Citrinin produced using strains of Penicillium citrinum from Liupao tea

Abstract The ability of a strain to produce citrinin was analysed in the growth inhibition zone using HPLC and UHPLC–MS. A total of 12 Penicillium citrinum strains isolated from Liupao tea were inoculated onto tea leaves and their capability for citrinin production were studied using different water content (15–45%) and temperatures (15–40 °C). The results provided a theoretical base for the safe manufacture of Liupao tea. Five strains of P. citrinum produced a clear growth inhibition zone with diameters of 11–22 mm. The citrinin contents in the liquid cultures of the 12 strains of P. citrinum ranged from 0.03 to 14.5 μg/mL. The citrinin contents of the teas with initial water content of 15 and 25% and those inoculated with P. citrinum were below the limit of detection during the fermentation. The citrinin content of the teas with initial water contents of 35 and 45% at 25 °C increased rapidly at first and then decreased during the fermentation. Similarly, the citrinin contents of the teas at 15 and 25 °C rapidly increased and then decreased. Meanwhile, P . citrinum was unable to produce citrinin at 35 and 40 °C. The optimum conditions were 45% water and 25 °C, generating the highest citrinin yield of 181 ng/g, which was higher than the limit of 50 ng/g citrinin in red yeast rice that can cause harm to human health. The highest citrinin yield in tea fermented for 50 days was 34.8 ng/g for stored teas with proper conditions. Therefore, storing teas with a low water content and temperature can reduce the content of citrinin.