Characterization and detection of toxoflavin-producingBurkholderiain rice straws andDaqufor Chinese Maotai-flavour liquor brewing

Abstract

Rice straws are widely used in Daqu (starter) preparation for Maotai-flavour liquor brewing to provide adequate thermal insulation, water retention and aeration. As the straws have direct contact with the Daqu during its preparation, the microorganisms carried by the straws can be transferred to the Daqu. In this study, yellow pigment-producing strains were isolated from the rice straws using a dilution plate method. Most of these strains were characterized as toxoflavin-producing Burkholderia spp. by 16S rRNA sequencing, toxA gene-specific PCR and toxoflavin detection. The PCR assays revealed the existence of Burkholderia in the Daqu samples. The toxoflavin content in a number of Daqu samples was determined using HPLC. The highest observed content of toxoflavin in the Daqu was >8 mg/kg, close to its LD50. Although no toxoflavin was detected in the distilled liquor, the safety problem regarding the use of rice straws in Daqu preparation is still noteworthy, since Burkholderia and toxoflavin can be transferred and can accumulate during the brewing process. The results can contribute to a further assessment of the contamination risk in liquor brewing caused by Burkholderia and to safer production in this traditional process. Copyright © 2015 The Institute of Brewing & Distilling