Abstract:
Sericulture (Silk farming) is the rearing of silk moths for the production of raw silk. Silk farming originated from China where it was secretly practiced for many years before spreading to other parts of the world. Silk moths are grouped into mulberry silk moths (domesticated) and wild silk moths. Silk moth cocoon has a double filament made of insoluble protein known as fibroin which is embedded in a water soluble protein called sericin. Prior to processing cocoons, are boiled in strong alkali so as to dissolve the sericin a process called degumming. Proteinases enzymes such as papain from papaya (Carica papaya) and bromelain from pineapple (Ananas cosmosus) characterised by their proteolytic activity have the potential to hydrolyse sericin, thus increasing its solubility in water. This study sought to investigate the effect of extracts from pineapple and papaya on the solubility of sericin protein from cocoons of three species of silk moths: Gonometa postica, Argema mimosae and Bombyx mori at different temperatures. Twenty cocoons of each species were cut open, cleaned to remove the pupae remains and weighed. The cleaned cocoons were immersed in the degumming agents at various temperatures and five cocoons were taken out at 30 minutes intervals for 120 minutes. These cocoons were dried for two hours and then re-weighed. The degumming agents used were crude extracts from papaya and pineapple, commercial papain, commercial bromelain and their effects were compared with that of the conventionally used sodium bicarbonate and distilled water. The efficiency of the degumming processes was assessed using mean weight loss at different temperatures and was subjected to analysis of variance (ANOVA). Where significant difference existed, mean separation was carried out using the StudentNewman-Keuls test. In G. postica cocoons, papain gave the highest mean weight loss at a temperature of 60°C for all time intervals. The highest mean weight loss from G.postica was 0.5 g at 60 ºC, 120 minutes in G. postica cocoons this was significantly different from the mean weight loss with other treatments. The least mean weight loss in G. postica was recorded in water and ripe papaya treatment which was significantly lower than the other treatments extract. A.mimosae cocoons showed highest weight loss with bromelain at 60°C, 90 minutes of but this was not significantly different with sodium bicarbonate. The least mean weight loss in A mimosae was recorded in papain and ripe papaya treatment 70°C, 120 minutes but this was not significantly lower than the other treatments extract. With B. mori cocoons, papain gave the highest mean weight loss of 0.12g at a temperature and time of 70° C, 60 minutes respectively, this was significantly different compared with the mean weight loss with all the other treatments. The results obtained from this study have shown that plant proteases can be utilised for effective degumming of cocoons. Commercial proteases were the best agent for degumming cocoons of G. postica and B. mori as it gave the highest mean sericin loss within the shortest duration. The results show that locally available fruit proteases can be used to remove sericin from silk moth cocoons. These offer farmers a cheaper local option while also shortening the time required for boiling hence saving fuel
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