Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N₂ or without flushing with N₂, lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1–1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly ( P > 0.05). Flushing packages of lettuce with 100% N₂ followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2–3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua , strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes , it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N₂ flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.     

Cooked and brined shrimps packed in a modified atmosphere have a shelf-life of >7 months at 0 °C, but spoil in 4–6 days at 25 °C

Summary Spoilage and safety of cooked, brined and modified atmosphere packed shrimps were studied at 0, 5, 8, 15 and 25 °C. Shrimps from two sources, cold and warm waters, were brined in a sodium–chloride brine containing benzoic, citric and sorbic acids. Shelf-life was above 7 months at 0 °C but only 4–6 days at 25 °C. Apparent activation energy for the effect of temperature on shelf-life was > 100 kJ mol^-1. This pronounced effect of temperature was explained by changes in spoilage microflora at different storage temperatures. Simple and empirical mathematical models for rates of spoilage were developed for the prediction of shelf-life at different temperatures. To evaluate safety, products were challenged with Listeria monocytogenes and spores of Clostridium botulinum . Above 5 °C growth responses of L. monocytogenes followed the square root model with a T_min-value of +0.2 °C. Cl. botulinum produced toxin at the time of spoilage at 25 °C but only in shrimps with < 3% water-phase salt.     

Survival and growth of Listeria species in a model ready-to-use vegetable product containing raw and cooked ingredients as affected by storage temperature and acidification

Summary The survival and growth of Listeria monocytogenes and L. innocua strains inoculated onto cooked sweet corn and fresh bean sprouts packed individually, and as components of a combination product, were examined at refrigeration and mild abuse temperatures. Growth rates were both temperature and vegetable dependent. Maximal growth rates (1.14 ± 0.1log CFU/day) were identified on cooked sweet corn at 12 °C. The inclusion of cooked sweet corn did not significantly increase ( P > 0.05) the growth rate or final Listeria population density of bean sprouts stored at 8 °C and 12 °C. The sensory quality of bean sprouts was relatively temperature independent for the initial 48 h of storage, but was maximized (4 days shelf life) at 3 °C. Acidification of sweet corn to pH 5, particularly with citric acid, slowed Listeria growth and could be an additional hurdle to supplement temperature in maintaining the safety of minimally processed vegetable combination products.     

Effect of Combined Ozone and Organic Acid Treatment for Control of Escherichia coli O157:H7 and Listeria monocytogenes on Lettuce

ABSTRACT: This study was conducted to determine the effects of ozonated water (1, 3, and 5 ppm) alone with different exposure times (0.5,1,3, or5min), and combinations of 3 ppm ozone with 1% organic acids (acetic, citric, or lactic acids) during 1-min exposure for inactivating Escherichia coli O157:H7 and Listeria monocytogenes on lettuce and to observe the regrowth of these pathogenic bacteria on treated lettuce during storage for 10 d at 15°C. Results showed that 5 ppm ozone treatment for 5 min gave 1.09-log and 0.94-log reductions of E. coli O157:H7 and L. monocytogenes , respectively, indicating insignificant reductions compared with 3 ppm ozone treatment for 5 min. Treatment with 3 ppm ozone combined with 1 % citric acid for 1 min immersing resulted in 2.31 - and 1.84-log reductions ( P < 0.05), respectively. During storage at 15°C for 10 d after combined treatment and packaging, populations of E. coli O157:H7 and L. monocytogenes increased to approximately 9.0-log colony forming unit (CFU) /g, indicating that this treatment did not have a residual antimicrobial effect during storage. Although the storage study did not show control of these pathogens, the combined ozone-organic acid treatment was more effective in reducing population levels of these pathogens on lettuce than individual treatments.     

Using mild heat treatment to improve the bioactive related compounds on fresh-cut green bell peppers

Bioactive related compounds of fresh-cut green bell peppers ( Capsicum annuum, L.) exposed to water immersion at 55 °C and 60 °C per 180 s were evaluated during storage. Their sensorial and microbial quality, acidity, sugar and chlorophyll content were also determined. Beneficial effects on sensorial attributes were observed in treated peppers with longer shelf life than in non-treated ones (5 days at 4 °C, 2 days at 10 °C). At the end of storage at 4 °C, phenols increased to 11% and quercetin and antioxidant capacity were retained, but in control peppers ascorbic acid dropped 16%. At 10 °C, there was no change in phenols; quercetin, ascorbic acid and antioxidant activity decreased (15%, 13% and 10% respectively) in treated peppers. Changes were more noticeable in non-treated products (phenols increased 21%, ascorbic acid decreased 28% and antioxidant activity 20%). Mild heat treatments applied to fresh-cut peppers seemed to preserve some of their bioactive compounds during storage.     

Behaviour of Listeria monocytogenes inoculated into Minas Frescal cheese made by direct acidification or lactic culture during refrigerated storage

The behaviour of Listeria monocytogenes Scott A artificially inoculated into Brazilian Minas Frescal cheese manufactured with the addition of a lactic culture or by direct acidification with lactic acid was evaluated at 5 and 10°C for 25 days. In cheese produced with a lactic culture, the counts remained almost unchanged during storage, whereas cheeses produced by direct acidification presented an increase in the counts of 2–3 log cycles. The profiles of the lactic bacterial counts, associated with those of L. monocytogenes, show a strong influence of the competitive starter culture on the survival of L. monocytogenes . This suggests that the addition of starter culture is an efficient way to control the growth of L. monocytogenes in these products.     

Inhibition, survival and growth of Listeria monocytogenes on poultry as influenced by buffered lactic acid treatment and modified atmosphere packaging.

The effect of the treatment with various concentrations (2%, 5% and 10% w/v) of lactic acid/sodium lactate buffer (pH 3.0), modified atmosphere (MAP) packaging (90% CO2 and 10% O2) and 10% (w/v) lactic acid/sodium lactate buffer (pH 3.0) combined with MAP on Listeria monocytogenes Z7 serotype 1 and on the shelf life of chicken legs stored at 6 degrees C was investigated. The initial contamination level of L. monocytogenes on the chicken legs surface was 8.3 x 10(2) cfu/cm2 of skin. After 2 days of storage at 6 degrees C the number of L. monocytogenes on legs treated with 2%, 5%, 10% lactic acid/sodium lactate buffer (pH 3.0) and 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP was significantly lower than the initial number of L. monocytogenes. Later, growth of L. monocytogenes was observed. After 13 days of storage at 6 degrees C the number of L. monocytogenes on legs treated with 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP was still similar to the initial number. Legs treated with 2%, 5%, 10% lactic acid/sodium lactate buffer (pH 3.0), MAP and 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP, have a shelf life at 6 degrees C of respectively 8, 9, 10, 13 and 17 days. This means a prolongation of 2, 3, 4, 7 and 11 days, respectively for storage at 6 degrees C. The antimicrobial effect of lactic acid buffer systems (pH 3.0) increased with increasing concentrations of lactic acid in the buffered system. The best results were obtained by the combined use of 10% acid/sodium lactate buffer (pH 3.0) and MAP.     

Effectiveness of trisodium phosphate against Listeria monocytogenes on excised and nonexcised chicken skin

The influence of sample type (i.e., excised versus nonexcised chicken skin) on the efficiency of trisodium phosphate (TSP) solutions in reducing Listeria monocytogenes populations and inhibiting their growth during refrigerated storage was studied. Whole chicken legs and excised chicken leg skin fragments inoculated with 10(8) CFU of L. monocytogenes per ml were dipped for 15 min in sterile tap water (control) or in a solution containing 8, 10, or 12% TSP. L. monocytogenes counts were determined after 0, 1, 3, and 5 days of refrigerated storage (2 degrees C). The decontamination effect of TSP was greater for excised skin than for whole legs. Microbial differences between control and TSP-treated samples were significantly larger for excised skin than for whole legs for 9 (75%) of 12 tested combinations of TSP concentrations and storage times. These differences varied from 1.05 +/- 0.26 log10 cycles (day 1) to 3.30 +/- 0.14 log10 cycles (day 5) for nonexcised-skin samples (whole legs) and from 1.54 +/- 0.48 log10 cycles (day 1) to 4.28 +/- 0.86 log10 cycles (day 5) for excised-skin samples. Significantly larger reductions were observed from the third day of refrigerated storage onward. The TSP concentration was a significant factor in the reduction of L. monocytogenes populations. These results suggest that bacteria are more readily accessible to TSP in excised than in nonexcised chicken skin and that the type of sample used to ascertain the efficacy of antimicrobial surface treatments may influence the findings of this type of study.     

Keeping quality and safety of minimally fresh processed melon

Fresh-cut Amarillo melon was stored under passive modified atmosphere packaging (MAP) for 14 days at 5 °C. Three commercial films were tested: microperforated polypropylene (MPP), bioriented PP (BPP), and oriented PP (OPP). As a control, a macroperforated PP film was used. The effect of a citric acid dip treatment (0.52 mM) on the quality of the melon pieces packaged in OPP film was also evaluated. A similar final gas composition (4 kPa O2 plus 12–13 kPa CO2) within packages was achieved by using the three tested films. This atmosphere was effective for maintaining sensorial quality and microbial safety and for avoiding weight loss and translucency. When citric acid dip was applied, a reduction of microbial counts, a low discoloration, an increase of lightness, and a general improvement of visual appearance were found. However, after 14 days of storage, neither MAP treatments nor citric acid dip were enough to avoid softening of at least 23%, although the highest value (32%) was found in control pieces. Taking into account safety, quality attributes and consumer acceptance, shelf life of fresh processed melon stored under the studied MAP conditions could be stabilised for 10 days.     

Microbial growth and colour of minimally processed shiitake mushroom stored at different temperatures

The effect of storage temperature on the microbiological and sensory characteristics of minimally processed shiitake was investigated. Shiitake mushrooms were washed, sanitised, packed in polystyrene trays, overwrapped with plastic film and stored at 7, 10 or 15 °C. Microbial counts, polyphenoloxidase activity, external lightness ( L* ) and acceptance tests were conducted. Mesophilic, aerobic psychrotrophic bacteria, yeasts and moulds predominated during storage. Pseudomonas was detected after 10 days' storage showing an increase of, approximately, 7 log cycles at 15 °C. Mushroom rejection occurred when the microbial population was lower than 10⁶ CFU g⁻¹, suggesting that, other factors, such as browning, affect mushroom spoilage more than microbial activity. Mushrooms treated with citric or ascorbic acids maintained high L * value during 10 days. The shelf life of minimally processed shiitake mushrooms was 10 days at 7 °C, but less than 5 days at 10 °C, and approximately 3 days at 15 °C.     

Modeling the lag phase and growth rate of Listeria monocytogenes in ground ham containing sodium lactate and sodium diacetate at various storage temperatures

ABSTRACT:  Refrigerated ready-to-eat (RTE) meats contaminated with Listeria monocytogenes were implicated in several listeriosis outbreaks. Lactate and diacetate have been shown to control L. monocytogenes in RTE meats. The objective of this study was to examine and model the effect of lactate (1.0% to 4.2%) and diacetate (0.05% to 0.2%) in ground ham on the lag phase duration (LPD, h) and growth rate (GR, log CFU/h) of L. monocytogenes at a range of temperatures (0 to 45 °C). A 6-strain mixture of L. monocytogenes was inoculated into ground ham containing lactate and diacetate, and stored at various temperatures. The LPD and GR of L. monocytogenes in ham as affected by lactate, diacetate, and storage temperature were analyzed and accurately represented with mathematical equations. Resulting LPD and GR equations for storage temperatures within the range of 0 to 36 °C significantly represented the experimental data with a regression coefficient of 0.97 and 0.96, respectively. Significant factors ( P < 0.05) that affected the LPD were temperature, lactate, diacetate, and the interactions of all three, whereas only temperature and the interactions between temperature and lactate and diacetate had a significant effect on GR. At suboptimal growth temperatures (≤12 °C) the increase of lactate and diacetate concentrations, individually or in combination, extended the LPD. The effect of higher concentrations of both additives on reducing the GR was observed only at temperatures that were more suitable for growth of L. monocytogenes , that is, 15 to 35 °C. These data may be used to assist in determining concentrations of lactate and diacetate in cooked ham products to control the growth of L. monocytogenes over a wide range of temperatures during manufacturing, distribution, and storage.     

Inactivation of Listeria innocua on frankfurters that contain potassium lactate and sodium diacetate by flash pasteurization

ABSTRACT:  Listeria monocytogenes , a psychrotrophic foodborne pathogen, is a recurring postprocess contaminant on ready-to-eat meat (RTE) products, including frankfurters. Potassium lactate (PL) and sodium diacetate (SDA) are FDA-approved antimicrobials that inhibit the growth of L. monocytogenes when incorporated into the formulation of fine emulsion sausage. Flash (steam) pasteurization (FP) has been shown to reduce levels of L. monocytogenes , and its surrogate L. innocua , on frankfurter surfaces. The ability of FP to inactivate and prevent the growth of the L. monocytogenes surrogate L. innocua in a pilot plant setting was investigated. FP treatment (1.5 s, 121 °C) of single layers of frankfurters that were surface-inoculated with either 5, 4, or 3 log CFU/g of L. innocua immediately before FP (1.5 s, 121 °C) resulted in log reductions of 1.97 (± 0.11), 2.03 (± 0.10), or 2.07 (± 0.14), respectively. Inoculum level had no effect on the inactivation of L. innocua . Following 8 wk of refrigerated storage (4 °C), L. innocua levels decreased by 0.5 log in non-FP-treated frankfurter packs, while the 2 log reduction of L. innocua was maintained for FP-treated frankfurters. FP (1.5 s, 121 °C) had no effect on frankfurter color or texture. Because the numbers of L. monocytogenes associated with contaminations of ready-to-eat meats are typically very low, the use of FP in combination with PL and SDA has the potential to reduce the number of frankfurter recalls and foodborne illness outbreaks.     

Efficacy of Pressure-Assisted Thermal Processing, in Combination with Organic Acids, against Bacillus amyloliquefaciens Spores Suspended in Deionized Water and Carrot Puree

ABSTRACT:  Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 °C), high pressure processing (HPP; 700 MPa, 35 °C), and thermal processing (TP; 105 °C, 0.1 MPa) was investigated.  Bacillus amyloliquefaciens  spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 × 10⁸ CFU/mL.  B. amyloliquefaciens  spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 °C. In conclusion, addition of some organic acids provided significant lethality enhancement ( P  < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.     

Influence of poultry carcass skin sample site on the effectiveness of trisodium phosphate against Listeria monocytogenes

The aim of this study was to determine the influence of skin sample site on the efficacy of trisodium phosphate (TSP) solutions in reducing Listeria monocytogenes populations on chicken carcasses during refrigerated storage. Chicken skin samples from the legs, the breasts, and the dorsal area inoculated with L. monocytogenes (10(8) CFU/ml) were dipped for 15 min in sterile tap water (control) or in 8, 10, or 12% TSP. L. monocytogenes counts and surface pH values were determined after 0, 1, 3, and 5 days of storage at 2 degrees C. For all sampling times and TSP concentrations, the reductions in L. monocytogenes numbers in breast skin were significantly larger (P < 0.05) than those in leg skin or dorsal skin. No significant differences were found in pH values as an effect of skin site. Our results suggest that skin sampling site is an important factor that needs to be considered when decontamination protocols are developed for poultry carcasses with the TSP treatment.     

Use of mild-heat treatment following high-pressure processing to prevent recovery of pressure-injured Listeria monocytogenes in milk

This study examined the inactivation of Listeria monocytogenes in milk by high-pressure processing (HPP) and bacterial recovery during storage after HPP. We developed a technique to inhibit the bacterial recovery during storage after HPP (550 MPa for 5 min) using a mild-heat treatment (30-50 degrees C). Various mild-heat treatments were conducted following HPP to investigate the condition on which the bacterial recovery was prevented. Immediately after HPP of 550 MPa at 25 degrees C for 5 min, no L. monocytogenes cells were detected in milk regardless of the inoculum levels (3, 5, and 7 log(10)CFU/ml). However, the number of L. monocytogenes cells increased by >8 log(10)CFU/ml regardless of the inoculum levels after 28 days of storage at 4 degrees C. Significant recovery was observed during storage at 25 degrees C; the bacterial number increased by >8 log(10)CFU/ml after 3 days of storage in the case of an initial inoculum level of 7 and 5 log(10)CFU/ml. Even in the case of an initial inoculum level of 3 log(10)CFU/ml, the bacterial number reached the level of 8 log(10)CFU/ml after 7 days of storage. No bacterial recovery was observed with storage at 37 degrees C for 28 days. Milk samples were treated by various mild-heat treatments (30-50 degrees C for 5-240 min) following HPP of 550 MPa at 25 degrees C for 5 min, and then stored at 25 degrees C for 70 days. The mild-heat treatment (e.g., 37 degrees C for 240 min or 50 degrees C for 10 min) inhibited the recovery of L. monocytogenes in milk after HPP. No recovery of L. monocytogenes in milk was observed during 70-day storage at 25 degrees C in samples that received mild-heat treatments such as mentioned above following HPP (550 MPa for 5 min). Moreover, the mild-heat treatment conditions (temperature and holding time) required to inhibit the recovery of L. monocytogenes in milk was modelled using a logistic regression procedure. The predicted interface of recovery/no recovery can be used to calculate the mild-heat treatment condition to control bacterial recovery during storage at 25 degrees C after HPP (550 MPa for 5 min). The results in this study would contribute to enhance the safety of high-pressure-processed milk.     

Evaluation of Listeria innocua as a suitable indicator for replacing Listeria monocytogenes during ripening of Camembert cheese

The suitability of Listeria innocua for use as an indicator for replacing Listeria monocytogenes during the cheese-making and ripening of Camembert cheese was evaluated. Pasteurized whole milk inoculated with either L. innocua or L. monocytogenes was used to make Camembert cheese, which were ripened in three stages. All cheese was ripened in three stages: room temperature (∼20 °C) and relative humidity of 60% for 36 h; 12 °C and relative humidity of 93% for 2 weeks; and 7 °C and relative humidity of 85% for 3 weeks. Results showed that population values of L. innocua and L. monocytogenes on day 1 were 7.16 and 6.11 log₁₀ CFU/g, respectively, which declined to 6.54 and 5.45 log₁₀ CFU/g, respectively, during subsequent 20 days. Thereafter, L. innocua and L. monocytogenes populations increased to 7.38 and 6.06 log₁₀ CFU/g on day 35 of ripening, respectively. During ripening, surface and interior of cheeses were analysed for populations of L. innocua and L. monocytogenes , respectively. The data were collected on day 1, 5, 10, 15, 20, 25, 30, and 35 of ripening. Generally, the growth of L. innocua and L. monocytogenes is faster in surface than in centre. Top centre, bottom centre and bottom surface locations had similar population values during ripening. There were no significant differences ( P  > 0.05) between batch and section of cheese. The ripening time and locations had significant effect ( P  < 0.05) on the survival and growth of L. innocua and L. monocytogenes . The trends of survival and growth of L. innocua and L. monocytogenes were similar. These results indicated that L. innocua can be considered as an indicator for L. monocytogenes during ripening of Camembert cheese.     

Reduction of Listeria monocytogenes populations during exposure to a simulated gastric fluid following storage of inoculated frankfurters formulated and treated with preservatives

The effect of a simulated gastric fluid (adjusted to pH 1.0 with HCl) on Listeria monocytogenes, inoculated postprocessing on pork frankfurters formulated with sodium lactate (SL) and sodium diacetate (SD) and not dipped or dipped in solutions of lactic acid or acetic acid, was evaluated during storage of the frankfurters at 10 degrees C for 40 days. Pork frankfurters containing 1.8% SL, 0.25% SD, 1.8% SL+0.125% SD, or 1.8% SL+0.25% SD were inoculated with 10(2)-10(3) CFU/cm2 of a 10-strain preparation of L. monocytogenes and were not dipped or dipped for 2 min in solutions of 2.5% lactic or acetic acid before they were vacuum-packaged and stored. Survival of L. monocytogenes was determined after exposure of frankfurters for 0, 20, 40, and 60 min to the simulated gastric fluid after storage for 0, 10, 20, 30, or 40 days. Growth of L. monocytogenes on frankfurters formulated with antimicrobials was inhibited in the order control 相似文献   

Inhibition of foodborne pathogens by native microflora recovered from fresh peeled baby carrot and propagated in cultures

ABSTRACT:  The inhibitory effect of fresh peeled baby carrot and associated microflora on the viability and growth of Listeria monocytogenes , Yersinia enterocolitica , Salmonella enterica , Escherichia coli O157:H7, and Pseudomonas marginalis was investigated. The population of viable L. monocytogenes was reduced by more than 2 logs following the dipping of sliced baby carrots in the bacterial suspension for 2 min. However, other pathogens subjected to the same treatment showed no reduction in the population. Surface sanitization of baby carrots reduced the number of native microflora and in turn increased the growth of each pathogen on this commodity by 2 to 3 logs. Filter-sterilized carrot homogenates exhibited no antimicrobial activity and were capable of supporting the growth of each pathogen to a density of over 2 × 10⁹ CFU/mL. However, the growth of each pathogen in carrot homogenates containing microflora recovered from baby carrot and propagated in tryptic soy broth was reduced 2 to 3 logs after incubation at 28 °C for 2 d. On pepper disks, which have no antilisterial activity and very low levels of background microflora, the addition of carrot microflora also reduced the growth of each pathogen 2 to 4 logs after 2 d at 20 °C. The reduction was dependent upon the ratio between the number of carrot microflora and pathogen tested. The growth of L. monocytogenes or Y. enterocolitica on pepper disks containing carrot microflora was almost completely stopped after storage at 8 °C for 8 d. The inhibitory effect of baby carrots on pathogens is in part due to the antimicrobial activity of carrot tissue and in part due to the antagonistic action of associated microflora.     

Quality of canned mushrooms acidified with glucono-δ-lactone

Summary The effect of sterilisation conditions (116 °C, 54 min; 121 °C, 24 min and 126 °C, 8 min) and acidification with glucono-δ-lactone as compared with other acids (citric, ascorbic and EDTA) on the yield and quality (colour, texture and taste) of canned whole mushrooms, has been studied using previously refrigerated raw material (1.5 or 2.5 days at 2 °C). Colour measurement of canned mushrooms by the determination of the L* parameter of ten mushroom pilei probed to be the most suitable method, among those studied, shown the greater F parameter in a variance analysis. Yield was higher when the raw material was stored under refrigeration for longer. Yield, texture and colour improved with the Highest Temperature and Shortest Time process (126 °C, 8 min). Glucono-δ-lactone appears to be a more suitable acidulant than citric acid as it provides equal colour, texture and yield without conferring as acid a taste as citric or an extraneous flavour.     

SURVIVAL AND GROWTH OF LISTERIA MONOCTYOGENES ON BEEF TISSUE SURFACES AS AFFECTED BY SIMULATED PROCESSING CONDITIONS

The numbers of Listeria monocytogenes Scott A were followed on experimentally inoculated lean and fat beef tissue handled under a variety of simulated storage conditions at 5°C, including high and low moisture storage, simulated spray chilling, and vacuum packaging. Under high moisture storage conditions, L. monocytogenes increased approximately 3 log cycles on both lean and fat tissue after 21 days. Similar growth was observed with vacuum packaged lean tissue. Under dry storage conditions, the population decreased approximately 2 logs during the first 14 to 21 days, but the counts remained constant for 42 days. Simulated spray chilling did not affect the growth or survival of L. monocytogenes on either lean or fat tissue .