Development of low-density polyethylene antioxidant active films containing α-tocopherol loaded with MCM-41(Mobil Composition of Matter No. 41) mesoporous silica

Highlights

• Antioxidant active packaging films were made by adding with α-tocopherol/MCM-41 assembly.

• Adsorption onto MCM-41 prolonged the release period of α-tocopherol from LDPE films.

• The newly developed film showed significant antioxidant activity.

Abstract

Antioxidant active packaging films are always prepared to help protect fatty food safety. In this study, a new LDPE (Low-Density Polyethylene) film containing α-tocopherol adsorbed on MCM-41 mesoporous molecular sieve was prepared by extrusion. The synthesized MCM-41 were thoroughly characterized before and after loading with α-tocopherol by powder X-ray diffraction, nitrogen adsorption isotherms, infrared spectroscopy, and thermogravimetric analysis. Physical properties of the new films including tensile strength, oxygen and water barrier properties were studied. In particular, the effect of loading α-tocopherol onto MCM-41 on the migration behavior of α-tocopherol from active films was investigated. Migration test were performed at 40 °C, using 95%(v/v) ethanol as fatty food simulants on LDPE films with pure α-tocopherol and the assembly of α-tocopherol and MCM-41. The results showed that, after being adsorbed on MCM-41, the releasing period of α-tocopherol in LDPE were prolonged by about 36%, and the diffusivity of the antioxidant decreased by 53%. Moreover, DPPH radical scavenging assay proved the effectiveness of the antioxidant in the new film. These demonstrated that the new kind of active film can be potentially used for controlled release antioxidant food packaging application.

Introduction

Antioxidant packaging have been investigated for a very long time, since lipid oxidation may cause a lot of quality problems which are not just on lipids but also on other components of food during storage and transportation (López-de-Dicastillo et al., 2012). Lipid oxidation of packaged food can be partly excluded by adding antioxidants to the packaged food, however, in order to make sure sustain release of antioxidant in a relatively long term and avoid food safety problems concerned by consumers, controlled release antioxidant active packaging, on the basis of active packaging, has been introduced and investigated. Controlled release packaging (CRP) means that active compounds release from packaging materials in a controlled manner which offers a prolonged delivery of active compounds at predictable and reproducible release rate (Koontz et al., 2010). Controlled release of antioxidants in food packaging films can be realized by the modification of structure and composition of packaging polymers (Gemili et al., 2010, LaCoste et al., 2005, Zhu et al., 2012). Moreover, the use of encapsulation technique has also been proved to be an effective method to control the release of active compounds, such as complexation by beta-cyclodextrin (Barba et al., 2015, Chen and Liu, 2016, Koontz et al., 2010, Liu et al., 2015, Siró et al., 2006) and incorporation into a mesoporous matrix (Gargiulo et al., 2013, Heirlings et al., 2004, Ruiz-Rico et al., 2015).

Since the development of ordered mesoporous molecular sieves in 1992 (Beck et al., 1992, Kresge et al., 1992), they have received noteworthy attentions from researchers. MCM-41 mesoporous molecular sieve was firstly proposed to be used in controlled drug-delivery system for its ability to accept and deliver organic compounds in 2001 (Vallet-Regi, Ramila, Del Real, & Perez-Pariente, 2001). Until now, considerable research has been conducted on ordered mesoporous silica materials including MCM-41 and SBA-15 (Santa Barbara-15) (Berlier et al., 2013, Datt et al., 2012, Manzano et al., 2008, Qu et al., 2006, Szegedi et al., 2012, Szegedi et al., 2011, Vallet-Regı́ et al., 2004, Yu and Zhai, 2009). Several advantages of these materials account for this phenomenon: stable mesoporous structure, regular and adjustable nano-pore size, and high surface area (Qu, Zhu, Lin, et al., 2006). As to the controlled release of antioxidant, the pore size of mesoporous materials determines the size of antioxidant molecule that can be adsorbed, and controls the antioxidant release rate according to pharmaceutical research (Horcajada et al., 2004, Vallet-Regí et al., 2007). Natural antioxidants, such as tocopherol, catechin, rosemary extract and quercetin, etc(Barbosa-Pereira et al., 2013, de Abreu et al., 2012, Graciano-Verdugo et al., 2010, Granda-Restrepo et al., 2009, Lopez-de-Dicastillo et al., 2010, Nerín et al., 2006, Wessling et al., 2000, Zhang and Zhao, 2014, Zhu et al., 2013) have been extensively studied because of the toxic potential of synthetic antioxidants. α-Tocopherol with the size of about 2.4 × 0.7 × 0.4 nm³ (Fig. 1), as one of them, has been added to LDPE, linear low-density polyethylene (LLDPE), polypropylene (PP) and other polymeric materials and investigated the migration behavior in foods and food simulating liquids (Gargiulo et al., 2013, Heirlings et al., 2004, Koontz, 2008, Koontz et al., 2010, Koontz et al., 2009, López de Dicastillo et al., 2013, Siró et al., 2006, Wessling et al., 1998). As a new approach to control the release kinetics of antioxidant, SBA-15 has been applied in the research of antioxidant active packaging on the one hand to protect α-tocopherol during extrusion and on the other hand to ensure a sufficient release of the antioxidant in a controlled manner, while the results showed the adsorption of α-tocopherol onto SBA-15 only made a small difference in the migration rate of α-tocopherol (Heirlings et al., 2004). Lately, Gargiulo et al(Gargiulo et al., 2013) has attempted to overcome this issue by loading the active compound onto functionalized SBA-15, and nearly 60% decreases in diffusivity has been found due to the reduced pore size and interactions between the antioxidant and functionalized carrier. Accordingly, in general, SBA-15 possesses large pore size of 4.6–30 nm (Zhao, Wan, & Zhou, 2012), normal MCM-41with pore size of 2–4 nm, by contrast, may be more suitable for control the release kinetics of α-tocopherol in terms of the pore size influence of unmodified mesoporous silica materials. Moreover, it has been demonstrated that as long as the pore size allows the drug to get into the matrix, the higher the surface area, the higher the amount of drug adsorbed, meanwhile, lager pore volumes may result in greater drug loading rate (Vallet-Regí et al., 2007). Specifically, MCM-41 has larger pore volume and surface area, which are both determining factors of loading amount.

Thus, the aim of this work is to develop a new kind of antioxidant active packaging film containing α-tocopherol adsorbed onto MCM-41 mesoporous silica sieve, which were chosen by taking the size of active compound molecule into consideration, to finely control the release of the antioxidant from packaging materials. Meanwhile, some properties of the new film were investigated to analyze the changes that may caused by the addition of the assembly.