The biodiversity of predominant lactic acid bacteria in dolo and pito wort for the production of sorghum beer.

AIM

To quantify and identify the predominant lactic acid bacteria (LAB) in dolo and pito wort processing, and to examine their biodiversity at strain level.

MATERIALS AND RESULTS

The processing of dolo and pito wort was studied at four production sites in Burkina Faso and Ghana. The succession of dominant micro-organisms, pH and titratable acidity were determined from sorghum malt through mashing and acidification to final wort. In the sorghum malt and during mashing, the LAB counts were 5.7-7.5 log CFU g(-1). Similar levels of yeasts and gram-negative, catalase-positive bacteria were observed. These levels decreased to 3.7-4.5 log CFU g(-1) and<or=2-3 log CFU g(-1), respectively, at the end of mashing, including a mild heat treatment. During acidification at ambient temperature (30-33 degrees C) lasting for 12-16 h, LAB counts increased to 8.8-9.9 log CFU g(-1), pH decreased from 5.55+/-0.12 to 3.72+/-0.24, and the titratable acidity calculated as lactic acid, increased from 0.13% to 0.61%. The gram-negative, catalase-positive bacteria and yeasts observed in the malt and during mashing were no longer detected. A total of 556 strains of LAB were isolated and purified. The LAB isolates were characterized and identified by a polyphasic approach based on phenotypic and genotypic methods, such as carbohydrate fermentation patterns using API 50 CHL, intergenic transcribed spacers-polymerase chain reaction/restriction fragment length polymorphism (ITS-PCR/RFLP), pulsed-field gel electrophoresis (PFGE) and 16S rRNA gene sequencing. Lactobacillus fermentum was identified as the dominant LAB species in the malt during mashing and during acidification. The other species observed during acidification were Lactobacillus delbrueckii ssp. delbrueckii, Lact. delbrueckii ssp. bulgaricus and Pediococcus acidilactici. These bacteria comprised a minor fraction of the bacterial population and no distinct microbial succession was observed for the LAB. At species level, the LAB profiles were similar for the four production sites; however, a pronounced diversity was observed at strain level. For one site, which had implemented a cleaning procedure between batches only, Lact. fermentum was found.

CONCLUSION

Lact. fermentum was found to be the dominant LAB species throughout the entire process to final dolo and pito wort, including the acidification. Lact. delbrueckii ssp. delbrueckii, Lact. delbrueckii ssp. bulgaricus and P. acidilactici occurred in low numbers. At strain level, a high diversity based on PFGE-RFLP was observed for Lact. fermentum within and between sites.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study for the first time gives details of the involvement of LAB in the production of dolo and pito wort, for West African traditional sorghum beer production. One species, Lact. fermentum was predominant throughout the process, and seems to harbour potential starter cultures to be selected according to technological characteristics determined at strain level.