Inactivation of gram-negative bacteria in milk and banana juice by hen egg white and lambda lysozyme under high hydrostatic pressure

The effect of hen egg white lysozyme (HEWL) and bacteriophage lambda lysozyme (LaL) in combination with high pressure (HP) treatment on the inactivation of four gram-negative bacteria (Escherichia coli O157:H7, Shigella flexneri, Yersinia enterocolitica and Salmonella typhimurium), was studied in skim milk (pH 6.8; a(w) 0.997) and in banana juice (pH 3.8; a(w) 0.971). In the absence of lysozymes, S. flexneri was more sensitive to HP in milk than in banana juice, while the opposite was observed for the other three bacteria. In combination with HP treatment, LaL was more effective than HEWL on all bacteria in both milk and banana juice. Depending on the bacteria, inactivation levels in banana juice were increased from 0.4-2.7 log units by HP treatment alone to 3.6-6.5 log units in the presence of 224 U/ml LaL. Bacterial inactivation in milk was also enhanced by LaL but only by 0.5-2.1 log units. Under the experimental conditions used, LaL was more effective in banana juice than in milk, while the effectiveness of HEWL under the same conditions was not significantly affected by the food matrix. This effect could be ascribed to the low pH of the banana juice since LaL was also more effective on E. coli in buffer at pH 3.8 than at pH 6.8. Since neither LaL nor HEWL are enzymatically active at pH 3.8, we analysed bacterial lysis after HP treatment in the presence of these enzymes, and found that inactivation proceeds through a non-lytic mechanism at pH 3.8 and a lytic mechanism at pH 6.8. Based on these results, LaL may offer interesting perspectives for use as an extra hurdle in high pressure food preservation.     

Lytic and nonlytic mechanism of inactivation of gram-positive bacteria by lysozyme under atmospheric and high hydrostatic pressure

A different behavior was observed in three gram-positive bacteria exposed to hen egg white lysozyme by plate counts and phase-contrast microscopy. The inactivation of Lactobacillus johnsonii was accompanied by spheroplast formation, which is an indication of peptidoglycan hydrolysis. Staphylococcus aureus was resistant to lysozyme and showed no signs of peptidoglycan hydrolysis, and Listeria innocua was inactivated and showed indications of cell leakage but not of peptidoglycan hydrolysis. Under high hydrostatic pressure, S. aureus also became sensitive to lysozyme but did not form spheroplasts and was not lysed. These results suggested the existence of a nonlytic mechanism of bactericidal action of lysozyme on the latter two bacteria, and this mechanism was further studied in L. innocua. Elimination of the enzymic activity of lysozyme by heat denaturation or reduction with beta-mercaptoethanol eliminated this bactericidal mechanism. By means of a LIVE/DEAD viability stain based on a membrane-impermeant fluorescent dye, the nonlytic mechanism was shown to involve membrane perturbation. In the absence of lysozyme, high-pressure treatment was shown to induce autolytic activity in S. aureus and L. innocua.     

BIOCHEMICAL AND ANTIBACTERIAL PROPERTIES OF LYSOZYME PURIFIED FROM THE VISCERA OF SCALLOPS (PATINOPECTEN YESSOENSIS)

A lysozyme was purified from the viscera of scallops by ion exchange, gel permeation and affinity chromatographies. The yield of the purified lysozyme was 1.52%, and its purification ratio was 411.9 folds. The molecular weight of the scallop lysozyme was about 14.5 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The optimal temperature for lysozyme activity was 20C, but the optimal stability temperature was between 20 and 30C.
The optimal pH for lysozyme activity was 5.0, but the optimal stability pH was between 5.0 and 6.0. Scallop lysozyme had antibacterial activities against both gram-positive and gram-negative bacteria in which gram-negative bacteria, Escherichia coli and Vibrio vulnificus, were inhibited more effectively than gram-positive bacteria. Egg white lysozyme inhibited gram-positive bacteria better than the scallop lysozyme, whereas the reverse was true for gram-negative bacteria. The N-terminal sequence of the scallop lysozyme consisted of 10 amino acids: proline, cysteine, valine, tyrosine, alanine, phenylalanine, methionine, asparagine, glutamic acid and aspartic acid.

PRACTICAL APPLICATIONS

Egg white lysozyme (EWL) has been used as a preservative or antibacterial agent in the pharmaceutical and food industry, but is limited to broaden its application because of poor antibacterial activity against gram-negative bacteria. Scallop viscera lysozyme has two times higher antibacterial activity against gram-negative bacteria ( Escherichia coli and Vibrio vulnificus ) than EWL. Therefore, scallop viscera lysozyme shows a promise as a bacteriostatic or prophylactic agent in food preservation and specialty product.     

Bacterial inactivation by high-pressure homogenisation and high hydrostatic pressure

The resistance of five gram-positive bacteria, Enterococcus faecalis, Staphylococcus aureus, Lactobacillus plantarum, Listeria innocua and Leuconostoc dextranicum, and six gram-negative bacteria, Salmonella enterica serovar typhimurium, Shigella flexneri, Yersinia enterocolitica, Pseudomonas fluorescens and two strains of Escherichia coli, to high-pressure homogenisation (100-300 MPa) and to high hydrostatic pressure (200-400 MPa) was compared in this study. Within the group of gram-positive bacteria and within the group of gram-negative bacteria, large differences were observed in resistance to high hydrostatic pressure, but not to high-pressure homogenisation. All gram-positive bacteria were more resistant than any of the gram-negative bacteria to high-pressure homogenisation, while in relative to high hydrostatic pressure resistance both groups overlapped. Within the group of gram-negative bacteria, there also existed another order in resistance to high-pressure homogenisation than to high hydrostatic pressure. Further it appears that the mutant E. coli LMM1010, which is resistant to high hydrostatic pressure is not more resistant to high-pressure homogenisation than its parental strain MG1655. The preceding observations indicate a different response of the test bacteria to high-pressure homogenisation compared to high hydrostatic pressure treatment, which suggests that the underlying inactivation mechanisms for both techniques are different. Further, no sublethal injury could be observed upon high-pressure homogenisation of Y. enterocolitica and S. aureus cell population by using low pH (5.5 7), NaCl (0 6%) or SDS (0-100 mg/l) as selective components in the plating medium. Finally, it was observed that successive rounds of high-pressure homogenisation have an additive effect on viability reduction of Y. enterocolitica and S. aureus.     

Grapefruit juice and its furocoumarins inhibits autoinducer signaling and biofilm formation in bacteria

Cell-to-cell communications in bacteria mediated by small diffusible molecules termed as autoinducers (AI) are known to influence gene expression and pathogenicity. Oligopeptides and N-acylhomoserine lactones (AHL) are major AI molecules involved in intra-specific communication in gram-positive and gram-negative bacteria respectively, whereas boronated-diester molecules (AI-2) are involved in inter-specific communication among both gram-positive and gram-negative bacteria. Naturally occurring furocoumarins from grapefruit showed >95% inhibition of AI-1 and AI-2 activities based on the Vibrio harveyi based autoinducer bioassay. Grapefruit juice and furocoumarins also inhibited biofilm formation by Escherichia coli O157:H7, Salmonella typhimurium and Pseudomonas aeruginosa. These results suggest that grape fruit juice and furocoumarins could serve as a source to develop bacterial intervention strategies targeting microbial cell signaling processes.     

Cross-reactivity and Heat Lability of Antigenic Determinants of Duck and Goose Lysozymes

Two panels of monoclonal antibodies (Mabs) raised against duck (Barbary) egg white lysozyme or hen egg white lysozyme, were tested in antigen-coated plate (ACP) and double antibody sandwich (DAS) ELISA for cross-reaction with various avian lysozymes. The antibodies to hen lysozyme cross-reacted with goose lysozyme, but most antibodies to duck lysozyme reacted with it. One antibody to duck lysozyme reacted more strongly with goose lysozyme than with the homologous antigen, a heterospecific reaction confirmed by biosensor technology. Many lysozyme epitopes recognized by different antibodies showed considerable resistance to heat denaturation. Such Mabs may be useful for detecting chicken liver adulterants in “foies gras” of goose or duck origin.     

乳酸乳球菌L9所产类细菌素Lactococcin GJ-9的初步研究

采用双层平板法 ,自 117株分离的乳酸菌中筛选出一株具有较广抑菌活性的菌株L9,经鉴定为乳酸乳球菌 (Lactococcuslactics)。在排除酸性产物和过氧化氢的干扰后 ,L9菌株发酵液对溶壁微球菌 (Micrococcuslysodeikticus)、金黄色葡萄球菌 (Staphylococcusaureus)和枯草杆菌 (Bacillussubtilis)等革兰氏阳性菌以及大肠杆菌 (Escherichiacoli)、鼠伤寒沙门氏菌(Salmonellatyphimurium )等革兰氏阴性菌有强烈的抑制作用。表明该菌株产生一具有广谱抑菌活性的物质。经胰蛋白酶、胃蛋白酶和蛋白酶K处理后发酵液抑菌活性不变 ,表明该活性物质为非蛋白成分 ,属于类细菌素 ,命名为LactococcinGJ 9。它具有很好的热稳定性 ,在酸性条件下稳定且活性高 ,对蛋白酶不敏感 ,且具有较广的抗菌谱     

Antibacterial activity of chitosans and chitosan oligomers with different molecular weights

Antibacterial activities of six chitosans and six chitosan oligomers with different molecular weights (Mws) were examined against four gram-negative (Escherichia coli, Pseudomonas fluorescens, Salmonella typhimurium, and Vibrio parahaemolyticus) and seven gram-positive bacteria (Listeria monocytogenes, Bacillus megaterium, B. cereus, Staphylococcus aureus, Lactobacillus plantarum, L. brevis, and L. bulgaricus). Chitosans showed higher antibacterial activities than chitosan oligomers and markedly inhibited growth of most bacteria tested although inhibitory effects differed with Mws of chitosan and the particular bacterium. Chitosan generally showed stronger bactericidal effects with gram-positive bacteria than gram-negative bacteria in the presence of 0.1% chitosan. The minimum inhibitory concentration (MIC) of chitosans ranged from 0.05% to >0.1% depending on the bacteria and Mws of chitosan. As a chitosan solvent, 1% acetic acid was effective in inhibiting the growth of most of the bacteria tested except for lactic acid bacteria that were more effectively suppressed with 1% lactic or formic acids. Antibacterial activity of chitosan was inversely affected by pH (pH 4.5-5.9 range tested), with higher activity at lower pH value.     

Antibacterial activity of Bacillus amyloliquefaciens phage endolysin without holin conjugation

To characterize the enzymatic activity and antibacterial activity of endolysin encoded by a Bacillus amyloliquefaciens phage, the open reading frame encoding endolysin was amplified by PCR and cloned into the expression plasmid pET21d(+). The resultant plasmid was used to transform Escherichia coli JM109(DE3). Production of endolysin in the cytosol facilitated cell lysis without coproduction of holin, which is considered to degrade or alter the cytoplasmic membrane. The phage endolysin was overexpressed and purified. Although the specific activity of the purified phage endolysin towards lyophilized Micrococcus luteus cells was 1/11 of the activity of chicken egg white lysozymes, the endolysin showed stronger antibacterial activity towards E. coli W3110, E. coli JM109(DE3) and Pseudomonas aeruginosa PAO1 than chicken egg white lysozymes. The antibacterial activity of the endolysin towards these three bacterial strains was marked when EDTA was added to the endolysin solution.     

Antibacterial activity of bioconverted eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) against foodborne pathogenic bacteria

The antimicrobial activity of bioconversion extracts of EPA and DHA against a range of foodborne pathogenic bacteria was investigated. The bioconverted EPA and DHA exhibited antibacterial activities against four gram-positive bacteria, Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus (ATCC 6538) and S. aureus (KCTC 1916) and seven gram-negative bacteria, Enterobacter aerogenes, Escherichia coli, E. coli O157:H7, E. coli O157:H7 (human), Pseudomonas aeruginosa, Salmonella enteritidis and S. typhimurium. The growth inhibition by both bioconverted EPA and DHA was similar against gram-positive bacteria, while the bioconverted extract of DHA was more effective than EPA against gram-negative bacteria as determined by minimum inhibitory concentration.     

Enhanced inactivation of foodborne pathogenic and spoilage bacteria by FD&C Red no. 3 and other xanthene derivatives during ultrahigh pressure processing

Variability among microorganisms in barotolerance has been demonstrated at genus, species, and strain levels. Identification of conditions and additives that enhance the efficacy of ultrahigh pressure (UHP) against important foodborne microorganisms is crucial for maximizing product safety and stability. Preliminary work indicated that FD&C Red No. 3 (Red 3), a xanthene derivative, was bactericidal and acted synergistically with UHP against Lactobacillus spp. The objective of this study was to determine the antimicrobial efficacy of Red 3 and other xanthene derivatives, alone and combined with UHP, against spoilage and pathogenic bacteria in citrate-phosphate buffer (pH 7.0). Xanthene derivatives tested were fluorescein, Eosin Y, Erythrosin B, Phloxine B, Red 3, and Rose Bengal. Halogenated xanthene derivatives (10 ppm) were effective at reducing Listeria monocytogenes survivors but ineffective against Escherichia coli O157:H7. When combined with UHP (400 MPa, 3 min), the presence of derivatives enhanced inactivation. Because Red 3 was the only xanthene derivative to produce synergistic inactivation of both pathogens, further studies using this colorant were warranted. Efficacy of Red 3 against gram-positive bacteria (Lactobacillus plantarum and L. monocytogenes) was concentration dependent (1 to 10 ppm). E. coi O157: H7 strains were resistant to Red 3 concentrations up to 300 ppm. When Red 3 was combined with UHP, the lethality against gram-positive and gram-negative bacteria was dose dependent, with synergy being significant for most strains at > or = 3 ppm. Additional gram-positive and gram-negative bacteria showed lethalities similar to those observed for L. plantarum or L. monocytogenes, and E. coli O157:H7, respectively. Red 3 is a potentially useful additive to enhance the safety and stability of UHP-treated food products.     

Sensitization of outer-membrane mutants of Salmonella typhimurium and Pseudomonas aeruginosa to antimicrobial peptides under high pressure

High pressure can sensitize gram-negative bacteria to antimicrobial peptides or proteins through the permeabilization of their outer membranes; however, the range of compounds to which sensitivity is induced is species and strain dependent. We studied the role of outer-membrane properties in this sensitization by making use of a series of rough and deep rough mutants of Salmonella enterica serovar Typhimurium that show an increased degree of lipopolysaccharide (LPS) truncation, along with Pseudomonas aeruginosa PhoP and PhoQ mutants with altered outer-membrane properties. The outer-membrane properties of P. aernginosa were also modulated through the use of different Mg2- concentrations in the growth medium. Each of these strains was challenged under high pressure (15 min at 270 MPa for Salmonella Typhimurium and 15 min at 100 MPa for P. aerttginosa) in phosphate buffer with lysozyme (100 microg/ml), nisin (100 IU/ml), lactoferricin (20 microg/ml), and HEL96-116 (100 microg/ml), a synthetic lysozyme-derived peptide, and sensitization levels were compared. The results obtained indicated that outer-membrane properties affected high-pressure sensitization differently for different compounds. LPS truncation in Salmonella Typhimurium was correlated with increased sensitization to lysozyme (up to 1.5 log10 units) and nisin (up to 1.2 log10 units) but with decreased sensitization to lactoferricin under pressure. For P. aeruginosa, the pattern of sensitization to lactoferricin and nisin resembled that of polymyxin B at atmospheric pressure, suggesting that pressure induces the self-promoted uptake of both peptides. Sensitization to HEL96-116 was not affected by outer-membrane properties for either organism. Hence, outer-membrane permeabilization by high pressure cannot be explained by a single unifying mechanism and is dependent on the organism, the outer-membrane properties, and the nature of the antimicrobial compound. On the basis of these findings, the use of antimicrobial cocktails targeting different bacteria and fractions of bacterial populations may enhance the efficacy of high pressure as a preservation treatment.     

Control of Listeria monocytogenes and Salmonella anatum on the surface of smoked salmon coated with calcium alginate coating containing oyster lysozyme and nisin

ABSTRACT:  This study investigated the antimicrobial effect of oyster lysozyme with or without nisin added to calcium alginate (CaAlg) coated on the surface of smoked salmon against Listeria monocytogenes and Salmonella anatum . L. monocytogenes or S. anatum inoculated smoked salmon samples (1 g) were dipped into CaAlg with either oyster lysozyme (OysL) or hen egg white lysozyme (HEWL), with or without added nisin (N), then stored at 4 °C for 35 d. Our results indicated that the effectiveness of oyster lysozyme or hen egg white lysozyme was enhanced when added to calcium alginate coatings. After 35 d at 4 °C the growth of L. monocytogenes and S. anatum was suppressed in the range of 2.2 to 2.8 log CFU/g with CaAlgNOysL or CaAlgNHEWL coatings compared to the control nontreated samples. There was no significant difference between oyster lysozyme and hen egg white lysozyme treatments against L. monocytogenes or S. anatum inoculated on the surface of salmon. Calcium alginate coatings containing lysozyme with nisin or without could be used to reduce the growth of L. monocytogenes and S. anatum on the surface of ready-to-eat smoked salmon at refrigerated temperatures.     

Prevalence and stability of lysozyme in cheese

The use of the preservative and potential allergen hen egg white lysozyme in cheese production has to be declared. In the present study, an HPLC method with fluorescence detection (HPLC-FLD) was optimised and validated for the analysis of lysozyme in cheese. Lysozyme was detected in concentrations between 30.8 and 386.2 mg/kg cheese in 30 out of 46 analysed commercial cheese samples. During cheese production and storage for 0–54 weeks a lysozyme satellite peak (LSP) was detected, which totals up to 18% of the lysozyme content. Mass spectrometry and peptide mass fingerprint revealed that LSP possesses the same primary structure as lysozyme. Since disulphide scrambling could not be detected, LSP was assigned to a conformational isomer of lysozyme. As a consequence, LSP was included in the HPLC-FLD analysis of lysozymes in cheese.     

蛋清溶菌酶与渗透剂对大肠杆菌的协同抑菌作用

为了提高溶菌酶对革兰氏阴性菌的抑菌性能,研究蛋清溶菌酶和渗透剂甘氨酸、EDTA-Na2复配对大肠杆菌ATCC25922、DH5α的抑菌效果,及细胞外膜渗透性和细胞表面形态的变化。结果表明：大肠杆菌ATCC25922对溶菌酶的敏感性明显强于DH5α,其外膜渗透性也高于大肠杆菌DH5α。当溶菌酶分别和渗透剂甘氨酸或EDTA-Na2复配后,对大肠杆菌ATCC25922和DH5α的抑菌性能都显著提高;三者共同作用时,对大肠杆菌ATCC25922的抑菌能力从101.0提高到103.45,对大肠杆菌DH5α则从100.35提高到103.15,表现出协同抑菌作用。细胞外膜渗透性的N-苯基-1-萘胺(NPN)测定结果表明：溶菌酶与甘氨酸、EDTA-Na2复配后,两种大肠杆菌的外膜渗透性相应提高,TEM电镜结果也证实溶菌酶与渗透剂对大肠杆菌细胞表面有协同破坏作用。因此改善大肠杆菌的外膜渗透性有助于增强溶菌酶对其抑菌效果。     

Sensitivities of foodborne pathogens to pressure changes

Eight foodborne pathogens were suspended in ultrahigh-temperature whole milk and treated at pressure levels of 0.1 to 690 MPa at 21.5 degrees C for 10 min. There was no clear trend in pressure resistance between gram-negative and gram-positive organisms. The order of the single strains tested, from most to least pressure sensitive, was Vibrio parahaemolyticus < Yersinia enterocolitica < Listeria monocytogenes < Salmonella enterica serovar Typhimurium < S. enterica serovar Enteritidis < Escherichia coli O157:H7 approximately equal to Staphylococcus aureus < Shigella flexneri. For each organism there existed a pressure range in which log(number of survivors) had a near linear relationship when plotted versus treatment pressure level. In this study, a decimal reduction pressure (Dp) value was defined and used to measure the sensitivity of these pathogens to pressure changes. L. monocytogenes and V. parahaemolyticus were most sensitive to pressure changes, and S. flexneri was most resistant. The D(P) values were 16.3 MPa for L. monocytogenes, 21.7 MPa for V. parahaemolyticus, and 127.0 MPa for S. flexneri. The most pressure-resistant gram-negative bacterium, S. flexneri, and most pressure-resistant gram-positive bacterium, S. aureus, were treated at 50 degrees C and pressures of 0.1 to 650 MPa for 10 min. High temperature considerably enhanced pressure inactivation of these two organisms and affected their sensitivities to pressure changes. The effect of treatment time on the D(P) values of L. monocytogenes and V. parahaemolyticus was also determined, and it was found that it did not significantly affect their D(P) values.     

Relationship between the stability of lysozymes mutated at the inside hydrophobic core and secretion in Saccharomyces cerevisiae

The relationship between the stability of lysozymes mutated at the inside hydrophobic core and secretion was investigated to understand the optimal secretion of mutant lysozymes in the Saccharomyces cerevisiae. S91T mutant lysozyme increased in the methyl residue inside the core greatly increased the conformational stability. The secretion amount of S91T in S. cerevisiae increased greatly compared with wild-type lysozyme. On the other hand, I55V and T40S/I55V mutant lysozymes decreased in methyl residue inside the core brought about their unstable conformation. The secretion amounts of these unstable mutant lysozymes significantly decreased. In addition, the effect of glycosylation on the secretion of these mutants was investigated. The secretion amounts of glycosylated lysozyme S91T/G49N with stable hydrophobic core greatly increased compared with that of glycosylated lysozyme G49N, while those of mutant I55V/G49N and T40S/I55V/G49N with unstable hydrophobic core greatly decreased. These results indicate that the secretion amounts of mutant lysozymes increase in proportion to the hydrophobic core stabilities and that a similar good correlation was obtained with glycosylated lysozymes.     

Bacterial contamination in an egg-breaking factory and its control

From January to November, 2003, bacterial contamination was surveyed in a small egg-breaking factory that produced non pasteurized liquid egg. Test egg samples were taken at various stages of the egg processing operation. Salmonella Enteritidis was isolated from liquid egg yolk and liquid egg white on October, but was not found in any other samples (50 liquid egg samples, 21 containers and 94 attached production facilities and gloves). The data suggest that the contamination rate (3.8%) is lower than those reported previously. Levels of bacterial standard plate counts, gram-positive bacterial counts and gram-negative bacterial counts were in the ranges of 2 to 5 log CFU/g, 2 to 3 log CFU/g, 2 to 5 log CFU/g, respectively. Liquid egg containers returned from customers was contaminated with bacteria at the level of 8 log CFU per container. However, washing and application of a sanitizer containing sodium hypochlorite reduced the bacterial counts.     

鸭蛋清溶菌酶的分离纯化及致敏性评估

鸭蛋中含有丰富的蛋白质和营养成分,鸭蛋清中含有溶菌酶,溶菌酶具有致敏性,食用鸭蛋后有可能产生过敏的风险。采用超滤法与离子交换层析法结合的方法分离纯化鸭蛋清溶菌酶,利用聚丙烯酰胺凝胶电泳法比对,能得到纯度较高的溶菌酶。采用免疫印迹的方法,分析抗溶菌酶的兔多抗血清和禽蛋过敏患者混合血清池分别与鸭蛋清溶菌酶IgE的结合能力,进行鸭蛋溶菌酶的致敏性评估,实验证明IgE结合能力非常显著,溶菌酶存在交叉反应。同时证实了食用鸭蛋会引起过敏反应,也为过敏患者能否食用鸭蛋提供了有效的信息。     

Interactions between high pressure homogenization and antimicrobial activity of lysozyme and lactoperoxidase

It was the objective of this work to evaluate the effect of high pressure homogenization on the activity of antimicrobial enzymes such as lysozyme and lactoperoxidase against a selected group of Gram positive and Gram negative species inoculated in skim milk. Lactobacillus helveticus, Lactobacillus plantarum and Listeria monocytogenes were the most pressure resistant species while Bacillus subtilis, Pseudomonas putida, Salmonella typhimurium, Staphylococcus aureus, Proteus vulgaris and Salmonella enteritidis were found to be very sensitive to the hyperbaric treatment. The enzyme addition enhanced the instantaneous pressure efficacy on almost all the considered species as indicated by their instantaneous viability loss following the treatment. Moreover, the combination of the enzyme and high pressure homogenization significantly affected the recovery and growth dynamics of several of the considered species. Although L. monocytogenes was slightly sensitive to pressure, the combination of the two stress factors induced a significant viability loss within 3 h and an extension of lag phases in skim milk during incubation at 37 degrees C. The hypothesis formulated in this work is that the interaction of high pressure homogenization and lysozyme or lactoperoxidase is associated to conformational modifications of the two proteins with a consequent enhancement of their activity. This hypothesis is supported by the experimental results also regarding the increased antimicrobial activity against L. plantarum of the previously pressurised lysozyme with respect to that of the native enzyme.