Abstract
When wetted, Plantago seeds become covered with a polysaccharide-rich gel called mucilage that has value as a food additive and bulking dietary fibre. Industrially, the dry husk layer that becomes mucilage, called psyllium, is milled off Plantago ovata seeds, the only commercial-relevant Plantago species, while the residual inner seed tissues are either used for low value animal feed or discarded. We suggest that this practice is potentially wasting a highly nutritious resource and here describe the use of histological, physicochemical, and chromatographic analyses to compare whole seed composition/characteristics of P. ovata with 11 relatives already adapted to harsh Australian conditions that may represent novel commercial crop options. We show that substantial interspecific differences in mucilage yield and macromolecular properties are mainly a consequence of differences in heteroxylan and pectin composition and probably represent wide differences in hydrocolloid functionality that can be exploited in industry. We also show that non-mucilage producing inner seed tissues contain a substantial mannan-rich endosperm, high in fermentable sugars, protein, and fats. Whole seed Plantago flour, particularly from some species obtained from harsh Australian environments, may provide improved economic and health benefits compared to purified P. ovata psyllium husk, by retaining the functionality of the seed mucilage and providing additional essential nutrients.
Highlights
Plants of the genus Plantago occur widely throughout the world
The species can be separated into clades by their origin, P. coronopus from Europe, P. lanceolata and P. ovata from Central Europe and Eurasia, and the remaining species from Australasia
We studied five additional Australian native species and found, owing to their relatedness (Fig. 1), P. turrifera and P. bellidioides to be strikingly similar to P. cunninghamii and P. debilis, and P. gaudichaudii to be most similar to P. varia
Summary
Plants of the genus Plantago occur widely throughout the world. Traditionally, all parts of the plant are used[1–5], but the seeds have particular importance as they produce a gel-like coating of mucilage upon wetting which has many folk food and medicinal uses. The limited studies that are currently available have shown that whole seed flour (WSF) from P. ovata and P. psyllium are useful hydrocolloid replacements in baking[42,43] with significant differences in product quality between the two species. These studies show the potential of WSF from different Plantago species to be a less wasteful, more nutritious alternative to psyllium husk for selectively manipulating food qualities based on interspecific differences in functionality. The results demonstrate great diversity in mucilage properties and composition that likely represent exploitable differences in hydrocolloid functionality and have provided the first comprehensive overview of Plantago seed composition, showing them to be rich in beneficial sugars, fats and protein. We suggest that the use of WSF from diverse Plantago species studied here will simultaneously allow selective manipulation of quality and nutritional enrichment of food products
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