The incidence and distribution of ochratoxin A in Daqu, a Chinese traditional fermentation starter

- A new USLE-SPE-UPLC-MS/MS method was developed to determine ochratoxin A in Daqu.
- The distribution rule of OTA in Daqu was revealed for the first time.
- The fermentation temperature is the key factor influencing OTA occurrence in Daqu.
- Some fungi may be able to synthesize OTA when the temperature exceeds 45 °C.

Daqu, a traditional starter culture mainly used to produce Chinese liquor and vinegar, is spontaneously fermented by diverse bacteria, yeasts and filamentous fungi under thermophilic condition. Therefore, mycotoxins may exist in Daqu, resulting in the contamination of end-foods. Ochratoxin A (OTA), a mycotoxin produced by certain species of Aspergillus and Penicillium, is not known whether existing in Daqu. However, specific method to detect OTA as well as OTA occurrence in Daqu has not been reported so far. With this in mind, a new method was developed to detect OTA in Daqu by the combination of ultrasound-assisted solid-liquid extraction (USLE), solid phase extraction (SPE) cleanup and UPLC-MS/MS. The USLE conditions of OTA from Daqu were optimized using Plackett-Burman (PB) design coupled with Box-Behnken (BB) design. Under the optimized conditions, no matrix effects were found, and the external standard method can be used to determine OTA in Daqu. The recoveries for spiked samples were 87-106% with the relative standard deviations (RSD) < 15%. The limits of detection and quantification were respectively 0.33 and 0.41 ppb. This approach was then applied to analyze 133 Daqu samples from different geographical regions in China, including 26 low temperature-, 33 medium temperature- and 74 high temperature-type Daqu. The results showed that OTA was detected in 66 samples with a maximum concentration of 28.87 ppb in low temperature Daqu, and the OTA incidence was on increase in the order of high temperature-, medium temperature- and low temperature-type Daqu. This implied that fermentation temperature is the key factor influencing OTA occurrence in Daqu. Moreover, there may be some fungi possessing the biosynthesis ability of OTA under high temperature environment (more than 45 °C).