Nanoencapsulation: A New Way of Using Herbs and Spices in Food and Its Related Products

Abstract

Research interests on the exploration of bioactive compounds especially for their use in the food processing have been significantly increasing. This phenomenon is due to their potential health benefits in addition to their conventional use as antioxidant and antimicrobial agent. A plenty of herbs and spices which was traditionally used for enhancing health or healing different kind of diseases is promising for uses in functional food formulations. However, using herb and spice in food formulation may have some drawbacks including alteration of the flavour of the food as well as its low bioavailability. To overcome these issues, nanoencapsulation is then developed by the scientists. This review discusses the recent updates of nanoencapsulation of herb and spice extracts. To give a deeper insight, the potential bioactive compounds contained in various herbs and spices are also covered in this review. At the end, the potential application of nanocapsules containing herb and spice extracts in food and its related products, including nutraceuticals and food packaging is given. This area of study may be interesting for the scientists to conduct researches for further development of the nanocapsules.

1. Introduction

Herbs and spices have been important agricultural products around the globe since centuries ago due to their economic significant. Previously, the use of herbs and spices were mainly for flavouring agent in foods. Nowadays, herbs and spices have been acknowledged as the source of phytochemicals having potential benefit for human health. Hence, they are potentially used, not only for giving a specific flavour in foods, but also for the formulation of functional food [1].

Functional food can be defined as “Foods and food components that provide a health benefit beyond basic nutrition (for the intended population)” [2]. In this context, therefore, adding food components having beneficial effect on health to a conventional formula of foods is one of strategic approaches to formulate functional food [1]. The herb and spice extracts are then added into food at a certain level to improve its health effect. Indeed, the use of herb and spice extracts in functional food formulation is actually adopted from the pharmaceutical industry. Therefore, the terminology of nutraceuticals is now well-known which is referring to a food or part of a food that provides benefits health in addition to its nutritional content. It is believed that nutraceutical is a new category which shades the frontier between drugs, including traditional medicine, and food [3]. Therefore, the pharmaceutical science is impossible to be avoided when discussing about health benefits of herbs and spices even though the application will be in the food and its related products.

Thus, many studies have shown that phytochemicals of herbs and spices are potential for significantly improving the positive health effect of foods. In addition, phytochemicals of herbs and spices are also potentially used for prolonging the shelf-life of foods because of their antioxidant and antimicrobial activity [4, 5]. The first step of using herbs and spices as functional food ingredients and preservative agent in foods is extraction. Depending on the type of the matrix and also the targeted compounds, different extraction techniques can be applied [1].

According to the results of many studies, however, using herb and spice extracts to improve health-promoting properties of foods, in one hand, is obviously prospective. However, the incorporation of herb and spice extracts in food, in the other hand, may alter the aroma and flavour profile of the food, and thus decreased the product acceptability [6,7]. To overcome the issue, the encapsulation of the herb and spice extract is then carried out attempting to cover the strong herb and spice aroma of the enriched food [8].

Recently encapsulation in a nano scale, also known as nanoencapsulation, have been extensively developed by scientists due to its advantages as compared to microencapsulation. This review, hence, discuses the recent development of nanoencapsulation techniques, particularly for encapsulating herb and spices extracts. To give a more comprehensive insight, the phytochemicals composition of selected popular herb and spices extracts are also covered. Later, the current use of the nanocapsule in food and its related products are also discussed. The examples of potential application of nanocapsule containing herb and spice extract to improve health-promoting properties as well as to prolong the shelf-life of the food are also provided. At the end, a recommendation for future studies is given.

2. Phytochemicals in herb and spice extracts

2.1 Herbs and spices as potential source of bioactive compounds

Herbs and spices were found to become one of potential sources of bioactive compounds. The identification and quantification of bioactive compounds from various herb and spice as well as the demonstration of the bioactivity have been reported in many works. The type and content of bioactive compounds of herbs and spices highly depend on the species and part of the plant (i.e., leaves, twig, roots, bark, seed and fruit) [1]. Turmeric and ginger are the two most popular root-based spices, while pepper and cumin are the two most seed-based spices widely used globally. Oregano, cinnamon and nutmeg are other examples of popular culinary herbs and spices used in many ethnics and studied by scientists nowadays [9]. In addition, origin and age of the plant may also have a significant impact of the phytochemical composition of herbs and spices. This may be due to varied ecological interaction between plants and its environment [10]. The molecular structures of phytochemicals commonly found in various herbs and spices is shown in Figure 1.

It has been widely known herbs and spices can be simply extracted using two methods namely distillation resulting in essential oils and solvent extraction yielding in oleoresins. The extraction method, such as distillation system (i.e., water distillation, steam distillation and water-steam distillation) and solvent extraction technique (i.e., maceration or reflux with different type of solvent) are important factors influencing the phytochemicals of herb and spice extract [1]. Essential oils typically contain a wide range volatile compounds constituting its specific aroma. As such, cinnamon essential oil was reported to contain cinnamaldehyde, α-pinene, α-copaene, bornyl acetate, limonene and linalool. The aroma of herb- or spice-based essential oils that can be perceived by human nasal depends on the concentration and odour activation value (OAV) of compounds constituting the essential oils. A compound which exists in high concentration and low odour activation value dominates the aroma of the essential oil [6]. Oleoresins usually contain not only volatile compounds, but also non-volatile compounds. For instance, cinnamon extract obtained by solvent extraction contained catechin, epicatechin, procyanidin B2, quercitrin, 3,4-dihydroxybenzaldehyde and protocatechuic acid [11]. The extract of herbs and spices obtained by distillation and solvent extraction is frequently considered as crude extract. The crude extract can be further purified to get pure or single bioactive compound. To increase the extraction efficiency of targeted a compound, several techniques can be applied, such as ultrasonic, microwave and pulsed electric field. With an ultrasound-assisted extraction method, for example, the cell walls of herbs or spices were effectively broken, and thus the release of the phenolic content was subsequently facilitated [12].

Figure 1: Molecular structures of phytochemicals commonly found in herbs and spices.

The structures were extracted from http://www.chemspider.com/

2.2. Phytochemical properties of selected herbs and spices

2.2.1. Turmeric

Turmeric (Curcuma longa, Zingiberaceae family) is one of the most used spices in Asia and Africa for culinary purposes due to its specific flavour and colour as well as for treatment of some diseases, such as diabetes, cough, anorexia and sinusitis. Curcuminoids, including curcumin, demethoxycurcumin and bis-demethoxycurcumin, are the most dominant compounds in turmeric [13]. Even though it has been successfully isolated since more than century, research in curcuminoids is still gaining a lot of interest. Curcuminoids are considered as safe and non-toxic substance posing various functional and nutraceutical activities such as antioxidant, antimicrobial, anti-inflammatory and anticarcinogenic activities [14, 15]. This potency makes curcuminoids attract not only the food industries but also pharmaceutical industry. Curcumin, however, is a hydrophobic compound which is poorly soluble in water, and thus having poor bioavailability. Moreover, curcumin has low stability and a high rate of photodegradation [16].

2.2.2. Ginger

Ginger (Zingiber officinale Roscoe, Zingiberaceae family) is a popular culinary spice originating from South-East Asia. Aside from its use as flavouring agent in food, this type of spice has been used as traditional medicine for particular disease, such as headaches, colds, osteoarthritis, muscle pains, nervous diseases, and asthma, in many ethnic groups in Asia [17]. Recently, ginger has been found to have a potency as anti-inflammatory, antioxidant, anti-cancer, anti-microbial and anti-diabetic agent, aside from its neuroprotective activity. Ginger contains starch, lipids, proteins, inorganic compounds and phytonutrients. Gingerol and shogaol, normally found as a pungent yellow substance, are the most important bioactive compounds in ginger having therapeutic properties and biological significance. Quercetin, zingerone, gingerenone-A, and 6-dehydrogingerdione are others phenolic compounds that are also commonly found in ginger [18]. Several homologs of gingerol existing in ginger has been identified which the most dominant compound is 6-gingerol. This compound yields 6-shoagol in a dehydration reaction resulting in a substance which has about twice as pungent as gingerol [19].

2.2.3. Pepper

Pepper (Piper nigrum L., Piperaceae family), also well-known as “King of Spices”, has been used for food flavouring and traditional remedies since ancient time. In addition, pepper is also used for a preservative agent due to its antioxidant and antimicrobial activity Nowadays, there are two types of peppers in the market namely white and black peppers that are actually yielded from similar plant but made from different time of harvest and processing techniques [20]. Piperine was found as the most important active compounds in pepper. Previous studies have shown its functionality to reduce the risk of tumour, angiogenesis, diabetes, obesity and allergy as well to have cardioprotective, neuroprotective, antiproliferative and immunomodulatory effects [21]. This compound is a natural alkaloid which is responsible to give pungency in pepper. Piperine is poorly soluble in water limiting its use in pharmacology. Some advises, therefore, are given such as to incorporate pipeline in a delivery system in order to improve its properties [22].

2.2.4. Black cumin

Black cumin (Nigella sativa L., Ranunculaceae family) is medicinal plant widely cultivated and used in Middle Eastern, Mediterranean region, South Europe, India, Pakistan and Turkey. Oil extracted from the seed is main product of this plant. Since centuries ago, this oil was used as therapeutic agent for a disease associated with respiratory (asthma and bronchitis), digestive tract, cardiovascular, kidney, liver, and immune system [23]. Recently, black cumin seed oil has been reported to have anti-microbial, anti-inflammatory, anti-cancer activity, anti-parasitic, anti-protozoal and anti-viral and cytotoxic [23, 24]. The important constituents of black cumin seed having biological activity includes oleic acid, palmitic acid, quinones (thymoquinone, dithymoquinone, thymohydroquinone), terpenes (α-phellandrene, carvacrol, p-cymene, α-pinene), phenols and flavonoids as well as other compounds such as isoquinonline alkaloids, pyrazol alkaloids, kaempferol, saponin, α-hederin) [25]. Thymoquinone, however, is still considered as the main compounds in black cumin seed posing substantial bioactivity. Similar to some other bioactive compounds, thymoquinone is highly sensitive to light. This compound is hydrophobic and unstable in water. Thymoquinone, therefore, has low bioavailability and thus limit its use in drug formulation and/or active compound in functional food formulation [26].

2.2.5. Oregano

Oregano (Origanum vulgare, Lamiaceae family) is an aromatic herb used by people in Mediterranean since long time ago for cooking and for healing some diseases, such as asthma, bronchitis, cough, diarrhea, stomach-ache and menstrual disorders [27]. In fact, there are more than 60 species have been identified so far and some of them have been scientifically proven to have some potential bioactivity including as antioxidant, anti-inflammation and anti-cancer. Flavonoids and phenolic acids are the compounds significantly contributing to these biological activities. Apigenin and luteolin are some phenols commonly found in oregano extract, but the concentration of the compounds highly depends on the species and the extraction method [28]. Apigenin, also chemically known as 4, 5, 7,-trihydroxyflavone , belongs to flavone class. This compound is soluble in organic solvent, but insoluble in water [29]. Like apigenin, luteolin which is chemically known as 3,4,5,7-tetrahydroxyflavone has been reported as a potent anti-cancer and anti-inflammation agent [30].

2.2.6. Cinnamon

Cinnamon (Cinnamomum Sp., family Lauraceae), is a widespread spice that is used in many ethnics in the world for cooking and traditional medicinal purposes. The genus of cinnamon actually consists of 250 species which are distinctive in their characteristic. Some of popular species include C. verum, C. cassia and C. burmanii [1]. In current years, many studies have shown that phytochemicals derived from cinnamon have a wide spectrum of functionality, including preventing microbial growth and oxidation process as well as controlling blood pressure, tumour growth, diabetes and diseases associated with neuron disorder [31]. Trans-cinnamaldeyde and eugenol are frequently found as the dominant components in cinnamon essential oils, while phenols are the important constituents in cinnamon oleoresins which is responsible to various beneficial effect of cinnamon for health. The presence of these compounds, however, still depends on the species, plant origin, part of plant and method of extraction [1]. Although many functions have been reported in many literatures, the use of trans-cinnamaldehyde for commercial purposes is still limited because cinnamaldehyde has a low solubility in water, a high sensitivity to light and air, and also low stability in blood [32]. Eugenol, also chemically known as 4-Allyl-2-methoxyphenol or 1-allyl-4-hydroxy-3-methoxybenzene or 4-allyl-2-methoxyphenol, is a yellowish liquid with a pleasant odour and taste. This compound has a good solubility in organic solvents and, unlike cinnamaldehyde, is moderately soluble in water [33].

2.2.7. Nutmeg

Nutmeg (Myristica fragrans Houtt, family Myristicaceae) is a highly valued tropical spice used the modern worldwide food, cosmetic and perfume industries. This spice has been reported to be traditionally used as a therapeutic agent for several diseases such as dyspepsia, musculoskeletal and arthritic disorders, particularly in Indonesia, Malaysia, India and Sri Lanka [34]. Nutmeg is rich in volatile compounds including aromatic ethers, monoterpenes and sesquiterpenes, with myristicin as the key compounds giving pleasant aroma in nutmeg [35]. Myristicin, also chemically called as 3-methoxy-4,5-methylenedioxy-allylbenzene, was also reported as a potential chemopreventive having anticancer and hepatoprotective effects. Myristicin is insoluble in water, but soluble in organic solvent, such as ethanol and acetone [36].

3. Nanoencapsulation of herb and spice extracts

Nowadays, nanoencapsulation of bioactive compounds, particularly from herbs and spices, as well as the incorporation of the nanomaterials in a food matrix, have gained considerable importance in the food industry and food science. As such, a simple study using “Google Scholar” as the search engine and keywords of “herb”, “spice”, “extract” and “nanoparticles” showed that the researches and publications related to these keywords significantly increased in the last few years (Figure 2).

Figure 2: Number of publications identified in Google Scholar searched with keywords of “herb”, “spice”, “extract”. and “nanoparticles”

Nanoencapsulation is one of techniques in the area of food nanotechnology. It is a technique to contrive a matter at nanoscale dimensions where a nanometer is equal to 10-9 m. However, there is a general consensus that nanomaterials exhibit a size in the range of 1-100 nm. Agglomerates or aggregates bigger than 100 nm can be included as nanomaterials as long as they still retain their characteristics [37]. Depending on the structure, the product of nanoencapsulation can be in the form of nanocapsules or nanospheres (Figure 3). In nanocapsule, the bioactive compound is in the centre of the particles and surrounded by wall material, while in nanosphere, the bioactive compounds are homogeneously dispersed in the particle. Generally, both nanocapsule and nanosphere are also called as nanoparticles [38]. To produce nanoparticles, top-down technique which is by reducing the size of the structures to nanoscale dimensions and a bottom-up technique which is by constructing molecules to form nanomaterials through self-assembly can be used. However, the latter is considered easier and more cost-effective. Some examples of bottom-up techniques include coacervation, inclusion complexation and anti-solvent precipitation [37, 39]. Nanoparticles are commonly developed particularly for the delivery system of bioactive compounds [40].

Figure 3: Structure of nanocapsules (a) and nanospheres (b)

The increasing trend of nano-scale encapsulation particularly for encapsulating herb and spice extract is understandable as nanoencapsulation has been reported to have some other advantages such as improving bioavailability, biological activity and stability as well as controlling the release of bioactive compounds [40]. This novel paradigm expands the old-fashioned rationale of carrying out encapsulation in food industry which were mostly used to control the release of odour component or preserve the intensity of colourant in food. As such, Saifullah et al. [41] has clearly reported that various compounds derived from herbs and spices such as d-limonen, β-pinene, heptanolide, carvone, menthone, linalool, heptanol, menthol, curcuminoids, capsaicinoids, ginger oleoresin, limonene, nicotine, cinnamaldehyde, 1,8-cineole, myrcene, terpineol, terpenes, carvacrol, citral, peppermint oil, carvacrol, ethylvanillin, eugenol and thymol were successfully encapsulated in various wall-matrices including sodium caseinate, carboxymethyl cellulose, starch, β-cyclodextrin, sodium alginate, wax, shellac, zein, maltodextrin, alginate, pectin and ethylcellulose, not only in micro- but also in nano-sized materials, in order to control the release of the aroma yielded from the compounds. Table 1 shows some examples of the recent development of nanoparticles containing selected herb and spice extracts.

Table 1: Recent reports related to the development of nanoparticles containing herb and spice extracts

Herb or spice extracts	Encapsulation Material	Technique	Characteristic of nanoparticles	Ref.
Turmeric	Silver	Green synthesis	・Spherical forms with particle size of 18 ± 0.5 nm ・Strong antimicrobial activities against food-borne pathogens	[42]
Ginger	Chitosan	Ionic gelation	・Spherical forms with particle size in the range of 154-188 nm ・Contained high phenolic content and exhibited antimicrobial activity	[43]
Pepper	Silver	Green synthesis	・Spherical forms with particle size of about 20 nm ・Strong antimicrobial activities against Escherichia coli and Salmonella	[44]
Black cumin	Platinum	Green synthesis	・Spherical forms with particle size in the range of 1-6 nm ・Exhibited anti-cancer activity	[45]
Oregano	Chitosan	Two-step methods	・Spherical forms with particle size in the range of 309.8–402.2 nm ・Chitosan nanoparticles controlled the release rate of oregano essential oil	[46]
Cinnamon	Shellac	Anti-solvent precipitation	・Spherical forms with particle size in the range of 73-366 nm depending on the concentration of stabilizer ・Contained high phenolic content and exhibited antioxidant activity	[47]
Nutmeg	Fe3O4–MgO	Green synthesis	・Spherical forms with particle size in the range of 10-15 nm ・Contained volatile compounds and exhibited strong anti-fungal, anti-bacterial and antioxidant activity	[48]
Cumin	Chitosan	Ionic gelation	・Spherical forms with particle size in the range of 30-80 nm ・Exhibited strong antioxidant activity and antimicrobial activity against bacteria, mould and yeast	[51]
Ginger	liposome	Self-assembly	・Spherical forms with the average particle size of 164.5 nm	[54]
Rosemary	Chitosan and γ-Poly glutamic acid	Ionic gelation	・Spherical forms with the average particle size of 212 nm	[60]

As shown in Table 1, there are some possible materials for fabricating nanomaterials containing herb and spice extract. Inorganic materials, including silver and platinum, resulted in a smaller particle size, while organic materials, like shellac and chitosan, resulted in a bigger particle size. To produce nanomaterials, these inorganic materials are commonly processed by a process namely “green synthesis”. This terminology refers to the synthesis of metal nanoparticles using biological bioactive agents. However, one of the limitations of using inorganic materials in producing nanomaterials for food application is its safety aspect. For food application, the selection of encapsulation materials is highly important, while for other applications, including in the pharmaceutical industries, it depends on how the application will be. The nanomaterials engineered using inorganic materials may be more suitable to be applied not directly in food but in the food packaging materials. Their anti-fungal, anti-bacterial and antioxidant activity may contribute to the shelf-life of the packed food.

In addition to the “green synthesis” methods, there are some other established bottom-up techniques for fabrication nanomaterials containing herb and spice extracts, including ionic gelation and anti-solvent precipitation. Moreover, as stated by Ezhilarasi et al. [38] emulsification, coacervation, inclusion and supercritical fluid have also been developed by the scientist for making nanomaterials. Thus, it is important to note that for selecting the most appropriate method for fabricating nanomaterials, the characteristic of materials must be taken into account. The selection of the materials and the techniques must consider the desired functionality of the engineered nanomaterials. Depending on the technique and the material, nanoencapsulation technology may results in various structures, and thus some of them are called as nanotube, micelle, liposome, nanogels, nanoshell and dendrimer (Figure 4).

It is also interesting to understand from the literatures that the extracts of herb and spice can be incorporated into nanocapsules, either in the form of crude extracts or a pure compound. However, using crude extract as core materials of nanocapsules is much more challenging as crude extract contains various compounds with different characteristic. In this case, some parts of the initial load may be well-encapsulated within nanocapsules, while the remaining part may still attach to the surface of the nanocapsules meaning that the encapsulation efficiency might be not satisfying. Particle size, stability and encapsulation efficiency are some of important quality parameters of nanocapsules [47].

4. Potential application of nanomaterials in food products and its related products

4.1. Improvement of antioxidant activity of food

Previous studies have shown that cinnamon extract has successfully nano-encapsulated using an anti-solvent precipitation method, and thus the nanoparticles were incorporated in chocolate and cocoa drink to improve antioxidant capacity of the products [49, 50]. The incorporation of the nanoparticles in cocoa drink even provided an additional advantage which improve suspension stability of the beverage [49]. The incorporation of the nanoparticles in chocolate reduced the aroma alteration of the product upon cinnamon extract enrichment. However, it was reported that the presence of the nanoparticle changes the characteristic of chocolate to some extent [50]. The improvement of antioxidant activity of products was positively correlated with its phenolic content sourced from the spice extract, thus, agreeing with the common theoretical recognition of the antioxidative features of phenols. Another study by Karimirad et al. [51] shows a significant improvement of antioxidant activity and phenolic content of button mushroom after enriched by chitosan nanoparticles containing cumin essential oil. It was reported that the nanoparticles were prepared using ionic gelation technique resulting in a size ranged from 30-80 nm. Moreover, the nanoparticles also exhibited antimicrobial activity against bacteria, mould and yeast, and hence prolonged the shelf life of the product.

Figure 4: Various structures of nanomaterials

An improvement of antioxidant capacity was shown in semi skimmed milk after enriched with nanoemulsion containing thyme essential oil. In this product, the nanoemulsion effectively protected protein from degradation and inhibited peroxide production, even though the performance was less efficient than free essential oil [52]. The essential oil of star aniseed (Illicium verum) encapsulated in chitosan was reported to substantially improve total phenols as well as antioxidant capacity of pistachio when tested under various antioxidant assays. Moreover, it also exhibited antiaflatoxigenic potency due to the presence of anthole and estragole [53]. Ginger extract was successfully encapsulated in liposome form with a mean size of 164.5 nm. The application of the liposomes was proven to increase the DPPH radical scavenging capacity, reducing power of Fe (III) and total antioxidant activity as well as to decrease the peroxide and thiobarbituric acid values of sunflower oil during storage which was even better than butylated hydroxytoluene (BHT) the synthetic antioxidant (BHT) [54]. In another study by Souza et al. [55] quercetin, a phenolic compound commonly found in various spices, was encapsulated in alginate-starch system and was beneficial for inhibiting canola oil oxidation.

The improvement of antioxidant activity and phenolic content of foods by the enrichment of herbs and spices is frequently associated not only with a prolonged shelf-life of the products but also an improved health-promoting property of the products [1]. This association is caused by the ability of antioxidant compound for the removal of free radicals in living systems and the inhibition of oxidative stress in the human body. As well-known, the oxidative stress in the cell caused free radicals and reactive oxygen species leads to damage to DNA, proteins and lipids, and thus it eventually induces many chronic diseases such as cancer, coronary heart diseases, diabetes, neural disorders, and atherosclerosis, as well as other degenerative diseases and aging [56]. These facts motivated the scientists to explore the potential antioxidant action as well as health effect of encapsulated herb or spice extract. However, to the best of our knowledge, the study of the application of encapsulated herb or spice extract in foods in terms of potential health benefit is still scarce. As such, the understanding of the effect of encapsulated herbs and spices in clinical studies are fairly absent. To provide an accurate scientific information, Gertsch [57] recommended consecutive experimental steps, including biopharmacy study (pharmacokinetics), animal experiment (verification, knockout models, in vivo efficacy) and clinical study. This is because the performance of herbs or spices may be different when tested individually or in a complex matrix. As such, a previous study has shown that cinnamon extract and cocoa possibly exhibited antagonistic effect in term of antioxidant activity. Cinnamon extract which was encapsulated in a shellac-xanthan gum system could not perfectly release in a simulated gastrointestinal condition when tested in chocolate matrix [50, 58]. Further research in this area is, therefore, still required.

4.2. Enhancement of antimicrobial activity of food

Oregano essential oil was successfully encapsulated using the phase inversion temperature method, and thus the nanocapsules were applied in cheese. As summarized in Table2, the nanocapsule was reported to effectively inhibit the growth of Cladosporium sp., Fusarium sp., and Penicillium sp. Both in vitro and after application in the cheese matrix [59]. In the study of Lee et al. [60], rosemary extract-loaded nanoparticles with average particle size of 212 nm have been fabricated by ionic gelation of chitosan and γ-Poly glutamic acid, and used to inhibit the growth of Bacillus subtilis in ready-to-drink barley tea. Another example of successful application of spice extract-loaded nanoparticles to inhibit microbial growth in food products was shown by Pinilla et al. who worked with garlic [61]. Garlic extract was encapsulated in a liposome system. The liposomes were then applied in wheat bread. It was reported that the liposome significantly reduced the growth of fungi, including Penicillium expansum, Aspergillus niger, Penicillium herquei, Fusarium graminearum and Aspergillus flavus resulting in an extended shelf-life of the bakery product. The similar research group also found that garlic extract that was co-encapsulated into liposomes showed a significant inhibitory effect against L. monocytogenes, S. aureus, E. coli and S. Enteritidis in milk [62]. An attempt also made by the research group of Jemma et al. [52] to prolong the storage time of milk using herb extract. They explained that nanoemulsion containing thyme essential oil significantly inhibited bacterial growth, particularly againts E. hirae.

Hadian et al. [63], in the other study, fabricated nanogel using chitosan and benzoic acid to encapsulate rosemary leaf extract. They found that the application of nanogel with an average size of below 100 nm at the concentration or 0.5 mg/g beef cutlet was able to significantly reduce S. typhimurium growth in the product, and thus extended the shelf-life of the product with effects on the colour values during storage. Thyme essential oil was encapsulated using complex coacervation technique in micro-sized particle. It was reported that the thyme essential oil substantially inhibits the growth of bacteria and moulds in cake, and thus the product had a shelf-life of 30 days without any additional preservative agent [64]. Clove oil incorporated in liposome system was also reported to have antibacterial activity, particularly against E. coli and S. aureus, mainly attributed to eugenol and eugenyl acetate content. The antibacterial effect was useful to maintain the quality of tofu during storage [65]. The longlist of research results validating the performance of encapsulated herb and spice extract in inhibiting microbial growth in various foods demonstrates that herb and spice extract encapsulation is a promising technology for preserving the quality and for extending the shelf-life of foods. It can be useful for replacing the use of synthetic preservative agent that may have adverse effect on health.

Table 2: Potential application of nanomaterials in food products

Herb or spice extracts	Nanomaterial type	Matrix	Important finding	Ref.
Cinnamon	Shellac nanoparticle	Cocoa drink	・Improvement of phenolic content and antioxidant activity ・Reduction of aroma alteration	[49]
Cinnamon	Shellac nanoparticle	Chocolate	・Improvement of phenolic content and antioxidant activity ・Improvement of suspension stability	[50]
Cumin	Chitosan nanoparticle	Button mushroom	・Improvement of antioxidant activity	[51]
Thyme	Nanoemulsion	Milk	・Protection of protein ・peroxide production inhibition	[52]
Star aniseed	Chitosan nanoparticle	Pistachio	・Improvement of phenolic content and antioxidant activity ・Antiaflatoxigenic potency due to the presence of anthole and estragole	[53]
Ginger	Liposome	Sunflower oil	・Improvement of phenolic content and antioxidant activity ・Prolonged the shelf life of sunflower oil	[54]
Oregano	Nanocapsule	Cheese	・Inhibition of Cladosporium sp., Fusarium sp., and Penicillium sp growth	[59]
Rosemary	Chitosan and γ-Poly glutamic acid nanoparticle	Barley tea	・Inhibition of Bacillus subtilis growth	[60]
Garlic	Liposome	Wheat bread	・Inhibition of Penicillium expansum, Aspergillus niger, Penicillium herquei, Fusarium graminearum and Aspergillus flavus growth ・Extension of wheat bread shelf life	[61]
Garlic	Liposome	Milk	・Inhibition of L. monocytogenes, S. aureus, E. coli and S. Enteritidis growth	[62]
Rosemary	Nanogel	Beef cutlet	・Inhibition of S. typhimurium growth	[63]
Clove	Liposome	Tofu	・Inhibition of E. coli and S. aureus growth ・Extension of tofu shelf life	[65]

4.3. Other applications in food-related products

Extending the shelf-life of foods by directly adding encapsulated herbs or spices in the food matrix is not the only way carried out by the food scientists and industries. Many studies have shown that encapsulated herbs or spices can be incorporated in food packaging, edible film or edible coating. For instance, cinnamon essential oil was encapsulated in nanoscale in chitosan by ionic gelation prior to incorporation in the low-density polyethylene (LDPE) film. It was demonstrated that LDPE containing nanocapsules had a great antioxidant activity to protect fresh pork against oxidation and a potent anti-microbial activity against Enterobacteriaceae and Pseudomonas spp. [66]. Chitosan was also used to nano-encapsulate essential oil of Paulownia tomentosa flower and clove. Edible coating containing nanoparticles successfully prolonged ready-to-cook pork chops and pomegranate arils, particularly due to the antioxidant and anti-microbial activity of the essential oils [67, 68]. Liu et al. [69] demonstrated that edible coatings made of nanoemulsion containing star anise essential oil, polylysine and nisin positively improved quality and shelf life of meat, and even the coating also improved the sensory acceptability of the product. Another study showed that edible coating made of nanoliposome-encapsulated bay leaf extract at a level of 1500 ppm prolonged the shelf-life of minced beef up to 16 days when stored in a refrigerator [70]. The extended shelf-life was attributable to the antioxidant and anti-microbial activity of bay leaf extract particularly against E. coli and S. aureus

Horison and co-worker [71] explained the functionality of edible coating made of nanoemulsion containing chitosan and nutmeg oil to preserve fresh strawberry against microbial, including mould and yeast. This result was in accordance with those of Martinez et al. [72], who previously worked with strawberry coated with edible chitosan containing thyme essential oil. Mentha piperita essential oils which was encapsulated using chitosan–cinnamic acid nanogel was previously applied for coating of fruit. It was reported that the edible coating containing nanocapsule at the level of 500 ppm effectively inhibited A. flavus growth in addition to prevent the loss of water during storage as the common function of edible coating [73]. Another research group showed that edible coatings enriched with zein-nanofiber containing the essential oils derived from bay leaf and rosemary effectively suppressed L. monocytogenes and S. aureus in cheese slices. The microbial activity was associated with the presence of 1,8 cineole [74]. Mackerel fish was also efficiently preserved by using chitosan film incorporated with Garcinia atroviridis extract as Garcinia atroviridis extract exhibited anti-microbial activity particularly against Pseudomonas aeruginosa, B. subtilis and S. aureus [75]. This result was supported by the finding obtained by Wai et al. [76] who preserve squids with chitosan edible films incorporated with musk lime extracts. Rice with prolonged shelf-life was reported by the research group of Das et al. [77] after the incorporation of chitosan nano biopolymer containing coriander (Coriandrum sativum) essential oil. This is because the nano biopolymer exhibited antifungal activity as well antioxidant activity.

5. Concluding remarks and future perspectives

The incorporation of herbs and spices in food at the level of giving a substantial effect in terms of antimicrobial and antioxidant activity as well as health benefit may alter the characteristic of food, and hence reduce the consumer acceptance. For this reason, encapsulation of herb or spice extract, either in a sub-micro scale, is then widely carried out by the scientists. To fabricate nanocapsules, several techniques have been successfully developed, including ionic gelation, green synthesis, anti-solvent precipitation, coacervation and inclusion complexation. Also, different wall materials are available for the making of nanocapsules. Therefore, the selection of the methods and materials must consider the suitability among the characteristic of the herb and spice extracts, the wall materials and the methods. The extracts of herb and spice can be incorporated into nanocapsules, either in the form of crude extracts or a pure compound. Encapsulating crude extract, however, is more challenging as it consists of a wide spectrum of bioactive compounds in which each compound has different properties. Particle size, encapsulation efficiency and stability are some of important quality parameters of nanocapsules that must be taken into consideration during nanocapsule fabrication. Therefore, there are still a big opportunity to conduct research in the area of nanocapsule development, particularly by employing different methods, herb and spice-based bioactive compounds as well as wall materials. The study can be expanded further into the application of the nanocapsules in a food system, including as anti-microbial and antioxidant agent. This study clearly shows a new trend in using herb and spice in food, and thus create a new paradigm for future studies.

Conflict of Interest

The authors declare that they have no conflict of interest.

Acknowledgments

The authors thank Universitas Sebelas Maret for supporting this research through the grant of Dana NON-APBN in the scheme of Penelitian Unggulan Terapan (Adendum - No. 2550/UN27.22/PT.01.03/2022).

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