The composition of Australian Plantago seeds highlights their potential as nutritionally-rich functional food ingredients

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.

The Renaissance of Plant Mucilage in Health Promotion and Industrial Applications: A Review

“…Arabinoxylan is a typical polysaccharide found in Plantago. Many reports describe its unusual branched structure β- (1,4) [142]. Plantago mucilage is a source of protein, dietary fiber, and saturated fatty acids.…”

“…It is also a rich source of both ω-3 and ω-6 polyunsaturated acids (>78% of total fatty acids). The monosaccharides found in the hydrocolloid fractions include xylose, arabinose, rhamnose, galactose, glucose and small amounts of mannose, galactose, and galacturonic and glucuronic acids [142]. In the case of P. lanceolata, P. ovata, and P. media, additional cellulose fibrils form a regular, radially arranged skeleton of pectin, which surrounds the seed surface [143].…”

Rain events at maturity severely impact the seed quality of psyllium (Plantago ovata Forssk.)

“…Colourimetric analysis presented here and used to determine the colour differences before and after rain damage showed that the rain event caused a significant darkening (reduction in L *) and a significant greening (reduction in a *) of the seeds (Figure 3a and b). The changes in seed colour determined using colourimetry likely reflect changes in the extractability and/or oxidation of pigments in the seeds which may be concentrated in an intensely stained layer between the mucilage polysaccharide layer and the endosperm tissues in P. ovata (Phan et al, 2020) and other Plantago species (Cowley et al, 2021; Jones & Albers, 1955; Patel et al, 2020; Qadry, 1963). Another possible explanation for the significant colour change in AR samples is microbial contamination.…”

Anchorage by seed mucilage prevents seed dislodgement in high surface flow: a mechanistic investigation

“…However, when looking in- depth at close relatives, there is often much variation (Figure 2D-E). Comparisons of many Plantago species reveal a wide variety of mucilage structure across the genus (Cowley & Burton, 2021, Cowley et al 2021) as does examining variation across populations of other widespread species or genera (e.g. Inceer et al, 2012; Villellas & Garcia, 2012, Poulain et al, 2019).…”