Evaluation of pulque sediment (Xaxtle) as a starter culture in order to obtain a low glycemic index baked product

Pulque bread is a traditional Mexican product that results from the fermentation by lactic acid bacteria (LAB) present in pulque or in its sediments (xaxtle). The objective of this study was to evaluate xaxtle as a starter culture in the fermentation of bread dough in order to obtain a low glycemic index baked product. Phenotypic and genotypic tests are used to identify bacteria of the genus Lactobacillus and yeasts of the genus of Saccharomyces as predominant organisms in xaxtle. Surface response methodology was used to obtain the optimum amount of lyophilized xaxtle, 3 g (~10⁸ UFC.g^-1) and the optimum time (90 min) of fermentation of the dough, considering the value D-optimum of the software DesignExpert. The microstructure of the bread dough fermented with xaxtle showed a partial hydrolysis of the protein matrix, conformed by gliadins and glutenins. Furthermore, the total starch content and available starch of the bread with xaxtle decreased by 9.8 % with respect to the bread made with S. cerevisiae (p=0.03) and the resistant starch was similar in both products (p=0.073). Fermentation with xaxtle reduced the hydrolyzed starch content in bread by approximately 4 %, thus classifying the product as low glycemic index bread. Therefore, the use of xaxtle as a starter culture in the fermentation of bread dough favored the reduction of the glycemic index due to the action of the microorganisms present.