Temperature Abuse Conditions Research Articles

Rapid safety assessment of reconstituted infant formula using electrical impedance analysis

A rapid method to assess freshness is crucial for the safe handling of reconstituted infant formula (RIF) and prevention of food-borne illnesses in infants. This study explored the use of electrical impedance measurement (EIM) at a constant frequency for real-time freshness evaluation of RIF. Initial electrical impedance of 89.16 ± 0.47 Ω decreased to 74.29 ± 0.23 Ω within 48 h at room temperature (20 °C) storage. Under temperature abuse conditions (30 °C), the electrical impedance rapidly dropped from 75.48 ± 0.52 Ω to 60.15 ± 4.76 Ω within 18 h, indicating more rapid spoilage. Notable changes in the electrical impedance were observed during temperature abuse. Empirical model analysis revealed a strong positive correlation between electrical impedance and conventional freshness parameters such as pH, protein, and microbial growth. This study demonstrates the potential of EIM for the rapid detection of freshness changes in RIF, offering valuable insights into the prevention of food-borne illnesses in infants.

Modeling the growth of Salmonella in raw ground pork under dynamic conditions of temperature abuse

Salmonella contamination of pork products is a significant public health concern. Temperature abuse scenarios, such as inadequate refrigeration or prolonged exposure to room temperature, can enhance Salmonella proliferation. This study aimed to develop and validate models for Salmonella growth considering competition with background microbiota in raw ground pork, under isothermal and dynamic conditions of temperature abuse between 10 and 40 °C. The maximum specific growth rate (μmax) and maximum population density (MPD) were estimated to quantitatively describe the growth behavior of Salmonella. To reflect more realistic microbial interactions in Salmonella-contaminated product, our model considered competition with the background microbiota, measured as mesophilic aerobic plate counts (APC). Notably, the μmax of Salmonella in low-fat samples (∼5 %) was significantly higher (p < 0.05) than that in high-fat samples (∼25 %) at 10, 20, and 30 °C. The average doubling time of Salmonella was 26, 4, 2, 1.5, 0.8, and 1.1 h at 10, 15, 20, 25, 30, and 40 °C, respectively. The initial concentration of Salmonella minimally impacted its growth in ground pork at any temperature. The MPD of APC consistently exceeded that of Salmonella, indicating the growth of APC without competition from Salmonella. The competition model exhibited excellent fit with the experimental data, as 95 % (627/660) of residual errors fell within the desired acceptable prediction zone (pAPZ >0.70). The theoretical minimum and optimum growth temperatures for Salmonella ranged from 5 to 6 °C and 35 to 36 °C, respectively. The dynamic model displayed strong predictive performance, with 90 % (57/63) of residual errors falling within the APZ. Dynamic models could be valuable tools for validating and refining simpler static or isothermal models, ultimately improving their predictive capabilities to enhance food safety.

Inhibition of Listeria monocytogenes and Clostridium botulinum in Uncured Shredded Pork and Turkey Packaged Under Reduced Oxygen Conditions

Cooked, uncured meat products packaged under reduced oxygen packaging conditions require the control of anaerobic and facultative anaerobic pathogens if they are held at temperatures greater than 3°C at retail or consumer level. The objective of this study was to determine the inhibition of Listeria monocytogenes and Clostridium botulinum in cooked, uncured shredded turkey and pork formulated with synthetic or clean-label antimicrobials. Treatments of shredded meat products were prepared with or without antimicrobials using turkey thigh or breast that were cooked to 85°C, shredded, and chilled before inoculation with the target pathogen. L. monocytogenes inoculated samples were stored at 7.2°C, whereas C. botulinum samples were stored at 12.8°C; triplicate samples were assayed every 2 weeks. In the first set of experiments, L. monocytogenes populations increased 2 to 3 logs within 2 weeks of storage at 7.2°C in both meat control treatments without antimicrobials and in pork with 4% lactate-diacetate blend (LD). A 1-log increase was observed in turkey with 4% LD and Pork with 2% cultured dextrose-vinegar-rosemary (CDVR) under the same storage conditions; a 1-log increase was observed in turkey with CDVR at 4 weeks. The second set of experiments tested the effect of pH reduction (to less than 5.5 by the addition of 0.5% citric acid) in combination with 2% CDVR when added to the brine precook or postcook during shredding. Populations of L. monocytogenes increased 4-log within 2 and 4 weeks at 7.2°C for the control turkey and pork formulations, respectively. No growth was observed in 12 weeks for any antimicrobial CDVR-CA treatments regardless of how antimicrobial was added. Similarly, botulinum toxin was detected in both control treatments at week 2 at 12.8°C, but no toxicity was observed in either antimicrobial treatment through 12 weeks. These data suggest that a combination of 2% cultured dextrose-vinegar-rosemary extract plus 0.5% citric acid to reduce pH inhibits the growth of L. monocytogenes and toxin production of C. botulinum in uncured shredded turkey and pork products stored under mild temperature abuse conditions for up to 12 weeks in reduced oxygen packaging.

Preservative effect of pomegranate-based marination with β-resorcylic acid and cinnamaldehyde on the microbial quality of chicken liver

Chicken liver is considered a delicacy in the Middle East where pomegranate molass is commonly used as a salad dressing and in marinade recipes. Marinated chicken liver is a common entrée and represents a value-added product compared to the otherwise unmarinated liver which commands a lower price. The aim of this study was to investigate the inhibitory effects of a pomegranate-based marinade alone or following the addition of cinnamaldehyde or β-resorcylic acid on the spoilage microorganisms present in chicken liver during storage for 14 d at 4°C or under mild temperature abuse conditions (10°C). The pH and microbial populations of total plate count (TPC), lactic acid bacteria (LAB), Pseudomonas spp. (PS), yeast and mold (YM), and Enterobacteriaceae (EN) were tested during the storage period and the shelf life was determined (defined as 107 log cfu/g). Sensory analysis was also conducted. The pH increased by a greater extent in unmarinated samples as compared to marinated samples (with or without antimicrobials) upon storage. The initial TPC, LAB, PS, YM, and EN microbial populations in the chicken liver were 3.85 ± 0.79, 3.73 ± 0.85, 3.85 ± 0.79, 3.73 ± 0.87, and 3.69 ± 0.23 log cfu/g, respectively. The marinade decreased the microbial populations by 2 to 4 log cfu/g. The marinade and antimicrobial mixture decreased the microbial populations by 3 to 4 log cfu/g. Except for 1 sample, none of the marinated chicken liver samples with or without antimicrobials reached the end of shelf life even up to 14 d of storage at both 4°C and 10°C. The overall sensory score was rated around 6/9 for the treated samples.

Evaluation of maximum growth rate of Listeria monocytogenes in ready-to-eat fresh-cut papaya and melon

Listeria monocytogenes has been identified on minimally processed fruit and vegetables, and can transmit a severe foodborne disease through the consumption of ready-to-eat (RTE) fresh-cut produce, mostly if the storage conditions are incorrect, and the cold chain is not abided to. The aim of the present work was to evaluate the behaviour of L. monocytogenes in RTE fresh-cut papaya and melon, two low-acid fruits stored in temperature-abuse conditions (10 and 8°C, respectively) during the shelf-life indicated by the producer (7 d). A microbiological challenge test was performed to assess the maximum growth rate (MGR) and the duplication time (Td) of the pathogen, testing three strains separately. We also assessed the behaviour of the indigenous microflora of the fruits. Results demonstrated that papaya and melon were two favourable substrates for L. monocytogenes. The MGR was 0.044 log CFU/g/h with a Td of 6.77 h for papaya, and 0.029 log CFU/g/h with a Td of 10.24 h for melon. The storage of RTE fresh-cut papaya and melon at an abusive temperature above 8°C could encourage the growth of L. monocytogenes with a possible risk to public health.

Microbiological, chemical and physical attributes and mathematical models for total volatile basic nitrogen formation of Asian seabass (Lates calcarifer) fillets stored under refrigerated and temperature-abuse conditions

Microbiological, chemical and physical attributes and mathematical models for total volatile basic nitrogen formation of Asian seabass (Lates calcarifer) fillets stored under refrigerated and temperature-abuse conditions

Examining the trade-offs in potential retail benefits of different expiration date modes: Insights into multidimensional scenarios

A significant challenge in today's food system is variable and unknown food quality affected by various temperatures, resulting in unreliable fixed expiration dates (FED) printed on food packaging. The dynamic expiration date (DED) mode is proposed as an alternative to the FED mode; however, practitioners must guard against some major uncertainties when setting expiration dates (shelf life) for fresh food. As such, we firstly developed a computer-simulated experiment based on a shelf life prediction model for multiple scenarios (i.e., fresh food's initial quality, quality change rate, and shelf temperature) to evaluate potential retail benefits of both date modes. The results show that the DED mode is a promising approach; yet a significant difference in retail benefits emerged between the DED and FED modes. On the one hand, the DED mode could reduce food waste by 10.02% at low temperatures (0−8 °C), but it may increase food waste by 15.94% and 31.71% under the temperature abuse conditions of 12−18 °C and 20−28 °C, respectively. On the other hand, the expired food sold rate within the FED mode is influenced by shelf temperatures, quality change rate, and initial quality of fresh foods. A one-at-a-time perturbation analysis finds that fresh food's shelf life associated with food quality is particularly sensitive to the food waste rate and expired food sold rate in both date modes. This study supports the trade-offs in retail benefits between the two modes while encouraging retailers to proactively optimize DED use.

Interface engineering by gelling sulfolane for durable and safe Li/LiCoO2 batteries in wide temperature range

Lithium-metal batteries (LMBs) with high energy densities have aroused intensive interest in electrical energy storage devices but suffer from the risk of thermal runaway, especially under harsh conditions of high temperature or thermal abuse. Pursuing intrinsically thermally stable electrolytes with higher performance and higher safety beyond commercial liquid electrolytes is a major challenge in this field. Here we report on a unique, highly durable sulfolane-based gel electrolyte constructed by a facile gelling strategy. This method takes advantages of thermotolerant sulfolane as a plasticizer and strong dipole-dipole interactions to achieve the gelation of polymer polyvinylidene fluoride/polyethylene oxide. We systematically investigated the influence of gelled sulfolane on gel formation, lithium plating/stripping, and solid electrolyte interphase. Benefiting from favorable interface engineering, the sulfolane-based gel electrolyte remarkably enhances the cyclic and safety performances of LMBs. When used in the Li/LiCoO2 battery, the resulting gel electrolyte enables long-term cycling stability at high temperatures up to 90°C. Moreover, the thermal safety of practical Li/LiCoO2 pouch cells (up to 190°C) has also been demonstrated by accelerating rate calorimetry. These results contribute to the development of high-safety LMBs that require abuse tolerance, high energy, and long calendar life.

Effects of temperature abuse on the growth and survival of Listeria monocytogenes on a wide variety of whole and fresh-cut fruits and vegetables during storage

Twenty types of fruits and vegetables representing a broad range of fresh produce categories were assessed for the growth potential and growth kinetics of Listeria monocytogenes under conditions reflecting commercial practices for storage and distribution and conditions reflecting sustained temperature abuse. Whole and fresh-cut produce was obtained from various commercial sources and inoculated with L. monocytogenes strains to evaluate the survival and growth for up to 25 days, depending on the projected commercial storage or retail shelf life for each commodity. The L.monocytogenes populations showed a sustained decline on all tested whole fruits, including avocado, blueberry, grape, mango, peach, green pepper, and tomato. Under “normal” storage conditions (defined as those reflective of common commercial practices), significant L. monocytogenes growth was only observed on fresh-cut cantaloupe (∼0.8 log) and fresh-cut mango (∼0.6 log). Exposure to temperature abuse conditions did not change the overall trends of L. monocytogenes survival on the whole fruits but did result in significant growth on several fresh-cut products, including celery, cauliflower, mango, onion, romaine lettuce, and cantaloupe. After inoculation on certain products (e.g., fresh-cut carrot and whole peach), L. monocytogenes seemed to lose cultivability rapidly but did retain viability as determined by the maintenance of cell membrane integrity.

Bacterial growth in chicken breast fillet submitted to temperature abuse conditions

Given possible temperature variations in the cold chain during retail display of chilled food, this work evaluated the growth of Salmonella choleraesuis and Staphylococcus aureus inoculated in chicken breast fillet submitted to different temperature abuses. The bacterial growth was evaluated in Luria–Bertani broth and previously inoculated chicken breast fillet cooled for 12h and incubated at different temperatures (5, 20, and 25 °C) for 12 h and 5 ºC for 12 days. The maximum growth rate and maximum growth were determined. The microorganisms grew at all studied temperatures, with a significantly lower growth at 5 °C compared with 20 and 25 °C. S. choleraesuis showed higher growth than S. aureus in both culture medium and chicken breast, and major maximum growth in culture medium than chicken breast, at all studied temperatures. Salmonella sp. and S. aureus were not detected in the control treatment maintained at 5 °C, and the thermotolerant bacteria remained within the standards allowed by Brazilian legislation when stored for 12 days. However, temperature abuse resulted in the vulnerability and spoilage of chicken breast fillet quality. The effects of temperature abuse caused by negligence on the microbial growth (Ymax) and growth rate (µmax) in chicken breast fillet, under industrial conditions was demonstrated.

Effect of Enterocins A and B on the Viability and Virulence Gene Expression of Listeria monocytogenes in Sliced Dry-Cured Ham

Dry-cured ham can be contaminated with Listeria monocytogenes during its industrial processing. The use of bacteriocins could ensure the safety of such meat products, but their effect on pathogen physiology is unknown. Therefore, the impact of enterocins A and B on the L. monocytogenes population, and the expression patterns of five genes (inlA, inlB, clpC, fbpA and prfA) related to adhesion/invasion and virulence regulation have been monitored in sliced dry-cured ham during 30 d of storage in refrigeration (4 °C) and temperature-abuse conditions (20 °C). L. monocytogenes strains S2 (serotype 1/2a) and S7-2 (serotype 4b) counts were reduced by 0.5 and 0.6 log units immediately after the application of enterocins A and B, a decrease lower than previously reported. Differences in gene expression were found between the two strains. For strain S2, expression tended to increase for almost all genes up to day seven of storage, whereas this increase was observed immediately after application for strain S7-2; however, overall gene expression was repressed from day one onwards, mainly under temperature-abuse conditions. L. monocytogenes strains investigated in the present work exhibited a mild sensitivity to enterocins A and B in sliced dry-cured ham. Bacteriocins caused changes in the expression patterns of virulence genes associated with adhesion and invasion, although the potential virulence of surviving cells was not enhanced.

Effect of Essential Oils and Vacuum Packaging on Spoilage-Causing Microorganisms of Marinated Camel Meat during Storage.

The use of essential oils (EOs) and/or vacuum packaging (VP) with meats could increase product shelf-life. However, no studies investigating the effect of EOs and VP on camel meat background microbiota have been conducted previously. The study aimed to analyze the antimicrobial effect of essential oils (EOs) carvacrol (CA), cinnamaldehyde (CI), and thymol (TH) at 1 or 2% plus vacuum packaging (VP) on the growth of spoilage-causing microorganisms in marinated camel meat chunks during storage at 4 and 10 °C. VP is an effective means to control spoilage in unmarinated camel meat (CM) and marinated camel meat (MCM) compared to aerobic packaging (AP). However, after EO addition to MCM, maximum decreases in spoilage-causing microorganisms were observed under AP on day 7. Increasing the temperature from 4 to 10 °C under AP increased the rate of spoilage-causing bacterial growth in CM and MCM; however, EOs were more effective at 10 °C. At 10 °C the maximum reductions in total mesophilic plate counts, yeast and molds, mesophilic lactic Acid bacteria, Enterobacteriaceae, and Pseudomonas spp. were 1.2, 1.4, 2.1, 3.1, and 4.8 log CFU/g, respectively. Incorporating EOs at 2% in MCM, held aerobically under temperature abuse conditions, delayed spoilage.

A simple time temperature indicator for real time microbial assessment in minimally processed fruits

Colorimetric time temperature indicator (TTI) which changes colour from colourless to brown due to phenol oxidation in the presence of Na2CO3 and ammonium per sulphate (APS; free radical initiator) is developed. Twelve TTI prototypes were prepared by using different concentrations of Na2CO3 (23–59 mM), APS (21–43 mM) with 2% (wt/vol) phenol. Significant (p < 0.05) effect of Na2CO3 and APS was observed on the activation energy (EaTTI) of TTI. Activation energy (Eamicrobial) of microbial spoilage in three minimally processed fruits (pineapple, pomegranate, jackfruit) was evaluated. Colour change of TTI having EaTTI similar to the fruits Eamicrobial demonstrated good correlation (R2 ≥ 0.7) with microbial growth in all the three fruits. Microbial counts in fruit samples stored under temperature abuse conditions were estimated within an error of ±1 Log10 CFU g−1 by analysing colour change in TTI using DSLR camera. TTI was successfully employed for rapid determination of microbial quality.

Inhibition of natural bacterial flora, Staphylococcus aureus, and enterotoxin A production in cooked ground chicken with oregano oil or tannic acid (TA) alone or combination

The effect of oregano oil and tannic acid (TA) on the aerobic plate count, Staphylococcus aureus growth, and staphylococcal enterotoxin A (SEA) production in cooked chicken breast meat held at abusive temperatures were evaluated. Five treatments, namely, control, 200 ppm oregano essential oil, 10 ppm TA, 200 ppm oregano oil + 10 ppm TA, and 5 ppm butylated hydroxyanisole (BHA), were prepared. The antimicrobial effect of TA was weaker than that of the oregano oil or BHA, and TA did not decrease the APC at the end of the storage at 10°C or 25°C. Oregano oil + TA treatment (combination) significantly suppressed the APC at all temperatures (10°C, 25°C, and 43°C) tested. Oregano oil + TA (combination) was the most effective treatment for inhibiting S. aureus growth at 10°C and 25°C. All treatments inhibited SEA production in cooked chicken at 25°C; however, oregano oil + TA (combination) was the most effective in inhibiting SEA production at 10°C and 43°C (7 days and 6 h, respectively). Based on these results, oregano oil has strong antimicrobial activity, which increases when combined with TA. Oregano oil + TA has a good potential for inhibiting the natural bacterial flora, growth of S. aureus, and SEA production in cooked chicken to enhance the microbial quality and safety under temperature abuse conditions.

Persistence of Salmonella enterica and Enterococcus faecium NRRL B-2354 on Baby Spinach Subjected to Temperature Abuse after Exposure to Sub-Lethal Stresses.

The exposure of foodborne pathogens such as Salmonella enterica to a sub-lethal stress may protect bacterial cells against distinct stresses during the production of leafy greens, which can constitute potential health hazards to consumers. In this study, we evaluated how the prior exposure of S. enterica to sub-lethal food processing-related stresses influenced its subsequent persistence on baby spinach under cold (4 °C for 7 days) and temperature abuse (37 °C for 2 h + 4 °C for 7 days) conditions. We also compared the survival characteristics of pre-stressed S. enterica and Enterococcus faecium NRRL B-2354 as its surrogate on baby spinach. A cocktail of three S. enterica serovars, as well as S. Typhimurium ATCC 14028 wild type and its ΔrpoS mutant, and E. faecium NRRL B-2354, was first exposed to sub-lethal desiccation, oxidation, heat shock, and acid stresses. Afterward, baby spinach was inoculated with unstressed or pre-stressed cells at 7.0 log CFU/sample unit, followed by 7-day storage under cold and temperature abuse conditions. The unstressed S. enterica (fresh cells in sterile 0.85% saline) decreased rapidly within the first day and thereafter persisted around 5.5 log CFU/sample unit under both conditions. The desiccation-stressed S. enterica showed the highest bacterial counts (p < 0.05) compared to other conditions. The unstressed S. enterica survived better (p < 0.05) than the oxidation- and acid-stressed S. enterica, while there were no significant differences (p > 0.05) between the unstressed and heat-shocked S. enterica. Unlike the wild type, temperature abuse did not lead to the enhanced survival of the ΔrpoS mutant after exposure to desiccation stress, indicating that the rpoS gene could play a critical role in the persistence of desiccation-stressed S. enterica subjected to temperature abuse. E. faecium NRRL B-2354 was more persistent (p < 0.05) than the pre-stressed S. enterica under both conditions, suggesting its use as a suitable surrogate for pre-stressed S. enterica by providing a sufficient safety margin. Our results demonstrate the merit of considering the prior exposure of foodborne pathogens to sub-lethal stresses when validating the storage conditions for leafy greens.

Short communication: Evaluating the recovery potential of injured cells of Listeria innocua under product temperature-abuse conditions and passage through simulated gastrointestinal fluids

Ice cream handling and serving conditions on the consumer side may result in temperature abuse before consumption. Under some extreme conditions, even the sporadic presence of injured bacterial cells might pose a health risk due to the possibility of recovery of those cells. We conducted this investigation to evaluate the potential of injured cells of Listeria innocua to recover under ice cream temperature abuse conditions and on exposure to simulated gastrointestinal (GI) fluids. Ice cream mix samples (42% total solids), spiked with 4 log10 cfu/g of Listeria innocua, were thermally treated at 69°C for 30 min. Potential heat-injured cells were recovered in buffered Listeria broth (BLEB), followed by isolation on Listeria-specific modified Oxford agar (MOX). The ice cream mix samples, containing potentially injured cells of Listeria innocua, were followed through overnight aging (7°C), freezing (-3.3°C), and overnight hardening (-40°C) steps to obtain the final ice cream samples. To simulate temperature abuse conditions, the samples were held for 12 h at 4.4°C, followed by 30 min at room temperature (22°C); this treatment was considered the first cycle of temperature abuse. To generate a worst-case scenario, the samples were exposed to 3 such consecutive temperature abuse cycles. At the end of each cycle, direct plating was done on MOX to recover viable cells, and BLEB enrichment verified the presence of potential injured cells. In addition, the ice cream samples, containing potential injured cells, were passed through simulated GI fluids. As a first step, samples were mixed (1:1) with simulated gastric fluids (pH 1.0 and 2.0 before mixing) and held at 37°C in a shaker incubator. Samples drawn at 15, 30, and 60 min were analyzed for viable and potential injured cells. To study the effect of sequential transit through simulated intestinal fluid, a mixture of ice cream and gastric fluid (1:1) from the gastric fluid experiment above was added to simulated intestinal fluid (pH 6.8) and held at 37°C. Samples were analyzed at 30 and 360 min for viable and potential injured cells. Three trials were conducted and the samples collected in duplicates. The temperature abuse or GI fluid exposure studies did not result in the recovery of potential injured cells of Listeria innocua in the ice cream samples under the conditions tested. Exposure to gastric fluids, however, did not eliminate the potential injured cells. Further studies are necessary to understand the exact risk implications of these findings.

Effect of vacuum cooling followed by ozone repressurization on Clostridium perfringens germination and outgrowth in cooked pork meat under temperature-abuse conditions

The effect of combining vacuum cooling with an ozone-based inhibition process (InhVac) on Clostridium perfringens spore germination and outgrowth in cooked pork meat after exponential chilling (from 54.4 to 7.2 °C in 12, 15, 18, or 21 h) and isothermal storage (20, 25, 30, 36, or 45 °C) was evaluated. Ice cooling (IC) and vacuum cooling (VC) were used to compare the effects with InhVac. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain concentration of ca. 3 log10 CFU/g. C. perfringens growth in samples treated by InhVac were 0.1, 0.37 and 0.9 log10 CFU/g after 15, 18 and 21 h of cooling from 54.4 to 7.2 °C respectively, significantly lower (P<0.05) than those in samples subjected to IC (1.01, 2.10 and 2.8 log10 CFU/g) and VC (0.56, 1.01 and 2.13 log10 CFU/g). Compared to VC and IC, InhVac treatment increased the lag phase (λ), decreased the growth rates (μmax), and extended the sample shelf-life (the time until a 1 log10 CFU/g increase in C. perfringes from the initial concentration value) at all storage temperatures. InhVac-treated samples not only had a longer shelf-life than those treated by VC, but also exhibited almost two times longer shelf-life compared to those subjected to IC regardless of storage temperatures. Additionally, statistical indexes showed that a primary modified Gompertz model and a secondary Square Root model could fit the data well. Industrial relevanceIn this study, an innovative inhibition approach (InhVac) was found to show a better antimicrobial effect on C. perfringens germination and outgrowth in cooked pork meat compared to ice cooling and vacuum cooling under temperature-abuse conditions. A primary modified Gompertz model and a secondary Square Root model could be used to predict the C. perfringens growth in samples subjected to InhVac treatment.

The microbiology of beef steaks stored aerobically or anaerobically in vacuum pack films with different oxygen barrier properties

The objective of this study was to investigate bacterial growth on beef steaks stored under different atmospheric conditions (aerobic, anaerobic and low, medium and high barrier film vacuum packs) at 2 °C and temperature abuse (20 °C) conditions while monitoring changes in physicochemical and colour stability. At 2 °C, packaged steaks did not show significantly (p≥0.05) reduced growth of mesophilic and psychrophilic total viable counts (TVCm and TVCp), Enterobacteriaceae or lactic acid bacteria populations compared to aerobically stored steaks but significantly (p ≤ 0.05) less populations of Pseudomonas and Brochothrix thermosphacta were recorded in high barrier and anaerobic packaging. At 20 °C, medium, high barrier and anaerobic packaged steaks showed significantly (p ≤ 0.05) less growth of TVCm, TVCp, Enterobacteriaceae, Pseudomonas spp. and B. thermosphacta compared to aerobically stored steaks. Overall, high barrier packaging with an oxygen transfer rate (OTR) of <3 cm3/m2·day· bar and anaerobic storage both showed the greatest potential at reducing spoilage bacteria on beef (Pseudomonas and B. thermosphacta) while retaining the redness of the meat for the longest duration.

Development of Enzymatic – Colorimetric Time – Temperature Integrator for Smart Packaging

A new enzymatic-colorimetric time-temperature integrator (ECTTI) to evaluate temperature abuse in refrigerated products was developed with Tributyrin, pH indicator, and lipase Calb. The kinetic behavior of the ECTTI (0.01 µL.L-1 enzyme) was assessed at 5, 10, 15, 20, and 25ºC, evaluating changes in pH (≤7.2) and color (ΔE ≥12). Storage at 5°C provided stability of the enzyme indicator for 16 days, and temperature abuses caused stability reduction to 15, 10, 0.5 0.3 days, with 10, 15, 20, and 25ºC of storage, respectively. The sequential abuse of temperature stability of ECTTI was assessed by exposure at 5.0ºC for 2 h and 25ºC for 1 or 5 min, returning to 5.0ºC for another 2 h, until the change in pH and color. The ECTTI subjected to temperature abuses for 5 and 1 min/25°C, remained stable for 5 and 9 cycles, respectively. The results of ECTTI stability before application, obtained with separate buffer/enzyme/water + substrate/indicator solutions, stored at 5 or 25ºC, before the reactive mixing of solutions, kept their stability, demonstrating the possibility of use as a tool against the temperature abuse conditions.

Growth of Listeria monocytogenes Inoculated on Packaged Fresh-Cut Turnips Stored at 4 and 10°C

The ecology of Listeria monocytogenes has been previously investigated in various whole and minimally processed raw vegetables, but not in turnips. A 2018 national Canadian recall for packaged fresh-cut turnips contaminated with L. monocytogenes raised concerns about turnips being able to support the growth of this microorganism. Thus, this study examined the growth potential of L. monocytogenes in fresh-cut turnips stored at 4 and 10°C. The bacterial microbiota of each brand of purchased turnips was also partially determined to evaluate the diversity of bacteria present on the product. Turnips were mist inoculated at an initial level of 3.0 log CFU/g using a five-strain L. monocytogenes cocktail. Samples were then stored at either 4 or 10°C for 10 days, with enumeration occurring at 0, 5, and 10 days. L. monocytogenes did grow on turnips stored at 10°C, with increases ranging from 0.87 to 1.84 log CFU/g over the 10-day storage period (P < 0.05). In contrast, L. monocytogenes was able to survive but not grow on turnips stored at 4°C for 10 days. This study reinforces the importance of strict temperature control within processing, retail, and household consumer settings. Avoiding temperature abuse conditions and storing packaged fresh-cut turnips under refrigerator conditions (≤4°C) can serve as an important hurdle to prevent and/or limit the growth of L. monocytogenes on these products.