Polysaccharide/gelatin blend films as carriers of ascorbyl palmitate – A comparative study
Introduction
In recent years, the concept of controlled release has attracted growing interest in terms of its use in the production of emitters – a group of modern active packaging whose task is to extend the shelf life or to preserve and improve the quality of food. Since many food products contain oxylabile compounds, the active antioxidant materials are one of the most important innovations of packaging technologies. The design of carrier material should enable releasing the active substance continuously and uniformly throughout the entire storage period, maintaining an effective concentration of the active ingredient on the surface of the packaged food, where the spoilage reactions run most intensively. The effectiveness of active packaging depends on the ability of an active substance to penetrate to or to stay in the reaction site. Both polar and non-polar antioxidants have predispositions to accumulate at the oil/air or O/W interfaces. These interfaces are in fact the sites where contact between the substrate and oxygen is facilitated. According to the theory of the so-called polar paradox, hydrophilic antioxidants are more effective in the less polar phase (e.g. oil, lard), whereas lipophilic compounds exhibit higher activity in the more polar phase (e.g. O/W emulsions, liposomes, biological membranes, tissues) (Laguerre et al., 2015). Furthermore, it can be assumed that in water-containing products, the polar antioxidants incorporated in films/coating may diffuse too readily into the aqueous phase, which in turn may lead to a decline in their effective concentration at the oil/air interface. Non-polar active substances could improve the water vapor barrier properties of packaging materials. Therefore, non-polar antioxidants can be a potentially more beneficial component of active packaging systems, than the polar ones.
Ascorbyl palmitate (AP) is a fatty acid ester of ascorbic acid (AA) often used as a strong antioxidant in fat-containing foods, e.g. flavoured fermented milk products, dehydrated milk, creams, cheese products, fats and oils, spreads and emulsions, nut butters and nut spreads (EFSA, 2015a). AP can be used as additive (E304(i)) mostly according to quantum satis except for foods for infants and young children. It is generally recognized as safe for human consumption and can be used legally as a human dietary supplement (CFR, 2020). According to the European Food Safety Authority (EFSA) Panel the available toxicological data are too limited to establish an ADI for AP, but there is no safety concern for its use at the reported uses and use levels (exposure estimates based on the high percentile for the maximum level exposure scenario range from 0.4 to 10.8 mg/kg body weight (bw)/day across all population groups). The presence of AP in oral supplements contributes to the AA content and helps protect fat-soluble antioxidants in the supplement. In the human digestive tract, the AP is fully hydrolyzed in the hepatic portal plasma and/or liver to AA and its respective fatty acid (EFSA, 2015a). Compared to water-soluble AA, AP is more stable (the esterification reduces the hydrolysis of AA) (Austria, Semenzato, & Bettero, 1997) and may be less easily lost in the urine. It could be assumed, the use of AP as a component of edible packaging would not only improve food quality but also the vitamin C nutriture of consumers (Johnston et al., 1994). Recently, AP has attracted extensive interest as an anticancer compound because of its lipophilic nature (Zhou et al., 2017).
Because of hydrophobic character of AP, the obtaining of stable emulsion is extremely difficult and requires addition of emulsifiers (e.g. Tween) (López-Martínez & Rocha-Uribe, 2017) and/or ethanol as a cosolvent (Han, Hwang, Min, & Krochta, 2008). Gelatin (GEL) is a surface-active protein that is capable of acting as an emulsifier. Moreover, because of excellent gelling properties, GEL can be used to prepare emulsions that are physically stable (Kowalczyk & Baraniak, 2014). Nevertheless, when used on its own GEL often produces relatively large droplet sizes during homogenization, so it has to be used in conjunction with other surfactants to improve its effectiveness as an emulsifier (Totre, Ickowicz, & Domb, 2011). The certain types of polysaccharides, such as gum Arabic (GAR), starch modified with octenyl succinic anhydride (OSA), and water soluble soy polysaccharides (WSSP) are commonly used as effective emulsifiers. A recent study by Łupina et al. (2019) suggests that the edible films based on the blends of GEL and the above mentioned polysaccharides could be used as effective emulsifying polymer network systems and carriers for hydrophobic biologically active substances. Combination of GEL with other polymers affects the release of active compounds. A high concentration of GEL in the carrier can significantly limit the diffusion mobility of the polymer-embedded substance (Kanth et al., 2017, Kowalczyk et al., 2020), which is not desirable since oxidation reactions on the food surface may start if the release of the antioxidant from the packaging film is too slow. Therefore, the aim of the present study was to assess the functional properties of edible 75/25 blend films based on polysaccharides (GAR, OSA, WSSP) and GEL incorporated with increasing AP contents (1% and 2%). Microstructure, water affinity, optical and mechanical properties, as well as AP release profiles and antioxidant activities of the films were investigated and compared.
Section snippets
Materials
Pork GEL (bloom strength of 240; McCormick-Kamis, Poland), GAR Agri-Spray Acacia R (Agrigum International, United Kingdom), starch sodium octenylsuccinate PurityGum®2000 (Ingredion, Germany), and WSSP (Gushen Biological Technology Group Co., China) were used in this study. AP, glycerol, Tween 80, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) were purchased from Sigma Chemical (USA), while ethanol (99.8%) and methanol (99.8%) were purchased from POCH (Poland).
Film preparation
Films were obtained from
Microstructure
Microscopic imaging showed that the GAR- and OSA-based FFSs were relatively homogenous (Fig. 1), indicating good solubility of the polymers in the water–ethanol mixture. In turn, the FFSs containing WSSP showed the grainy structure, which reveals the limited solubility of the WSSP and confirms the globular nature of soy polysaccharides in solution (Wang, Huang, Nakamura, Burchard, & Hallett, 2005). The AP was present in the emulsions both in the form of longitudinal crystals and microglobules.
Conclusion
The AP, as an ester formed from AA, slightly decreased the pH of the films. Although, in general, the AP did not improve surface hydrophobicity of most films, its presence reduced the water solubility. The amphiphilic character of AP increased the MC of the films. The WVP and TS of the OSA-based carrier were not affected by AP. In the case of the GAR-based system, the fortification with AP had beneficial effects by improving water vapor barrier properties and TS. The increase in AP
CRediT authorship contribution statement
Katarzyna Łupina: Conceptualization, Methodology, Data curation, Formal analysis, Visualization, Investigation, Writing - original draft. Dariusz Kowalczyk: Conceptualization, Methodology, Supervision, Validation, Writing - original draft. Emilia Drozłowska: Investigation, Visualization, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was financially supported by the National Science Centre (Poland) under grant number 2019/35/N/NZ9/01795.
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