Evaluation of reactive oxygen species generating AirOcare system for reducing airborne microbial populations in a meat processing plant

The microbial contamination of meat and meat products is of continuing concern to the meat industry and regulatory agencies. Air has been established as a source of microbial contamination in slaughter and processing facilities. The objective of this research was to determine the efficacy of reactive oxygen species (ROS) generating AirOcare equipment in reducing airborne bacteria in a meat processing environment. Bacterial strains found in ground beef were used to artificially contaminate the air using a 6-jet Collison nebulizer. Airborne bacterial populations in the meat processing room were monitored every 24 h at multiple locations using a Staplex 6 stage air sampler. Total aerobic, Gram-negative, and lactic acid bacterial populations were determined by sampling on R₂A agar, MacConkey agar and Lactobacilli MRS agar, respectively. Approximately 3 log reductions of lactic acid bacteria and Gram-negative bacteria were observed after 24 h of treatment (p < 0.05) compared to ~1.5 log reduction in the control treatment. Further exposure with ROS significantly reduced lactic acid bacteria and Gram-negative bacteria in the air at 48 and 96 h sampling intervals. These findings reveal that reactive oxygen species treatment using AirOcare unit significantly reduces airborne contamination in a meat processing environment. Mention of trade names or commercial products does not imply recommendation or endorsement to the exclusion of other products by the U.S. Department of Agriculture.     

Acid, bile, and heat tolerance of free and microencapsulated probiotic bacteria

ABSTRACT:  Eight strains of probiotic bacteria, including Lactobacillus rhamnosus , Bifidobacterium longum, L. salivarius, L. plantarum , L. acidophilus , L. paracasei , B. lactis type Bl-O4, and B. lactis type Bi-07, were studied for their acid, bile, and heat tolerance. Microencapsulation in alginate matrix was used to enhance survival of the bacteria in acid and bile as well as a brief exposure to heat. Free probiotic organisms were used as a control. The acid tolerance of probiotic organisms was tested using HCl in MRS broth over a 2-h incubation period. Bile tolerance was tested using 2 types of bile salts, oxgall and taurocholic acid, over an 8-h incubation period. Heat tolerance was tested by exposing the probiotic organisms to 65 °C for up to 1 h. Results indicated microencapsulated probiotic bacteria survived better ( P < 0.05) than free probiotic bacteria in MRS containing HCl. When free probiotic bacteria were exposed to oxgall, viability was reduced by 6.51-log CFU/mL, whereas only 3.36-log CFU/mL was lost in microencapsulated strains. At 30 min of heat treatment, microencapsulated probiotic bacteria survived with an average loss of only 4.17-log CFU/mL, compared to 6.74-log CFU/mL loss with free probiotic bacteria. However, after 1 h of heating both free and microencapsulated probiotic strains showed similar losses in viability. Overall microencapsulation improved the survival of probiotic bacteria when exposed to acidic conditions, bile salts, and mild heat treatment.     

Inhibition of Salmonella Typhimurium and Listeria monocytogenes in mung bean sprouts by chemical treatment

This study was undertaken to compare the efficacies of chlorous acid (268 ppm), sodium hypochlorite (200 ppm), and lactic acid (2%) in eliminating total mesophilic microorganisms, Salmonella Typhimurium, and Listeria monocytogenes on commercial mung bean sprouts immediately after treatment and during posttreatment refrigerated storage. Treatment with sodium hypochlorite for 10 min did not reduce the total aerobic count. However, treatment with lactic acid and chlorous acid for 10 min initially reduced the total aerobic count by 0.6 and 0.8 log CFU/g, respectively, and maintained the same level or a lower level of the total aerobic count during the storage time. Treatment with chlorous acid reduced Salmonella Typhimurium from 5.0 log to undetectable levels (<0.48 log CFU/g), and the pathogen remained undetectable over a 9-day storage period. Treatment with lactic acid resulted in an initial 3-log reduction and further reduced the number of Salmonella Typhimurium cells to undetectable levels after 3 days. For L. monocytogenes, treatment with chlorous acid resulted in an initial 5-log reduction, and treatment with lactic acid resulted in a 2-log reduction at the beginning and undetectable levels after 9 days. When chemically injured cells were investigated by the selective overlay method, no statistical difference was observed (P < 0.05) between the number of injured cells recovered following treatment with chlorous acid and the number of bacteria counted on selective media, whereas sodium hypochlorite generated more injured cells than the other treatments did. These data suggest that treatment with chlorous acid may be useful in reducing total mesophilic microorganisms, Salmonella Typhimurium, and L. monocytogenes in commercial mung bean sprouts.     

Use of UV light for the inactivation of Listeria monocytogenes and lactic acid bacteria species in recirculated chill brines

Ready-to-eat meat products have been implicated in several foodborne listeriosis outbreaks. Microbial contamination of these products can occur after thermal processing when products are chilled in salt brines. The objective of this study was to evaluate UV radiation on the inactivation of Listeria monocytogenes and lactic acid bacteria in a model brine chiller system. Two concentrations of brine (7.9% [wt/wt] or 13.2% [wt/wt]) were inoculated with a approximately 6.0 log CFU/ml cocktail of L. monocytogenes or lactic acid bacteria and passed through a UV treatment system for 60 min. Three replications of each bacteria-and-brine combination were performed and resulted in at least a 4.5-log reduction in microbial numbers in all treated brines after exposure to UV light. Bacterial populations were significantly reduced after 5 min of exposure to UV light in the model brine chiller compared with the control, which received no UV light exposure (P < 0.05). The maximum rate of inactivation for both microorganisms in treated brines occurred between minutes 1 and 15 of UV exposure. Results indicate that in-line treatment of chill brines with UV light reduces the number of L. monocytogenes and lactic acid bacteria.     

Microbial Reduction Efficiencies of Filtration, Electrostatic Polarization, and UV Components of a Germicidal Air Cleaning System

ABSTRACT: This study determined the effectiveness of components of a germicidal air-cleaning system involving filtration, electrostatic polarization, and UV light on the reduction of airborne bacteria and molds. The filter alone, filter and electrostatic polarization combined, and the filter, electrostatic polarization, and UV light were found to be effective ( P < 0.05) in reducing a given concentration of M. luteus and S. marcescens by 90 to 92%. The same components were also found to be effective ( P < 0.05) in reducing indigenous airborne bacteria and molds from ambient air in processing plant production conditions by 62 to 77% after only 1 pass through the filtration system. A germicidal air-filtration system utilizing electrostatic polarization and ultraviolet light can be used to reduce the chance of contaminating surfaces with airborne bacteria and molds.     

Effect of negative air ions on Escherichia coli ATCC 25922 inoculated onto mung bean seed and apple fruit

The effect of negative air ions on the reduction of Escherichia coli ATCC 25922 inoculated onto mung bean sprout seed and whole or fresh-cut apple fruit was studied. Mung bean seeds, whole Gala apples, and Gala apple slices were inoculated with E. coli ATCC 25922 before being exposed to negative air ions for up to 18 h at room temperature (-23 degrees C). Results revealed a less than 0.5-log reduction of E. coli on mung bean seed even after 18 h of exposure. The reduction of E. coli on the surface of whole apples increased with increasing exposure time from 0.5 to 3 h, but the maximum reduction was less than 1 log CFU/g. Increasing exposure time from 3 to 18 h did not lead to increased treatment efficacy. No reduction of E. coli was observed on apple slices after 3 h of treatment. When the negative air ion system was applied with acetic acid vapor, no additive or synergistic effect of negative ions on the reduction of E. coli was found. These results suggest that negative air ions have a very limited effect on the population of E. coli on mung bean seed and apples.     

扬州酱菜中降解亚硝酸盐乳酸菌的筛选、鉴定及性能研究

以扬州地区传统酱菜为研究对象,采用离子色谱（IC）法从32株乳酸菌中筛选降解亚硝酸盐能力较强的乳酸菌菌株,采用形态观察、生理生化试验和16S rDNA序列分析对其进行鉴定,并对其生长性能进行测定。结果表明,从扬州地区传统酱菜中筛选出一株降解亚硝酸盐能力较强的乳酸菌菌株,编号为DGJ-17,其亚硝酸盐降解率为91.7%;菌株DGJ-17被鉴定为乳酸肠球菌（Enterococcus lactis）;菌株DGJ-17的最适生长温度为30 ℃,培养12 h后进入对数生长期,30 h后细胞生物量趋于稳定。     

Validation of acid washes as critical control points in hazard analysis and critical control point systems

A 2% lactic acid wash used in a large meat-processing facility was validated as an effective critical control point (CCP) in a hazard analysis and critical control point (HACCP) plan. We examined the microbial profiles of beef carcasses before the acid wash, beef carcasses immediately after the acid wash, beef carcasses 24 h after the acid wash, beef subprimal cuts from the acid-washed carcasses, and on ground beef made from acid-washed carcasses. Total mesophilic, psychrotrophic, coliforms, generic Escherichia coli, lactic acid bacteria, pseudomonads, and acid-tolerant microorganisms were enumerated on all samples. The presence of Salmonella spp. was also determined. Acid washing significantly reduced all counts except for pseudomonads that were present at very low numbers before acid washing. All other counts continued to stay significantly lower (P < 0.05) than those on pre-acid-washed carcasses throughout all processing steps. Total bacteria, coliforms, and generic E. coli enumerated on ground beef samples were more than 1 log cycle lower than those reported in the U.S. Department of Agriculture Baseline data. This study suggests that acid washes may be effective CCPs in HACCP plans and can significantly reduce the total number of microorganisms present on the carcass and during further processing.     

Inactivation of Escherichia coli O157:H7, Salmonella enterica serotype enteritidis,and Listeria monocytogenes on lettuce by hydrogen peroxide and lactic acid and by hydrogen peroxide with mild heat

Iceberg lettuce is a major component in vegetable salad and has been associated with many outbreaks of foodborne illnesses. In this study, several combinations of lactic acid and hydrogen peroxide were tested to obtain effective antibacterial activity without adverse effects on sensory characteristics. A five-strain mixture of Escherichia coli O157:H7, Salmonella enterica serotype Enteritidis, and Listeria monocytogenes was inoculated separately onto fresh-cut lettuce leaves, which were later treated with 1.5% lactic acid plus 1.5% hydrogen peroxide (H2O2) at 40 degrees C for 15 min, 1.5% lactic acid plus 2% H2O2 at 22 degrees C for 5 min, and 2% H2O2 at 50 degrees C for 60 or 90 s. Control lettuce leaves were treated with deionized water under the same conditions. A 4-log reduction was obtained for lettuce treated with the combinations of lactic acid and H2O2 for E. coli O157:H7 and Salmonella Enteritidis, and a 3-log reduction was obtained for L. monocytogenes. However, the sensory characteristics of lettuce were compromised by these treatments. The treatment of lettuce leaves with 2% H2O2 at 50 degrees C was effective not only in reducing pathogenic bacteria but also in maintaining good sensory quality for up to 15 days. A < or = 4-log reduction of E. coli O157:H7 and Salmonella Enteritidis was achieved with the 2% H2O2 treatment, whereas a 3-log reduction of L. monocytogenes was obtained. There was no significant difference (P > 0.05) between pathogen population reductions obtained with 2% H2O2 with 60- and 90-s exposure times. Hydrogen peroxide residue was undetectable (the minimum level of sensitivity was 2 ppm) on lettuce surfaces after the treated lettuce was rinsed with cold water and centrifuged with a salad spinner. Hence, the treatment of lettuce with 2% H2O2 at 50 degrees C for 60 s is effective in initially reducing substantial populations of foodborne pathogens and maintaining high product quality.     

Antimicrobial potential of immobilized Lactococcus lactis subsp. lactis ATCC 11454 against selected bacteria

Immobilization of living cells of lactic acid bacteria could be an alternative or complementary method of immobilizing organic acids and bacteriocins and inhibit undesirable bacteria in foods. This study evaluated the inhibition potential of immobilized Lactococcus lactis subsp. lactis ATCC 11454 on selected bacteria by a modified method of the agar spot test. L. lactis was immobilized in calcium alginate (1 to 2%)-whey protein concentrate (0 and 1%) beads. The antimicrobial potential of immobilized L. lactis was evaluated in microbiological media against pathogenic bacteria (Escherichia coli, Salmonella, and Staphylococcus aureus) or Pseudomonas putida, a natural meat contaminant, and against seven gram-positive bacteria used as indicator strains. Results obtained in this study indicated that immobilized L. lactis inhibited the growth of S. aureus, Enterococcus faecalis, Enterococcus faecium, Lactobacillus curvatus, Lactobacillus sakei, Kocuria varians, and Pediococcus acidilactici. Only 4 h of incubation at 35 degrees C resulted in a clear inhibition zone around the beads that increased with time. With the addition of 10 mM of a chelating agent (EDTA) to the media, results showed growth inhibition of E. coli; however, P. putida and Salmonella Typhi were unaffected by this treatment. These results indicate that immobilized lactic acid bacteria strains can be successfully used to produce nisin and inhibit bacterial growth in semisolid synthetic media.     

Sensitization of gram-negative and gram-positive bacteria to jenseniin G by sublethal injury

Jenseniin G, a bacteriocin produced by Propionibacterium thoenii P126, is active against related propionibacteria and some lactic acid bacteria and is sporostatic to botulinal spores. The objective of this study was to evaluate the effects of sublethal stress on jenseniin G activity. Bacillus cereus, Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Salmonella Typhimurium, Shigella flexneri, Staphylococcus aureus, and Yersinia enterocolitica were subjected to temperature, acid, and osmotic stresses in the presence of jenseniin G. The bacteriocin reduced the viability of sublethally injured cultures, although the extent of reduction varied with strain and treatment. E. faecalis was the most sensitive to temperature stress; no reduction of viable counts occurred in the absence of jenseniin G, and a 1.5-log reduction occurred in the presence of jenseniin G. B. cereus, L. monocytogenes, and S. aureus were more sensitive to jenseniin G when exposed to heat stress than when exposed to cold stress, whereas E. coli, Salmonella Typhimurium, and S. flexneri were more sensitive to jenseniin G when exposed to cold stress than when exposed to heat stress. When comparing an acid stress test alone to a combination of acid stress and jenseniin G, E. faecalis and L. monocytogenes showed the greatest sensitivities with 4.87- and 2.82-log reductions, respectively, after 7 days. All cultures except for S. aureus were adversely affected by the combination of salt stress and jenseniin G. Salmonella Typhimurium showed the greatest sensitivity to salt stress with jenseniin G (a 1.54-log reduction at day 7) when compared to salt stress alone (a 0.55-log reduction at day 7). Jenseniin G, like bacteriocins produced by other gram-positive species, has broader activity against stressed organisms.     

传统发酵牦牛酸乳中细菌素产生菌的筛选与鉴定

从西藏羊八井地区、云南香格里拉的传统牦牛酸乳中分离出26株乳酸菌,以枯草芽孢杆菌、大肠杆菌、金黄色葡萄球菌以及酿酒酵母为指示菌。采用牛津杯双层琼脂扩散法检测菌株的抑菌谱大小,并经过有机酸排除、过氧化氢排除、蛋白酶水解检测试验,最终筛选得到5株产细菌素的菌株,编号分别为3、23、24、21和25。通过微生物形态学与16SrDNA序列同源性分析,鉴定这些菌株分别为干酪乳杆菌、植物乳杆菌和乳酸乳球菌乳球亚种。抑菌谱试验表明,这些细菌素能够抑制部分食源性革兰氏阳性菌和阴性致病菌,对真菌无抑菌活性。     

Effect of Lactic Acid Bacterial Fermentation on the Characteristics of Minced Mackerel

ABSTRACT: To improve the functionality and quality of seafood, mackerel minces were fermented with lactic acid bacteria (LAB) ∼ Lactobacillus plantarum CCRC10069, Lactococcus lactis subsp. lactis CCRC 12315, Lactobacillus helveticus CCRC 14092, or their combination at 37 °C. Rapid growth of LAB, decline in pH, suppress of main microflora, increases in whiteness, Hunter L, nonproteinous nitrogen, sensory quality, and free amino acids related to taste were observed. However, VBN of samples fermented with LAB were still d ≤ 25 mg/100g after 36 h fermentation. SDS-PAGE indicated the obvious degradation of water- and salt-soluble muscle proteins after 12 h fermentation. Animal test demonstrated the LAB-fermented mince has the functionality on reduction of blood pressure, glucose, and total cholesterol of SHR.     

Homofermentative lactic acid bacteria of a traditional cheese, Comlek peyniri from Cappadocia region

Comlek peyniri is a typical artisanal cheese in Central Anatolia. This type of cheese was made by using the indigenous lactic acid bacteria (LAB) flora of cow or ewes' milk. Majority of the samples were taken from fresh cheese because the aim was to isolate homofermentative LAB. Initially 661 microbial isolates were obtained from 17 cheese samples. Only 107 were found to be homofermentative LAB. These isolates were selected and identified by using both phenotypic and molecular methods. Phenotypic identification included curd formation from skim milk, catalase test, Gram staining and light microscopy, growth at different temperatures and salt concentrations, arginine hydrolysis, gas production from glucose, and carbohydrate fermentation. Molecular identification was based on the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the 16S rRNA gene-ITS (internally transcribed spacer) region. By combining the phenotypic and molecular identification results, isolates belonging to each of the following genera were determined at species or subspecies level: 54 Lactococcus lactis subsp. lactis, 21 Enterococcus faecium, 3 Ec. faecalis, 2 Ec. durans, 10 Ec. sp., 15 Lactobacillus paracasei subsp. paracasei, and 2 Lb. casei strains. Technological characterisation was also performed by culturing each of the strains in UHT skim milk, and by monitoring pH change and lactic acid production at certain time intervals through the 24 h incubation. Results of the technological characterisation indicated that 33% of the isolates (35 strains) were capable of lowering the pH of UHT milk below 5.3 after 6 h incubation at 30 degrees C. Thirty four of these strains were Lc. lactis subsp. lactis, and only one was an Ec. faecium strain.     

Microbial and quality attributes of ground pork prepared from commercial pork trim treated with combination intervention processes.

The effects of combination intervention treatments of commercial pork trim on microbial and quality attributes of the subsequent ground pork were examined. Fresh commercial pork trim was inoculated with swine feces and subjected to five different intervention treatments: (i) control (untreated), (ii) water (15 degrees C, 120 s), (iii) water followed by 2% lactic acid wash (15 degrees C, 75 s), (iv) Combination 1 (water plus lactic acid plus hot air [510 degrees C, 90 s]), and (v) Combination 2 (hot air plus water plus hot air). Following treatment, the pork trim was stored at 4 degrees C for 24 h, then ground, stuffed, vacuum packaged, and stored at 4 degrees C for 21 days. Populations of aerobic bacteria, coliforms, Escherichia coli, and lactic acid bacteria in the ground pork were monitored before treatment, after treatment (day 0), and at 2, 7, 14 and 21 days. In addition, uninoculated pork trim was treated as described above, and the color and emulsion stability of the ground product was evaluated. Ground pork prepared from trim treated with any of the treatment processes had lower initial microbial populations compared to the untreated samples. The applications of water plus lactic acid or Combination 1, which included a lactic acid wash, were more effective than water or Combination 2 at both reducing initial populations and suppressing the growth of aerobic bacteria, coliforms, and E. coli in ground pork during refrigerated storage. By day 21, populations of aerobic bacteria in ground pork prepared from control, water-treated, and Combination 2-treated trim were 8.22 to 8.32 log CFU/g, but in water plus lactic acid and Combination 1 ground pork, populations were 6.32 and 4.90 log CFU/g, respectively. Among the trim interventions examined, Combination 1 was most detrimental to the color and emulsion stability of the ground pork. The water plus lactic acid treatment provided the greatest microbial reduction and inhibition without large negative effects on quality attributes of the ground pork.     

摩洛哥发酵橄榄汁中乳酸菌的分离鉴定及其多样性研究

为了分离、保藏自然发酵食品中乳酸菌资源,丰富自然发酵食品中乳酸菌多样性信息,本文采用纯培养方法和宏基因组16S rRNA基因测序技术对采集自摩洛哥的2份自然发酵橄榄汁中的乳酸菌进行分离鉴定和多样性研究。结果表明:2份样品中共分离鉴定出52株乳酸菌,分属于3个属、4个种,其中乳酸乳球菌（Lactococcus lactis）为摩洛哥卡萨布兰卡地区发酵橄榄汁中的优势菌种,占总分离株的42.31%,同时还分离到植物乳杆菌和肠球菌;利用PacBio SMRT16S rRNA测序技术,将橄榄汁中的细菌归为5个门、40个属和80个种,优势菌种同样为Lactococcus lactis,其次还检测到干酪乳杆菌（Lactobacillus casei）和植物乳杆菌（Lactobacillus plantarum）。     

The effect of delayed ensiling and application of a propionic acid-based additive on the fermentation of barley silage

Prolonged exposure to air can adversely affect the silage fermentation process. To investigate a possible method to overcome this problem, we determined if a buffered propionic acid-based additive, applied to chopped, whole-plant barley exposed to air before ensiling, would affect the subsequent fermentation. Wilted forage was chopped and treated with nothing, or with 0.1% (wt/wt wet forage) of a buffered propionic acid-based additive and ensiled immediately in quadruplicate 20-L laboratory silos. Portions of the chopped forage, untreated and treated, were left in loose piles in a barn for 24 h before ensiling. Another portion of the untreated silage exposed to air for 24 h was also treated with 0.1% of the additive just before ensiling. Prolonged exposure to air before ensiling increased the numbers of yeasts on forages by more than 1,000-fold. The concentrations of water-soluble carbohydrates decreased by more than 50%; the ammonia-N concentrations increased 40%, and pH increased by more than 1 unit as a result of exposure to air. These changes were less in forage that was treated with the additive at chopping. After 60 d, silages of forages that were exposed to air before ensiling had a higher pH, higher concentrations of ammonia-N and butyric acid, and lower concentrations of lactic and acetic acids than silages of forage that had been ensiled immediately after harvest. In situ DM digestibility was lowest in untreated silages that had been exposed to air before ensiling. In contrast, treatment with the additive, applied before or after exposure to air, prevented the reduction in in vitro digestion.     

Quantification of microbial populations associated with the manufacture of vacuum-packaged, smoked vienna sausages

Sources of contamination of vacuum-packaged vienna sausages by spoilage microorganisms were examined in a meat-processing plant. Microbial numbers present in the environment, on working surfaces and workers' hands and aprons were quantified by plate counting on selective media. Product line samples were taken at critical control points in the manufacturing process and analysed before and after preliminary incubation of vacuum-packaged samples at 25 degrees C for 24 h. In all samples the numbers of aerobic bacteria, Enterobacteriaceae, lactic acid bacteria and yeasts were determined by standard procedures. Contamination of sausage surfaces by lactic acid bacteria occurred as a result of the manufacturing and handling processes. The environment and specifically packers' hands, as well as working surfaces contributed to microbiological contamination of various types after removal of the peel from individual sausages. The preliminary incubation procedure allowed detection of low numbers of spoilage microorganisms.     

Development of a multiple-step process for the microbial decontamination of beef trim

A multiple-hurdle antimicrobial process for beef trim was developed. The microbial profiles of inoculated lean beef trim tissue (BTL) and fat-covered lean beef trim (BTF) were monitored during prolonged refrigerated storage following the application of successive multiple antimicrobial treatments applied to inoculated beef trim on a processing conveyor belt set at a belt speed of 1 cm/s. Beef trim (meat size approximately 15 by 15 cm) was preinoculated with bovine feces before all treatments that included the following: control, no treatment; water wash at 65 psi for five passes; water plus lactic acid (2% [vol/vol] room temperature lactic acid wash at 30 psi for three passes); combination treatment 1 (water plus 65 degrees C hot water at 30 psi for one pass plus hot air at 510 degrees C for four passes plus lactic acid), combination treatment 2 (water plus hot water at 82 degrees C for one pass plus hot air at 510 degrees C for five passes plus lactic acid), and combination treatment 3 (water plus hot water at 82 degrees C for three passes plus hot air at 510 degrees C for six passes plus lactic acid). The effects of treatments on bacterial populations were monitored by enumerating mesophilic aerobic bacteria (APC), presumptive lactic acid bacteria (PLAB), psychrotrophic bacteria (PCT), coliforms, and Escherichia coli biotype 1 on product stored for up to 7 days at 4 degrees C. In the case of BTL, the numbers of APC, PCT, and PLAB increased during storage at 5 degrees C, whereas the numbers of coliform and E. coli decreased on average by 1.8 log CFU/cm2, then remained constant following the initial reduction. Negligible effects on color quality were observed from multihurdle treatment combination 1. In the case of the BTF, the microbial reductions by treatments were much greater than the reduction on BTL. The pH of treated BTF increased more slowly than the pH of treated BTL, resulting in further reduction of the microflora on BTF. Except for control and water treatments, all sample treatments involving lactic acid resulted in continuously decreasing microbial populations. Based on microbial reduction and quality aspects, it was concluded that successively applied combination antimicrobial treatments for meat trim could offer potential food safety benefits.     

Purification and characterization of X-prolyl-dipeptidyl-aminopeptidase from Lactobacillus lactis and from Streptococcus thermophilus

X-Prolyl-dipeptidyl-aminopeptidase recently was found in several lactic acid bacteria. This article describes the purification of the enzymes from Lactobacillus lactis and Streptococcus thermophilus and compares their characteristics. Enzymes from both strains are serine-peptidases. They both have a molecular weight of about 165,000 daltons, an isoelectric point near 4.5, and are constituted of two subunits. The pH optimum of the enzyme isolated from L. lactis is 7.0, whereas the enzyme from S. thermophilus possesses a broad pH optimum between 6.5 and 8.2 with glycyl-L-prolyl-aminomethylcoumarin as substrate. Below pH 5, both enzymes are unstable; however, that from S. thermophilus is more rapidly denatured. The enzyme from S. thermophilus is more sensitive to heat than the corresponding enzyme from L. lactis. Enzymes from the both strains have different specificities towards various substrates and are differently effected by metals, chelators, and other inhibitors. The importance of this enzyme for the metabolism of lactic acid bacteria is discussed.