Rice straw-derived nanocellulose and pomegranate peel polyphenols for active biodegradable food packaging: A review

Introduction

The persistent presence of conventional plastic packaging in the environment and its role in global pollution has been become a major issue. Increased awareness of sustainability has led to the creation of biodegradable packaging systems using renewable resources. Agricultural residues represent an appealing source of biopolymers (Mohanty et al., 2002; Santhosh et al., 2021; Ali et al., 2024) [2,24,33] . Because they are inexpensive, available in abundance, and environmentally friendly. Rice is one of the most produced agricultural by products worldwide. However much of it is burned after harvest, leading to significant air pollution and greenhouse gas emissions (Islam et al., 2022; Ren et al., 2024) [11,35] . Recently it has been proven to be an excellent source of cellulose and nanocellulose for biodegradable packaging applications. Nanocellulose is known for its high tensile strength, biodegradability, low density, and good barrier properties, making it an effective reinforcing agent in packaging materials. (Klemm et al., 2011; Moon et al., 2011; Perumal et al., 2022) [3,16,25] .

Pomegranate peel constitutes about one-third to one half of the fruit's weight and is usually discarded during the processing of pomegranate juice (Akhtar et al., 2015; Singh et al., 2018; Ramos et al., 2022) [1,23,42] . Despite being considered waste, it contains high levels of polyphenols, tannins, flavonoids, and phenolic acids which have strong antioxidants and antimicrobial activity (Kumar et al., 2022) [18] Rice straw mainly consists of cellulose, hemicellulose, lignin and silica, with cellulose content typically ranging from 35% to 45%, making it suitable for nanocellulose production. (Islam et al., 2022; Lu and Hsieh, 2012) [11,22] Open field burning of rice straw causes environmental pollution and results in the loss of valuable biomass resources. Therefore, the transformation of rice straw into nanocellulosebased materials has attracted considerable scientific attention. (Bangar et al., 2023; Ren et al., 2024) [5,35] . Common methods used for extracting nanocellulose include alkali treatment, bleaching and acid hydrolysis. Alkali treatment removes hemicellulose and waxes, the bleaching process removes lignin, and cellulose nanocrystals are obtained through sulfuric acid hydrolysis. Other methods such as enzymatic hydrolysis and ultrasonication have also been studied for their potential to enhance sustainability and reduce usage. (Trache et al., 2017; Lu and Hsieh, 2012; Oun and Rhim, 2016) [6,22,30] . Nanocellulose has favourable properties such as high crystallinity, a large surface area, good mechanical properties, and biodegradability. (Klemm et al., 2011; Moon et al., 2011) [16,25] . The purified BNC free of lignin or hemicellulose is composed of an interwoven network of nanofibers (20-100 nm in diameter) with extremely high properties. These properties allow its incorporation in starch, protein and polysaccharide-based packaging films, which results in enhanced strength and barrier properties. (Rhim et al., 2013; Jadaun et al., 2023) [12,36] . Nanocellulose based packaging materials are one of the most promising reinforcing agents for biodegradable food packaging. Its high aspect ratio and nanoscale dimensions allow for strong interactions with polymer matrices, resulting in improved tensile strength and film integrity. Research has shown that incorporating nanocellulose into biodegradable films improves their mechanical properties, increases thermal stability, and reduces oxygen permeability. (Rhim et al., 2013; Perumal et al., 2022; Ren et al., 2024) [3,35,36] . Additionally, these films are flexible, transparent and environmentally friendly. These advantages make nanocellulose a viable replacement for synthetic packaging materials. (Siracusa et al., 2008; Sharma et al., 2017) [41,43] . Recent studies have focused on active packaging systems where nanocellulose serves as a carrier for antioxidant and antibacterial compounds in addition to providing structural support. (López-Rubio et al., 2006; Primožič et al., 2021) [21,32] These versatile materials are being explored more extensively for their application in food preservation.

Rice straw: In the form of nanocellulose and nanocrystals

Rice straw is a significant agricultural by-product containing approximately 35% to 45% cellulose. The extraction of Rice Straw Nanocellulose (RSNC), usually in the form Cellulose Nanofibers (CNF), offers a sustainable pathway for certainly high value materials. (Lu and Hsieh, 2012; Islam et al., 2022; Ren et al., 2024) [11,22,35] This material can be extracted from agricultural by-products such as rice straw, banana tree, or bagasse. (Johar et al., 2012; Trache et al., 2017) [6] . Rice straw was chosen as the raw material in this study.

Extraction and yield dynamics: to convert raw rice straw into nanocellulose, lignin and hemicellulose must be removed through bleaching and alkaline treatment, which is followed by mechanical or chemical disintegration (Lu and Hsieh, 2012; Trache et al., 2017) [6,22] . The percentage yield is commonly used to assess the effectiveness of the extraction process. Crystallinity is improved by removing amorphous areas through acid hydrolysis (using H 2 SO 4 ), leading to an increase in the crystallinity index (CrI). (Lu and Hsieh, 2012; Oun and Rhim, 2016) [22,30] . Crystallinityindex values for rice-straw nanocellulose commonly fall within the range of approximately 65% to 80%, although the exact value depends on the raw material, pretreatment conditions, acid concentration, hydrolysis time, and purification procedure (Islam et al., 2022; Ren et al., 2024) [11, 35] .

Effect on mechanical properties and composite composition

Because of its high aspect ratio and large surface area, ricestraw nanocellulose is frequently used as a reinforcing agent in polymer matrices such as polylactic acid, polyvinyl alcohol, and starch (Bangar et al., 2023; Perumal et al., 2022) [3,5] . Tensile strength can increase through hydrogen bonding and the formation of a continuous or percolating nanocellulose network within the polymer matrix (Moon et al., 2011; Rhim et al., 2013) [25,36] . The theoretical Young's modulus of a composite can be estimated using the rule of mixtures:

Where 𝐸 𝑐 Ec is the composite modulus, 𝐸 𝑓 Ef is the modulus of the nanocellulose reinforcement, 𝐸 𝑚 Em is the modulus of the polymer matrix, and 𝑉 𝑓 Vf is the volume fraction of nanocellulose. The actual modulus may differ from this theoretical value because of fibre orientation, dispersion, interfacial adhesion, defects, moisture content, and processing conditions (Faruk et al., 2012; Thakur and Thakur, 2014) [27,47] . The reinforcing efficiency of rice-straw cellulose depends strongly on concentration and dispersion. In many biodegradable-film systems, low nanocellulose concentrations can improve tensile strength, whereas excessive concentrations may cause aggregation and reduce mechanical performance (Bangar et al., 2023; Jadaun et al., 2023) [5,12] .

Effect on barrier and thermal properties (WVP):

Ricestraw nanocellulose can reduce water-vapour and gas permeability by creating a tortuous pathway through the polymer matrix. This pathway increases the distance that water vapour and gas molecules must travel through the film (Rhim et al., 2013; Perumal et al., 2022) [3,36] . The magnitude of the improvement depends on nanocellulose content, dispersion, film structure, relative humidity, and the hydrophilicity of the matrix. Nanocellulose can also influence the thermal stability of biodegradable composites. Sulfuric-acid hydrolysis may introduce sulphate groups onto the cellulose surface, which can lower the onset temperature of thermal degradation. At the same time, removal of lignin and hemicellulose can alter the thermal behaviour of the purified cellulose fraction (Trache et al., 2017; Islam et al., 2022) [6,11] . Reported maximum degradation temperatures vary according to the extraction and testing conditions; therefore, values such as 𝑇 max = 320 CTmax=320 ∘ C should be reported only when supported by experimental measurements or a directly comparable study.

Environmental and adsorption effects:

Because of its high density of hydroxyl (-OH) groups, RSNC is effective as an adsorbent for dyes and heavy metals in waste treatment. Adsorption capacity: The equilibrium adsorption capacity, denoted as 𝑞 𝑒 qe, can be calculated using:

Where 𝐶 0 C0 and 𝐶 𝑒 Ce are the initial and equilibrium concentrations, respectively, in mg L -1 mgL-1; 𝑉V is the solution volume in LL; and 𝑊W is the mass of rice-straw nanocellulose in gg Source: Islam et al. (2022) [11] https://DOI.org/10.1016/j.tifs.2022.11.020 2022) [23,42] . These compounds are known for their strong anti-inflammatory, antibacterial, antioxidant, and free radical scavenging effects. ((Akhtar et al., 2015) [1] . The antioxidant activity of pomegranate peel is typically higher than that of the edible arils. Therefore, it has become a valuable ingredient in food systems and a natural preservative. (Akhtar et al., 2015; Kumar et al., 2022) [1,18] . Typically, ethanol-water mixtures, methanol, ultrasoundassisted extraction, microwave-assisted extraction, or other eco-friendly extraction methods are used to extract polyphenols. (Akhtar, S.et al., 2015; Loizzo and Silva, 2021) [1,20] . Extraction conditions strongly affect antioxidant capacity and phenolic yield. ((Loizzo and Silva, 2021; Rodrigue z, et al., 2025) [20,37] .

Source: (Singh et al., 2018) [42] [34,45] . Due to the growing demand for clean-label food preservation, natural polyphenols are increasingly used as active ingredients. Starch, chitosan, gelatine and polylactic acid films have successfully incorporated pomegranate peel extract. (Kumar, N. et al.,2022; Soleimanzadeh et al., 2024) [18,44] These films offer enhanced food preservation, increased antioxidant activity, improved antibacterial properties, and better UV protection. (Suneetha, Jessie et al., 2018) [45] Pomegranate peel extract has been found to inhibit common foodborne pathogens like Staphylococcus aureus and Escherichia coli (Kumar et al., 2022; Singh et al., 2018) [18,42] . The antibacterial action is mainly due to phenolic compounds that disrupt microbial cell membranes and alter cellular metabolism.

Potential synergy between pomegranate peel polyphenols and rice straw nanocellulose

The combination of pomegranate peel polyphenols with rice straw nanocellulose. The combination of pomegranate peel polyphenols with rice straw nanocellulose offers a unique opportunity to develop versatile active packaging materials. (Dufresne, Alain 2012) [12] pomegranate peel polyphenols provide antibacterial and antioxidant properties, while nanocellulose offers structural support. (Anand Babu Perumal 2022, Primožič, et al., 2021) [3,32] Adding polyphenols to nanocellulose-reinforced films can improve:  Tensile strength  Oxygen barrier properties  Antioxidant capacity  Antimicrobial activity  Shelf-life extension Such as dual functional packaging technologies align with the principles of circular bioeconomy by simultaneously utilizing agricultural by products and food processing waste. (López-Rubio, et al., 2006) [21] .

Uses for food preservation

Active biodegradable packaging that uses natural bioactive compounds can be used to preserve fruits, vegetables, meat products, dairy items, and baked goods (Appendini, Realini and Marcos, 2014) [34] . Films enhanced with pomegranate peel extract have shown potential in reducing lipid oxidation, inhibiting microbial growth, and preserving sensory quality over time (Kumar et al., 2022; Soleimanzadeh et al., 2024) [18,44] . The use of nanocellulose improve the durability and barrier performance of the packaging, making it more suitable for commercial food applications (Perumal et al., 2022; Ren et al., 2024) [3,35] . Possible applications include  Fresh fruit packaging  Vegetable packaging  Meat packaging  Ready-to-eat foods  Useful food packaging

Summary of properties

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