Opinion
Volume 1 Issue 3 - 2017
Sericulture `Waste’ Silkworm Pupae as Alternate Source for Animal Protein
IK Pai*
Department of Zoology, Goa University, Goa-403 206, India
*Corresponding Author: IK Pai, Department of Zoology, Goa University, Goa-403 206, India.
Received: July 19, 2017; Published: August 14, 2017
One of the major problems, the world facing today, is to feed the ever galloping population, which has already crossed 7 billion mark. Though, the agricultural community is working hard, to combat these bottleneck drawbacks, more than 1/3 of the world population goes to sleep without having a food. When one talks about the food, biomolecules such as carbohydrate, proteins and lipids have to be considered. Agriculturists concentrate mainly to provide carbohydrates in the form of wheat, paddy and other staple food and lipid and proteins to a lesser extent. Source of plant as well animal protein is limited Hence millions of people are facing the problem of deficiency of proteins in particular in their food [Udani, 1979]. Commercially available protein supplements are beyond the reach of not only poor people but also middle class people category as well. By and large plant protein is made available from dicotyledonous plants such as lentils, grams, peanut while fish happen to be is major source of animal protein, which could be affordable by poor and middle class category also population. If one looks for alternate source for animal protein in particular, silkworm pupa, which is presently considered as waste material in the process of silk reeling, seem to be promising source for animal protein [Finke, 2002].
  Sericulture is an agro-based rural cottage industry, where the `biological machine’ silkworm converts plant protein such as Morin into animal protein such as silk. This is one of a few industries where money flows from rich to poor. Although there are several commercial species of silkworms such as Tasar, Muga, Eri, Anaphe silks available, it is the mulberry silkworm Bombyx mori available, is the most widely reared and used apart from being intensively studied. Silk was first produced in China as early as the  Neolithic  period [Vainkar, 2004]. Today, China followed by India is the world leader in silk production accounting about 60% of total world’s silk production. According to  Confucian  text, the discovery of silk production dates to about 2700 BC, although archaeological records point to silk cultivation as early as the  Yangshao  period (5000-3000 BC) [Barber, 1992]. 
Silk is a continuous protein fiber produced by the silkworm during their larval-pupal metamorphosis, where it forms its cocoon [Cook, 1968]. Though `silk fibres’ are also produced by some spiders belonging to Fl: Arachnidae [Cook, 1968, Robson, 1985] as they cannot be commercially produced or spun unlike silkworms. Silk fibre is a mix of mainly two proteins viz., yellow colored, brittle, no-elastic sericin, which is also known as `silk gum’ having antibacterial activities along with some other minor component such as waxes, fats, pigments etc., and fibroin, the main silk fiber.
The silk is obtained by placing the silk cocoons in hot water, by which the `silk gum’ gets dissolved and core fiber fibroin gets exposed and is reeled Once silk is extracted, the pupae inside the cocoon comes in contact with hot water and gets killed. Generally these pupae are discarded as waste. Silkworm pupae are the by-product after the silk-thread has been wound-off from the cocoon and can serve as a feedstuff. However, as the people became aware of the nutritive value of the silkworm pupae they started utilizing them as food since last couple of decades. Today, in  Assam, India, they are boiled for extracting silk and the boiled pupae are eaten directly with salt or fried with chili pepper or herbs as a snack or dish.
In Korea, pupae are boiled and seasoned to make a popular snack food known as Beondegi. In China, street vendors sell roasted silkworm pupae. In Japan, silkworms are usually served as a Tsukudani i.e., boiled in a sweet-sour sauce made with  soy sauce  and sugar. In  Vietnam, this is known as con nhộng. Silkworms have also been proposed for cultivation by astronauts as  space food  on long-term missions [Choi, 2009].
Silkworm pupae contains α-glucosidase inhibitor. The percentages of total protein and lipid contents by dry weight were 55.6 and 32.2%, respectively. Silkworm pupae protein had high levels of essential amino acids such as valine, methionine and phenylalanine [Tomotake., et al. 2010]. The contents of essential amino acids in silkworm pupae protein satisfied the FAO/WHO/UNU suggested requirements in 2007. In addition, they also possessed n-3 fatty acids, especially α-linolenic acid (36.3%), as a major component. The 50% ethanol extract of silkworm pupae contained 1-deoxynojirimycin (DNJ), which is a potent α-glucosidase inhibitor [Kumar., et al. 2011]. These results suggest that silkworm pupae are a new source of high quality protein, lipid, and α-glucosidase inhibitor. The silkworm pupae is rich source of undeoiled and deoiled dry matter, Organic matter, Crude protein, Crude fat, Ash, Crude fibre, N-free extract etc., [Table-1]
Unde-oiled De-oiled
  Mean Variation Mean Variation
Dry matter 88.9 68.5 -95.1 91.9 90.4-98.5
Organic matter 89.6 87.9-91.8 91.8 84.2 -88.8
Crude protein 55.1 49.4-60.9 72.8 44.5-77.6
Crude fat 23.2 14.2-30.3 2.0 0.7-7.0
Ash 3.8 2.2-7.5 5.6 4.4-9.1
Crude fiber 5.5 4.9-8.8. 6.2 4.6-9.8
N-free extract 6.4 5.5-10.8 7.3 6.7-9.8
(Source: Hertrampf and Piedad-Pascual (2000)).
Table 1: Chemical composition of silkworm pupae meal (% in dry matter) (Nehring, (1955) Friede, (1977) Zaher and Mazid (1993) and Hossain (1991).
The mean crude protein content of silkworm pupae meal has widely varied crude protein contents. The mean Crude protein mean content of fat extracted silkworm pupae meal is higher (72.8%) than that of the fat containing meal (55.1%). Several important amino acids such as lysine, methionine, arginine, histidine and threonine are also present in a limited quantity. The protein of silkworm pupae meal is not of high value [Friede, 1977] based on the EAA-Index (essential amino acid) and the biological value (BW) (51.6%) [StegerandPiatkowski, 1959]. Apart from the above essentials, the silkworm pupae meal fat has a lecithin content of 2.12% [Steger and Piatkowski, 1959].
Silkworm pupae also contains saturated fatty acids (20.7%), unsaturated fatty acids such as Palmitic acid (20.7%), Oleic acid (70.1%), Linoleic acid (14.0%), Linolenic acid (9.1%), Other fatty acids amounting to 24.6%, of which, Linolenic acid: accounts for 14.0% and other fatty acids are present at 8.4% [Hertrampf and Piedad-Pascual, 2000] An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized de novo (from scratch) by the organism, and thus must be supplied in its diet. Among nine amino acids humans cannot synthesize phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine and histidine. However, the silkworm pupae contains several of the essential aminoacids such as Arginine, Histidine, Isoleucine Leucine, Lysine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine in considerable amount [Table-2].
  Mean Variation
Arginine 6.0 3.6 - 7.8
Histidine 3.3 3.2-3.3
Isoleucine Leucine and Lysine 7.8 7.5-8.0
Lysine 6.1 2.5-10.1
Methionine 1.9 1.8-1.9
Phenylalanine 2.5 1.8-3.2
Threonine 4.6 3.6-5.6
Tryptophan 1.1 0.6-1.5
Valine 4.7 ----
(Source: Hertrampf and Piedad-Pascual (2000)).
Table 2: Essential amino acid profile of silkworm pupae meal (Steger and Piatkowski (1959) Koyama., et al. (1961) Lakshminarayana and Thirumala (1971), and New (1987).
The crude fiber of silkworm pupae meal is mostly chitin which is hardly utilized by animals [Friede, 1977]. Information on the mineral and vitamin content of silkworm pupae meal is shown in Table-3. Based on the above it is possible to utilize the one of the `wastes’ of sericulture industry viz. silkworm pupae, which is generally discarded or at the most used as fish or poultry feed, for human consumption to reduce the load of providing animal protein to humans.
Minerals Vitamin (mg per 100g)
Calcium 0.63% Vitamin E 1000
Phosphate 1.25% Vitamin B1 15
Sodium 0.03% Vitamin B2 80.0
Potassium 1.07% Vitamin B12 0.5
(Source: Hertrampf and Piedad-Pascual (2000)).
Table 3: Mineral and vitamin contents of silkworm pupae meal.
References
  1. Barber EJW. “Prehistoric textiles: the development of cloth in the Neolithic and Bronze ages with special reference to Aegean”. Princeton University Press (1992): 31.
  2. Choi Charles Q. "Care for a Silkworm with Your Tang?" Science NOW Daily News (2009):
  3. Cook JG. “Handbook of textile fibers (Natural fibers)”. Woodhead Publishing (1968): 157.
  4. Finke MD. “Complete nutrient composition of commercially raised invertebrates used as food for insectivores”.  Zoo Biology 21 (2002): 269-285.
  5. Friede HJ. “Seidenraupenpuppenschrot. In: Kling, M.; Wöhlbier, W: Handelsfuttermittel. Verlag Eugen Ulmer, Stuttgart/Germany”. (1977):
  6. Hertrampf JW and F Piedad Pascual. “Silkworm Pupae Meal. Handbook on Ingredients for Aquaculture feeds”. Springer (2000): 372-378.
  7. Hossain MA., et al. “Evaluation of silkworm pupae meal as dietary protein source for catfish (Heteropneustes fossiles Bloch)”. Proc. Fish Nutrition in Practice (1991): 785-791.
  8. Koyama H., et al. “Studies of fish food substitute for silkworm pupae as available foods for carp-culturing in farm ponds. II. Experiment about availability of soybean cake, Ko meal and fish meal. Bull. Freshwater Fish”. (1961): 49-55.
  9. Kumar S., et al. “α-glucosidase inhibitors from plants: A natural approach to treat diabetes”. Pharmacognosy Reviews 5.9 (2011): 19-29.
  10. Lakshminarayana T and Thirumala T. (1971): Quoted from: Friede, H.J. (1977).
  11. Nehring K. “Lehrbuch der Tierernährung and Futtermittelkunde (5th edition). Neumann Verlag, Radebeul and Berlin/Germany”. (1955):
  12. New MB. “Feed and feeding of fish and shrimps - A manual on the preparation and presentation of compound feeds for shrimps and fish in aquaculture”. (1987):
  13. Robson RM. “Silk: Composition, structure and properties (in: Handbook of fibre Science and Technology, Vol IV (Ed: Lewin, M and E. M. Pearce) Marcel Dekkar Inc”. (1985): 649-700.
  14. Steger H and Piatkowski B. “(1959): Quoted from: Friede HJ”. (1977):
  15. Tomotake H., et al. “Silkworm pupae (Bombyx mori) are new sources of high quality protein and lipid”. Journal of Nutritional Science and Vitaminology 56.6 (2010): 446-448.
  16. Udani PM. “Nutritional problems in developing countries”. Paediatrician 8.1 (1979): 48-63.
  17. Vainker S. “Chinese Silk: A Cultural History. Rutgers University Press”. (2004): 20.
  18. Zaher M and Mazid MA. Aquafeeds and feeding strategies in Bangladesh. In: New, M.B.; Tacon, A.G.J.; Csavas, I. (Eds.): Farm made aquafeeds”. RAP (1993):
  19. Publication 1993/18, AADCP/PROC/5, Bangkok/Thailand, 75-86.
  20. Webliography: “10 Weird Foods Eaten In India”.
Citation: IK Pai. “Sericulture `Waste’ Silkworm Pupae as Alternate Source for Animal Protein”. Innovative Techniques in Agriculture 1.3 (2017): 119-122.
Copyright: © 2017 IK Pai. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.