Efficiency of high pressure treatment for destruction of Listeria monocytogenes in fruit juices

The objective of this study was to compare high pressure resistance of Listeria monocytogenes strains at 25degreesC and 50degreesC at 350 MPa and to use high pressure (250 MPa and 350 MPa) at 30degreesC and 40degreesC for the inactivation of the relatively most pressure resistant strain inoculated in pasteurized apple, apricot, cherry and orange juices. L. monocytogenes CA was found to be the relatively most pressure resistant strain and increasing pressurization from 250 MPa to 350 MPa at 30degreesC had an additional three to four log cycle reduction in viability, still leaving viable cells after 5 min. When 350 MPa at 40degreesC for 5 min was applied more than eight log cycle reduction in cell population of all fruit juices was achieved. This study demonstrated that low temperature (40degreesC) high pressure (350 MPa) treatment has the potential to inactivate relatively pressure resistant L. monocytogenes strains inoculated in different fruit juices within 5 min. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved

CITRININ RISK IN BLACK AND GREEN TABLE OLIVES: SIMULTANEOUS DETERMINATION WITH OCHRATOXIN-A BY OPTIMIZED EXTRACTION AND IAC-HPLC-FD

Mycotoxin citrinin (CIT) and ochratoxin A (OTA) were simultaneously identified using immunoaffinity column-high performance liquid chromatography with fluorescence detection (IAC-HPLC-FD) (Ex.333 nm; Em:495 nm) after an optimized extraction procedure. Both mycotoxins were eluted on a C(18) RP support (250 x 4.6 mm I.D., ODS2, 5 mu m particles) using an isocratic eluent consisting of acetonitrile/water/formic acid (60/38/2, v/v/v), acidified to pH 2.5 and pumped at a flow rate of 1.0 mL min(-1). The four categories of citrinin levels [0-0.55; 1.56-2.0; 0.66-2.64; 5.76-14.55 mu g kg(-1) of CIT] and three categories of ochratoxin levels [0 - < 0.1; 0.1-0.25; 0.30- 0.46 mu g kg(-1) of OTA] were found in 88 groups of olive samples. Recovery studies [y= 21416x - 7919.4 (R(2)=0.9998) for citrinin and y= 0.0001x + 0.0074 (R(2)=0.9999) for ochratoxin A] were performed and the mean analytical recoveries detected in CIT and OTA in table olives ranged from 92.65 - 96.83% and 88.92 - 95.58%, respectively. Limit of detection (LOD) was equivalent to 0.05 mu g/kg for both CIT and OTA. With the proposed method, CIT and OTA were both quickly determined in table olives and could be used to detect of mycotoxinic risks in a HACCP quality system of olive and olive-based food products

Recovery of Escherichia coli O157 : H7 and Salmonella in milk and cream of chicken soup from high hydrostatic pressure (HHP) and bacteriocin applications upon storage

By the application of HHP; more than 8 log cycle reduction was achieved for E. coli O157:H7 933 and Salmonella FDA in milk and cream of chicken soup in 5 min. Storage of HHP treated milk samples showed absence of both bacteria for 24 h at 4degreesC and for 48 h at 37degreesC. The population of the strains in cream of chicken soup exceeded their initial value after 5 days of storage at 25degreesC. BP1 was combined with HHP and used for inhibition of surviving bacterial species in cream of chicken soup. There was at least 7 log cycle reduction in E. coli O157:H7 933 and Salmonella FDA after 5 and 7 days of storage at 25 C respectively, when compared to HHP alone. Combination of HHP with BP1 extended the shelf life of cream of chicken soup for both bacterial species an additional 2 days at 25 degreesC when compared with HHP treatment alone

Studies on an inhibitor produced by lactic acid bacteria of wines on the control of malolactic fermentation

Malolactic fermentation is the microbiological process in wines, where lactic acid bacteria (LAB) govern the process of converting L-malic acid into L-lactic acid. During this process a high microbial load of LAB may lead to an unwanted spoilage phenomena by formation of excessive amounts of undesirable flavor compounds. This study is mainly focused on the isolation of LAB from the native flora of the wine, which has an inhibitory potential against malolactic activity of LAB inherent in wines. An isolate of Leuconostoc mesenteroides subsp. cremoris was found to produce an inhibitory compound against the LAB of wines. This compound was found to be a bacteriocin-like inhibitory substance (BLIS), which has a molecular weight of 32,000 Da, and it was shown that this BLIS was effective in the control of malolactic fermentation

Inactivation of Staphylococcus aureus and Listeria monocytogenes in milk and cream of chicken soup by high hydrostatic pressure and bacteriocins

By the application of HHP; 5.50 and 5.70 log cycle reduction was obtained for S. aureus 485, in milk and cream of chicken soup samples, respectively. Storage of HHP treated milk samples for 24 h at 4degreesC gave positive result for S. aureus 765 where no growth was observed for L. monocytogenes strains. Incubation of food samples for an additional 48 h at 37degreesC showed growth of L. monocytogenes strains as S. aureus strains. When a bacteriocin-based biopreservative (BP1) was combined with pressurization more than 8 log-cycle reduction in cell population of the resistant strains of S. aureus and L. monocytogenes was achieved in milk. Milk and cream of chicken soup samples were stored at 25degreesC and milk samples showed no growth up to 30 day where as Gram-positive bacterial strains in cream of chicken showed growth after 3 days with a rapid increase in cell number thereafter

The combined effect of high hydrostatic pressure, heat and bacteriocins on inactivation of foodborne pathogens in milk and orange juice

The objective of this study was to combine pressure (345 MPa) with heat (50 degrees C), and bacteriocins (5000 AU/ml sample) for a short time (5 min) for the inactivation of relatively pressure-resistant strains of four foodborne pathogens: Staphylococcus aureus, Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella in pasteurized milk and orange juice. Without bacteriocin addition, 5.5 log-cycle reduction was obtained for S. aureus 485 in milk whereas more than 8 log-cycle reduction was achieved for all the other strains studied. After storage of samples for 24 h at 4 degrees C, S. aureus 765 also gave positive results on selective media, where no growth was observed for all the other micro-organisms assayed. Incubation of the same pressurized samples at 37 degrees C for 48 h showed growth of L. monocytogenes strains in addition to S. aureus strains, where still no growth was observed for E. coli O157:H7 and Salmonella strains in their respective selective media. For orange juice samples, more than 8 log-cycle reduction was achieved for all the bacterial species studied. No growth was seen for these species on their respective selective media agar plates after storage at 4 degrees C for 24 h and at 37 degrees C for 48 h. When a bacteriocin-based biopreservative (BP1) was combined with pressurization, more than 8 log-cycle reduction in cell population of the resistant strains of S. aureus and L. monocytogenes were achieved in milk after pressurization. Milk samples were stored at 25 degrees C up to 30 days to test the effect of treatment and samples showed no growth whereas all the controls were positive

Effects of high hydrostatic pressure on shelf life of lager beer

Filtered bright lager beer samples were either treated with high hydrostatic pressure (HHP, 350 MPa for 3 and 5 min at 20 C) or conventional heat pasteurization (60 C for 15 min). A storage period of 56 days showed that HHP and heat pasteurization had similar results in terms of pH and color (p<0.05). However HHP-treated samples had lower bitterness and protein sensitivity and higher chill haze values than the heat pasteurized samples at the end of the storage period. The microbiological stability of HHP-treated beers was the same as that of heat-treated beers, and the development of both lactic and acetic acid bacteria was inhibited for 56 days of storage. Although more studies should be carried out to investigate the effects of HHP treatment on different types of lagers and ales, our results revealed that HHP could be successfully used to increase the shelf life of beer even at temperatures well below those required for heat pasteurization

Use of Weibull frequency distribution model to describe the inactivation of Alicyclobacillus acidoterrestris by high pressure at different temperatures

The survival curves of Alicyclobacillus acidoterrestris by high hydrostatic pressure were obtained at two pressures (350 and 450 MPa) and three temperature levels (35, 45 and 50 degreesC) in BAM broth. Tailing (upward concavity) was observed in all survival curves. Weibull model was fitted to these data and goodness of fit of this model was investigated. Regression coefficients (R-2), root mean square (RMSE) values and residual plot strongly suggested that Weibull model produced good fit to the data. A better fit was observed for the data at lower pressure (350 MPa). Shape factors of the Weibull model (n values) for 350 NMPa at 35, 45 and 50 degreesC were significantly different from each other (P < 0.05). Two linear emprical equations were obtained for scale factors (b values) at the temperature values studied for 350 and 450 MPa. Such pressure-temperature inactivation models form the engineering basis for design, evaluation and optimization of high hydrostatic pressure processes as a new preservation technique

Use of Pulse Electric Field (PEF) for reduction of viable cell counts in food systems

Pulsed Electric Field (PEF) processing is a non-thermal technique offering the advantages of low processing temperatures, low energy utilization and minimum losses of flavours, nutrients and a fresh-like taste, while inactivating spoilage and pathogenic bacteria. The low processing temperatures used in this non-thermal technology allow the process to be energy-efficient, which leads to lower costs and fewer environmental impacts