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Lemon Myrtle (Backhousia citriodora) Oils
Chapter 59
Lemon Myrtle (Backhousia citriodora) Oils Yasmina Sultanbawa The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation (QAAFI), Brisbane, QLD, Australia
INTRODUCTION Lemon myrtle leaves are used in food applications as a fresh or dried herb, while the essential oil (EO) is used as food flavoring because of its distinct aroma and flavor. In 1889, Joseph H. Maiden reported on the potential use of lemon myrtle for commercial production and a German company, Schimmel & Co., was the first to identify citral as an active component (Robbins, 2008). Citral is a major chemical component in the leaf and also the EO. Citral derives its name from Backhousia citriodora F. Muell from where it was originally extracted and isolated, and is responsible for the characteristic lemon flavor (Southwell et al., 2000). Lemon myrtle EO has over 90% citral, compared with the other lemon-flavored EOs, such as citrus (3–10%), lemon grass (75%), and tropical verbena (74%) (Robbins, 2008). Lemon myrtle has also been used in herbal teas which have been gaining popularity in western countries, with a major market in the United States followed by Europe. Lemon myrtle teas are available as pure or blended samples and the antioxidant properties are comparable to the black teas from Camellia sinensis (Chan et al., 2010). Lemon myrtle is one of the most cultivated and commercially mature species in the native food industry in Australia (Clarke, 2012). This chapter reviews the application of lemon myrtle essential oil in food and its general usage, botanical aspects, and chemical properties (Figure 1).
BOTANICAL ASPECTS The plant genus Backhousia is endemic to Australia and belongs to the family Myrtaceae. The most common chemotype, B. citriodora F. Muell, is also known as lemon-scented myrtle, lemon ironwood, and sweet verbena tree. It is a large shrub to medium-sized tree endemic to rainforest areas of coastal Queensland between Brisbane to Cairns and is a very aromatic plant (Taylor, 1996). It is a perennial tree crop and typically planted in rows. The leaves contain about 95% citral, which gives the characteristic lemon flavor and the flowers and seeds also have lemon flavors (Ahmed and Johnson, 2000). Horticultural development has progressed through the years with the selection of clones for growth with potential for high citral and oil capacity. There are two main commercial clones being planted: the line commonly referred to as Limpinwood shows superior ornamental presentation, high biomass, high oil yield, and citral content; and the variety commonly referred to as Line B or Eudlo clone is slightly lower in biomass, oil yield, and citral content (Robbins, 2008). In Australia, lemon myrtle can be harvested all year round; however, harvesting during the monsoonal rainy periods may be restricted in Northern Queensland. This species exists in two chemical forms: a variety characterized by an essential oil with a high content of citral, and a variety characterized by an essential oil rich in laevo-citronellal, which is rare. The leaves contain 1.1–3.2% oil. The citral chemotype, is the most common one used in food, cosmetics, personal care, and aromatherapy, and is grown commercially in Queensland as well as the Lismore area of northern New South Wales (Lassak, 2012; Brophy et al., 1995).
USAGE AND APPLICATIONS Lemon myrtle is an Australian native herb and is used as the dried and milled product or steam distilled to obtain lemon myrtle essential oil (Clarke, 2012). The indigenous Australians have used lemon myrtle traditionally for cooking and healing purposes. In Europe too, lemon myrtle is becoming popular both for use in cuisine and phytotherapy (Horn et al., 2012). The aroma and flavor of the lemon myrtle as a dried milled leaf has been described as the aroma of lemon candy, perfumed with some menthol notes. The flavor is strong lemon with some sweetness and cooling on the palate (Smyth et al., 2012). Since the mid-1990s, the essential oils, foliage, flowers, and seeds of lemon myrtle have been used widely Essential Oils in Food Preservation, Flavor and Safety. http://dx.doi.org/10.1016/B978-0-12-416641-7.00059-6 Copyright © 2016 Elsevier Inc. All rights reserved.
517
518 PART | II Named Essential Oils
FIGURE 1 Lemon myrtle shrubs (picture kindly provided by Australian Rainforest Products).
as ingredients in perfumes, food flavorings, herbal teas, and personal care products such as soaps, creams, shampoos, and conditioners (Taylor, 1996; Clarke, 2012). The antimicrobial activity of lemon myrtle has also been used in the treatment of certain diseases such as molluscum contagiosum in children, which is a common contagious viral disease affecting children globally, a 10% (v/v) solution of lemon myrtle EO as a topical application has shown a reduction of greater than 90% in the number of lesions in children (Burke et al., 2004). Lemon myrtle EO has also been effective in inhibiting methicillinresistant Staphylococcus aureus, which has been identified as a multidrug-resistant bacterium (Chao et al., 2008) and also shown very good antifungal activity, indicating the potential of using this EO as an antiseptic (Wilkinson et al., 2003).
USAGE AND APPLICATIONS IN FOOD SCIENCE For essential oil production from B. citriodora, specialized machines cut the stems and leaves into smaller particle sizes. The cut leaves are placed in stainless steel bins and then steam distilled to obtain the essential oil, which predominantly contains citral (3,7-dimethyl-2-7-octadienal) with two main isomeric aldehydes: neral and geranial. The essential oil is stored in stainless steel or glass containers and not in plastic as the EO is very corrosive to this material (Robbins, 2008). Lemon myrtle is used as a dried herb, flavoring agent, and herbal tea in Australia and is approved in the European Union under the novel food category. Food products to be approved under this category must be excluded from potential health risks and thorough testing of these plants and their parts in food preparations is a prerequisite (Horn et al., 2012). The chemical composition of the lemon myrtle EO is given in Table 1 (Hayes and Markovic, 2002; Southwell et al., 2000; Brophy et al., 1995), the physical properties assessed were relative density (0.888–0.910), refractive index (1.4853–1.4909), and optical rotation (−1.5° to + 0.4°) (Southwell et al., 2000).
ANTIMICROBIAL PROPERTIES The antimicrobial activity of B. citriodora EO is believed to be directly related to the high citral content (Lis-Balchin et al., 1998); however, the importance of other minor components such as linalool, citronellal, and β-myrcene in combination with citral for enhanced antimicrobial activity has also been reported. A study by Sultanbawa et al. (2009) revealed complete inhibition of Escherichia coli at 0.313% and S. aureus at 0.156% when evaluated against lemon myrtle EO; however, the levels of citral alone required to completely inhibit E. coli and S. aureus were 2.5% and 0.625%, respectively. The higher levels of citral on its own, compared with lemon myrtle EO suggests an enhanced antibacterial activity with the EO possibly due to synergies between the major and minor chemical components. A study on four lemon myrtle EOs with citral contents between 93% and 98% were evaluated for antibacterial and antifungal activity against 21 organisms. This study in general reported that antimicrobial activity of lemon myrtle EO was greater than citral alone. In addition, the EO was an effective antibacterial agent and an excellent antifungal agent. This indicates the potential of using lemon
Lemon Myrtle (Backhousia citriodora) Oils Chapter | 59 519
TABLE 1 Chemical Composition of the Essential Oil of Lemon Myrtle Component
Percentage
β-Myrcene
0.1–0.7
6-methyl-5-Hepten-2-one
0.1–2.5
(±)Linalool
0.3–1.0
Citronellal
0.1–0.9
Iso-neral (Cis-iso citral)
0.6–2.7
Iso-geranial (Trans-iso citral)
1.0–4.2
Neral (citral A)
32.0–40.9
Geranial (citral B)
46.1–60.7
Trans-geraniol
0.4–0.7
myrtle EO as a surface disinfectant and as a natural preservative in the food industry (Wilkinson et al., 2003). The shelflife of barramundi fillets was extended when treated with both the oregano and a mix of oregano and lemon myrtle EO compared with the controls. Based on microbiological data, the shelf-life of barramundi fillets during vacuum storage was 10–12 days. Dipping in antimicrobial solutions of 0.1% (v/w) of oregano and a mixture of 0.05% oregano (v/w) + lemon myrtle 0.025% (v/w) extended the shelf-life of the fish fillets by an additional 4 days. This study also indicates the potential of reducing the concentration of essential oils used by developing blends that have synergies (Sultanbawa et al., 2012). One of the challenges of using EO as natural preservatives is the strong flavor it can impart to the food, and if the concentration can be reduced by blending then it becomes more attractive to use as a natural antimicrobial in food applications. The effectiveness of lemon myrtle against postharvest fungal diseases in nectarines has been reported. The essential oils, lemon myrtle (B. citriodora), cinnamon bark (Cinnamomum zeylanicum), oregano (Origanum vulgare), thyme oil (Thymus vulgaris), clove bud (Eugenia caryophyllata), valerian (Valeriana officinalis), and Australian tea tree oil (Melaleuca alternifolia) in controlling brown rot caused by the fungus Monilinia fructicola in nectarines was evaluated. This study revealed lemon myrtle essential oil as the most potent fumigant to control the mycelium growth and spore germination (Lazar-Baker et al., 2011). Clostridium perfringens is the causative agent of necrotic enteritis in poultry. Economic production of poultry meat with intensive growing techniques is threatened by bacteria showing multiple resistances to antibiotics compounded by the restriction in the European Union of in-feed use of antibiotic growth promoters. This has resulted in the increase of necrotic enteritis and the search for natural alternatives to reduce gut colonization of C. perfringens. Use of four essential oils, lemon myrtle (B. citriodora), eucalyptus oil (Eucalyptus citriodora), lemon tea tree oil (Leptospermum petersonii), tea tree oil (M. alternifolia), and other secondary plant metabolites have indicated that the fermentative activity of C. perfringens is inhibited by all essential oils tested with the most effective being lemon myrtle with a minimum inhibitory concentration of 0.05%. This indicates the possibility of using lemon myrtle EO as a feed additive in poultry to control the gut colonization of this pathogen (Zrustova et al., 2006).
FLAVORING AGENT Lemon myrtle EO in Australia is used as a source of lemon flavoring in the food and beverage industries. A study of the sensory properties of lemon myrtle EO assessed the main contributing compounds to the lemon and sweet aromas of lemon myrtle to be neral and geranial, citronellal, and linalool (Forbes-Smith and Paton, 2002). Lemon myrtle EO is used as a lemon flavor replacement in milk-based products, such as cheesecake or ice cream to prevent curdling associated with the acidity of lemon fruits (Horn et al., 2012). However, like other essential oils lemon myrtle is sensitive to light and oxygen and this can affect the shelf-life and limits its application in the food industry (Buchaillot et al., 2009). To stabilize the EO, encapsulation by spray drying to powder form has been reported by The Vien et al. (2008). In this study, the optimized microencapsulated blend contained 18% of the essential oil. The benefit of such powders is the solubility in aqueous phase which is an advantage when used as a flavoring agent in food applications. These encapsulated flavors can also be used in shortbread, pasta, and macadamia and vegetable oils (Horn et al., 2012). Lemon myrtle has been used as a herb in speciality
520 PART | II Named Essential Oils
cheeses in Australia; these cheeses are semihard, vacuum packed, and are matured for less than 3 months. This market is growing as the consumer is looking for new flavors (Agboola and Radovanovic-Tesic, 2002).
SAFETY OF LEMON MYRTLE ESSENTIAL OILS Lemon myrtle essential oil has a high content of the aldehyde, citral (>90%), which is known to be a potential skin sensitizer; however, the risk is relatively low (Pengelly, 2003). A study by Hayes and Markovic (2002), where an in vitro toxicity test was performed based on the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, or MTT, carried out cytotoxicity assay. This test revealed that products containing 1% lemon myrtle oil were found to be low in toxicity and could potentially be used in the formulation of topical antimicrobial products. There is a lemon myrtle EO standard for Australia, AS 4941 published in 2001, that is under revision to reflect the current commercial quality of the oil. Three aldehydes: caprylic aldehyde, pelargonic aldehyde, and caprinic aldehyde, that are not present in lemon myrtle essential oil, have been found in some of the lemon myrtle oils in the global market. In order to protect the Australian lemon myrtle EO and also to prevent adulteration the Australian standard is currently under revision. These three aldehydes must not be present in lemon myrtle EO and the range for geraniol is recommended to be amended to 0.6–2.5% (Lassak, 2012).
SUMMARY POINTS Leaves of lemon myrtle (Backhousia citriodora) are steam distilled for the production of the essential oil. Citral is the major chemical component contributing to the lemon flavor of the essential oil. l Lemon myrtle EO is used in the food and beverage industry globally as a flavoring agent. l It has broad spectrum antimicrobial activity and has the potential to be used as a natural food preservative. l Antifungal activity enables the application in postharvest disease management. l The characteristic lemon flavor in the EO can be used as a flavor in a wide range of food and beverage products. l l
REFERENCES Agboola, S.O., Radovanovic-Tesic, M., 2002. Influence of Australian native herbs on the maturation of vacuum-packed cheese. Leb. Wiss. Technol. 35, 575–583. Ahmed, A.K., Johnson, K.A., 2000. Turner review no. 3. Horticultural development of Australian native edible plants. Aust. J. Bot. 48, 417–426. Brophy, J.J., Goldsack, R.J., Fookes, C.J.R., Forster, P.I., 1995. Leaf oils of the genus Backhousia (Myrtaceae). J. Essent. Oil Res. 7, 237–254. Buchaillot, A., Caffin, N., Bhandari, B., 2009. Drying of lemon myrtle (Backhousia citriodora) leaves: retention of volatiles and color. Dry. Technol. 27, 445–450. Burke, B.E., Baillie, J.E., Olson, R.D., 2004. Essential oil of Australian lemon myrtle (Backhousia citriodora) in the treatment of molluscum contagiosum in children. Biomed. Pharmacother. 58, 245–247. Chan, E.W.C., Lim, Y.Y., Chong, K.L., Tan, J.B.L., Wong, S.K., 2010. Antioxidant properties of tropical and temperate herbal teas. J. Food Compos. Anal. 23, 185–189. Chao, S., Young, G., Oberg, C., Nakaoka, K., 2008. Inhibition of methicillin-resistant Staphylococcus aureus (MRSA) by essential oils. Flavor Fragr. J. 23, 444–449. Clarke, M., 2012. Australian Native Food Industry Stocktake. RIRDC Publication No. 12/066. Union Offset Printing, Canberra, Australia. Forbes-Smith, M., Paton, J.E., 2002. Innovative Products from Australian Native Foods. RIRDC Publication No. 02/109. Union Offset Printing, Canberra, Australia. Hayes, A.J., Markovic, B., 2002. Toxicity of Australian essential oil Backhousia citriodora (Lemon myrtle). Part 1. Antimicrobial activity and in vitro cytotoxicity. Food Chem. Toxicol. 40, 535–543. Horn, T., Barth, A., Ruehle, M., Haeser, A., Juerges, G., Nick, P., 2012. Molecular diagnostics of Lemon Myrtle (Backhousia citriodora versus Leptospermum citratum). Eur. Food Res. Technol. 234, 853–861. Lassak, E., 2012. Revision of Backhousia citriodora Essential Oil Standard. R. I. R. D. C. Publication No. 11/37. Union Offset Printing, Canberra, Australia. Lazar-Baker, E.E., Hetherington, S.D., Ku, V.V., Newman, S.M., 2011. Evaluation of commercial essential oil samples on the growth of postharvest pathogen Monilinia fructicola (G. Winter) Honey. Lett. Appl. Microbiol. 52, 227–232. Lis-Balchin, M., Deans, S.G., Eaglesham, E., 1998. Relationship between bioactivity and chemical composition of commercial essential oils. Flavor Fragr. J. 13, 98–104. Pengelly, A., 2003. Antimicrobial activity of lemon myrtle and tea tree oils. Aust. J. Med. Herbal. 15, 11–19. Robbins, J., 2008. The New Crop Industries Handbook—Native Foods. R. I. R. D. C. Publication No. 08/021. Union Offset Printing, Canberra, Australia. Smyth, H.E., Sanderson, J.E., Sultanbawa, Y., 2012. Lexicon for the sensory description of australian native plant foods and ingredients. J. Sens. Stud. 27, 471–481.
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Southwell, I.A., Russell, M., Smith, R.L., Archer, D.W., 2000. Backhousia citriodora F. Muell. (Myrtaceae), a superior source of citral. J. Essent. Oil Res. 12, 735–741. Sultanbawa, Y., Currie, M., Cusack, A., Mayze, J., Slattery, S., 2012. Potential of using oregano and lemon myrtle essential oils to extend the shelf-life of fish fillets. In: Seventh Dubai International Food Safety Conference and IAFP’s first Middle East Food Safety Symposium, 21–22 February, Dubai. Sultanbawa, Y., Cusack, A., Currie, M., Davis, C., 2009. An innovative microplate assay to facilitate the detection of antimicrobial activity in plant extracts. J. Rapid Methods Autom. Microbiol. 17, 519–534. Taylor, R., 1996. Lemon myrtle, the essential oil. Rural. Res. 18–19. The Vien, H., Caffin, N., Dykes, G.A., Bhandari, B., 2008. Optimization of the m icroencapsulation of lemon myrtle oil using response surface methodology. Dry. Technol. 26, 357–368. Wilkinson, J.M., Hipwell, M., Ryan, T., Cavanagh, H.M.A., 2003. Bioactivity of Backhousia citriodora: antibacterial and antifungal activity. J. Agric. Food Chem. 51, 76–81. Zrustova, J., Mares, P., Brooker, J.D., 2006. Secondary plant metabolites to control growth of Clostridium perfringens from chickens. Br. Poult. Abstr. 2, 26–27.
Lemon Myrtle (Backhousia citriodora) Oils Yasmina Sultanbawa The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation (QAAFI), Brisbane, QLD, Australia
INTRODUCTION Lemon myrtle leaves are used in food applications as a fresh or dried herb, while the essential oil (EO) is used as food flavoring because of its distinct aroma and flavor. In 1889, Joseph H. Maiden reported on the potential use of lemon myrtle for commercial production and a German company, Schimmel & Co., was the first to identify citral as an active component (Robbins, 2008). Citral is a major chemical component in the leaf and also the EO. Citral derives its name from Backhousia citriodora F. Muell from where it was originally extracted and isolated, and is responsible for the characteristic lemon flavor (Southwell et al., 2000). Lemon myrtle EO has over 90% citral, compared with the other lemon-flavored EOs, such as citrus (3–10%), lemon grass (75%), and tropical verbena (74%) (Robbins, 2008). Lemon myrtle has also been used in herbal teas which have been gaining popularity in western countries, with a major market in the United States followed by Europe. Lemon myrtle teas are available as pure or blended samples and the antioxidant properties are comparable to the black teas from Camellia sinensis (Chan et al., 2010). Lemon myrtle is one of the most cultivated and commercially mature species in the native food industry in Australia (Clarke, 2012). This chapter reviews the application of lemon myrtle essential oil in food and its general usage, botanical aspects, and chemical properties (Figure 1).
BOTANICAL ASPECTS The plant genus Backhousia is endemic to Australia and belongs to the family Myrtaceae. The most common chemotype, B. citriodora F. Muell, is also known as lemon-scented myrtle, lemon ironwood, and sweet verbena tree. It is a large shrub to medium-sized tree endemic to rainforest areas of coastal Queensland between Brisbane to Cairns and is a very aromatic plant (Taylor, 1996). It is a perennial tree crop and typically planted in rows. The leaves contain about 95% citral, which gives the characteristic lemon flavor and the flowers and seeds also have lemon flavors (Ahmed and Johnson, 2000). Horticultural development has progressed through the years with the selection of clones for growth with potential for high citral and oil capacity. There are two main commercial clones being planted: the line commonly referred to as Limpinwood shows superior ornamental presentation, high biomass, high oil yield, and citral content; and the variety commonly referred to as Line B or Eudlo clone is slightly lower in biomass, oil yield, and citral content (Robbins, 2008). In Australia, lemon myrtle can be harvested all year round; however, harvesting during the monsoonal rainy periods may be restricted in Northern Queensland. This species exists in two chemical forms: a variety characterized by an essential oil with a high content of citral, and a variety characterized by an essential oil rich in laevo-citronellal, which is rare. The leaves contain 1.1–3.2% oil. The citral chemotype, is the most common one used in food, cosmetics, personal care, and aromatherapy, and is grown commercially in Queensland as well as the Lismore area of northern New South Wales (Lassak, 2012; Brophy et al., 1995).
USAGE AND APPLICATIONS Lemon myrtle is an Australian native herb and is used as the dried and milled product or steam distilled to obtain lemon myrtle essential oil (Clarke, 2012). The indigenous Australians have used lemon myrtle traditionally for cooking and healing purposes. In Europe too, lemon myrtle is becoming popular both for use in cuisine and phytotherapy (Horn et al., 2012). The aroma and flavor of the lemon myrtle as a dried milled leaf has been described as the aroma of lemon candy, perfumed with some menthol notes. The flavor is strong lemon with some sweetness and cooling on the palate (Smyth et al., 2012). Since the mid-1990s, the essential oils, foliage, flowers, and seeds of lemon myrtle have been used widely Essential Oils in Food Preservation, Flavor and Safety. http://dx.doi.org/10.1016/B978-0-12-416641-7.00059-6 Copyright © 2016 Elsevier Inc. All rights reserved.
517
518 PART | II Named Essential Oils
FIGURE 1 Lemon myrtle shrubs (picture kindly provided by Australian Rainforest Products).
as ingredients in perfumes, food flavorings, herbal teas, and personal care products such as soaps, creams, shampoos, and conditioners (Taylor, 1996; Clarke, 2012). The antimicrobial activity of lemon myrtle has also been used in the treatment of certain diseases such as molluscum contagiosum in children, which is a common contagious viral disease affecting children globally, a 10% (v/v) solution of lemon myrtle EO as a topical application has shown a reduction of greater than 90% in the number of lesions in children (Burke et al., 2004). Lemon myrtle EO has also been effective in inhibiting methicillinresistant Staphylococcus aureus, which has been identified as a multidrug-resistant bacterium (Chao et al., 2008) and also shown very good antifungal activity, indicating the potential of using this EO as an antiseptic (Wilkinson et al., 2003).
USAGE AND APPLICATIONS IN FOOD SCIENCE For essential oil production from B. citriodora, specialized machines cut the stems and leaves into smaller particle sizes. The cut leaves are placed in stainless steel bins and then steam distilled to obtain the essential oil, which predominantly contains citral (3,7-dimethyl-2-7-octadienal) with two main isomeric aldehydes: neral and geranial. The essential oil is stored in stainless steel or glass containers and not in plastic as the EO is very corrosive to this material (Robbins, 2008). Lemon myrtle is used as a dried herb, flavoring agent, and herbal tea in Australia and is approved in the European Union under the novel food category. Food products to be approved under this category must be excluded from potential health risks and thorough testing of these plants and their parts in food preparations is a prerequisite (Horn et al., 2012). The chemical composition of the lemon myrtle EO is given in Table 1 (Hayes and Markovic, 2002; Southwell et al., 2000; Brophy et al., 1995), the physical properties assessed were relative density (0.888–0.910), refractive index (1.4853–1.4909), and optical rotation (−1.5° to + 0.4°) (Southwell et al., 2000).
ANTIMICROBIAL PROPERTIES The antimicrobial activity of B. citriodora EO is believed to be directly related to the high citral content (Lis-Balchin et al., 1998); however, the importance of other minor components such as linalool, citronellal, and β-myrcene in combination with citral for enhanced antimicrobial activity has also been reported. A study by Sultanbawa et al. (2009) revealed complete inhibition of Escherichia coli at 0.313% and S. aureus at 0.156% when evaluated against lemon myrtle EO; however, the levels of citral alone required to completely inhibit E. coli and S. aureus were 2.5% and 0.625%, respectively. The higher levels of citral on its own, compared with lemon myrtle EO suggests an enhanced antibacterial activity with the EO possibly due to synergies between the major and minor chemical components. A study on four lemon myrtle EOs with citral contents between 93% and 98% were evaluated for antibacterial and antifungal activity against 21 organisms. This study in general reported that antimicrobial activity of lemon myrtle EO was greater than citral alone. In addition, the EO was an effective antibacterial agent and an excellent antifungal agent. This indicates the potential of using lemon
Lemon Myrtle (Backhousia citriodora) Oils Chapter | 59 519
TABLE 1 Chemical Composition of the Essential Oil of Lemon Myrtle Component
Percentage
β-Myrcene
0.1–0.7
6-methyl-5-Hepten-2-one
0.1–2.5
(±)Linalool
0.3–1.0
Citronellal
0.1–0.9
Iso-neral (Cis-iso citral)
0.6–2.7
Iso-geranial (Trans-iso citral)
1.0–4.2
Neral (citral A)
32.0–40.9
Geranial (citral B)
46.1–60.7
Trans-geraniol
0.4–0.7
myrtle EO as a surface disinfectant and as a natural preservative in the food industry (Wilkinson et al., 2003). The shelflife of barramundi fillets was extended when treated with both the oregano and a mix of oregano and lemon myrtle EO compared with the controls. Based on microbiological data, the shelf-life of barramundi fillets during vacuum storage was 10–12 days. Dipping in antimicrobial solutions of 0.1% (v/w) of oregano and a mixture of 0.05% oregano (v/w) + lemon myrtle 0.025% (v/w) extended the shelf-life of the fish fillets by an additional 4 days. This study also indicates the potential of reducing the concentration of essential oils used by developing blends that have synergies (Sultanbawa et al., 2012). One of the challenges of using EO as natural preservatives is the strong flavor it can impart to the food, and if the concentration can be reduced by blending then it becomes more attractive to use as a natural antimicrobial in food applications. The effectiveness of lemon myrtle against postharvest fungal diseases in nectarines has been reported. The essential oils, lemon myrtle (B. citriodora), cinnamon bark (Cinnamomum zeylanicum), oregano (Origanum vulgare), thyme oil (Thymus vulgaris), clove bud (Eugenia caryophyllata), valerian (Valeriana officinalis), and Australian tea tree oil (Melaleuca alternifolia) in controlling brown rot caused by the fungus Monilinia fructicola in nectarines was evaluated. This study revealed lemon myrtle essential oil as the most potent fumigant to control the mycelium growth and spore germination (Lazar-Baker et al., 2011). Clostridium perfringens is the causative agent of necrotic enteritis in poultry. Economic production of poultry meat with intensive growing techniques is threatened by bacteria showing multiple resistances to antibiotics compounded by the restriction in the European Union of in-feed use of antibiotic growth promoters. This has resulted in the increase of necrotic enteritis and the search for natural alternatives to reduce gut colonization of C. perfringens. Use of four essential oils, lemon myrtle (B. citriodora), eucalyptus oil (Eucalyptus citriodora), lemon tea tree oil (Leptospermum petersonii), tea tree oil (M. alternifolia), and other secondary plant metabolites have indicated that the fermentative activity of C. perfringens is inhibited by all essential oils tested with the most effective being lemon myrtle with a minimum inhibitory concentration of 0.05%. This indicates the possibility of using lemon myrtle EO as a feed additive in poultry to control the gut colonization of this pathogen (Zrustova et al., 2006).
FLAVORING AGENT Lemon myrtle EO in Australia is used as a source of lemon flavoring in the food and beverage industries. A study of the sensory properties of lemon myrtle EO assessed the main contributing compounds to the lemon and sweet aromas of lemon myrtle to be neral and geranial, citronellal, and linalool (Forbes-Smith and Paton, 2002). Lemon myrtle EO is used as a lemon flavor replacement in milk-based products, such as cheesecake or ice cream to prevent curdling associated with the acidity of lemon fruits (Horn et al., 2012). However, like other essential oils lemon myrtle is sensitive to light and oxygen and this can affect the shelf-life and limits its application in the food industry (Buchaillot et al., 2009). To stabilize the EO, encapsulation by spray drying to powder form has been reported by The Vien et al. (2008). In this study, the optimized microencapsulated blend contained 18% of the essential oil. The benefit of such powders is the solubility in aqueous phase which is an advantage when used as a flavoring agent in food applications. These encapsulated flavors can also be used in shortbread, pasta, and macadamia and vegetable oils (Horn et al., 2012). Lemon myrtle has been used as a herb in speciality
520 PART | II Named Essential Oils
cheeses in Australia; these cheeses are semihard, vacuum packed, and are matured for less than 3 months. This market is growing as the consumer is looking for new flavors (Agboola and Radovanovic-Tesic, 2002).
SAFETY OF LEMON MYRTLE ESSENTIAL OILS Lemon myrtle essential oil has a high content of the aldehyde, citral (>90%), which is known to be a potential skin sensitizer; however, the risk is relatively low (Pengelly, 2003). A study by Hayes and Markovic (2002), where an in vitro toxicity test was performed based on the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, or MTT, carried out cytotoxicity assay. This test revealed that products containing 1% lemon myrtle oil were found to be low in toxicity and could potentially be used in the formulation of topical antimicrobial products. There is a lemon myrtle EO standard for Australia, AS 4941 published in 2001, that is under revision to reflect the current commercial quality of the oil. Three aldehydes: caprylic aldehyde, pelargonic aldehyde, and caprinic aldehyde, that are not present in lemon myrtle essential oil, have been found in some of the lemon myrtle oils in the global market. In order to protect the Australian lemon myrtle EO and also to prevent adulteration the Australian standard is currently under revision. These three aldehydes must not be present in lemon myrtle EO and the range for geraniol is recommended to be amended to 0.6–2.5% (Lassak, 2012).
SUMMARY POINTS Leaves of lemon myrtle (Backhousia citriodora) are steam distilled for the production of the essential oil. Citral is the major chemical component contributing to the lemon flavor of the essential oil. l Lemon myrtle EO is used in the food and beverage industry globally as a flavoring agent. l It has broad spectrum antimicrobial activity and has the potential to be used as a natural food preservative. l Antifungal activity enables the application in postharvest disease management. l The characteristic lemon flavor in the EO can be used as a flavor in a wide range of food and beverage products. l l
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