Search

Sourdough is an ancient culture comprising flour and water, and fermented to allow leavening capacity from wild yeasts, producing bread that is preferred by the consumers. Agave bagasse (AB) is an abundant by-product in Mexico, rich in fiber and carbohydrates, but mostly wasted. This work aimed to revalorize AB as an ingredient for wheat sourdough. Different ratios (5%, 10%, and 15%, by weight) of AB powder were mixed with wheat flour, hydrated with 10% (w/v) water, and incorporated with Lactococcus lactis (NRRL B-50307). The fermentation was monitored for 6 days; physicochemical parameters (pH, titratable acidity [TTA], leavening capacity) were analyzed, and sourdough bread was produced. The population of lactic acid bacteria, yeasts, and molds, and adaptation of the added strain were monitored. Leavening capacity increased during fermentation, and L. lactis grew about 2 log CFU/day. Analysis of the sourdough showed a pH range of 3.6–4.9, and TTA ranged from 8 mg/mL to 11 mg/mL of lactic acid. Proximate analysis (%, w/w) revealed 28.95 ± 0.4 protein, 12.33 ± 0.98 fat, 37.68 ± 0.65 total carbohydrates, and 1.04 ± 0.32 ash. Sourdough bread added with AB + L. lactis showed significantly higher (p < 0.05) firmness (35.42 N ± 0.034 N) and volume (70.24 mL ± 4.67 mL) than using wheat only (20.48 N ± 4.04 N, and 49.10 mL ± 6.35 mL, respectively). AB is a good source of fiber and other compounds like minerals, suggesting its potential as a food ingredient, and encouraging the agave industry towards more sustainable development. [ABSTRACT FROM AUTHOR]

This study characterized the microflora present in four Queso Fresco-style cheeses made from raw milk (RM) and two cheeses made from pasteurized milk (PM) obtained directly from six different producers in Mexico. Microbial isolates were initially analyzed on 8 different selective media and further analyzed by 16S rRNA gene sequence analysis. Sequence analysis identified Lactococcus lactis ssp. lactis as an isolate growing on M17 agar in four cheese samples. L. lactis ssp. lactis was the only lactic acid bacterium identified which is traditionally used as a cheese starter culture. Sequence analysis of isolates from MRS medium supplemented with vancomycin identified Leuconostoc mesenteroides in all six cheese samples. A high number of coliforms, enterococci and coagulase-positive staphylococci were identified in all RM cheeses. The numbers of total coliform species were lower in both PM samples (by 2 log10), but the numbers of staphylococci were lower in only one sample (by 3 log10). The numbers of enterococci were high in both PM samples, and sequence analysis identified Enterococcus faecium as the only enterococcal species isolated from all six cheeses. These results suggest that L. lactis ssp. lactis, L. mesenteroides and E. faecium are species that may contribute to the organoleptic qualities of Queso Fresco-style cheeses analyzed in this study. PRACTICAL APPLICATIONS This work was performed to define the natural microflora present in traditional-style Queso Fresco in order to identify bacterial species that may contribute to the organoleptic qualities of the cheese. Identification and enumeration of the “generally regarded as safe” (GRAS) lactic acid bacteria may allow for the development of new culture blends for the production of Queso Fresco using pasteurized milk, while maintaining the desired qualities of the raw milk varieties. In addition, bacteria recovered from the raw milk cheeses may be novel strains offering advantages over commercially available starter and adjunct LAB currently being used to make Queso Fresco. The work also identified potential pathogens and spoilage bacteria associated with traditional-style Queso Fresco, stressing the importance in developing a desirable pasteurized milk cheese. [ABSTRACT FROM AUTHOR]

Hepatic cirrhosis is a chronic disease that affects one fifth of the World's population and is the third leading cause of death in Mexico. Attempts have been made to develop treatments for this hepatic cirrhosis, which include manipulating the intestinal microbiota and thus decreasing the early inflammatory response. The microbiota is reportedly altered in patients with cirrhosis. Due to its immunomodulatory properties and its ability to survive in the gastrointestinal tract, Lactococcus lactis (L. lactis) has been used as a therapeutic measure in inflammatory disorders of the colon. The objective of the present study was to evaluate the efficacy of the L. lactis probiotic NZ9000 in preventing tetrachloromethane (CCl4)-induced experimental hepatic fibrosis. The following 4 groups were included in the experimental stage (n=5): i) Control group; ii) L. lactis group; iii) CCl4 group; and iv) L. lactis-CCl4 group. For the first 2 weeks, L. lactis was orally administered to the L. lactis and L. lactis-CCl4 groups; CCl4 was then peritoneally administered to the lactis-CCl4 group for a further 4 weeks (in addition to the probiotic), while the L. lactis group received the probiotic only. For the CCl4 group, CCl4 was administered for 4 weeks. The experimental groups were all compared with the control group and the L. lactis + CCl4 group. Tissue samples were analyzed histologically and biochemically, and the gene expression levels of interleukin (IL)-1, IL-10 and forkhead box protein P3 (FoxP3) were determined. L. lactis decreased hepatic cirrhosis by preventing steatosis and fibrosis, and by reducing the levels of AST and ALT. Subchronic CCl4 injury induced upregulation of the IL-1β gene in the liver, which was decreased by L. lactis. It was also found that the group treated with L. lactis showed increased expression of Foxp3 in the liver and IL-10 in the gut. These results suggested that oral administration of L. lactis may be a potential probiotic to prevent or protect against CCl4-induced liver injury. [ABSTRACT FROM AUTHOR]

Lactococci strains obtained from raw-milk Oaxaca cheese through its production process in two factories from the Tulancingo Valley, Mexico, were isolated and characterized. A total of 120 colonies were selected from the growth in M17 and MRS agars. Twenty were identified as lactococci strains, all Lactococcus lactis , and were characterized by molecular and phenotypic methods including carbohydrate use, enzymatic profile, acidifying capacity, and antibiotic and phage resistance. High phenotypic diversity was observed and confirmed among the Lactococcus lactis strains by rep-PCR fingerprints. Fifty percent of the strains were resistant to streptomycin and 35% to erythromycin. Nine isolates were considered as fast acidifying strains. The predominant volatile compounds produced were 3-methylbutanol, 3-methylbutanal and butane-2,3-dione. A selection of strains isolated in this study has shown satisfactory characteristics to be used as potential starters for the industrial production of Oaxaca cheese. • Lactococci strains from Mexican Oaxaca cheese were identified and characterized. • Lactococcus lactis spp. isolates showed high phenotypic and molecular diversity. • Nine fast-fermenting strains (pH < 5.0 in milk) were found. • Strains have technological properties as starters for industrial cheese production. [ABSTRACT FROM AUTHOR]

Lactococcus lactis is the lactic acid bacteria most frequently used for the production of cheese starter cultures, mainly because of their efficient production of aroma compounds. However, commercial cultures do not always produce the typical aroma notes of artisanal raw-milk cheeses. Thus, the objective of this study was to characterize the volatile compounds generated by wild L. lactis strains in Mexican Fresco cheese made with pasteurized milk. Four strains of wild L. lactis were evaluated for their aroma production in Mexican Fresco cheese using sensory and instrumental analysis. The aroma profiles were evaluated by descriptive sensory analysis. Volatiles were determined by solid-phase microextraction and gas chromatography-mass spectrometry. Principal component analysis was applied to interpret analytical and sensory data. Mexican Fresco cheese aroma was described as milkfat, yogurt, yeasty, barny, dirty socks, and Fresco cheese. Cheese with L. lactis strains R7 or B7 were most similar to commercial raw milk Fresco cheese in all aroma descriptors. Volatiles identified in all cheeses were esters, acids, alcohols, ketones, and aldehydes, but the main differences were found for total volatile relative abundance. Also, volatile concentrations (µg/g) in commercial raw milk Fresco cheese and cheeses made with L. lactis R7 or B7 were 4 methyl esters [C4 (4.15 vs. 5.47-13.74), C6 (0.12 vs. 1.53-15.34), C8 (1.06 vs. 0.32-6.65), and C10 (0.62 vs. 0.41-3.74)], 7 acids [C4 (1.92 vs. 0.30-9.29), C6-C10 (0.05-4.48 vs. 0.11-30.45), and C12 (0.13 vs. 0.28-0.30)], 2 alcohols [(3-methyl-1-butanol (3.48 vs. 3.4-13.13) and phenylethyl alcohol (0.10 vs. 0.63-2.04)], and 1 ketone (acetoin; 1.22 vs. 0.28-0.99). The first 3 principal components explained 78.2% of the total variation and clearly distinguished 3 main groups. Cheese made with L. lactis R7 was classified in the same group as key compounds associated with Fresco cheese aroma and show potential as a starter in Mexican Fresco cheese manufacture., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Queso Fresco is the most popular variety of Hispanic-style cheese consumed in the United States and Mexico. It is traditionally made from raw milk without specific starter cultures and the functional and flavor properties of the cheese are determined by the native microflora present in the raw milk. In the U.S., Queso Fresco is made from pasteurized milk with non-specific starter cultures resulting in a product with different organoleptic qualities from the traditional cheese. In this ARS-CIAD study, the indigenous microflora from six commercial Queso Fresco cheeses, obtained from Sonora, Mexico, were analyzed to identify bacterial species which may function as specific starter cultures. Four of the cheeses analyzed were made from raw milk and two from pasteurized milk. Classification of bacterial species was based on growth on selective media and 16S rDNA sequencing. The highest colony counts were obtained on M17 and MRS agar used for the selection of streptococci and lactobacilli respectively. Growth on MRS agar supplemented with vancomycin suggested that Leuconostoc species were present in all six samples. A high number of coliforms, enterococci and coagulase-positive staphylococci were identified in all raw milk samples. The number of enterococci remained high in cheese samples made from pasteurized milk but a 2 log10 reduction of coliforms was observed. Coagulase-positive staphylococci were reduced by 3 log10 in one pasteurized milk sample but remained high in the other (log 6.26 CFU/g). 16S rDNA sequence analysis revealed that lactobacilli were not present in any sample. Lactococcus lactis ssp. lactis was identified in four samples and Leuconostoc mesenteriodes and Entercoccus faecium were identified in all six samples. The results suggest that these species need further study to explore their potential as starter cultures for the production of cheese made from pasteurized milk while preserving the organoleptic qualities of traditional Queso Fresco. [ABSTRACT FROM AUTHOR]