RESUMO
Corn tortillas are a staple in the diet among the Mexican population, and are traditionally produced through a process known as nixtamalization. This traditional process involves steeping whole-kernel corn in an alkaline solution overnight and then grinding the corn into dough (masa), which is then baked. While the masa is held before baking, significant microbial change can occur which leads to fermentation and spoilage. The objective of this research was to characterize and identify the microflora of nixtamalized corn masa from six different commercial tortilla mills throughout Guadalajara, Mexico. The identification of samples was conducted using the microbial identification system (MIS), which analyzes cellular fatty acids via gas chromatography to identify bacterial species. Lactic acid bacteria and aerobic mesophiles were the predominant organisms, with both groups having counts ranging from 10(4) to 10(7)cfu/g across all mills. Coliform populations were observed at counts of 10(2) to 10(3)cfu/g, while yeast and mold counts were typically less than 10(1)cfu/g. Some mills showed no presence of coliforms or yeast or mold. Streptococcus bovis and Lactobacillus oris were isolated from all mills, and were the most prevalent organisms representing 43% and 17% of all lactic acid bacteria isolated, respectively. S. bovis was also isolated on the aerobic tryptic soy plates and was the most prevalent species representing 19% of the total organisms from these aerobic plates.
Assuntos
Biodiversidade , Manipulação de Alimentos , Microbiologia de Alimentos , Zea mays/microbiologia , Técnicas de Tipagem Bacteriana , Contagem de Colônia Microbiana , Lactobacillus/isolamento & purificação , Metilglicosídeos/química , México , Leveduras/isolamento & purificação , Zea mays/químicaRESUMO
The cestodes constitute important but understudied human and veterinary parasites. Their surfaces are rich in carbohydrates, on which very little structural information is available. The tissue-dwelling larva (hydatid cyst) of the cestode Echinococcus granulosus is outwardly protected by a massive layer of carbohydrate-rich extracellular matrix, termed the laminated layer. The monosaccharide composition of this layer suggests that its major carbohydrate components are exclusively mucin-type O-glycans. We have purified these glycans after their release from the crude laminated layer and obtained by MS and NMR the complete structure of 10 of the most abundant components. The structures, between two and six residues in length, encompass a limited number of biosynthetic motifs. The mucin cores 1 and 2 are either nondecorated or elongated by a chain of Galpbeta1-3 residues. This chain can be capped by a single Galpalpha1-4 residue, such capping becoming more dominant with increasing chain size. In addition, the core 2 N-acetylglucosamine residue is in cases substituted with the disaccharide Galpalpha1-4Galpbeta1-4, giving rise to the blood P(1)-antigen motif. Larger, also related, glycans exist, reaching at least 18 residues in size. The glycans described are related but larger than those previously described from an Echinococcus multilocularis mucin [Hulsmeier, A. J., et al. (2002) J. Biol. Chem. 277, 5742-5748]. Our results reveal that the E. granulosus cyst exposes to the host only a few different major carbohydrate motifs. These motifs are composed essentially of galactose units and include the elongation by (Galpbeta1-3)(n) and the capping by Galpalpha1-4, novel in animal mucin-type O-glycans.