Profiling of 2-Acetyl-1-Pyrroline and Other Volatile Compounds in Raw and Cooked Rice of Traditional and Improved Varieties of India.

Deepak Kasote,Vivek Kumar Singh,Nese Sreenivasulu,Ashok Kumar Singh,Haritha Bollinedi,Ahmed Regina

doi:10.3390/foods10081917

Abstract

Herein, optimized headspace solid phase microextraction with gas chromatography–tandem mass spectrometry (HS-SPME-GC-MS/MS) was used to estimate the 2-acetyl-1-pyrroline (2-AP) in raw and cooked rice samples of ten different traditional and improved varieties. Furthermore, HS-SPME-GC-MS-based volatile profiling was subjected to untargeted analyses to identify major odorants in raw and cooked rice samples, and to understand chemical proximities among volatile profiles. Results showed that 2-AP content was remarkably increased in cooked rice compared to raw. Among the varieties studied, Pusa-1652 (Improved Kala Namak) and Kala Namak-2 were superior in the 2-AP content than Basmati varieties. Additionally, Govind Bhog, Kala Jeera and Jeera-32 had 2-AP content equivalent to or superior to Basmati rice varieties. Altogether, 18 and 22 volatiles were identified in the raw and cooked rice samples studied, respectively. Of these, ethyl butyrate, ethyl 3-methylbutanoate, 2-undecanone, ethyl benzoate, ethyl benzeneacetate, 2-methylnaphthalene, and 1-methylnaphthalene were characteristically detected in the cooked rice. The high amount of 2-ethyl-1-hexanol was uniquely found in raw rice samples, which can be a marker compound for freshly milled rice. Along with 2-AP, butanoic acid and benzoic acid derivatives, phenylethyl alcohol, ethyl 3-hydroxybutyrate, and indole may be responsible for the overall perceived characteristic Basmati-like aroma in cooked rice.

Highlights

At present, over 150 different volatile compounds have been reported in raw and cooked milled rice, which are mainly from the classes, alkanes, aldehydes, alcohols, esters, ketones, phenols, fatty acids, benzyl derivatives, enones, furans, furanones, monoterpenoids, sesquiterpenoids, naphthalenes, xylenes, pyridines, and pyrroles [1,2,3,4]
A strong positive correlation was observed between ethyl benzoate and ethyl benzeneacetate in cooked rice, which indicates they may be formed together during the cooking process. 2-AP showed moderate to high correlations with ethyl benzoate, ethyl benzeneacetate, ethyl butyrate, ethyl 3-methylbutanoate and phenylethyl alchohol, ethyl
The observed moderate to the high correlation of 2-AP with ethyl benzoate, benzene acetic acid, ethyl ester, ethyl butyrate, ethyl 3-methylbutanoate, and phenylethyl alchohol, ethyl 3-hydroxybutyrate, and indole in cooked rice suggests the role of these compounds in the overall perceived characteristic Basmati-like aroma in cooked rice

Summary

Introduction

Over 150 different volatile compounds have been reported in raw and cooked milled rice, which are mainly from the classes, alkanes, aldehydes, alcohols, esters, ketones, phenols, fatty acids, benzyl derivatives, enones, furans, furanones, monoterpenoids, sesquiterpenoids, naphthalenes, xylenes, pyridines, and pyrroles [1,2,3,4]. Only some of these volatiles are responsible for the overall perceived aroma of rice [5]. The perceived aroma depends on the levels of primary odorant and on their interactions [7]. For the past several decades, 2-AP has been considered a primary determinant of flavor in aromatic rice due to the loss of function of betaine aldehyde dehydrogenase 2 (OsBADH2) and it has frequently been used as a marker compound to distinguish aromatic and non-aromatic rice varieties [8].

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Results

Conclusion