Physico-chemical characterization and evaluation of bio-efficacies of black pepper essential oil encapsulated in hydroxypropyl-beta-cyclodextrin
Graphical abstract
Introduction
Black pepper (Piper nigrum L.) is considered the king of spices because of its pungent of piperine (Srinivasan, 2007). It can be used for different purposes such as medicine, human dietaries, preservatives and biocontrol agents (Awen et al., 2010, Hussain et al., 2011, Srinivasan, 2007). It has been already reported that essential oil from black pepper possesses antioxidant (Singh, Marimuthu, Catalan, & de Lampasona, 2004) and antimicrobial activities (Dorman & Deans, 2000). Black pepper oil is basically composed of terpenes which have been found to be β-caryophyllene, limonene, δ-3-carene and pinene (Menon et al., 2003, Singh et al., 2004). The major component of black pepper oil was found to be β-caryophyllene (Menon et al., 2003, Singh et al., 2004). Nevertheless, some active compounds in essential oils are sensitive towards the chemical modification under effect of some external factors such as: temperature, light, oxygen etc. (Dima et al., 2014). Besides, to apply with food products, an extremely low flavor threshold of essential oils can drastically change the sensory properties of foods, and highly water insoluble may have limited contact with pathogens (Kalemba & Kunicka, 2003).
The use of cyclodextrins for the essential oils encapsulation can protect the active compounds of essential oils from environmental conditions (Hedges, Shieh, & Sikorski, 1995, pp. 60–73; Qi & Hedges, 1997, pp. 231–243) and improve the aqueous solubility of essential oils for increasing their capacity to functionalize the products in which it is used as additive (Helena & Cabral, 2010). Cyclodextrin (CD) are cyclic oligosaccharides consisting of glucopyranosyl units linked by α-(1,4) bonds (Schmann & Schollmeyer, 2002). The widely used natural cyclodextrins are α-, β- and γ-cyclodextrin consisting of 6, 7 and 8 glucopyranose units, respectively. The cyclodextrin molecules have a unique structure with a hydrophobic cavity and a hydrophilic surface which can form inclusion complex with a wide variety of guests. Among those cyclodextrins, β-cyclodextrin is the most widely applicable kind because of its suitable cavity size for common guests with molecular weights between 200 and 800 g/mol and its availability and reasonable price (Waleczek, Marques, Hempel, & Schmidt, 2003). In some cases, there is a need to enhance water solubility of β-cyclodextrin by adding the hydroxyalkyl groups on the β-cyclodextrin surface. A hydroxyalkylated or hydroxypropyl-β-cyclodextrin derivative (HPβCD) is relatively high aqueous solubility with low toxicity and satisfactory inclusion ability (Garnero, Zoppi, Genovese, & Longhi, 2010).
The purpose of this study was to characterize the physico-chemical properties and bio-efficacies, antioxidant and antibacterial activities, of the encapsulated black pepper essential oil in hydroxypropyl-β-cyclodextrin (HPβCD).
Section snippets
Microorganisms
The indicator bacteria used for testing antimicrobial activity were Staphylococcus aureus (representative for gram-positive bacteria) and Escherichia coli (representative for gram-negative bacteria). These strains were provided from the Microorganisms Collection of Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Thailand. The indicator bacteria were cultivated in Tryptic Soy Broth (TSB) and incubated at 37 °C with shaking at 200 rpm for 24 h. All
Encapsulation of black pepper essential oil
Black pepper oil was encapsulated in HPβCD through inclusion complex formation. The inclusion complex was prepared via the freeze-drying method (Karathanos, Mourtzinos, Yannakopoulou, & Andrikopoulos, 2007). The 0.5 g of black pepper oil was slowly added to an aqueous solution of hydroxypropyl-β-cyclodextrin (HPβCD) (5 g of HPβCD in 25 mL of water). The mixture was left in a sealed container under stirring at room temperature (∼25 °C) and protected from the light for 24 h. The encapsulated
Encapsulation efficiency of black pepper oil
Encapsulation efficiencies of black pepper oil and its major component, β-caryophyllene, were evaluated and showed in Table 1. This difference in encapsulation efficiency of the pure compound and the black pepper oil would result from the presence of other components in the black pepper oil such as limonene, δ-3-carene and pinene (Singh et al., 2004) which have also high affinities for HPβCD. These components then competed with the major compounds for inclusion complex formation with the HPβCD.
Conclusions
The particle shape and morphology of the corresponding inclusion complex were similar to that of free HPβCD. Instead, the particle size of the free HPβCD was much larger than that of the encapsulated product by hydrogen bonding of the free HPβCD producing the cluster of HPβCD. The characteristic FT-IR and UV bands of the black pepper oil disappeared in the spectrum of the inclusion complex, since the oil entered the cavity of HPβCD. The difference in encapsulation efficiency of the pure
Acknowledgments
This work was financially supported by the Graduate School of Prince of Songkla University and Thai Government under Grant No. AGR560387S.
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