## 1 Introduction  
Recently, the Flavor and Extract Manufacturers Association (FEMA) started to review the safety of more than 250 naturally occurring flavor complexes (NFCs) currently utilized in food industry. In this review, 23 NFCs have been confirmed as generally recognized as safe (GRAS) when they are used as flavor ingredients in accordance with the examination of each NFC on the basis of the view of threshold of toxicological apprehensiveness [1]. Among the 23 NFCs, highly produced oils such as castor oil (6690 kg), lemongrass oil (3980 kg), and citronella oil (1830 kg) are included in the GRAS-affirmed list; moreover, the lowest produced, NFC massoa oil (MO, 0.4 kg), is also in the list [1]. However, this review has not considered the safety of other purposed uses as dietary supplements or other ingestible preparations. Furthermore, more scientific information to properly determine NFC's toxicity is necessary to understand the role of NFC in epigenetic modifications rather than genotoxic changes in humans or other mammals. This is because the evaluation process of toxicity includes the steps to find the exposure routes and possible toxicity of the recognized components [1; 2; 3]. MO is derived from the bark of _Massoa aromatica_ (Becc, Lauraceae), which is native to Indonesia, Papua New Guinea, and Australia. MO possesses anti-_Candida_ properties toward _Candida albicans_ with 0.074% (\(v/v\)) of IC\({}_{50}\)[4] and an antiaflatoxicien effect on _Aspergillus flavus_ at the 0.5 ppm level [5]. These biological activities are derived from the main component of MO, known as C10 massoa lactone (C10), as it inhibits the hyphal formation and hyphal growth of _C. albicans_ as well as the mycelian growth of _A. flavus_[4; 5]. C10 has been quantitatively determined using a chromatographic analysis such as gas chromatography-mass spectrometry (GC-MS), accounting for over 40% of the total components in MO [5]. The antifungal activities of other main lactones such as C12 massoia lactone (36.7%) and C14 massoia lactone (1.4%) were excluded from this study because researchers can hardly obtain these compounds as they are commercially not available. Moreover, in inhibiting the growth of 21 plant pathogens, C10 decreased ergosterol formation, which is an important component of fungal cell structure with an increasing amount of reactive oxygen species in fungal cells [6]. On the contrary, C10 and C12 were isolated from MO, and C10 showed larvicidal activities on _Aedes albopictus_ with 100% mortality at a treatment level of 50 ppm, whereas C12 showed 100% lethal effect on the mosquito larvae at a treatment level of 25 ppm [7]. According to [7], C10 was the major lactone in MO as it reached 79.97% as analyzed by GC-MS. The developmental toxicity of various chemicals has been assessed using zebrafish as they are easy to study because of the transparency of their eggs, high similarity with human genomes, formation of all organs, and large numbers of offsprings after mating [8; 9]. To evaluate the developmental toxicity, the transgenic lines of zebrafish can be used to understand the phenomenal modification on organ development, including the heart, liver, brain, and blood vessels with blood flow [10; 11; 12]. Recently, piperlongumine as one of potential anticancer drug caused severe inhibition on heart and liver development of zebrafish embryos, although its efficacy to control cancer cells has been well reported [13; 14]. Therefore, we believe that preclinical examination using zebrafish embryos can bridge the gap between in vitro to in vivo tests, and studies such as ours provide more useful information when a scientific panel decides to use some natural products as GRAS in food industries [15]. In this study, C10 was used to evaluate its developmental toxicity on zebrafish embryos. First, acute toxicities were determined with the two endpoints as lethal effects hatching rates of C10-treated zebrafish embryo groups.