Changes in LC-MS-based Untargeted Non-volatile Metabolites of Infused Black Tea according to Different Storage Temperature and Period

This study examined changes in liquid chromatography-mass spectrometry-based untargeted metabolites of infused black tea during storage. Infused black tea was deposited at 25°C and 4°C for six days. During storage, the Hunter a* and b* values of the infused black tea stored at 4°C increased gradually, but the Hunter L* value decreased. The Hunter a* value of the infused black tea stored at 25°C showed a more significant change than that stored at 4°C. The 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) radical scavenging activities of infused black tea samples stored at 4°C and 25°C decreased during storage. Untargeted metabolites in infused black tea were analyzed using ultra-high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry. Eighty-four compounds were found in the infused black tea, including theaflavins, thearubigins, catechins, and flavonoids. Partial least squares discriminant analysis revealed a significant difference between the infused black tea samples stored at 4°C and 25°C. There was no clear discrimination in the infused black tea samples stored at 4°C. In particular, the infused black tea samples stored at 25°C could be clearly distinguished. The main metabolites having a high VIP score (>1.25) were 12 compounds, including theaflavins, theaflavic acid, gallocatechins, theasinensins, and tyrosine. The concentrations of these compounds decreased gradually during storage and seriously changed in infused black tea stored at 25°C than that stored at 4°C. A heatmap plot suggested that most metabolites were reduced in the infused black tea samples during storage. On the other hand, the concentrations of glucogallin, ellagic acid, 6,7-dihydroxycoumarin, isoschaftoside, and vicenin 2 increased in the infused black tea during storage. The metabolites in infused black tea changed seriously at 25°C rather than at 4°C during storage. These results provide useful information for drinking infused black tea during short storage periods.