You're using an outdated browser. Please upgrade to a modern browser for the best experience.
Please note this is an old version of this entry, which may differ significantly from the current revision.
Subjects:
Food Science & Technology
Asian plants (AP) have long been used as natural food preservatives in the food industry. Asian plant extracts (APE) and essential oils (EOs) with antioxidant and antimicrobial properties were incorporated into edible film (EF) for the inhibition of microbial growth in the food matrix.
- Asian plant extracts
- essential oils
- edible film
1. Introduction
Edible film (EF) is a thin covering that is applied as a separate layer between food components or directly to the food to act as a barrier for gas, moisture, oil, and vapors [1]. It is made of food-grade materials and can be consumed alongside the package and food during application. Biopolymers commonly applied in EF including polysaccharides (gums, alginate, agar, and starch), proteins (gelatin, casein, and whey), and lipids (glycerides, waxes, and paraffin). Food is shielded and protected from deterioration by EF on a physical, chemical, and biological level while also improving the visual appearance [2]. They also act as barriers and carriers for bioactive compounds (e.g., antioxidants, antimicrobials, flavorings, and colorants) which help to improve food quality by extending shelf life and improving food safety [3].
Asia has a diverse range of plants due to the wide variation of continents in latitude, elevation, and climate. Aside from that, the monsoonal climate of some regions produces hot and rainy summers, giving rise to a diverse range of temperate and tropical plants. Asian has Asian medicinal plants and spices which are used not only for medical purposes but also as food preservatives and flavorings [4]. The addition of natural additives such as APE and EOs can considerably improve the antioxidant and antimicrobial activity of the EF. Several studies have correlated various APE and EOs, for example, hawthorn berry, black soybean, and mangosteen peel, for properties which inhibit microbial growth in the food matrix [5,6,7]. Other advantages of incorporating these natural additives are to retard the oxidation rate of the product (fresh food), and to reduce the microbial load which can lengthen the storage of food products [8,9,10,11].
One of the AP such as Moringa (Moringa oleifera Lam. moringaceae) is a highly valuable plant that is mostly grown in the tropics and subtropics. This plant has been investigated by incorporating Moringa oleifera Lam. leaf extract (ethanol extract) with pufferfish skin gelatin to make an EF. This helps to increase the mechanical strengths of the film, which are the tensile strength (TS) and elongation at break (EAB). The film also demonstrated antibacterial activity against Listeria monocytogenes with improved antioxidant activity [12]. On the other hand, in eastern Asia countries, black soybean with black seed coatings is a functional food that is nutritionally rich. The incorporation of black soybean seed extract (ethanol extract) in chitosan EF showed outstanding barrier properties, for example, the water vapor (WVP) and UV-vis light and strengthen mechanical strength (TS and EAB), compared to the control (chitosan film). The black soybean seed extract chitosan film also demonstrated improved antioxidant activity, with 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging activities of the film gradually increasing as black soybean seed extract content increased from 5% to 15% (w/w) [6].
Besides APE, EOs, composed in a complex way with volatile chemicals produced by plants (aromatic), are also used as natural preservatives in the food industry. The addition of EO may also impact the mechanical and functional properties of the film [13]. Chrysanthemum EO is a liquid substance (aromatic) produced from the Chrysanthemum morifolium, one of 300 species in the Asteraceae (Compositae) family that was first cultivated in China as a blooming herb. The addition of the Chrysanthemum morifolium EO (1% to 6% (v/v)) in chitosan EF improved the scavenging effect of the antioxidant assay (from 4.97% to 18.63%) and the meat storage (raw chicken and beef) from 3 to 5 days during storage by maintaining the pH level (safe to consume), with an increase in Chrysanthemum morifolium concentration and with antibacterial activity against Staphylococcus aureus [14]. There is a trend reported that with nanoemulsified ginger, EO in gelatin EFs improve their thickness while reducing their water solubility, moisture content, and surface hydrophobicity when combined with montmorillonite (MMT) [15].
The incorporation of various types of APE and EOs as additive to EF provides benefits, as EF can provide different functional properties and also ensure consumer acceptability [16]. These extracts may come from different parts of the plant and spices including leaves, buds, roots, seeds, fruits, flowers, and barks which contain various phenolic compounds attributing to the biological properties [17].
2. EF Formulations Containing Different APE and EOs
Due to its antioxidant and antibacterial properties, AP have also been extensively utilized in industries such as in the food industry as preservatives and flavorings [4,21]. Antioxidant and antibacterial agents from PE extracted using different solvents such as ethanol, methanol, and aqueous were previously incorporated into EF [6,22,23]. EOs from AP are also commonly extracted using hydro-distillation for use in natural medicine or natural food preservation [14,21]. Recent studies have shown that incorporating these extracts into different biopolymers (polysaccharides, protein, and lipids) could help in enhancing the qualities of active EF. Different food grade ingredients, processing aids, and additives were used as plasticizers or solvents to develop an EF that shows enhanced properties, with the addition of APE and EOs to produce the film, forming suspensions. Table 1 lists examples of the various APE and EOs incorporation of EF.
Table 1. Various APE and EOs incorporation of EF.
| Asian Plant | Plant Part | Extract | Base | Other Ingredients | References | |
|---|---|---|---|---|---|---|
| Type | Amount (%) | |||||
| Black soybean | Seed | Ethanolic extract | 5, 10, 15 (w/w) | Chitosan | Acetic acid (1% (v/v)) Glycerol (0.6% (w/v)) |
[6] |
| Chrysanthemum morifolium |
N/A | Essential oil | 0, 1, 2, 3, 4, 5, 6 (v/v) | Chitosan | Acetic acid (1% (v/v)) Glycerol (0.75% (w/v)) Tween 80 (0.2% (v/v)) |
[14] |
| Eriobotrya japonica Lindl. | Leaves | Ethanolic extract | 2, 3, 4 (w/w) | Banana peel starch | Cornstarch (1.4% (w/v)) Glycerol (0.76% (w/v)) |
[24] |
| Ginger | N/A | Essential oil | 2 (w/w) | Gelatin | Montmorillonite (MMT) (5% (w/w)) Glycerol (30% (w/w)) |
[15] |
| Ginger, turmeric and plai | Root | Essential oil | 25, 50, 100 (w/w) | Fish skin gelatin | Glycerol (30% (w/w)) Tween 20 (25% (w/w)) |
[25] |
| Hawthorn berry (Crataegus pinnatifida) | Fruits | Ethanolic extract | 1, 2, 3, 4 (v/v) | Alginate | Glycerol (0.75% (v/v)) Calcium chloride (1% (w/v)) |
[5] |
| Kiam (Cotylelobium lanceolatum craih) |
Wood | Aqueous extract | 1, 2, 3, 4, 5 (v/v) | Hydroxypropyl methylcellulose (HPMC) | Sorbitol (0.4% (w/w)) |
[22] |
| Mangosteen | Peel | Ethanolic extract | 1 (v/v) | Porang glucomannan | Sorbitol (3% (v/v)) |
[7] |
| Moringa oleifera Lam. | Leaves | Ethanolic extract | 0.03, 0.05, 0.07, 0.1 (w/v) | Gelatin (Pufferfish skin) | Sorbitol (2% (v/v)) |
[12] |
| Neem (Azadirachta indica) |
Flowers and leaves | Aqueous extract | 0, 0.1, 0.3, 0.5 (w/v) | Gelatin | Glycerol (25% (w/w)) |
[11] |
| Piper Betle Linn. | Leaves | Aqueous extract | 1, 2, 3 (v/v) | Chitosan | N/A | [26] |
| Sophora japonica | N/A | Ethanolic extract | 1, 3, 7, 9 (w/w) | Artemisia sphaerocephala Krasch. Gum (ASKG) | Glycerin (0.3% (w/v)) |
[10] |
| Turmeric (Curcuma longa L.) |
N/A | Aqueous extract | 13 (w/w) | Alginate | Glycerol (1% (v/v)) Calcium chloride (1% (w/v)) |
[9] |
Various APE (e.g., black soybean, Chrysanthemum morifolium, Eriobotrya japonica Lindl., ginger, turmeric and plai, hawthorn berry, kiam, mangosteen, neem, Moringa oleifera Lam., Piper Betle Linn., and Sophora japonica) have been selected to incorporate into different polymer-based EFs to improve the functional properties of food packaging [5,6,7,9,10,11,12,14,15,22,24,25,26]. Most of the research used ethanolic PE in the EF in concentrations ranging from 1% to 15% (w/w), with some incorporating aqueous extracts and EOs. These studies used different polysaccharides and protein polymer bases to produce EFs with APE; however, most of the studies used gelatin as the base for EF development. Gelatin was incorporated with extracts of neem and Moringa oleifera Lam leaves [11,12]. Glycerol or sorbitol are common plasticizers used in gelatin EFs [11,12,15,25].
APE have been extensively researched with their incorporation into gelatin EF. This combination is possibly due to the widespread use of gelatin in different industries’ aspects [27]. This could be owing to its functional properties (water-binding, gel formation, foam forming, film forming, and emulsification ability). Most importantly, gelatin has excellent gas barrier characteristics which are perfect for food packaging properties; conversely, it has poor mechanical strength with high water vapor permeability [28]. As a result of its poor water vapor barrier performance, gelatin’s application as a packaging material is restricted [29]. However, by combining gelatin with other ingredients (functional or active agents) such as APE and EO, this can be improved [30].
When compared to gelatin (0.03% to 0.5% (w/v)), alginate and chitosan EFs have a higher range of APE (5% to 15% (w/w)). Glycerol (a plasticizer) and calcium chloride (a firming agent) are common ingredients in the production of alginate-based EFs [9]. The glycerol content of EF is typically 0.75% to 1% (w/v). Studies showed that turmeric (Curcuma longa L.) and hawthorn berry extract were incorporated into alginate EFs [5,9]. The APE can be added in amounts ranging from 0.13% to 1% (v/v) to form an alginate EF. Chitosan was also used in the making of EFs containing APE [6,14,26]. Glycerol was also used as a plasticizer in chitosan EF incorporated with AP [6,14]. In most formulations, 1% acetic acid is added to the chitosan solution, as acetic acid is commonly used to solubilize chitosan [31]. APE, such as black soybean seed coat (BSSC) and Piper Betle Linn. leaf (PBLL) extract, have been added into chitosan EFs [6,26]. With APE in the concentration range of 0.1% to 5% (v/v), a chitosan EF could be formed.
Other polymers, such as hydroxypropyl methylcellulose (HPMC), porang glucomannan, and Artemisia sphaerocephala Krasch. gum, have been incorporated with kiam wood, mangosteen peel, and Sophora japonica extract, respectively [7,10,22]. Sorbitol was used as a plasticizer in hydroxypropyl methylcellulose (HPMC) and porang glucomannan-based EFs, whereas glycerin was used in Artemisia sphaerocephala Krasch. Based on Table 1, the EO content of EF is comparable to APE, which contain less than 6% (v/v). Hydro-distillation was used to extract EO from Chrysanthemum morifolium, ginger, turmeric and Plai root [14,15,25]. Previous literature has reported that Asian plant essential oils (APEOs) incorporated into EF, and EF incorporated with EOs require an emulsifier such as Tween 80 or Tween 20 to mix different bases of solution (oil-based and water-based) [32].
In addition to the ingredients, knowing the types of materials delivered by PE and EOs in EF is very crucial in order to make EF. Common active compounds found in PE and EOs include antioxidant and antimicrobial agents. The EF produced can act as a carrier for these active compounds, providing a novel method for improving food safety and shelf life [33]. Some of the antimicrobial substances that could possibly be used in EF include organic acids, polypeptides, plant Eos, and nitrites and sulfites [34].
According to Lim et al. [5], the antibacterial effects of hawthorn berry extract were most likely due to its specific constituents, specifically the favones and procyanidins [35] delivered by the alginate EF. Because black soybean is high in anthocyanins [6], the extract-incorporated EF served as a carrier for antioxidant agents, which helped to improve the EF’s 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging activity. Curcumin contains polyphenol, which is responsible for its antioxidant capacity when incorporated into EF [9]. Mangosteen peel, on the other hand, contains xanthones, that are very favorable to the body for biological purposes (antioxidant and antibacterial) and could be delivered by using EF as a carrier for this compound when used as food packaging [7].
Artemisia sphaerocephala Krasch. Gum (AsKG) with Sophora japonica extract (SJe) has the potential to be an antioxidant EF [10]. In addition, Sophora japonica has been widely used in studies for the extraction of flavonoids, particularly rutin, which has a high ability to scavenge DPPH and superoxide anion radicals [36]. Because of these active antioxidant compounds (phenolic, flavonoids, and limonoids), neem leaf extract has shown high antioxidant activity (DPPH radical scavenging activity increased from 0% to 0.5% (w/v)) when incorporated into EF [11]. On the other hand, in Moringa oleifera Lam. Extract, there are flavonoids (kaempferol and quercetin), and many other phytochemicals that exhibit good antioxidant and antimicrobial properties. Gelatin EF can serve as a carrier for these phytochemical compounds, helping to improve food quality during storage [12].
Kiam with high concentrations of polyphenolic compounds can contribute to the antibacterial activity of hydroxypropyl methylcellulose EF by inhibiting the growth of various bacteria (Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus) [22]. EFs containing Eriobotrya japonica Lindl. extract contain phenolic compounds, which are assessed by finding out the total phenolic compound content. The film with the highest extract content demonstrated the highest values (6.6 mg GAE/g−1 of total phenolics) [24]. Because of the polyphenol compounds found in the PE, chitosan EF with Piper Betle Linn. extract had the potential to serve as an antibacterial EF. These natural compounds can cause cell membrane permeability denaturation, nucleic acid synthesis inhibition, and physiological changes in cell membranes, ultimately leading to cell death [37].
This entry is adapted from the peer-reviewed paper 10.3390/coatings13020245
This entry is offline, you can click here to edit this entry!