Study on the Effect of Stretching on the Strength of Natural Silk Based on Different Feeding Methods

Study on the Structure and Properties of Silk Fibers Obtained from Factory All-Age Artificial Diets

The traditional production mode of the sericulture industry is no longer suitable for the development requirements of modern agriculture; to facilitate the sustainable development of the sericulture industry, factory all-age artificial diet feeding came into being. Understanding the structural characteristics and properties of silk fibers obtained from factory all-age artificial diet feeding is an important prerequisite for application in the fields of textiles, clothing, biomedicine, and others. However, there have been no reports so far. In this paper, by feeding silkworms with factory all-age artificial diets (AD group) and mulberry leaves (ML group), silk fibers were obtained via two different feeding methods. The structure, mechanical properties, hygroscopic properties, and degradation properties were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Structurally, no new functional groups appeared in the AD group. Compared with the ML group, the structure of the two groups was similar, and there was no significant difference in mechanical properties and moisture absorption. The structure of degummed silk fibers is dominated by crystalline regions, but α-chymotrypsin hydrolyzes the amorphous regions of silk proteins, so that after 28 d of degradation, the weight loss of both is very small. This provides further justification for the feasibility of factory all-age artificial diets for silkworms.

Silkworm Hemolymph and Cocoon Metabolomics Reveals Valine Improves Feed Efficiency of Silkworm Artificial Diet

Artificial silkworm diets significantly impact farm profitability. Sustainable cocoon production depends on the continuous improvement of feed efficiency to reduce costs and nutrient losses in the feed. This study used metabolomics to explore the differences in silkworm cocoons and hemolymph under two modes of rearing: an artificial diet and a mulberry-leaf diet. Nine metabolites of silkworm cocoons and hemolymph in the mulberry-leaf group were higher than those in the artificial-diet group. Enrichment analysis of the KEGG pathways for these metabolites revealed that they were mainly enriched in the valine, leucine, and isoleucine biosynthesis and degradation pathways. Hence, the artificial silkworm diet was supplemented various concentrations of valine were supplemented to with the aim of examining the impact of valine on their feeding and digestion of the artificial diet. The results indicated that valine addition had no significant effect on feed digestibility in the fifth-instar silkworm. Food intake in the 2% and 4% valine groups was significantly lower than that in the 0% valine group. However, the 2% and 4% valine groups showed significantly improved cocoon-production efficiency, at 11.3% and 25.1% higher, respectively. However, the cocoon-layer-production efficiencies of the 2% and 4% valine groups decreased by 7.7% and 13.9%, respectively. The research confirmed that valine is an effective substance for enhancing the feed efficiency of silkworms.

Effect of cocooning conditions on the structure, carbon and nitrogen isotope ratios of silks

The stable isotope technique provides the possibility to trace ancient textiles because the technique is associated with advantages such as trace indication, fast detection, and accurate results. Since different cocooning conditions may impact cocoons even under identical habitats, it is important to investigate the effects of different cocooning temperatures and humidity on the isotope incorporation values in the cocoons. In this study, silk fibers were reeled under different conditions of temperature and humidity, followed by analysis of the secondary structure of cocoon proteins and isotope incorporation patterns. We found that the deviations in carbon isotope values of silk under different cocooning conditions could reach up to 0.76‰, while the deviation in carbon isotope values at different locations of a single silk was 2.75‰. Further, during the cocooning process, depletion of the 13C-isotope at different locations of the silk fibers was observed, reducing the δ13C values. We proposed that the changes in carbon isotopes in silk were related to the content of sericin and silk fibroin in silk. Finally, we did not observe a significant difference in isotope ratios in degummed cocoons. In summary, the 13C isotope was enriched in sericin, whereas 15N was enriched in fibroin, and these findings provide basic information for tracing the provenance of silks.

Effects of artificial diet breeding on intestinal microbial populations at the young stage of silkworm (Bombyx mori)

The silkworm (Bombyx mori) is an economically important insect and serves as a model organism for Lepidoptera. To investigate the effects of the intestinal microbial population on the growth and development of larvae fed an artificial diet (AD) during the young stages, we analyzed the characteristics of the intestinal microbial population using 16S rRNA gene sequencing technology. Our results revealed that the intestinal flora of the AD group tended to be simple by the 3rd-instar, which Lactobacillus accounting for 14.85% and leading to a decreased pH in the intestinal fluid. In contrast, the intestinal flora of silkworms in the mulberry leaf (ML) group showed continuous growth of diversity, with Proteobacteria accounting for 37.10%, Firmicutes accounting for 21.44%, and Actinobacteria accounting for 17.36%. Additionally, we detected the activity of intestinal digestive enzymes at different instars and found that the activity of digestive enzymes in the AD group increased by larval instar. Protease activity in the AD group was lower during the 1st- to 3rd-instars compared to the ML group, while α-amylase and lipase activities were significantly higher in the AD group during the 2nd- and 3rd-instar compared to the ML group. Furthermore, our experimental results indicated that changes in the intestinal population decreased the pH and affected the activity of proteases, which might contribute to the slower growth and development of larvae in the AD group. In summary, this study provides a reference for investigating the relationship between artificial diet and intestinal flora balance.