Natural benzaldehyde from Prunus persica (L.) Batsch

ABSTRACT

Benzaldehyde is one of the most important molecules in the flavour industry. Presently, most of its industrial requirement is met through synthetic route. In this research, leaf essential oil of Prunus persica (L.) Batsch. extracted in different seasons was analysed using GC-FID, GC-MS, and NMR (¹H and ¹³C) techniques. The oil was characterised by higher amounts of benzaldehyde (63.1%–98.3%). The yield of benzaldehyde was higher during rainy (0.45 g/100 g fresh leaves) and autumn (0.44 g/100 g fresh leaves) seasons. In conclusion, leaves of P. persica can be used as a natural source of benzaldehyde for flavour industry.

KEYWORDS:

• Prunus persica
• Rosaceae
• Leaves
• Essential oil
• Natural benzaldehyde

Introduction

In recent times, the consumer preferences for natural products have led to an increasing demand for natural food additives, such as vanillin, benzaldehyde, and β-phenyl ethyl alcohol.^[1] Based on consumption, benzaldehyde is the second most important molecule in the flavour industry. It is widely used in food flavour, beverage, and fragrance industries. However, most of the quantity of benzaldehyde comes from synthetic route. The annual world production of synthetic and natural benzaldehyde is 7000 tons and 100 tons, respectively.^[2] About 80% of natural benzaldehyde is obtained by retroaldol reaction of natural cinnamaldehyde, while the remaining amount is obtained from the kernels of the apricots, peaches, prunes, and bitter almonds by enzymatic hydrolysis, which also produces toxic HCN.^[1,2] The status ‘natural’ of benzaldehyde produced from retroaldol reaction is questionable as it involves the use of synthetic chemicals.^[1] The natural benzaldehyde is commonly used in baking as a flavour enhancer and also as a key ingredient in cherry and other natural fruit flavours.^[3]

Prunus persica (L.) Batsch.(Rosaceae), commonly known as peach, is a deciduous tree, commercially cultivated in various states in northern India, viz. Uttarakhand, Himachal Pradesh, Punjab, Haryana, and Uttar Pradesh, for its fruits.^[4] The fruits of the plant are consumed fresh or in the form of squash and processed products. In traditional medicine, it is used in the treatment of dysentery and diarrhoea,^[5] rheumatoid arthritis, and amenorrhea.^[6] However, the leaves of the plant are known to possess various pharmacological properties, for example, diuretic, laxative, astringent, febrifuge, parasiticide, demulcent, expectorant, and sedative.^[7] The fatty oil obtained from the kernel is used in the preparation of various cosmetics and pharmaceutical products.^[4] This oil is rich in unsaturated fatty acid, phenolic compounds, and nutrient-rich food oil.^[8] The plant is reported to have antioxidant,^[9] antiacetylcholinesterase,^[10] antiinflammatory,^[11,12] hypermenorrhea, dysmenorrhea, leiomyoma, infertility, antitumour promoter and antioketsu syndrome,^[13] anthelmintic, laxative, sedative, antimalarial, hepatoprotective, antiasthmatic, anticoagulant, antifungal, cholinomimetic, calcium antagonist,^[14] antimite,^[15] antibacterial,^[16] and antiallergic inflammatory properties.^[17] Moreover, various cyanogenic glycosides, glycerides, sterols, and fatty acids have been reported in this plant.^[8,18]

The essential oil compositions of various Prunus spp. have been studied previously from different countries,^[19–22] but no attempt has been made till date to characterise the leaf essential oil composition of P. persica from India. Therefore, in continuation of our research on the exploration of unexplored aromatic plants for sustainable industrial exploitation, here we are reporting leaf aroma profile of P. persica from India. In this research, leaf essential oil of P. persica was extracted round the year and subsequently analysed by GC-FID, GC-MS, ¹H-NMR, and ¹³C-NMR techniques.

Materials and methods

Plant material and isolation of essential oil

The fresh leaves of P. persica were collected during five different seasons, viz. spring, summer, rainy, autumn, and winter, from the foothill region (Subhash Nagar, Nainital) of Uttarakhand. The sampling site is located between at 29° N and 79.31° E, and at an altitude of 240 m above mean sea level, experiencing the subtropical, humid climate. The maximum temperature ranges between 35°C and 45°C and minimum between 2°C and 5°C. The plant material was authenticated at CSIR-CIMAP, Research Centre Pantnagar by one of the authors (AC). The freshly harvested leaves were subjected to hydrodistillation for 3 h in a Clevenger apparatus for extraction of the essential oil. The yield of essential oil (g/100 g) was determined on fresh weight basis. The oil samples were dried over anhydrous Na₂SO₄, filtered, and used for analyses.

GC-FID, GC-MS, and ¹H- NMR and ¹³C-NMR analyses

GC-FID and GC-MS analyses of the essential oil for the quantification and characterisation of the constituent were carried out according to a procedure described earlier.^[23] NMR spectra (¹H and ¹³C) of the sample were recorded on a Bruker Avance (500 MHz) spectrometer using CDCl₃ as a solvent and tetramethylsilane (TMS) as an internal standard. About 35 mg of the compound having purity >98.0% (GC-FID) was dissolved in CDCl₃, and the spectra were recorded.

Identification of essential oil constituent (Benzaldehyde)

Characterisation of the essential oil constituent was carried out on the basis of retention index (determined with reference to the homologous series of n-alkane, C₇-C₃₀), mass spectra library search, and by comparing the mass spectrum and the retention index with literature.^[24] The identity of major constituent of the essential oil, that is, benzaldehyde (RI: 955; MS, EI, 70 eV, m/z (rel. int.%): 106 (M⁺, C₇H₆O) (100), 105 (99), 77 (68), 51 (42), 50 (17) was further confirmed by ¹H-NMR and ¹³C-NMR data. ¹H-NMR (CDCl₃-TMS, 500 MHz) δ(ppm): 7.41 (2H, dd, aromatic), 7.52 (1H, t, aromatic), 7.79 (2H, d, aromatic), 9.85 (1H, CHO); ¹³C-NMR (CDCl₃-TMS, 125MHz) δ(ppm): 129.34 (CH/CH), 129.74 (CH/CH), 134.57 (CH), 136.09 (C), 192.87 (CHO); DEPT-45, 90 and 135 NMR: CH (06), C (01).

Results and discussion

The fresh leaves of P. persica harvested over five different seasons (spring, summer, rainy, autumn, and winter) gave 0.05 ± 0.02 to 0.46 ± 0.05 g/100 g colourless essential oil having bitter almond-like aroma (Table 1). The yield of essential oil was higher in the rainy season (0.46 ± 0.05 g/100 g fresh leaves), followed by autumn (0.45 ± 0.01 g/100 g fresh leaves) and summer season (0.42 ± 0.02 g/100 g fresh leaves). However, the essential oil yields were lower in spring (0.14 ± 0.02 g/100 g fresh leaves) and winter (0.05 ± 0.02 g/100 g fresh leaves) seasons. Further, drying of leaves for one week caused total loss of essential oil. Therefore, drying of P. persica leaves before distillation cannot be recommended. Moreover, resulting essential oils from different seasons were analysed by GC-FID, GC-MS, and NMR. The oil composition was exclusively dominated by benzaldehyde. The content of benzaldehyde ranged from 63.1% to 98.3% with the higher in the oils collected from spring to autumn seasons. However, its content dropped considerably during the leave senescence period, that is, during winter season (Table 1). The yield of benzaldehyde ranged from 0.032 to 0.450 g/100 g fresh leaves during the year with the maximal in the rainy season (0.450 g/100 g fresh leaves), followed by autumn (0.440 g/100 g fresh leaves) and summer season (0.406 g/100 g fresh leaves). However, the yield of benzaldehyde was quite low during spring (0.138 g/100 g fresh leaves) and winter (0.032 g/100 g fresh leaves) seasons. Thus, in terms of benzaldehyde yield, rainy and autumn seasons were suitable for harvesting P. persica leaves.

Table 1. Collection time, phenophase, essential oil yield, and benzaldehyde yield of Prunus persica from India.

Collection time	Phenophase	Essential oil yield (g/100 g fresh leaves)^a	Benzaldehyde (%) in essential oil^b	Benzaldehyde yield (g/100 g fresh leaves)^b
Spring season	Flowering phase	0.14 ± 0.02	98.3	0.138
Summer season	Fruiting phase	0.42 ± 0.02	96.7	0.406
Rainy season	Vegetative phase	0.46 ± 0.05	97.9	0.450
Autumn season	Vegetative phase	0.45 ± 0.01	97.7	0.440
Winter season	Senescence phase	0.05 ± 0.02	63.1	0.032

^aEstimated on fresh weight basis; ^bmean of minimum two samples.

Previously, the leaf essential oil compositions of various other Prunus species have been studied. The leaf oils of Prunus phaeosticta^[20] and Prunus laurocerasus^[22] were dominated by benzaldehyde. However, the oils from Prunus padns, Prunus serotina, and Prunus arborea contained benzoic acid,^[25] α-methoxy toluene/benzyl alcohol,^[21] and (E,E)-α-farnesene/benzaldehyde^[19] as dominant constituents, respectively. Therefore, it seems that benzaldehyde and/or its derivative are characteristic constituents of the genus Prunus. Thus, the occurrence of benzaldehyde or its derivatives could be of chemotaxonomic significance.

Benzaldehyde is one of the most important aromatic aldehydes having a considerable industrial use in perfumery and pigment processing.^[26] Natural benzaldehyde is one of the important materials for making food flavouring agents and for preparing industrial dyestuffs and spices. It is also an essential intermediate for many pharmaceutical products.^[27] This molecule has also been reported as best repellent for driving bees^[28] and also known for anti-tumour,^[29] antibacterial, and antifungal activities.^[30] Moreover, the present supply of benzaldehyde is met by synthetic route and chemical reactions from bitter almond oil containing fruit kernels or natural cinnamon oil. This process often produces harmful by-products.^[31] Therefore, the leaf oil of P. persica examined in this study from India may serve as a potent natural source of benzaldehyde for flavour, perfumery, and herbal ingredients.

Conclusion

The present study explored the utility of P. persica leaves as a potent natural source of benzaldehyde (0.450 g/100 g fresh leaves). The essential oil and benzaldehyde contents were found to be higher in the rainy and autumn seasons. Therefore, after harvesting the fruits in the summer, farmers can harvest the leaves in the rainy or autumn season for extraction of the essential oil. Thus, natural benzaldehyde, a co-product of peach cultivation, can be an additional source of income for the peach growers.

Acknowledgements

Authors are grateful to the Director, CSIR-CIMAP for continuous encouragement and support and to Central Chemical facility for GC-MS analysis.

Funding

Authors are thankful to CSIR, New Delhi for the financial support (BSC-0203).

Additional information

Funding

Authors are thankful to CSIR, New Delhi for the financial support (BSC-0203).