Short communication Isolation and characterization of the microflora of nixtamalized corn masa Stephen J. Adolphson, Michael L. Dunn, Laura K. Jefferies, Frost M. Steele ⁎ a Department of Nutrition, Dietetics and Food Science, Brigham Young University, S-221 ESC, Provo, UT 84602, United States abstract article info Article history: Received 19 December 2012 Received in revised form 29 April 2013 Accepted 11 May 2013 Available online 19 May 2013 Keywords: Microflora Masa Corn Nixtamalization Lactic acid bacteria 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 ob- jective of this research was to characterize and identify the microflora of nixtamalized corn masa from six dif- ferent 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. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Corn tortillas are a common staple in the diets of Mexican and many Central American populations. It has been estimated that in cer- tain areas of Mexico, the corn tortilla provides approximately 50% of the individual energy intake, constituting 60–90% of cereal grain in- take (Villalpando, 2004). Traditionally, corn tortillas are prepared by steeping whole-kernel corn in a hot, alkaline solution, containing 1.5–2% lime (CaO), and subsequently grinding the drained and rinsed corn (now referred to as nixtamal) into a fresh dough called masa. The ground masa typically exits the grinding stones at a temperature near 56 °C (Chapman et al., 2010). Tortillas are produced using this process in tens of thousands of very small neighborhood mills scattered throughout towns and cities across Mexico and Central America. Many of these mills have limited sanitation capabilities, which can lead to a diverse and abundant microbial population in the masa dough. Due to the short shelf life of fresh tortillas (Aida et al., 1996), as well as the daily demand, and the increasing tendency for one mill to transport masa to multiple tortillerias in an expanded distribution area, the fresh masa is often held for a period of time before baking into tortillas. In commercial tortilla mills, the hot masa is often stacked and stored in large pails or sacks at ambient temperature for anywhere from a few minutes to several hours before being formed into tortillas and baked (Chapman et al., 2010). Due to the availability of nutrients, the high moisture content (approximately 56%) (Ramirezwong et al., 1994), and warm storage temperature, significant microbial growth can occur while the masa is being held for extended periods. Natural fermentation and souring of the masa usually leads to spoilage with- in 4 to 6 h (personal communication: Lorenzo Vital, Todo de Maiz, Guadalajara, Mexico). Published research regarding the microflora of maize products focuses primarily on products such as pozol, sekete, chorote and other fermented products, and monitors the changes in microbial populations throughout the fermentation process (Adegoke et al., 1995; Diaz-Ruiz et al., 2003; Morales et al., 2005; Sefa-Dedeh et al., 2004; Wacher et al., 1993; Wacher et al., 2000). Since microorgan- isms are responsible for the fermentation process, it is reasonable that most of the research regarding bacterial diversity and character- ization relate to these commonly fermented foods. While tortilla masa is not purposefully fermented, studies of fermented maize foods can still offer some knowledge and insight into the microflora of nixtamal and other fresh, unfermented maize products. Wacher et al. (2000) found lactic acid bacteria present at 10 5 –10 6 cfu/g in pozol, a fermented corn dough often consumed as a beverage in Mexico, and identified 25 bacterial isolates to the genus level. They used selective plating and carbohydrate utilization methods to tenta- tively identify Leuconostoc and Lactococcus as the primary genera in this fermented product. Escalante et al. (2001) used 16S rDNA sequenc- ing to identify a variety of Lactobacillus species, including Lactobacillus lactis, Lactobacillus alimentarium, Lactobacillus plantarum, as well as International Journal of Food Microbiology 165 (2013) 209–213 ⁎ Corresponding author. Tel.: +1 801 422 6670; fax: +1 801 422 0258. E-mail address: frost_steele@byu.edu (F.M. Steele). 0168-1605/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijfoodmicro.2013.05.010 Contents lists available at SciVerse ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro