains 250 and 150 kDa. It has a unique amino acid composition with about 16.8% of nitrogen. Journal of Medicine, Radiology, Pathology & Surgery ● Vol. 4:2 ● Mar-Apr 2017 13 Ghosh, et al. Dietary sericin Table 1: Applications of sericin[7,21] Skin Hair Food industry Fabrics Medicinal uses Other uses Combat melanin, and Repair damaged hair Combat constipation In fabrics to absorb Biomaterial to Treating industrial whiten skin by providing basic and obesity moisture contradict cold wastewater with nutrients adsorptive pollutants Protect skin and increases Protect hair In porridge, to improve Cleaning fabrics Tonics rich in amino skin elasticity its taste and touch acids Preserves and maintains Hair conditioner Beverage rich in amino Improved Development of contact moisture of skin can be acids antibacterial activity lenses used in foundation creams and eyeliners Prevents wrinkles and Shampoo containing Edible antioxidant used To develop durable Suppresses development aging of skin sericin and pelarogenic in greasy food. Prevents and bioactive finish of bowel cancer and acid of pH<6 are useful browning reactions of on polyester for use colon tumors has for hair cleaning various foods in medical and sports antitumor properties garments Antioxidant used in Antioxidant applied in Wound healing cosmetics dairy products properties Additive applied in Accelerates the cosmetics to ameliorate its absorption of minerals guarantee period Additive as nourishment In nail cosmetics, prevents nail from chapping and brittleness Sericin C Table 2: Properties of sericin[7,8] Consists of the deepest layer, which lies adjacent to fibroin and is Attributes Properties insoluble in warm water. It is separated from fibroin by treating Characteristics White/yellow, water, soluble, odor free, and sweet in taste. Moisture content is 10‑17% with hot dilute acid or alkali. On acid hydrolysis it yields proline and amino acids present in sericin B. It also contains about 16.6% Morphology Wrinkled particles due to collapse of hollow spherical structures on rapid evaluation of nitrogen.[5,7] Sericin can also be classified based on the color of cocoons Molecular weight Ranges from 17100 to 18460 or 90‑125 KDa from which it is obtained. White sericin is the low viscosity Solubility Insoluble in cold water, soluble in hot water. sericin. Yellow sericin, is the one which is medium viscosity Solubility increases with addition of polyacrylate sericin, used in salad dressing. Yellow-green sericin, is the and decreases with addition of formaldehyde high viscosity sericin, contains flavonol pigments, which has Isoelectric pH As it contains more of basic amino acids, its antioxidative property, which is mostly incorporated in baking isoelectric pH is 4.0 [5,7,8] of bread. The properties of sericin are mentioned in Table 2. Sol‑gel transition It gets transformed to fluid at 50‑60°C and returns to gel form on cooling Sericin-extraction Extraction with the aid of heat Extraction of sericin with enzymes Sericin belongs to the category of structural glue proteins Extraction is carried out using enzyme alkylase or alkaline synthesized within the silk gland cells and secreted into the lumen protease at 60°C for 90 min, at a pH 10. Following which, of the gland. Presently, sericin is obtained from cocoon when the hydrolysis is done with trypsin for the retrieval of sericin.[9] raw silk is processed into fibers. Sericin in the cocoon layers is extracted with hot water or mildly alkaline solution. Apart from Proteins and its Importance the proteins, many other constituents such as carbohydrates, wax, pigments, and minerals are also present in layers. Of these Proteins are the biomolecules or macromolecules comprising constituents, the lower molecular weight accumulates along a chain of amino acids. It has wide spectrum of functions with sericin layers and emerges when sericin is extracted. Sericin ranging from catalyzing various biochemical reactions, sample is prepared by dialysis of this extract fluid which removes transport of biomolecules, DNA replication and many more. the low molecular weight components, except the pigments, The recommended dietary allowance (RDA) for proteins followed by freeze-drying.[7] is 0.8 mg/kg of body weight. If protein is consumed more than 14 Journal of Medicine, Radiology, Pathology & Surgery ● Vol. 4:2 ● Mar-Apr 2017 Dietary sericin Ghosh, et al. 1.5 mg/kg of body weight, which is almost the twice of RDA for the oxidation of fatty acids. The suppressive effect of sericin for proteins causes oxidative stress on the kidney, increases on free fatty acids is associated with increased peripheral glucose glomerular filtration rate, hypertrophy of the contralateral uptake, bringing about a better glucose tolerance. It has been kidney and can lead to formation of renal calculi.[10,11] reported that a dietary addition of 2% sericin, significantly Whereas, decreased protein intake can lead to growth reduces the oxidative stress in rats. Recently, it has been found retardation, reduced osmotic pressure causing extravasation of that sericin increases the antioxidant activity in rats by inhibiting fluid to the interstitium, leading to edema. Decreased protein tyrosinase.[13,15] It has an anti-constipative effects, as it causes intake can lead to malnutrition in children and can affect the increased excretion of fecal nitrogen, thereby causing increased growth, intelligence and several other functions in children. evacuation in rats.[16,17] Furthermore, sericin increases intestinal Sericin is a treasure, as it is generated free of cost and if utilized absorption of various trace elements such as zinc, magnesium, properly can combat the protein-energy malnutrition in and iron, and the resultant is increase in bioavailability of these India.[12,13] substances.[10] Sericin is also an anti-frosting agent, and coating In oral cancer, the requirement of protein increases, and it of it if applied on raw fruits and vegetables can prevent them becomes difficult for the patients of low socioeconomic class to from freezing.[8] The composition of sericin food grade powder combat with the needs.