Effect of nisin and high temperature pasteurization on the shelf-life of whole milk

Two experiments were conducted to assess the effectiveness of nisin on the keeping quality of pasteurized whole milk. After pasteurization, milk samples were stored at 10°C and samples were analysed at intervals for total plate count (TPC), Lactobacillus count, calcium ion concentration, pH and total acidity (TA). In the first experiment nisin was added to milk samples in the range 0 to 50 IU ml^-1 prior to pasteurization at 72°C for 15 s. AH concentrations of nisin used were effective in controlling microbial growth. Milk containing 40 and 50 IU ml^-1 nisin had not spoiled after 41 days' storage compared to spoilage time of 14 days for the control milk. In the second experiment 40 IU ml^-1 of nisin was combined with three 'pasteurization' processes: 72°C for 15 s, 90°C for 15 s and 115°C for 2 s. The milk processed at 72°C for 15 s with nisin showed an increased keeping quality of about 7 days compared with the control and showed a significantly lower count for Lactobacillus. In contrast, nisin had a much greater effect on TPC counts in the milk pasteurized at 90°C for 15 s, and after 28 days' storage at 10°C the milk was still acceptable. Milks treated both with and without nisin at 115°C for 2 s were microbiologically acceptable after 28 days, with counts less than 10 ml^-1. However, the milk with nisin was superior in flavour, as no noticeable off-flavours were apparent after 32 days. All these results are consistent, as shown by the microbiological and chemical analyses. Addition of nisin to milk prior to pasteurization provides an opportunity to achieve extended shelf-life in regions with poor refrigeration.     

Reduction of pasteurization temperature leads to lower bacterial outgrowth in pasteurized fluid milk during refrigerated storage: a case study

Bacterial numbers over refrigerated shelf-life were enumerated in high-temperature, short-time (HTST) commercially pasteurized fluid milk for 15 mo before and 15 mo after reducing pasteurization temperature from 79.4°C (175°F) [corrected] to 76.1°C (169°F). Total bacterial counts were measured in whole fat, 2% fat, and fat-free milk products on the day of processing as well as throughout refrigerated storage (6°C) at 7, 14, and 21 d postprocessing. Mean total bacterial counts were significantly lower immediately after processing as well as at 21 d postprocessing in samples pasteurized at 76.1°C versus samples pasteurized at 79.4°C. In addition to mean total bacterial counts, changes in bacterial numbers over time (i.e., bacterial growth) were analyzed and were lower during refrigerated storage of products pasteurized at the lower temperature. Lowering the pasteurization temperature for unflavored fluid milk processed in a commercial processing facility significantly reduced bacterial growth during refrigerated storage.     

Shelf-life of minimally processed cabbage treated with neutral electrolysed oxidising water and stored under equilibrium modified atmosphere

Minimally processed vegetables (MPV) have a short shelf-life. Neutral electrolysed oxidising water (NEW) is a novel decontamination method. The objective of this study was to test the potential of NEW to extend the shelf-life of a MPV, namely shredded cabbage. Samples of shredded cabbage were immersed in NEW containing 40 mg/L of free chlorine or tap water (control) up to 5 min, and then stored under equilibrium modified atmosphere at 4 degrees C and 7 degrees C. Proliferation of aerobic mesophilic bacteria, psychrotrophic bacteria, lactic acid bacteria and yeasts were studied during the shelf-life. Also pH and sensorial quality of the samples as well as O(2) and CO(2) composition of the headspace of the bags was evaluated. From the microbial groups, only psychrotrophic counts decreased significantly (P<0.05) due to the effect of NEW, but the counts in treated samples and controls were similar after 3 days of storage at 4 degrees C and 7 degrees C. Packaging configurations kept O(2) concentration around 5% and prevented CO(2) accumulation. pH increased from 6.1-6.2 to 6.4 during the shelf-life. No microbial parameter reached unacceptable counts after 14 days at 4 degrees C and 8 days of storage at 7 degrees C. The shelf-life of controls stored at 4 degrees C was limited to 9 days by overall visual quality (OVQ), while samples treated with NEW remained acceptable during the 14 days of the experiment. The shelf-life of controls stored at 7 degrees C was limited to 6 days by OVQ and browning, while that of samples treated with NEW were limited to 9 days by OVQ, browning and dryness. According to these results, a shelf-life extension of at least 5 days and 3 days in samples stored respectively at 4 degrees C and 7 degrees C can be achieved by treating shredded cabbage with NEW. NEW seems to be a promising method to prolong the shelf-life of MPV.     

Effect of Processing and Storage Conditions on the Fate of Vitamins B1, B2, and C and on the Shelf-Life of Goat's Milk

Goat's milk was heat-processed under different time-temperature conditions of pasteurization and sterilization. Losses of thiamin, riboflavin, and total vitamin C in HTST, Flash, and UHT were less than that by LTLT and Autoclave. Also residual oxygen in the milk affected the loss of total vitamin C during storage. A longer shelf-life of pasteurized milk was obtained with HTST, HTST overpasteurization, and Flash process; however, there was no significant difference between UHT and Autoclave sterilized products. From the above results, HTST pasteurization was considered the best process to preserve milk quality.     

Validation of apple cider pasteurization treatments against Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes.

Time and temperature pasteurization conditions common in the Wisconsin cider industry were validated using a six-strain cocktail of Escherichia coli O157:H7 and acid-adapted E. coli O157:H7 in pH- and degrees Brix-adjusted apple cider. Strains employed were linked to outbreaks (ATCC 43894 and 43895, C7927, and USDA-FSIS-380-94) or strains engineered to contain the gene for green fluorescent protein (pGFP ATCC 43894 and pGFP ATCC 43889) for differential enumeration. Survival of Salmonella spp. (CDC 0778. CDC F2833, and CDC H0662) and Listeria monocytogenes (H0222, F8027, and F8369) was also evaluated. Inoculated cider of pH 3.3 or 4.1 and 11 or 14 degrees Brix was heated under conditions ranging from 60 degrees C for 14 s to 71.1 degrees C for 14 s. A 5-log reduction of nonadapted and acid-adapted E. coli O157:H7 was obtained at 68.1 degrees C for 14 s. Lower temperatures, or less time at 68.1 degrees C, did not ensure a 5-log reduction in E. coli O157:H7. A 5-log reduction was obtained at 65.6 degrees C for 14 s for Salmonella spp. L. monocytogenes survived 68.1 degrees C for 14 s, but survivors died in cider within 24 h at 4 degrees C. Laboratory results were validated with a surrogate E coli using a bench-top plate heat-exchange pasteurizer. Results were further validated using fresh unpasteurized commercial ciders. Consumer acceptance of cider pasteurized at 68.1 degrees C for 14 s (Wisconsin recommendations) and at 71.1 degrees C for 6 s (New York recommendations) was not significantly different. Hence, we conclude that 68.1 degrees C for 14 s is a validated treatment for ensuring adequate destruction of E. coli O157:H7, Salmonella spp., and L. monocytogenes in apple cider.     

Effect of heat treatment of milk on activation of Bacillus spores

The quality and shelf life of fluid milk products are dependent on the amount and type of microorganisms present following pasteurization. This study evaluated the effects of different pasteurization processes on the microbial populations in fluid milk. The objective was to determine whether certain pasteurization processes lead to an increase in the amount of bacteria present in pasteurized milk by activating Bacillus spores. Samples of raw milk were collected on the day of arrival at the dairy plant. The samples were pasteurized at 63 degrees C for 30 min (low temperature, long time), 72 degrees C for 15 s (high temperature, short time), 76 degrees C for 15 s, and 82 degrees C for 30 min. The pasteurized samples were then stored at 6 and 10 degrees C for 14 days. The samples were analyzed for standard plate count and Bacillus count immediately after pasteurization and after 14 days of storage. Pasteurization of milk at 72 and 76 degrees C significantly (P < 0.05) increased the amount of Bacillus spore activation over that of 63 degrees C. There was no detection of Bacillus in initial samples pasteurized at 82 degrees C for 30 min, but Bacillus was present in samples after storage for 14 days, indicating that injury and recovery time preceded growth. The majority of isolates were characterized as Bacillus mycoides and not Bacillus cereus, suggesting that this organism might be more a cause of sweet curdling of fluid milk than previously reported.     

Moderate electric field pasteurization of milk in a continuous flow unit: Effects of process parameters,energy consumption,and shelf-life determination

This study presents a new non-thermal moderate electric field (MEF) process for milk pasteurization. To evaluate the applicability of this process, fresh milk was treated by MEF at electrical field strength (EFS) of 8.33, 14.58, and 20.80 V/cm and mass flow rates (MFR) of 0.018, 0.042 and 0.077 kg/s to compare the microbiological quality, alkaline phosphatase activity, chemical composition, and some physical properties of the product with those of conventionally pasteurized (15 s at 72 °C) and raw milk. The changes in the total count of bacteria (TCB) and titratable acidity of samples were observed during 18 days of storage at 5 °C for shelf-life estimation. The results showed that MEF reduced energy consumption by 63% in comparison with thermal pasteurization. Also, MEF treatment inactivated coliforms (100%), Staphylococcus aureus (100%), psychrophiles (100%), yeasts and molds (100%), and alkaline phosphatase (100%) while keeping the processing temperature below 22 °C. Also, TCB of sample was reduced by increasing the EFS from 8.33 to 20.8 V/cm and decreasing the MFR from 0.0774 to 0.0185 kg/s. The longest shelf-life of MEF samples, i.e., 15 days, was observed at EFS of 20.80 V/cm and MFR of 0.018 kg/s which was better than that of thermal pasteurization samples, i.e., 9 days.     

Polyphenol oxidase activity as a potential intrinsic index of adequate thermal pasteurization of apple cider

In response to increasing concerns about microbial safety of apple cider, the U.S. Food and Drug Administration has mandated treatment of cider sufficient for a 5-log reduction of the target pathogen. Pasteurization has been suggested as the treatment most likely to achieve a 5-log reduction, with Escherichia coli O157:H7 as the target pathogen. Regulators and processors need a reliable method for verifying pasteurization, and apple cider polyphenol oxidase (PPO) activity was studied as a potential intrinsic index for thermal pasteurization. The effect of pasteurization conditions and apple cider properties on PPO activity and survival of three pathogens (E. coli O157:H7, Salmonella, and Listeria monocytogenes) was studied using a Box-Behnken response surface design. Factors considered in the design were pasteurization conditions, i.e., hold temperature (60, 68, and 76 degrees C), preheat time (10, 20, 30 s), and hold time (0, 15, 30 s), pH, and sugar content ((o)Brix) of apple cider. Response surface contour plots were constructed to illustrate the effect of these factors on PPO activity and pathogen survival. Reduction in PPO activity of at least 50% was equivalent to a 5-log reduction in E. coli O157:H7 or L. monocytogenes for cider at pH 3.7 and 12.5 (o)Brix. Further studies, however, are needed to verify the relationship between PPO activity and pathogen reduction in cider with various pH and (o)Brix values.     

Microbial levels in Michigan apple cider and their association with manufacturing practices

In recent decades, apple cider has been implicated in a series of outbreaks of foodborne illness. The objective of this study was to determine the presence and concentrations of pathogenic and indicator microorganisms in apple cider processed in Michigan and to evaluate the impact of thermal pasteurization, UV light radiation, and implementation of hazard analysis critical control point (HACCP) plans on these microbes. Cider samples were obtained from Michigan mills between 1997 and 2004 and analyzed for Escherichia coli O157:H7, Salmonella, generic E. coli, total coliforms, and aerobic bacteria. Neither E. coli O157:H7 nor Salmonella were detected in any tested cider samples, suggesting a very low frequency of pathogens in Michigan apple cider. The persistent and relatively high frequency of generic E. coli observed in samples obtained in all years indicates a continued risk of pathogen contamination in Michigan apple cider, especially when it is untreated. The use of thermal pasteurization or UV light radiation and reported implementation of HACCP plans were associated with lower frequency and counts of generic E. coli, total coliforms, and aerobic microorganisms. However, the relatively high counts of indicator organisms in some cider samples that were claimed to be treated according to these pathogen reduction measures indicates that some processors had inadequate practices, facilities, or equipment for pathogen reduction or did not consistently or adequately apply practices or pathogen-reduction equipment in an effective manner.     

INACTIVATION OF E. COLI 0157:H7 IN APPLE CIDER BY OZONE AT VARIOUS TEMPERATURES AND CONCENTRATIONS

The effect of temperature (5–20C) at 860 ppm (v/v) ozone and different gaseous ozone concentrations above 1,000 ppm on inactivation of E. coli O157:H7 in apple cider was studied. Lag times ranged from 3.5 min at 20C to 6.7 min at 10C before the on-set of E. coli O157:H7 inactivation. D-values ranged from 0.6 to 1.5 min at 20C and 5C, respectively. After ozone treatment of cider for 14 min, dissipation of ozone from cider was slow, decreasing to about 5 mg/L after 2 h at 5C. At high gaseous ozone concentration, log time was shortest and D-value lowest. There was a critical concentration of dissolved ozone of about 5–6 mg/L at 20C, before the on-set of E. coli O157:H7 inactivation in the cider. Total processing times, based on lag time plus 5D, ranged from about 4 to 14 min depending on temperature and ozone concentration. Overall, inactivation of E. coli O157:H7 by ozone was fast enough to allow practical applications in cider production, and it should be considered as an alternative to thermal pasteurization.     

Pasteurization of carrot juice by combining UV-C and mild heat: Impact on shelf-life and quality compared to conventional thermal treatment

The combination of UV-C radiation and mild heat (UV-H) treatment is a promising strategy for synergistically increasing microbial inactivation in low UV-transmitting juices. In this research, we explored the suitability of UV-H treatment in carrot juice pasteurization and its impact on juice quality during shelf-life compared to that of thermal pasteurization. UV-H treatment at 60 °C (3.92 J/mL, 3.6 min) enabled reductions of over 5 log₁₀ cycles in the reference pathogens and a significant reduction in spoilage yeasts, bacteria, and bacterial spores. The activity of pectin methylesterase and polyphenol oxidase was reduced by UV-H treatment to levels close to those of low-temperature pasteurization (60 °C/18.1 min). The native population of total aerobic bacteria, lactic acid bacteria, and yeasts and molds of UV-H-treated juice remained undetectable during 29 days of cold storage. Furthermore, viscosity, cloud stability, and the color of fresh juice were better preserved by UV-H treatment than by thermal pasteurization throughout storage.Industrial relevanceThis study demonstrates that UV-H treatment is a beneficial alternative to conventional thermal processing in carrot juice pasteurization, since appropriate inactivation levels of pathogenic and spoilage microorganisms can be reached while better preserving the quality attributes of fresh juice throughout its shelf-life.     

Effect of storage temperature on galactose formation in UHT milk

Galactose has been studied from the standpoint of its suitability as a heat-induced parameter for processed milk. Galactose content in two directly and two indirectly UHT treated liquid milk samples were studied during storage until the end of its shelf-life (12 weeks) period at temperatures of 6, 20, 30, 40, and 50°C. No significant differences during storage were found with reference to the type of thermal process applied, nor with respect to the initial galactose content of the sample. Galactose formation was just directly related to storage time and temperature, being more significant at temperatures higher than 20°C. Galactose increased slightly during storage at ambient temperature (20°C) after the first weeks but kept constant under temperature of refrigeration until end of storage. Thermal history of the processed milk, mainly at a temperature above 20°C, could affect the usefulness of galactose as a heat-induced parameter.     

Dense phase carbon dioxide treatment of mango in syrup: Microbial and enzyme inactivation,and associated quality change

Dense phase carbon dioxide (DPCD) has been mainly explored as a new non-thermal pasteurization method for liquid foods. However, it's pasteurization efficacy absolutely needs to be further investigated for solid-liquid food mixtures, such as mango in syrup. This study aimed to investigate pasteurization and enzyme inactivation effects for DPCD treatment, and evaluate quality changes by comparing with traditional thermal pasteurization (TP) method. Optimal DPCD treatment (20 MPa, 60 °C, 30 min) was determined by conducting single factor and orthogonal experiments. Staphylococcus aureus CICC 10384 and Escherichia coli CICC 10003, which were selected as representative gram-positive and gram-negative pathogens in mango in syrup, could be completely inactivated by the optical DPCD treatment with initial concentrations of >8-log CFU/mL. Polyphenol oxidase and peroxidase activities could be completely inactivated after the optimal DPCD processing. Less adverse effect on pH and color, and higher amounts of vitamin C and total phenols of samples were observed after DPCD treatment when compared with TP treatment. The shelf-life of mango in syrup treated with DPCD was estimated to be <86 days (25 °C) based on an accelerated shelf-life testing (ASLT). This study demonstrated that DPCD treatment can be considered as a promising pasteurization technology for solid-liquid mixtures without exceedingly influencing their quality attributes.     

STORABILITY AND POTABILITY OF PASTEURIZED AND STERILIZED "KUNUN-ZAKI": A FERMENTED SORGHUM BEVERAGE

The possibility of extending the shelf-life of "Kunun-zaki", a nonalcoholic sorghum based fermented beverage after pasteurization and sterilization was investigated. The traditional method of production was adopted and microbiological studies carried out. The predominant microorganisms isolated from the fermented beverage were Lactabacillus plantarum and Bacillus subtilis. Enterobacter spp. and Saccharomyces spp. occurred in small numbers. Proximate analysis of unpasteurized samples showed a decrease in total sugar and increased moisture content after one week storage at refrigeration temperature. Pasteurized samples were most acceptable to the taste panel up to two weeks of refrigerated storage, but rejected thereafter. Although the sterilized "Kunun-zaki" was shelf-stable for the two weeks of investigation, its flavor and color were adversely affected, and therefore unacceptable to the panelists. This study has shown that the shelf-life of "Kunun-zaki" (usually 24–36h) can conveniently be prolonged without serious effects on the usual organoleptic properties for up to two weeks with pasteurization.     

Low temperature pasteurization to reduce the risk of vibrio infections from raw shell-stock oysters

Vibrio vulnificus and V. parahaemolyticus are natural inhabitants of estuarine environments and may be transmitted to humans by ingestion of raw oysters. This study focused on the use of low temperature pasteurization, to reduce these Vibrio spp. to nondetectable levels, thus reducing the risk of infection associated with raw oyster consumption. Artificially inoculated V. vulnificus and V. parahaemolyticus and naturally-contaminated V. vulnificus in live oysters were pasteurized at 50%deg;C for up to 15min. Samples of processed and unprocessed oysters were enumerated for V. vulnificus, V. parahaemolyticus, and aerobic spoilage bacteria for 0-14 days. Low temperature pasteurization was effective in reducing these pathogens from > 100000 to non-detectable levels in less than 10min of processing. Spoilage bacteria were reduced by 2-3 logs, thus increasing the shelf-life for up to 7 days beyond live unprocessed oysters. Vibrio vulnificus in control oysters was reduced by 102 during ice storage alone. Following pasteurization and during a temperature storage abuse study (24h at 22°C), V. vulnificus was not recovered. During this storage period spoilage bacteria exceeded 1 million/g oyster meat.     

THE EFFECTS OF THERMAL AND NONTHERMAL PROCESSING METHODS ON APPLE CIDER QUALITY AND CONSUMER ACCEPTABILITY

Due to increased concern about the safety of fruit, vegetable and juice products, the FDA has mandated that these must undergo a 5‐log reduction in pathogens. The development of various processing methods for juice products has caused the need to determine the effects of these methods on said products. The effect of thermal pasteurization, UV irradiation and ozone treatment on apple cider quality and consumer acceptability was studied over 21 days. Thermally pasteurized samples were different in color and less preferred in all areas of consumer acceptability. UV‐irradiated samples were lower in soluble solids for the first 7 days and showed no significant difference in consumer acceptability. Ozone‐treated cider had greater sedimentation, lower sucrose content and a decrease in soluble solids by day 21. UV irradiation allows for a more cost‐effective method to produce safe apple cider with minimal quality and consumer acceptability differences.     

A Comparative Study of the Quality of Strawberry Purée Preserved by Continuous Microwave Heating and Conventional Thermal Pasteurization During Long-Term Cold Storage

This study was aimed at monitoring changes in the quality of strawberry purée preserved by continuous microwave heating (MV) at 90 and 120 °C for 10 s and conventional thermal pasteurization (CTP) at 90 °C for 15 min during cold storage (6 °C), and determining its shelf-life. The shelf-life of MV and CTP-preserved products established on the basis of microbiological changes was more than 52 weeks (<1 log cfu of yeasts, moulds, and total microbial count per gram). During this time, 43 and 34 % of polyphenols, 89 and 58 % of anthocyanins, as well as 57 and 52 % of antioxidant capacity decrease were noted, for MV and CTP-preserved samples respectively; vitamin C was completely degraded. Color changes were more visible for MV (ΔE?=?10.82) compared with the CTP-preserved sample (ΔE?=?5.14). The kinetic rate of degradation of nutrients was higher for MV- compared to CTP-preserved purée. The recommended cold shelf-life for the MV-preserved purée was estimated at 100 days, during which time it was of a superior quality compared with CTP-preserved purée.     

Effect of inhibitory extracts derived from liquid smoke combined with postprocess pasteurization for control of Listeria monocytogenes on ready-to-eat meats

Surface pasteurization was examined in combination with low-phenolic antimicrobial extracts derived from liquid smoke to inhibit and prevent the growth of Listeria monocytogenes during the shelf life of ready-to-eat meats. In preliminary trials with retail frankfurters, one smoke derivative (2-min dip) produced a 0.3-log reduction of L. monocytogenes and a 1-min in-bag pasteurization (73.9 degrees C) produced a 2.9-log reduction, whereas a combination of the two treatments produced a 5.3-log reduction that resulted in no detectable Listeria by week 3 under accelerated shelf-life conditions (10 degrees C). In trials with frankfurters manufactured without lactate or diacetate that were treated with a shortened 1-s dip, this smoke extract and one with reduced smoke flavor and color both produced a > 4.5-log reduction of L. monocytogenes on frankfurters when heated at 73.9 degrees C for 1 min, with no recoverable Listeria detected for 10 weeks when stored at 6.1 degrees C. When deli turkey breast chubs manufactured without lactate, diacetate, or nitrite were treated with a 1-s dip in combination with radiant-heat pasteurization (270 degrees C), growth of L. monocytogenes was retarded but not prevented. However, in a similar study in which smoke extract treatment of deli turkey breast was combined with in-bag postpackage pasteurization (water submersion at 93.3 degrees C), a 60-, 45-, or even 30-s heat treatment resulted in a 2- to 3-log reduction of L. monocytogenes, with no growth on the meat during 10 weeks of storage at 6.1 degrees C. These findings indicate that reduced-acid low-phenolic antimicrobial liquid smoke derivatives combined with surface pasteurization are capable of reducing or preventing growth of L. monocytogenes to meet the criteria for the U.S. Department of Agriculture Food Safety and Inspection Service Alternative 1 process for ready-to-eat deli meat products manufactured without lactate or diacetate.     

Shelf-Life of Pasteurized Fluid Milk as Affected by Age of Raw Milk

Increasing raw milk storage time prior to pasteurization may affect product shelf-life. Raw milk was stored at 4.5°C for 0, 2, 4, and 6 days prior to pasteurizing. Milk samples from each pasteurized lot were analyzed after continuous storage at 4.5°C for 0, 4, 8, 12, 16, and 20 days. Both raw and pasteurized samples were analyzed for coliforms, psychrotrophs, and total bacteria counts. Flavor scores were also determined. No correlations were significant between raw or pasteurized samples and total bacteria or coliform counts. Related were flavor score and days held raw, shelf-life of the resulting pasteurized product, and interaction of days held raw and shelf-life of the pasteurized product. Psychrotrophic counts and age of the raw milk were correlated. From correlations of flavor scores with shelf-life of the milk, a predictive equation was: Flavor score = 8.00 – .88 R – .11 P – .0015 P² – .009 R P, where R is days held raw and P is shelf-life of the pasteurized product.