The scientists, who published their findings in the journal Bioresource Technology, claim that the consumption of about 10 g of king palm flour would represent about 28 per cent of the FAO/WHO recommended daily requirement for dietary fibre for adults.
Heart of palm (palmito) is a vegetable harvested from the inner core and growing bud of certain palm trees with the residues from its processing such as leaves and leaf sheathes constituting 80 to 90 per cent of the total palm weight, report the researchers.
They argue that by-products from agro-industries have not been extensively commercialized but could be a promising source of dietary fibres, antioxidants, essential fatty acids, antimicrobials, and minerals.
And the goal of their study, explained the authors, was to evaluate the chemical composition, microstructure, and antioxidant capacity of flour produced from king palm residue to determine its efficacy as a new dietary fibre source.
Residues from organic king palm processing were supplied by Brazilian company, Vegetal Brasil, said the research team.
King palm flour leaf sheathes were washed and oven-dried in an air forced oven. The dried raw material was milled in a hammer mill to a dry 42-sieve size powder and screened to pass through a 60 mesh sieve, with the resulting flour packaged in an airtight plastic bag and stored in a freezer until required.
Moisture, total ash, lipid, and crude protein were determined by standard Association of Official Analytical Chemists (AOAC), said the researchers.
Extracts for the determination of total polyphenols and antioxidant activity were prepared using 2 g flour and mixed with 50 mL of 80 per cent methanol or distilled water by shaking for one hour. The extract was filtrated and transferred into amber bottle and purged with a stream of nitrogen.
The total polyphenols content (TPC) of king palm flour was determined according to the Folin–Ciocalteu procedure modified, explained the researchers.
And, they added, the free radical scavenging capacity of king palm flour extracts was determined by using the stable 2,2-diphenyl-1-picrylhydrazyl radical (DPPH_) and 2,20-azino-di(3-ethylbenzthiazoline sulphonate) (ABTS_+) methods.
The results showed that the king palm flour exhibited high levels of dietary fibre (70.85 per cent) and ash (3.2 per cent), but low contents of protein (3.51 per cent) and lipid (0.91 per cent.).
“The presence of primary and secondary cell walls lignified in leaf sheath contributed to high levels of dietary fibre detected in king palm flour,” reported the authors.
They also determined that the flour contained high levels of mineral content, with iron, magnesium, calcium and potassium levels at 7.31, 517.03, 801.33 and 1041.95 mg/100 g, respectively.
The researchers explained that the micrographs of leaf sheath showed the presence of druses, characterized as calcium oxalate deposition, which contribute to the calcium content in king palm flour.
They said that methanol and aqueous extracts of king palm flour showed 1.27 and 0.95 mg/g (Gallic Acid Equivalents) of total polyphenol content (TPC), respectively.
And the researchers added that the TPC of the extracts was higher than that of sorghum flour, rye flour and oat bran, while the methanol extract yielded higher phenolic content than that of wheat bran but similar results for rye bran.
The authors said that further research is needed to investigate the chemical components that contribute to total antioxidant activity and to determine the relationship between antioxidant activity and different phenolic compounds of king palm flour.
Additional studies are also required, they said, to elucidate the polysaccharides present in leaf sheath of king palm, as well as determining their functionality in human health.
But the authors concluded that king palm derived flour "can be considered an important source of nutrients for human nutrition, mainly due to its content of dietary fibres and minerals.”
Source: Bioresource Technology
Published online ahead of print: doi:10.1016/j.biortech.2010.02.053
Title: Microstructure, nutrient composition and antioxidant capacity of king palm flour: A new potential source of dietary fibre
Authors: R, D.M.C. Amboni et al