Abstract
Sporopollenin is a physically robust and chemically resilient biopolymer that comprises the outermost layer of pollen walls and is the first line of defense against harsh environmental conditions. The unique physicochemical properties of sporopollenin increasingly motivate the extraction of sporopollenin exine capsules (SECs) from pollen walls as a renewable source of organic microcapsules for encapsulation applications. Despite the wide range of different pollen species with varying sizes and wall thicknesses, faithful extraction of pollen-mimetic SECs has been limited to thick-walled pollen capsules with rigid mechanical properties. There is an unmet need to develop methods for producing SECs from thin-walled pollen capsules which constitute a large fraction of all pollen species and have attractive materials properties such as greater aerosol dispersion. Herein, we report the first successful extraction of inflated SEC microcapsules from a thin-walled pollen species (Zea mays), thereby overcoming traditional challenges with mechanical stability and loss of microstructure. Morphological and compositional characterization of the SECs obtained by the newly developed extraction protocol confirms successful protein removal along with preservation of nanoscale architectural features. Looking forward, there is excellent potential to apply similar strategies across a wide range of unexplored thin-walled pollen species.
Highlights
The evolutionary adaptation of pollen capsules with sophisticated wall features has been a key factor in the inhabitation and prevalence of plants[1,2]
With the disintegration of its internal counterpart and corrosive effects of the treatment conditions, the exine sheath becomes susceptible to extrinsic forces and fragile from the chemical treatment eventually leading to structural failure
Through the systematic approaches taken here, various factors involved in acid hydrolysis of natural Zea mays pollen grains were evaluated
Summary
Walled Pollen received: 12 February 2016 accepted: 17 May 2016 Published: 15 June 2016. Being the first line of defense, sporopollenin is equipped with various evolutionary-driven resilient properties tailored for protection and endurance to stay viable for extended lengths of time Due to these attractive properties along with a large and renewable supply, pollen grains have gained the attention of the wider scientific community and are proving to be excellent microcapsules for encapsulation applications[3,16,17]. Taking these factors into consideration, we have developed an improved method to obtain morphologically intact, thin-walled SECs from Zea mays pollen capsules using a one-pot acid hydrolysis process while bypassing complete dehydration in the intermediate stage To our knowledge, this is the first report of thin-walled SECs with conserved inner structural features in both the microscale and nanoscale regimes. The findings indicate that thin-walled SECs can be obtained with 82% protein removal efficacy by using an acid hydrolysis extraction method in 85 (w/v)% phosphoric acid (H3PO4) within 2.5 hours
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