Molecular and biochemical characterisation of aroma in biriyanicheera rice genotype

Abstract

Rice is the dietary staple food for as high as 62.8 per cent of world’s population and it contributes to 20 per cent of the total calorific intake of the people. Rice possesses many unique qualities which determine its value and preference in the market. The fragrance of rice has been one such special character that provides an extra preference to scented rice and fetches premium price in rice market.

The aromatic rice cultivars are found to possess higher fragrance, when grown in relatively cooler conditions in hilly regions. Hence the production of such plant types is confined to only a few locations of India. The early maturing selection from a Kerala local landrace with short grains, named ‘Biriyanicheera’, when grown in normal tropical conditions was observed to have sufficient aroma. In this context, the present study focuses on the analysis of aroma in ‘Biriyanicheera’ rice genotype through molecular and biochemical methods. The research programme was carried out at CPBMB during 2017-2019.

The seeds of aromatic rice varieties Biriyanicheera, Gandhakasala (from Palakkad, Thrissur and Ernakulam districts) and non-aromatic rice variety Triveni were used for the study. The biochemical characterisation was performed using finely powdered rice grains of all varieties through Gas Chromatography and Mass Spectroscopy (GC-MS). The GC-MS analysis revealed the presence of a diverse profile of volatiles present in the rice grains. The volatile compound Benzothiazole was detected in all the varieties, where as Ethyl acetate was the highest in Triveni, Biriyanicheera (Palakkad) and Gandhakasala (Ernakulam). The compounds, Nonanal and 2-hydroxy Benzaldehyde were found to be the major volatile compounds for aroma of Biriyanicheera in Palakkad region. Similarly, 4 nitrobenzylamine and 2-pentyl furan in Thrissur location and 4 nitrobenzylamine, 5- ethenyldihydro-5-methyl-2(3H)-Furanone, and Lincomycin in Ernakulam

location were identified as the major compounds present in the aroma profile of the rice grains.

The cooking quality parameters such as, Gelatinisation temperature, Amylose content and Gel consistency were evaluated for all the rice varieties. Alkali spreading test showed medium gelatinisation index for all three varieties which is optimum for the rice quality. Amylose content in rice grains was determined by treating the fine powder of rice with 0.1 N NaOH. The Biriyanicheera rice variety was found to contain 24.62 per cent of amylose content whereas, Gandhakasala and Triveni varieties showed 13.85 and 23.85 per cent respectively. Gel consistency of the rice varieties was analysed by measuring the gel length produced by boiling the rice powder. The gel length for Biriyanicheera (105mm), Gandhakasala (107.3mm) and Triveni (95mm) falls under soft category.

Aroma strength detection by sensory evaluation was performed using the DUS (Distinctness, Uniformity and Stability) protocol. The Biriyanicheera variety grown in Palakkad district showed exceptionally higher aroma than the other locations. Similarly, Gandhakasala variety produced maximum aroma in Palakkad region. From the above results Palakkad district was found to influence in aroma production of aromatic varieties.

Molecular characterisation was performed by amplifying the BADH2 gene present in all the three rice varieties. The amplified PCR products of genomic DNA were sequenced to analyse the presence of any mutations in BADH2 gene. The sequencing results of aromatic varieties Biriyanicheera and Gandhakasala revealed the presence of an 8 base pair mutation in exon 7 in both the varieties, whereas this mutation was absent in the non-aromatic variety Triveni. Hence it can be inferred that the aroma production in Biriyanicheera variety is due to similar mutation as that of the Basmati rice variety.