Identification of Structural and Immunity Genes of a Class IIb Bacteriocin Encoded in the Enterocin A Operon of Enterococcus faecium Strain MXVK29.

The Enterococcus faecium strain MXVK29, isolated from fermented sausages, produces a bacteriocin with a molecular mass of 3.5 kDa that belongs to the class of enterocins II.1, according to the terminal amino acid sequence, and has been identified as enterocin A. This bacteriocin is active against selected strains of Listeria, Staphylococcus, Pediococcus, and Enterococcus. In this study, we identified the genes adjacent to the structural gene for this bacteriocin, such as the immunity gene (entI) and the inducer gene (entF). Accessory genes for this bacteriocin, such as entK, entR, and entT, were identified as well, in addition to the orf2 and orf3, showing a high identity with class IIb peptides bacteriocins. The orf2 shows the consensus motif GxxxG, similar to those shown by bacteriocins such as PlnNC8α, EntCα, and Ent1071A, whereas orf3 shows a consensus motif SxxxS similar to that present in PlnNC8ß (AxxxA). PlnNC8 is expressed only in bacterial cocultures, so there is the possibility that the expression of this two-peptide bacteriocin can be induced by a similar mechanism. So far, only the expression of enterocin A has been found in this strain; however, the presence of the genes ent29α and ent29ß opens the possibility for further research on its induction, functionality, and origin. Although there are reports on this type of bacteriocin (EntX, EntC, and Ent1071) in other strains of E. faecium, no report exists yet on an Enterococcus strain producing two different classes of bacteriocin.

Assessment of virulence factors, antibiotic resistance and amino-decarboxylase activity in Enterococcus faecium MXVK29 isolated from Mexican chorizo.

Enterococcus faecium MXVK29 has the ability to produce an antimicrobial compound that belongs to Class IIa of the Klaenhammer classification, and could be used as part of a biopreservation technology through direct inoculation of the strain as a starter or protective culture. However, Enterococcus is considered as an opportunistic pathogen, hence, the purpose of this work was to study the food safety determinants of E. faecium MXVK29. The strain was sensitive to all of the antibiotics tested (penicillin, tetracycline, vancomycin, erythromycin, chloramphenicol, gentamicin, neomycin, kanamycin and netilmicin) and did not demonstrate histamine, cadaverine or putrescine formation. Furthermore, tyrosine-decarboxylase activity was detected by qualitative assays and PCR. Among the virulence factors analysed for the strain, only the genes encoding the sexual pheromone cCF10 precursor lipoprotein (ccf) and cell-wall adhesion (efaAfm ) were amplified. The presence of these genes has low impact on pathogenesis, as there are no other genes encoding for virulence factors, such as aggregation proteins. Therefore, Enterococcus faecium could be employed as part of a bioconservation method, because it does not produce risk factors for consumer's health; in addition, it could be used as part of the hurdle technology in foods. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of molecular techniques has allowed, in recent years, to detect pathogenicity genes present in the genome of starter cultures used in food processing and preservation. The presence of these genes is undesirable, because horizontal transfer may occur with the natural biota of consumers. For this reason, it is important to analyse the presence of pathogenicity genes in such cultures. In this work, virulence factors and antibiotic resistance of Enterococcus faecium strain MXVK29, producing an antimicrobial compound with high antilisterial activity, were analysed. The results indicate that the strain is safe to be used in food processing as starter culture.

Quality traits of pork semimembranosus and triceps brachii muscles sourced from the United States and Mexico.

The study included fresh pork semimembranosus (SM, n=289) and triceps brachii (TB, n=283) muscles sourced from meat packers of Mexico and the USA. Samples were analyzed for moisture, protein, and fat content, pH, shear force (WBSF), cook loss, water holding capacity (WHC), instrumental color, emulsion capacity (EC) and stability (ES), and consumer sensory ratings. SM from the USA had lower WBSF (P<0.05) than that from Mexico (26.7 vs. 29.7N), higher WHC (44.7 vs. 38.4%; P<0.05) and a better appearance, as indicated by its lower h* (52.3 vs. 56.6; P<0.05) and higher C* (23.1 vs. 21.3; P<0.05). Consumer acceptance of SM was similar (P>0.05) across countries. TB from Mexico had higher (P<0.05) fat content (2.5 vs. 2.0%), lower (P<0.05) WBSF values (32.0 vs. 36.9N), and received more positive ratings by Mexican consumers (87.1 vs. 81.7%) than its US equivalent. In general, US pork exhibits better technological properties, while country of origin has less effect on consumer acceptability.

Effects of heat and pH treatments and in vitro digestion on the biological activity of protein hydrolysates of Amaranthus hypochondriacus L. grain.

The aim of this work was to assess the effects of temperature (T), time (t) and pH treatments and an in vitro digestion on the stability of the angiotensin I-converting-enzyme-inhibitory activity (ACEIA) and antithrombotic activity (ATA; assessed as inhibition of platelet aggregation) of selected protein hydrolysates of amaranth named Alb1H103 and GloH88 and GluH24 with dipeptidyl peptidase IV inhibitory activity (DPPIVIA). Heat treatment (40-100 °C) for 1 h showed no significant differences among ACEIA, DPPIVIA and ATA of the heated hydrolysates at pH 4 and 7. There was no statistically significant loss of any bioactivity under heat treatment for 3 h at pH 4.0. Alb1H103 and GluH24 maintained the inhibitory activity of ACE and ATA at pH 7.0 for 3 h, whereas GloH88 maintained ACEIA and ATA for 2.0 h at pH 7.0. The pH effect on hydrolysates bioactivity was assessed in the range of 2.0-12.0. This was negligible on ACEIA, ATA and DPPIVIA. The in vitro digestion was performed using pepsin, trypsin (T) and α-chymotrypsin (C). A previous treatment of hydrolysates with pepsin improved the proteolytic activities of T and C. The hydrolysates kept at 100 °C for 1 h at pH 4.0, showed a significant increase in bioactivity. Conversely, a treatment at pH 7.0 showed no significant difference (p < 0.05) in the hydrolysates bioactivities after their digestion. Thus, biological activity of hydrolysates may be preserved or enhanced, depending on their processing conditions.

Improving appearance and microbiologic quality of broiler carcasses with an allostatic modulator.

An important priority of poultry producers is to guarantee animal welfare during animal production; however, broilers are exposed to unavoidable chronic stress (also known as allostasis) when they are captured, caged, and transported to the processing plant. This antemortem management causes allostatic load, animal injuries, and poor carcass quality. The aim of the present study was to evaluate the effects of an allostatic modulator (AM) on antemortem stress by measuring the appearance and microbiological quality of broiler carcasses. The AM consisted of a liquid formula containing ascorbic acid, acetyl salicylic acid, and electrolytes, administered orally 48 h before shipment to the processing plant. A total of 600 chickens (49-days-old) were used under a factorial arrangement 2 × 2 × 2 [2 commercial hybrid lines, 2 feed withdrawal programs (10 and 16 h), and 2 water treatments (control and AM)]. Each treatment included 25 chickens per pen and was carried out in triplicate. The broilers were shipped, slaughtered, and processed in a commercial processing plant where carcass defects (bruises and broken bones caused by antemortem management), crop pH, and carcass bacterial counts were evaluated in all experimental groups. Broilers under AM treatment showed a reduction in carcass defects (P = 0.015), crop pH (P = 0.0001), coliforms counts (P = 0.014), and total aerobic mesophilic bacteria (P = 0.0001) when compared to the control treatment. The present study indicates that the AM can be used to improve carcass quality in broilers. Our study provides a novel and economic alternative to reduce the allostatic load in broilers.

Antioxidant effect rosemary (Rosmarinus officinalis L.) and oregano (Origanum vulgare L.) extracts on TBARS and colour of model raw pork batters.

Herbs and spices are traditional used as food ingredients as well as for their antioxidant properties. The objective of this work was to study the concentration of carnosol, rosmarinic and carnosic acids in rosemary (Rosmarinus officinalis L.) and oregano leaves (Origanum vulgare L.), and their effect on the oxidation and colour of model pork batters. Extracts were obtained by maceration with ethanol and reflux with chloroform. Rosemary extracts showed higher antioxidant activity, even more than the phenol compounds separately. These extracts also showed the highest antioxidant capacity, possibly due to the presence of high concentrations of carnosic acid and carnosol and unidentified active compounds. However, ethanol oregano extracts containing high concentrations of phenols, mainly rosmarinic acid, efficiently prevented colour deterioration. The antioxidant effect of the studied extracts depends, not only on the concentration of phenol compounds (rosmarinic acid, carnosol and carnosic acid), but also on the extraction method and solvent.

Changes in fatty acids and microbial populations of pork inoculated with two biopreservative strains.

Meat surface fermentation has been reported as an efficient method to reduce undesirable microbial population of this food commodity in tropical areas with high ambient temperatures and humidity. However, in order to efficiently apply this method, growth of biopreservative strains and changes in the meat substrate should be studied. Changes in long-chain fatty acids as well as pH and microbial growth (lactic acid bacteria and enterobacteria) were studied in pork inoculated with two biopreservative strains (Lactobacillus alimentarius and Staphylococcus carnosus) and stored at 4 and 20 °C. Both tested strains produced more than 6 mg lactic acid/g tissue, however, S. carnosus was more efficient in reducing enterobacteria populations at 20 °C. No significant increase in long-chain fatty acid concentration in samples stored at 4 °C was observed but there was a rapid increase of free fatty acids when stored at 20 °C.