Physical properties of chitosan films incorporated with natural antioxidants
Introduction
Global packaging market has demonstrated constant growth in the past decades, reaching in 2014 the value of $812 billion dollars (2.8% higher than 2013) (all4pack, 2016). According to Smithers Pira forecast this amount will stand around $997 billion dollars in 2020, with a growing rate of 3.5% per year (Smithers Pira, 2013). In the five main categories of the global packaging market (metal, glass, paper and board, rigid and flexible plastic and wood), plastic material stood out, corresponding to almost half of materials in value (22.8% rigid plastic and 24.85% flexible plastic) (all4pack, 2016).
Data from the European market shows that 80.9% of 2015 flexible packaging market has, as main client, the food sector (all4pack, 2016). Despite of the current stage of technology, about 1.3 billion ton per year of the food produced for human consumption are still lost or wasted globally (FAO, 2011), partly because of lack of adequate packaging. Therefore, some strategies of packaging optimisation have been proposed, such as varying pack sizes and developing active and intelligent packaging that maintain food quality and also increase its shelf life (Realini and Marcos, 2014, WPO, 2016). Moreover, the increasing concern on environmental issues has pushed the industry to try to substitute the non-biodegradable petrochemical-based plastic to biodegradable ones (Souza and Fernando, 2016). The latter has advantages over the former since are derived from renewable sources, but comparing their functional properties, the biopolymers (such as chitosan) have relatively poor mechanical and barrier properties, which limits its use by the food packaging industry (Rhim and Ng, 2007, Tang et al., 2012).
Strategies to improve the properties of biopolymers, go through the reinforcement of the matrices. Incorporation of antioxidant compounds in the biomaterial is an approach to meliorate the antioxidant properties of the polymers (Tian et al., 2013). Antioxidants are synthetic or natural substances used to retard deterioration, rancidity and discoloration resulting from the oxidation (FDA, 2012), and that can be used to help preserve food (Araújo, 2011, Ramalho and Jorge, 2006). Natural antioxidants (mainly polyphenols extracted from plants and fruits, and vitamins, Acosta-Estrada et al., 2014, Moo-Huchin et al., 2014, Viuda-Martos et al., 2014) are being preferred over synthetic ones due to the possible harmful effects of the latter ones to humans (Santana et al., 2013). Due to the high content of phenolic compounds, fruits (grape (Silva et al., 2013), jabuticaba (de Castro et al., 2014, Leite-Legatti et al., 2012), açaí (Del Pozo-Insfran et al., 2004), pomegranate (Fischer et al., 2011), carambola (Zainudin et al., 2014), blackberries (de Souza et al., 2014), passion fruit (de Assis et al., 2009, Spínola et al., 2015), cashews (Moo-Huchin et al., 2015), among others) and plants (black and green teas (Balasundram et al., 2006), essential oils (Regnier et al., 2012), Pistacia lentiscus (Dahmoune et al., 2014), kenaf leaves (Pascoal et al., 2015), thyme leaves (Lee et al., 2005, Vallverdú-Queralt et al., 2014), basil leaves (Lee et al., 2005), rosemary (Ribeiro-Santos et al., 2015 Vallverdú-Queralt et al., 2014), among others) are recognized as excellent sources of bioactive compounds that are able to stabilize free radicals, such as reactive oxygen substances (ROS), through the transfer of hydrogen molecules, reducing and stabilizing them, and consequently avoiding the oxidative process (Kolakowska and Bartosz, 2014). The oxidative processes, along with the microbiological growth, is one of the mechanisms of food quality deterioration (Araújo, 2011, Cushen et al., 2012, Kolakowska and Bartosz, 2014), being responsible for many important changes such as loss of nutritional values, texture modifications, development of undesirable compounds such as off-flavors, colored and even toxic substances to humans (Pazos and Medina, 2014). Therefore, antioxidant active packaging (Realini and Marcos, 2014) that can use natural compounds, is being highlighted as a new mechanism to prevent food oxidation (Barbosa-Pereira et al., 2014, Barbosa-Pereira et al., 2013, Contini et al., 2014, López-de-Dicastillo et al., 2012, Moradi et al., 2012, Nerín et al., 2008, Siripatrawan and Noipha, 2012, Tian et al., 2013).
Although there are some studies on the properties of biofilms incorporated with natural antioxidants (Pola et al., 2016, Siripatrawan and Harte, 2010, Siripatrawan and Vitchayakitti, 2016), there are no relevant studies that compare the properties of biofilms incorporated with different natural antioxidants. Thus, the aim of this work was to develop an active packaging based on chitosan, a biodegradable biopolymer from natural resource, incorporated with several natural antioxidants extracted from different plant crops (five essential oils and six hydro-alcoholic extracts) and to characterize its physical properties. All extracts and EO’s used have proven antioxidant activity due to their rich phenolic content being suitable to be used as oxidation preservatives by the food processing industry. As active extracts may interfere on the final properties of the material, resulting in a film either with improved or worsened characteristics (Sarantópoulos et al., 2002), this comparative study will allow to categorize the antioxidant active biofilms for future application.
Section snippets
Materials and reagents
Chitosan with high molecular weight was purchased from Sigma Aldrich, Germany. Five different food grade essential oils from Biover (Belgium) were purchased in local market: Ginger EO (Zingiber officinale Roscoe); Rosemary EO (Rosmarinus officinalis L. ct. camphor); Sage EO (Salvia lavandulifolia Vahl); Tea tree EO (Melaleuca alternifolia (Maiden & Betche) Cheel); and Thyme EO (Thymus zygis Loefl. ex L. ct. linolol). Six different dried plants were used to obtain the hydro-alcoholic extracts
Film preparation and film thickness
Biodegradable films were successfully produced by casting method resulting on homogenous plastic specimens, predominant yellowish, transparent, flexible and with average thickness around 50–70 μm (Table 1).
Beyond all antioxidant incorporated, only two types of essential oils (Ginger and Thyme) resulted in films with different thickness from each other (p < 0.05), although when compared with pristine chitosan films (control sample) this difference was not significant (p > 0.05).
Films incorporated
Conclusions
Biodegradable active films were successfully developed using a variety of natural antioxidants. The thickness of the biomaterial did not change and functional properties evaluated did not demonstrated strong differences due to the incorporation of active compounds. The higher light barrier of the films is an additional advantage of the novel biomaterials as a further mechanism against food deterioration by oxidizing reactions. This change was more significant for the bioplastics incorporated
Acknowledgements
The authors acknowledge CAPES (APQ-1 2009/02 E-26/110.414/2010, APQ-1 2011-2 E-26/110.269.2012, E-26/111.435/2012 − CsF/Brazil − BEX 11943-13-0) and CNPq/Brazilfor providing the financial support to develop this work. The authors also acknowledge the funding of CENIMAT/I3N by COMPETE 2020, through FCT/MCTES, under the project UID/CTM/50025/2013 and FCT/MCTES as the funding entity of MEtRiCS unit under the project UID/SEM/04077/2013.
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