Sabrina Tozzi

Quantitative analysis of indigo and indigo precursors in leaves of Isatis spp. and Polygonum tinctorium

Analysis of extracts from two woad species (Isatis tinctoria and Isatis indigotica) and Polygonum tinctorium revealed that only one indigo precursor (indican) was present in Polygonum, but two precursors were found in Isatis spp. This was done using high performance liquid chromatography (HPLC), coupled to an evaporative light scattering detector (ELSD). In Isatis spp., the indigo precursors indican and a fraction representing isatan B were identified. The proportion of indican and isatan B was different between the two Isatis spp. tested. For the first time, it was possible to quantify the precursors in woad plant species, and the results were found to be in good agreement with those made from total indigo quantification using two different spectrophotometric methods or a derivatization technique.

A New HPLC‐ELSD Method To Quantify Indican in Polygonum tinctorium L. and To Evaluate β‐Glucosidase Hydrolysis of Indican for Indigo Production

A method to quantify the indigo precursor indican (indoxyl‐β‐d‐glucoside) in Polygonum tinctoriumL. has been developed. Plant material was extracted in deionized water, and indican was identified and quantified using high performance liquid chromatography (HPLC) coupled to an evaporative light scattering detector (ELSD). Results confirmed that with this method it is possible to measure indican content in a short time, obtaining reliable and reproducible data. Using this method, leaf indican content was quantified every 15 days during the growing season (from May to October) in P. tinctorium crops grown in a field experiment in Central Italy. Results showed that indican increased along the growing season until flowering and was positively affected by photosynthetic active radiation (PAR). Indican is naturally hydrolyzed by native β‐glucosidase to indoxyl and glucose, the indoxyl yielding indigo. The activity of two enzymes, sweet almond β‐glucosidase and Novarom G preparation, were compared with P. tinctorium native β‐glucosidase to evaluate indigo production. Results showed that the ability to promote indigo formation increased as follows: almond β‐glucosidase ≤ Novarom G.

Light Quality Influences Indigo Precursors Production and Seed Germination in Isatis tinctoria L. and Isatis indigotica Fort.

Isatis tinctoria L. and Isatis indigotica Fort. are biennial herbaceous plants belonging to the family of Cruciferae that are used as a source of natural indigo and show several morphological and genetic differences. Production of indigo (indigotin) precursors, indican (indoxyl β‐D glucoside) and isatan B (indoxyl ketogluconate), together with seed germination ability were compared in Isatis tinctoria and Isatis indigotica grown under six different light conditions (darkness, white, red, far red, blue, yellow light) at 25°C. Light quality influenced both germination and production of indigo precursors in the two Isatis species. Different responsiveness to far red and blue light was observed. Indeed, a detrimental effect on germination by blue and far red light was found in I. tinctoria only. Different amounts of isatan B were produced under red and far red light in the two Isatis species. In I. tinctoria, the level of main indigo precursor isatan B was maximal under red light and minimal under far red light. Whereas in I. indigotica far red light promoted a large accumulation of isatan B. The photon fluence rate dependency for white and yellow light responses showed that the accumulation of indigo precursors was differently influenced in the two Isatis species. In particular, both white and yellow light enhanced above 40 μmol m−2s−1 the production of isatan B in I. indigotica while only white light showed a photon fluence dependency in I. tinctoria. These results suggest a different role played by the labile and stable phytochrome species (phyA and phyB) in the isatan B production in I. tinctoria and I. indigotica. I. indigotica, whose germination percentage was not influenced by light quality, demonstrated higher germination capability compared with I. tinctoria. In fact, I. tinctoria showed high frequency of germination in darkness and under light sources that establish high phytochrome photoequilibrium (red, white and yellow light). Germination in I. tinctoria was negatively affected by far red and blue light. I. indigotica seeds appear to be indifferent to canopy‐like light (far red). Our results provide further insights on the distinct behaviour of I. tinctoria and I. indigotica that belong to two different genetic clusters and different original environments.

Characterization of traditional dyes of the Mediterranean area by non-invasive UV-Vis-NIR reflectance spectroscopy

Abstract An understanding of the composition of natural and synthetic dyes used in ancient textiles and rugs is important for conservation purposes and to determine the origin of a textile or rug. Colorants or dyes are traditionally analysed by means of separation methods and ultraviolet–visible spectroscopic techniques that require sampling. This contribution focuses on establishing a fast, non-invasive, and in situ measurement procedure based on ultraviolet–visible–near infrared reflectance spectroscopic techniques for the characterization of dyes in ancient textiles or rugs manufactured in the Mediterranean basin and Middle East. For this purpose a collection of specimens on wool supports was prepared following ancient dyeing recipes. The samples were subsequently measured in the 230–2500 and 350–1700 nm ranges to create a spectroscopic database that was then compared with spectra acquired from textiles and rugs in order to characterize the dyes present.