UNTARGETED AND TARGETED AROMA PROFILE ANALYSIS OF RAW AND BAKED JUJUBE

Winter jujube is described as having fresh and green aroma characteristics. However, there was no systematic research to clarify the geographical distribution effect on the aroma of winter jujube. The quality of red jujube from Xinjiang Province, China, is superior to other regions, but no studies have been carried out to reveal its regional aroma characteristics. Besides, the aroma of baked red jujube has not been revealed yet.
Firstly, gas chromatography-ion mobility spectrometry (GC-IMS), GC-mass spectrometry (MS), and E-nose were applied for the aroma analysis of winter jujube from different regions. The results showed benzyl alcohol, octanoic acid, 2-hexenal, linalool, 2-nonenal, and ethyl decanoate were the most common compounds presented in all winter jujubes. 1-Penten-3-ol, ethyl hexanoate, methyl laurate, and 2-methylbenzaldehyde were induced as the potential markers of XJAKS with a green and fruity aroma. SXYC could be labeled by acetone and 2-methoxyphenol with woody and pungent aroma.
Secondly, six cultivars of red jujubes (cv. JC, JZ, HZ, QYX, HTDZ, and YZ) grown in Xinjiang Province, China were collected. GC-IMS and E-Nose were used to study the volatile profile. JC, JZ, HZ, and YZ were different from the others, while QYX and HTDZ were similar to each other. Acetoin, E-2-hexanol, hexanal, acetic acid, and ethyl acetate were crucial for the classification. Correlation analysis showed jujube ID might be related to phenylacetaldehyde and isobutanoic acid that formed by the transamination or dehydrogenation of amino acids.Meanwhile, the sweet attribute was correlated with amino acids including threonine, glutamic acid, etc.
Thirdly, the particular aroma of baked red jujube has not been evaluated until now. Molecular sensory sciences were applied for the identification of key odors. 5-Methyl-2-furancarboxaldehyde, β-damascenone, benzaldehyde, limonene, hexanoic acid, 5-butyltetrahydro-2-furanone, and DDMP were the key odorants for baked red jujube. The baking process stimulated the formation of aromatic hydrocarbon compounds like 1H-pyrrole-2-carboxaldehyde and DDMP.
Finally, HS-SPME-GC-MS/MS was applied to quantitatively analyze targeted compounds. DDMP (2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one), formed during the baking of red jujube, is characterized by bitter odor and potential toxicity. Alkyl-substituted pyrazines perceived as nutty, roasted, or sweet odors contribute a lot to red jujube aroma. The standard curve of DDMP was linear between the ranges of 0.01 and 100 μg/mL, with a limit of detection at 0.1 ng/g below the sensory threshold of DDMP (2.06 μg/g). Good linear correlation coefficients (0.9947–0.9988) were obtained over the ranges of 1–10000 ng/mL for the alkyl pyrazines. The limits of detection (LODs) and limits of quantitation (LOQs) for the pyrazines were in the range of 0.5–10 pg/g and 1.5–30 pg/g, respectively. Trimethylpyrazine, which accounted for 38.71%–59.50% of the total pyrazine, was the main alkyl pyrazine in raw red jujube. Methylpyrazine accounted for 35.52%–49.76%, the highest portion of alkyl pyrazine in baked red jujube. The baking process might stimulate the dealkylation of alkyl pyrazines.