Natural biocolourant selectivity from mulberry leaves to natural coloured cocoon silkworm excrement

Abstract With the development of biological and genetic technology, coloured silk cocoons have become more and more popular. Silkworm excrement (SE) is an important by‐product from the sericulture industry. When the application and recycling of SE involves SE from coloured‐cocoon silkworms, it is necessary to know about the discrepancy from conventional SE produced by white‐cocoon silkworms. In this study, white‐cocoon and yellow‐cocoon domestic silkworms were fed mulberry leaves from the same source and their SE was investigated for natural colourants of chlorophyll and carotenoids. The results showed that, for both types of SE, although a proportion of chlorophyll from mulberry leaves was transformed into magnesium‐free chlorophyll derivatives in SE via the silkworm's digestive system, and that the de‐magnesium reaction occurred primarily in chlorophyll a , the chemical components of chlorophyll and its derivatives were mainly the same in both types of SE. The chlorophyll concentration was slightly higher in SE from the white‐cocoon silkworm than that from the yellow‐cocoon silkworm. Quantitative analysis through high‐performance liquid chromatography unveiled lutein content of 99.1 ± 9.2 μg/g and β‐carotene content of 180.7 ± 14.3 (μg/g) for SE from the yellow‐cocoon silkworm, representing a rate of decrease of ca. 7.6% for lutein and of ca. 6.3% for β‐carotene compared with that of SE from the white‐cocoon silkworm. The anti‐oxidant capacity of SE from the white‐cocoon silkworm was found to be superior to that from the yellow‐cocoon silkworm, as investigated through free radical cation scavenging assay. The outcomes of the current study are expected to act as a reference guide towards the application and recycling of SE for better and more effective utilisation of this by‐product as a renewable natural bioresource.