Effects of processing on stable isotopic fingerprints of instant sweet tea [Lithocarpus litseifolius (Hance) Chun]

In order to investigate the effects of processing methods on the stable isotopic fingerprints of instant sweet tea (Lithocarpus litseifolius (Hance) Chun), and to validate the feasibility of tracing the geographical origin of sweet tea and its instant tea by δ¹³C and δ¹⁵N, four raw materials of sweet teas including old leaves and young leaves were prepared by oven drying and microwave drying, respectively. The instant teas were further produced by hot water extraction, centrifugation, and drying (freeze-drying and spray-drying) to obtain spray-dried instant tea (ITSD), freeze-dried instant tea (ITFD), and instant tea by-products (ITBP). The δ¹³C and δ¹⁵N values of samples were determined using an element analysis-isotope ratio mass spectrometer (EA-IRMS). The results indicated that the δ¹³C and δ¹⁵N values had significant differences among different regions (Hunan, Sichuang, and Jiangxi) (P < 0.05). Significant differences were also found between sweet tea raw materials prepared by oven drying and microwave drying (P < 0.05), and among instant tea products (raw material, instant tea, and its product) (P < 0.05). Whilst, highly significant correlations (P < 0.01) were found among all samples by different drying methods. The results could provide theoretical basis for the geographical traceability of sweet tea raw materials or its instant tea using δ¹³C and δ¹⁵N fingerprints. (authors)