Recalcitrant Structures in Lemongrass Leaf Blades

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Recalcitrant Structures in Lemongrass Leaf Blades - Needs for Systemic Process Analytics

Arniza Ghazali^1*, Nur Haffizah Azhar¹, Nur Fadzlyiana Wahab², Muhammad Al Amin Zaini³, Radhiyatul Akma Mohammad Zani¹, Shamsul Bahar Mohd Nor^{4, 5},

Norliza Muhammad⁴

1 Division of Bioresource Technology, School of Industrial Technology, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia.

2 Opulent Solutions Sdn Bhd, Plot 1111, Bayan Lepas Industrial Park, Lebuhraya Kampung Jawa, 11900 Bayan Lepas, Pulau Pinang, Malaysia.

3 Dainippon Ink and Chemicals (M) Sdn Bhd, HICOM Industrial Park, 40400 Shah Alam, Selangor, Malaysia.

4 Saham Utama Sdn Bhd, 15, Taman Matang Damai, 34750 Simpang, Perak, Malaysia.

5 Green Tech Malaysia, Malaysian Green Technology and Climate Change Centre, No.2, Jalan 9/10, Persiaran Usahawan, Seksyen 9,43650 Bandar Baru Bangi,Selangor Darul Ehsan, Malaysia

*Corresponding Author: [email protected]

Accepted: 15 September 2020 | Published: 30 September 2020

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Abstract: The commodity-loaded leaf biomass of lemongrass (Cymbopogon citratus) has long been the plantation waste requiring strategic management. To understand the usability of the biomass, C. citratus leaf blades were deconstructed by applying alkaline peroxide and subsequent milling. The process, hereby denoted APES, was pre-optimized for high-quality fibre generation from non-wood vascular bundles. Analyses of the processed biomass, however, revealed the recalcitrant structures that denied fibre liberation. Nano-pitted sheaths were the physical barrier for effective chemical impregnation. Perhydroxyl-scavenging residual citrals were among the retarding factor while geranial chromophores added to the competing reactions between alkaline peroxide and other bio-constituents. Despite being the potential consumer of alkaline peroxide, the found calcium druses were the flagship micro- elements offering surface sheen effects. Analysis revealed that the APES equivalent condition effective for fibre liberation from oil palm biomass could partially deconstruct lemongrass leaves to expose the calcium druses. An outcome which appeared as an outlier in the fibre extraction database led to an application that calls for APES analytics for strategic biomass management and circular economy.

Keywords: Lemongrass; alkaline peroxide; recalcitrant structure; circular economy; biomass _________________________________________________________________________

1. Introduction

Biomass, the physique of biota, is renewable and offers limitless applications due to the associated wealth of biochemical and structural variations by the botanical parts. Leaves are the floral biomass with micro-complex photosynthetic factory oftentimes a huge waste post- harvest of such primarily intended botanical parts as the fruits, bulbs, and stems.

Cymbopogon citratus (lemongrass) as a whole floral structure is one example of a cultivated crop of versatile applications influencing climate stability (Copolovici et al., 2005), among the prominent ecosystem functions. Lemongrass roots are essential for gripping the soil and preventing localized erosion (Skaria et al., 2006) while as other lemongrass botanical parts, roots are also the rich source of essential oil. Lemongrass bulb, is famous for such a plethora

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of uses as culinary flavouring (Skaria et al., 2006), medicinal herb (Olorunnisola et al., 2014), aromatic volatiles supporting the perfumery industry (Miron et al., 2012), an anti-microbial agent of diverse uses (Simone and Crizel, 2017; Guttirez-Pachero et al., 2016; Tarik and Ibrahim, 2016), oil stabilizer (Hasim et al., 2015), pesticide, insect repellent and many more.

The non-edible leaves become the by-product of plantation and the natural product industry.

Often regarded as waste (Hasim et al., 2015; Kaur and Dutt, 2013), such physiological factor as the presence of thorns, irritants (Konyar et al., 2014), and pungency of the protective materials occupying 65-85% of the plant's essential oil (Copolovici et al., 2005; Hasim et al., 2015; Zheljazkov et al., 2011), are the reasons for the disagreeable use of lemongrass leaves as ruminant feed, although as additives, found to assist digestion of lactating goats (Khattab et al., 2017). In certain plantations, the leaves are burnt if not left to stand as soil covering.

While burning generally emits tremendous unknown and the known hazard like greenhouse gasses and various sizes of particulate matters, leaves left on the grounds are the breeding grounds for fungi which in turn spread spores that are potential air-borne health hazards (Sorenson, 1999; Baxi et al., 2016). The long process of degradation and nutrient recycling allows color transition as a result of chlorophyll losing metal from its molecular cage and turning into a linear molecule. Apparent as green turning to rusty brown, the underlying biochemical process emits carbon monoxide (Bekele et al., 2017), and as the leaves lose their biocides, the accumulated waste becomes a shelter for pests and wastage of the otherwise commodity from the by-products.

Potentially world's best-selling essential oil with 75% conquest of end-user segment market (Future Market Insight, 2019; Future Market Insight, 2020), lemongrass oil production is very likely to contribute to the 30 million tonnes (Krautler, 2016) estimate of the planet’s leafy by-product. With alpha-cellulose occupying less than half its principal biostructure, the extraction of lemongrass fibers or pulp demand for an extreme chemical condition. This suggests that the level of yield exceeding 50% incorporates non-cellulosic mass and the incurring challenges. The pulp from sarkanda grass, for instance, offered up to 59% yield despite 36- -cellulose (Sharma et al., 2020). Cymbopogon winteranius (Dutt et al., 2007; Sharma et al., 2020), Cymbopogon nardus (Kamoga et al., 2015), Cymbopogon martini (Dutt et al., 2007), and Cymbopogon citratus (Kaur and Dutt, 2013) and kans (Sharma et al., 2019) are pulp of leaf origin with a verified mix of cellulosics and parenchyma tissues. As a consequence of an uncontrolled consumption of rosin by the ground tissues, an extra amount of alum is required at the papermaking line (Kaur and Dutt, 2013). Moreover, unlike wood, leaf biomass contains high silica, and its dissolution adds viscosity of black liquor, which triggers scaling of the recovery boiler (Ghazali et al., 2006) and other ensuing issues.

Considering the complex processing required of Cymbopogon biomass to generate papermaking quality cellulosic fibres as described in previous studies (Kaur and Dutt, 2013;

Sharma et al. , 2018; Kamoga et al, 2015; Dutt et al., 2007; Sharma et al., 2019), the large amount of commodity lost in the black liquor and the extra capital taxed at the papermaking line, this study focuses on an alternative management of the biomass to rule out the uncertain turnover of paper pulp production from C. citratus. A rapid, high-yield technique maximising the power of perhydroxyl radicals from the reaction between alkali and hydrogen peroxide was employed. Proven successful for mill and plantation wastes such as oil palm biomass (Ghazali et al., 2006; Ghazali et al., 2014a; Ghazali et al., 2014b; Kamaluddin et al., 2012), the outcome applying the alkaline peroxide reaction system (APES) on the biochemically and architecturally complex lemongrass leaves aims principally at examining the morphological

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aspect of the alkaline peroxide treated and refined Cymbopogon citratus mass to evaluate the level of fit of the postulated management system to the sectors involved in the circular economy.

2. Methodology

Sampling

Lemongrass (Cymbopogon citratus) leaf blades from the plantation in Simpang, Taiping (Tropical climate; 3187 mm average annual rainfall; 27.3^oC average temperature) were collected, washed and dried. The sampled leaves were sundried to rusty brown, downsized, fractionated with Retsch AS200 sieve and shaker and stored for further processing. All oven- dry weights were calculated based upon the moisture contents determined using Denver Instrument IR120 Moisture Analyzer.

Alkaline Peroxide System (APES)

The concept of alkaline peroxide reaction optimised for the pulp production from oil palm biomass was applied on the downsized lemongrass to examine the relative variation in the fibrillated mass. The particles of the downsized green lemongrass leaf blades (PGL) were soaked in distilled water at 70°C for 30 minutes in a water bath and pressed at 15 psi to achieve 80% dryness. DLB mass was then submerged in alkaline peroxide (AP) at 10-to-1 liquor-to-PGL for 30 minutes with alkaline peroxide formulated from mixing 4% NaOH (Sigma-Aldrich ACS Reagent >97% Sodium hydroxide) and 4.5% H₂O₂, (Merck KgaA EMD Millipore Corporation 30% Hydrogen peroxide) at 70^oC and ambient pressure to allow perhydroxyl radical formation and reaction with the chromophoric constituents of the plant biomass (Ghazali et al. , 2014a; Ghazali et al., 2014b; Kamaluddin et al., 2012). The alkaline perhydroxyl radical-treated PGL was next refined using Sprout-Bauer 12” single disc refiner with 54.95 kWh/t specific refining energy for 4% consistency and refining temperature of 33.5^oC, completing the APES protocol to yield the refined radical-treated PGL, hereon denoted RARE.

Microscopic Analyses

A portable microscope was used to pre-assess the PGL and the RARE particles on a routine basis prior to an advanced microscopic analysis. Gold-coated samples were examined using Carl Zeiss Leo Supra 50VP scanning electron microscope (SEM) interfaced with the Energy Dispersive Analysis of X-ray (EDAX) system.

Wood Furnish by Glazing

The unpolished woodblock of 10x10 cm² area was segmented to four sections. While two sections were polished, two other sections were analysed as control surface. Several glazing particles were studied; ground green lemongrass blades (PGL), the perhydroxyl-treated mass (RARE) and the commercial padding material. The outcome of sanding with the commercial Dewalt DWE6423 5” random orbit sander was also compared with the result of 10 minutes clockwise friction between the led lemongrass particle on the surface of the woodblock. The latter was performed with minimal hand pressure and by random strokes. The relative emission of particulate matter, the time required to achieve the desired sheen, and the ensuing

‘comfort’ experience from skin contact of several volunteers were recorded.

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Analysis of PGL and RARE

Shimadzu 11650 Ultraviolet-visible spectrophotometer was used to examine the relative intensity of lemongrass leaves leaching components giving signals in the 250-800 nm wavelength range. These were performed on the spent liquor collected after 30 minutes soaking of the biomass in water, ethanol, and alkaline peroxide. The analysis was supplemented with chromaticity data acquired via Konica-Minolta Spectrophotometer CM- 700/600d” for the values of L*, a*, and b* in the CIELAB chromaticity corresponding to lightness, redness, and yellowness, respectively to understand the reaction occurring in the APES protocol.

3. Results and Discussion

Morphology of Perhydroxyl-treated Lemongrass Mass

Microscopic examination of the perhydroxyl-treated lemongrass leaf blades via Scanning electron microscopy reveals a parallel venation of the well-developed vascular bundles having widths ranging from 15 micrometers to 20 micrometers (Fig. 1a), housing the lowest measured 5 m width fiber (Sharma et al., 2020) mass of C. citratus generated via Soda and Kraft pulping.

The observed undisrupted structure manifests the recalcitrant structure muffling the vascular bundles, serving as a protective compartment for storing terpenes and citral compounds that are biochemically interactive. These biochemical-loaded structures serve as a defense against parasites, thermo-tolerance (Tajidin et al., 2012), and protection of the photosynthetic apparatus (Copolovici et al., 2005) at the ad-axial surface of leaf mesophyll of parenchyma tissue (Tajidin et al., 2012) housing chlorophylls. As a result of housing the photosynthetic bluish-green pigments, C. citratus (Lawal et al., 2017) manifests dark bluish-green (L=41.22±0.01, a=3.21±0.01; b=16.17±0.01) in comparison to the rusty bluish green (L=39.60±0.01, a=6.62±0.01; b=14.65±0.01) sundried leaf blades. The over two-fold increase in the redness explains the formation of red intermediate bilin type catabolite characterized and reviewed by Krautler (2016) for chlorophyll degradation. Owing to the

‘stay-green’ photosynthetic mutant (Krautler, 2016), the green tone persisted despite reaction in the APES system. The analysis points to the need for a harsher condition (to dissolve the bio-chemicals and non-cellulosic structure) typical of the adopted chemical pulping systems reported by Kaur and Dutt in 2007 and 2013. In spite of the severity of the reported systems, the co-generated ground tissues were only crushed to fines (defined as the mass passing the 200-mesh screen, P200 (Kamaluddin et al., 2012)) instead of being dissolved. These fines were found to adversely impact drainage and paper making process (Kaur and Dutt, 2013).

Architectural Complexity of Leaf Blades

The intricate architecture of leaf blades is revealed by the more intense rupture undergone by the sundried lemongrass. Unlike the green lemongrass leaf mass (PGL), a close -up look at the radical-treated refined mass of RARE (Fig. 1b) shows evidence of pre-degradation enhanced by the non-cellulosic components such as lignin and other susceptible photosynthetic pigments (Cannella et al., 2016). The photo-induced reaction degraded the sheath layers, exposing the micro-scale pores of the spongy structures not typically encountered in the mass of green leaves.

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Figure 1: Lemongrass leaf blades (a) downsized as PGL mass, (b) degraded feature showing multilayer sheaths and (c) the radical-treated mass refined via APES protocol

Peeling of the recalcitrant bundle sheaths unveiled the invaded micro-pores which appeared to be distributed two to five micro-meters away throughout the surface of the well -developed vascular bundles, characteristics of monocot grass. The 0.5 m pores made their way outwards via the pitted multi-layering sheaths, giving rise to what can be visualized as converging tunnels pointing towards the exterior of the vascular bundles. The resultant traverse tubes also render the vessels a multi-pathway structure. At the external, some of these appear as nano-porous sieves, plausibly the semi-permeable conduit reported as allowing water exchange (Sevanto, 2014) between xylem and phloem. It was the nano-sieves that had allowed the penetration of perhydroxyl radicals to partially weaken the lignified vascular structure (via reaction equation 1), hence semi-exposing the biominerals in Fig. 1c.

…[1]

The biochemical constituents of the PGL reacted at maximum with the radicals accounting for the 8:4:3 relative area ratios (Fig. 2). An extra heterogeneous reaction occurring between the more accessible sites in PGL after pre-dissolution of the biochemicals in non-aqueous solvent. The observation is analogous to the reported ease in mass transfer in other pulping techniques (Kaur and Dutt, 2013; Dutt et al., 2007) upon rupturing of the oil-housing structure via steam distillation condition (Kaur and Dutt, 2013; Dutt et al., 2007).

Analysis of the leaching substances with the rare high end-pH (10.2 to 9.7) instead of the common complete peroxide consumption marked by neutrality (Ghazali et al., 2006; Ghazali et al., 2014a; Ghazali et al., 2014b; Kamaluddin et al., 2012) suggests the release of the alkaline substances associated to the residual therapeutic from lemongrass leaf biomass. The noise corresponding to 250-300 nm region in Figure 2 is commonly attributed to tannin from the ground tissue structure, mesophyll. Among other uv-visible active components contributing to the high intensity signals are the theoretical isomeric effects of the superoxide-scavenging (Olorunnisola et al., 2014) citral (250 nm), and the chromophoric aggregate such as lignin at around 300 nm, geranial chromophore, as well as limonene at 350 nm (Li et al., 2014).

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Figure 2: Ultraviolet visible spectroscopic responses of the active biochemicals released from the lemongrass leaf blades.

Arising from the aforesaid 8:4:3 absorbance intensity ratios of leaching materials (Fig. 2), the resultant hollower RARE structure granting higher chances of alkaline peroxide penetration and a better probability for fiber liberation. The results in Fig. 2 rationalize the more apparent fibrillation marks amidst the predominating ground tissue (Fig. 1c, arrow). The exposed minute (20 m in length, 0.5-2 m in width) fibres dangling at the broken ends of the recalcitrant ground tissue are plausibly the fibrils making up the primary cell wall. This explains the recalcitrant nature of the ground tissue accounting for the higher yield of chemical pulp (40-50% range) despite a lower percentage range (30-44%) of the -cellulose (Kaur and Dutt, 2013; Kamoga et al., 2015; Dutt et al., 2007; Sharma et al., 2020). The reported strengthening effects (Kaur and Dutt, 2013; Kamoga et al., 2015; Dutt et al., 2007;

Sharma et al., 2020; Danielewicz and Surma-Slusarska, 2019) of ‘parenchyma tissues’ in the grass pulp mass on paper web strengths could indeed be the effects of leaf fibrils making up the primary cell wall of the ground tissue or specifically chlorenchyma sheath encircling the vascular bundle, as reinforced by the anatomical description on lemongrass (Eltahir and AbuEReish, 2010).

For the relatively mild APES protocol, the presence of geranial chromophore (Miron et al., 2012), residual extractives, minerals and metals released by the organometal complex (Krautler, 2014) were the potential consumers of alkaline peroxide chemicals (Ghazali et al., 2016). This resulted in demi-rupture of the fiber-bearing vascular structure, hence releasing only the druses domiciling the vessel structure. Elemental analysis of the semi-exposed crystals shows the presence of calcium co-existing with carbon and oxygen, suggesting the oxalate form of biominerals (Table 1).

Table 1: Elemental Constituent of the Druses in Lemongrass

Elements Weight % Atomic %

Na (K) 2.08 1.28

Ca (K) 10.18 3.61

B (K) 13.39 17.60

O (K) 35.66 31.70

C (K) 38.69 45.81

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The radical-lignin reaction leading to calcium druses surfacing the sheath (Fig. 1c) gave rise to a mass of calcium-loaded ground tissue (CLG). These were the radical-treated and refined form of lemonsgrass leaf mass initially denoted RARE. Full removal of the sheath revealed the vessel structure (Fig. 4c) with denser calcium deposits (Fig. 1c – circles). These genetically controlled (Konyar et al., 2014) crystals serve as plants’ defense mechanisms, calcium storage, de-oxalation, detoxification of metals as well as protection against insects and foraging animals by irritation mechanism (Konyar et al., 2014).

In its entirety, the obtained CLG or RARE were found suitably used for the rapid surface glazing. Trials associated to glazing effects were attempted on the nails of the researchers as the cue for assessing sheen and comfort of CLG-glazed wooden surfaces. Analysis unravelled an eliminated risk of the particulate matter emission on top of the rapid sheen and comforting feel (Fig. 3). The phenomenon occurred in such a way due to the embedment of the calcium druses in the ground tissue matrices.

Figure 3: Relative comparison of surface sheen by comparing the (a) CLG-glazed surface to (b) commercial desanding effects and the (c) surface at origin

RARE as Cue for Analytics – A Fit for Circular Economy

A critical feature of consideration for Cymbopogon citratus, among other oil plants (Casiglia et al., 2015; Hanaa et al., 2012) is the needs for a highly efficient oil extraction system (Prychid and Rudall, 1999; Alam et al., 2018) as this influences oil constituents. These are critical considerations for systems employing alkaline peroxide as 75-85% of citral has superoxide-scavenging activities (Olorunnisola et al., 2014; Sigma, 2010; Petrocelli, 2005).

Rescuing the oil commodity efficiently would improve the selectivity of perhydroxyl radicals reaction upon the chromophoric groups and subsequent liberation of cellulosic fibers in conditions aiming for fiber-based bio-products. Chemical formulation to dissolve the recalcitrant sheaths, parenchyma and other non-lignified tissue is essential to improve fiber yield and reduce problems at the papermaking line. In this regard, a pulping approach that degrades the oil in lemongrass in an irrecoverable manner or requiring a complex recovery and purification of the degraded commodity needs proper cost and turnover evaluations. The approach simultaneously simplifies the downstream process management, which in turn engenders the ‘green process’ and thus, a more strategic way of managing lemongrass leaf biomass as suggested in Fig. 4.

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Figure 4: RARE in the APES process analytics gives products traditionally regarded as outli ers better economic impression

APES process analytics with future extensive pool of research data are to also assist manufacturing acumen by providing a database to guide on the range of product types and quality offered by an equivalent process condition. In the original APMP process conditions that generated high-quality papermaking fibers from oil palm biomass (Ghazali et al. , 2006;

Ghazali et al., 2014a; Ghazali et al., 2014b; Kamaluddin et al., 2012), the APES equivalent process yields the calcium- loaded ground (CLG) tissue or “RARE” (Fig. 4) with semi- exposed fibrils. At the current stage of knowledge, the CLG tissue has been demonstrated as a potential renewable glazing material for diverse surfaces instead of papermaking. In this regard, Fig. 5 provides an insight into the circularity of RARE production related to the various sectors defined by the Australian Pulp and Paper Industry Technical Association.

Figure 5: Double circular economy with initial feedstock being lemongrass biomass for manufacturing product 1 (P1) hailed as “RARE” (Bioglaze) which then becomes the feedstock in the recycling sector.

Production of RARE from lemongrass leaves is part of the circular economy as the used product can be the feedstock for fertiliser production, for instance by minor processing or directly applied on soil. The chain routing one used product as feedstock to other factory fulfils the cradle-to-cradle lifecycle. The fact that fertilizer (Product 2) may be used to enrich

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the soil of lemongrass plantation illustrates to renewability nature of precursor of Product 1 and the double circular economy of RARE production. Such small labels as disposal instruction is therefore important in ensuring that RARE does not end up at the landfill but repeats itself as a functional product.

Alongside the circular economy criteria, the triangulation between bioinformatics, processing (materials, chemistry, and engineering) and the predictive outcome (product and risks) backed by sound evidence from literature would cut down the time and cost pertinent to additional comprehensive research prior to a feasibility study and support the desired informed manufacturing. Furthermore, the possibility of availing clean technology can be realized by programming hazard alert at the materials selection stage. The step allows recognition of the sort of agents that are likely to reduce the occupational as well as process safety and jeopardize the sustainability of the process. This re-emphasizes the crucial role of APES process analytics for the handling of complexly huge data in curbing hazards from the manufacturing lines and thus a promise for a safe Industry4.0 implementation.

4. Conclusion

Understanding the responses of the recalcitrant structures towards the alkaline peroxide reaction system (APES) protocol led to a prominent appreciation of a new product application. The occupancy of calcium druses in lemongrass leaf structures unearthed by the APES protocol also attested its non-suitable use in certain applications The calcium-loaded ground tissue (CLG) or “RARE” was found to offer superb surface glazing – not offered by fresh ground mass of lemongrass leaf blades. Envisaging the lifecycle of the produced CLG led to an appreciation that RARE production defines a double-circular economy and full- fledged criteria for renewability. The recalcitrant structures giving rise to CLG also cued for APES process analytics that inserts new element in informed manufacturing - that an outlier (product) of a benign process may point to other fascinating application. This would transform past failure in the traditional systemic thinking into future manufacturing opportunity.

Acknowledgement

The various votes from Research University funding 1001/PTEKIND/8011020 enabled execution of the presented work.

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