Analysis of rhizome colour content, bioactive compound profiling and ex-situ conservation of turmeric genotypes (Curcuma longa L.) from sub-Himalayan terai region of India

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Highlights

  • Colour content of turmeric rhizomes reveals association with medicinal properties.

  • Turmeric Redness Index (TRI) can be indicator for medicinal superiority.

  • An elite medicinally superior turmeric genotype is identified.

  • Dark coloured turmeric rhizome may be unexplored source of bio-actives.

  • Ex-situ multiplication and conservation protocol for elite genotype is standardized.

Abstract

Turmeric (Curcuma longa L.), the golden spice of India, offers a myriad of health benefits primarily due to the presence of polyphenolic curcuminoid pigments. It is believed that the dark orange colour of turmeric rhizome has wide-spread health benefits; but no reliable evidential proof for this is available till date. It is crucial to discern the association of rhizome colour with health benefits. It is also of prime importance to investigate whether the curcuminoids present in the rhizomes are the sole bioactive compounds contributing to its medicinal properties. In the present study, forty five turmeric genotypes were collected from the sub-Himalayan terai region of India which differed in their rhizome colour. Here, the Turmeric Redness Index (TRI) in terms of rhizome colour content (a*/b*) of the genotypes revealed strong correlation with curcuminoid content (+0.93), total phenol content (+0.76), total flavonoids content (+0.82), iron content (+0.55) and antioxidant activity (–0.90 and –0.92 for DPPH and ABTS assays and +0.82 and +0.95 for TAC and CUPRAC assays, respectively, with p < 0.001). Among the studied genotypes, TCP 2 (Turmeric Collection Pundibari 2) having dark orange coloured rhizome turned out to be a superior genotype in terms of its antioxidant potential, curcuminoid and iron content. Quantification of phenolic and flavonoid compounds of TCP 2 revealed that other than the three isoforms of curcuminoids, different therapeutically important bioactive compounds like p-coumaric acid (162.46 mg/kg), catechin (107.67 mg/kg), sinapic acid (417.36 mg/kg) and flavonoid like quercetin (2746.21 mg/kg) are also present in the rhizome, suggesting that along with curcuminoid these compounds also contribute towards its antioxidant potential. The GC–MS analysis of the essential oil of TCP 2 revealed the presence of thirty three volatile compounds with significantly high ar-turmeron (28.57 %), curlone (10.05 %), eucalyptol (10.13 %) and chemigran (13 %). A rapid and improved micro-propagation protocol was also developed for TCP 2 using single rhizome bud sprout as explants. A media composition of MS with 6 ppm BAP and 2 ppm NAA was found to be the best for rapid and efficient micro shoot development.

Introduction

Curcuma longa L. (syn. C. domestica Val.), from family Zingiberaceae is a rhizomatous perennial herb and native of South East Asia. Turmeric, commonly known as haldi (in Bengali and Hindi), is one of the most ancient and important medicinal plants in the world (Peter, 2008). The dried powder of turmeric rhizomes has wide applications in daily culinary activities in household kitchen of the sub-continent as flavouring and colouring agent since time immemorial. It also has extensive applications in dyeing, drug and cosmetic industry. This multipurpose and sacred spice of India, also known as ‘Indian saffron’, finds its place in the offerings in religious and ceremonial occasions (Khan et al., 2014). India is the largest producer and exporter of turmeric in the world accounting for more than 50 % of the international trade, thereby fulfilling 90 % of the global demand (APEDA, 2018; Olojede et al., 2009). Turmeric occupies about 6% of the total area under spices and condiments cultivation in India, and has considerable importance in Indian economy (Choudhary and Rahi, 2018). Turmeric has already gained importance all over the world for therapeutic uses owing to its anti-inflammatory, anti-diabetic, anti-carcinogenic, anti-hepatotoxic, anti-viral, choleretic, antibiotic, anti-venomous and anti-rheumatic properties (Singh and Aggarwal, 1995; Wilken et al., 2011; Lin et al., 2008; Kaypee et al., 2015) and is frequently used in ayurvedic medicine of India as ‘haridra’. Predominant reason for its numerous health benefits is the presence of several bioactive compounds, with their ability to exert health promoting effect on living cells, tissues or on a living organism as a whole (Priyadarshini, 2014; Mandal et al., 2017). Turmeric is harvested when the aerial part of this plant senesces and its rhizomes develop bright yellow to orange yellow colour. The characteristic yellowish colour is due to the presence of polyphenolic pigment curcuminoids which makes up 2–5% of the rhizome mass (Sandur et al., 2007). Presumably, in addition to curcumin and two of its derivatives namely demethoxycurcumin and bisdemethoxycurcumin, a number of bioactive compounds under different chemical classes with varied chemical properties may play important roles in the diverse biological activity exhibited by turmeric. But correlation between the rhizome colour and health promoting compounds or antioxidant activity present in turmeric is completely unknown. No colour index for selection of medicinally superior turmeric genotype is available till date. In addition, the detailed bioactive compound profiling of turmeric exploring the contents of other medicinally relevant phenolic and flavonoid compounds has not been carried out. The sub-Himalayan hills and terrain plains of India are bestowed with abundant but hitherto unexplored germplasms of turmeric. In the present study we have collected forty five such accessions of C. longa from different tribal belts of sub-Himalayan hills and terrain plains having considerable visual difference in their rhizome colour. We have estimated the variation in the rhizome colour, antioxidant activity, total phenol, total flavonoid, curcuminoid and iron content of turmeric genotypes and identified medicinally most superior cultivar. We have further quantified the individual phenolics with known health benefits and the volatile constituents from the rhizome of medicinally most superior accession. Additionally, a successful attempt has been made for the ex situ conservation of this medicinally superior turmeric accession through micropropagation technique.

Section snippets

Plant materials and crop management

A total of forty five turmeric genotypes were collected from the stock maintained at the All India Coordinated Research Project (AICRP) on Spices, Uttar Banga Krishi Viswavidyalaya, Cooch Behar Centre. Most of these were collected from different locations of terai and Dooars plains of northern part of West Bengal (state of India) along with a few from southern part of West Bengal (Table 1). The field experiments were conducted during the period from 2015−16 to 2017−18 at the Instructional Farm

Estimation of rhizome colour content

The rhizome colour of the collected germplasms varied from dark orange, orange yellow to light yellow as per visual estimation (Fig. 1, A–C). The quantification of the different parameters of colour was estimated using CIELab system (Braga et al., 2018). The colour of rhizome of forty five genotypes varied significantly (p < 0.05) in their L*, a*, b*, and h° parameters (Table 2). The L* value signifying lightness in colour ranged from 44.31–65.63 among the genotypes. The a* value signifying

Conclusion

Turmeric has wide phenotypic variability in the nature for leaf shape, leaf colour, rhizome colour, aroma, pungency, etc. But none of these phenotypes has been linked to the medicinal properties of turmeric. Although curcuminoid content was influenced by genotype- environment interaction (Aarthi et al., 2020), nevertheless a prediction model for the estimation of curcuminoid content based on artificial neural network (ANN) was developed to map genome environment interaction, soil and climatic

CRediT authorship contribution statement

Kumaresh Pal: Validation, Methodology, Formal analysis, Investigation, Writing - original draft. Sayan Chowdhury: Validation, Methodology, Formal analysis, Investigation, Writing - original draft. Sudip Kumar Dutta: Software, Validation, Formal analysis, Investigation, Data curation. Soumendra Chakraborty: Validation, Resources, Investigation. Moumita Chakraborty: Methodology, Resources, Project administration. Goutam Kumar Pandit: Methodology, Resources, Supervision, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors are grateful for financial support under the project “Generation of elite, disease free planting material of turmeric through micro-propagation and its distribution among tribal farmers of terrain plain of West Bengal” funded by DST-SEED, Govt of India under SYST scheme with project reference number SP/YO/084/2016. The authors would also like to acknowledge Directorate of Research, UBKV for fund support to the ‘Plant Tissue Culture Unit’ (Ref: UBKV/DR/74) and Dean, Faculty of

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