Effects of Different Citrus Varieties and Harvesting Time on the Quality of Citrus Dark Tea

The genus Citrus consists of Tangerines (Citrus × reticulata), Mandarins (Citrus × reticulata), Oranges (Citrus × sinensis), Grapefruits (Citrus maxima), Lemons (Citrus × limon), and other citrus fruits. This study investigated the effects of 74 different citrus species and harvesting time on the quality of citrus dark tea using Hubei green brick tea as the raw material. Oranges (Citrus × sinensis) were found to outperform other species in improving the quality of citrus dark tea. Additionally, the impact of orange harvesting time (August to December) on the quality of orange dark tea was investigated by using the Peach leaf orange with the highest sensory score as the subject of the study. Results revealed that harvesting time can considerably impact the flavor quality of orange dark tea, but not its infusion color or scent. Specifically, the orange dark tea processed with September-harvested Peach leaf orange exhibited a strong fruity scent, a sweet and smooth flavor, and a harmonious tea and fruit aroma. With the delay of harvesting time, a downtrend was observed in the content of soluble proteins, flavonoids, hesperidin, synephrine, and limonin, as well as total volatile components, with the largest decrease in synephrine and flavonoids. However, the polysaccharide content increased in the peel of Peach leaf orange. Functional analysis revealed that the delay of harvesting time can diminish the inhibitory capacity of orange-dark tea on α-glucosidase and α-amylase. Organoleptic quality and physiological activity analysis demonstrated September as the optimal time for harvesting Peach leaf oranges for processing orange dark tea.