Correlations between growth parameters of spoilage micro-organisms and shelf-life of pork stored under air and modified atmosphere at -2, 4 and 10 degrees C

The correlations of the growth parameters (the initial cell number (N(0)), maximum cell number (N(max)), maximum specific growth rate (mu(max)), lag-phase (lambda)) of typical spoilage micro-organisms (lactic acid bacteria (LAB), coliforms, pseudomonads, Brochothrix thermosphacta) growing on sliced pork to the sensory shelf-life and microbial shelf-life were investigated. The changes in sensory quality and proliferation of micro-organisms on pork shoulder were studied at different atmosphere conditions (air and 40%CO(2)/59%N(2)/1%O(2)) and temperatures (-2, 4 and 10 degrees C). Microbial counts were fitted to the modified-Gompertz equation to obtain the growth parameters of different micro-organisms. B. thermosphacta and coliforms were predominant bacteria associated with spoilage of pork under all temperatures and air conditions. However, pseudomonads could only dominate under regular atmosphere condition. Using multiple linear regression, high correlations were found between the lag-time (lambda) of LAB (0.9814, 0.9830), B. thermosphacta (0.9895, 0.9849), or the maximum specific growth rate (mu(max)) of coliforms (-0.9583, -0.9695) and the microbial shelf-life and sensory shelf-life, respectively. The mu(max) and lambda of micro-organisms correlated well with microbial and sensory shelf-life. The shelf-life of pork is mainly correlated with the growth parameters of mu(max) and lambda than by N(max).     

Microbiological quality of 18 degrees C ready-to-eat food products sold in Taiwan

A total of 164 samples of 18 °C ready-to-eat (RTE) food products, purchased in 1999–2000 from convenience stores and supermarkets in central Taiwan, were examined to determine the microbiological quality of these products. The 18 °C RTE food products, manufactured by 16 factories, were divided into groups based on the type of food and their major ingredients. Aerobic plate count, coliforms, Escherichia coli, Bacillus cereus, Staphylococcus aureus and psychrotrophic Pseudomonas spp. were evaluated. The incidence of E. coli and coliforms in these 18 °C RTE food products was 7.9% and 75.0%, respectively, while 49.8% and 17.9% of the samples were found to contain B. cereus and S. aureus, respectively. Among the samples tested, 1.3% of the food products contained more than 10⁵ CFU g⁻¹ of B. cereus and 0.7% contained more than 10⁵ CFU g⁻¹ of S. aureus. The pH values of the samples were all below 7.0, except for cold noodles, which had pH values ranging from 5.18 to 8.20. Among the five types of 18 °C food products tested, the highest incidence of E. coli (16%) and Pseudomonas spp. (64.0%) were detected in hand-rolled sushi in a cone shape. On the other hand, the highest incidence rate of coliforms, B. cereus, and S. aureus were found in sandwiches (88%), cold noodles (66.7%) and rice balls rolled in seaweed (25.0%), respectively. Food products made of ham contained the highest incidence of coliforms (88.0%) and E. coli (16.0%), while food products containing meat and ham as the major ingredients had the highest incidence rates of B. cereus (62.5%) and S. aureus (26.1%), respectively. For coliforms, E. coli, B. cereus and S. aureus, the percentage of 18 °C RTE food products exceeding the microbiological standards for RTE food accepted by Republic of China was 75.0%, 7.9%, 49.8% and 17.9%, respectively.     

Microbiological quality of Port Salut Argentino cheese stored at two temperature treatments

Microbiological quality of Port Salut Argentino cheese was studied during 10 days (after ripening) at two storage temperature treatments: (a) 4°C and (b) a temperature combination of both 4 and 20°C (4/20°C), which implied 12 h at 4°C and 12 h at 20°C. Total coliforms were not higher than 10³ cfu/g among samples. E. coli was detected at both treatments. Thirty three percent of the cheese contained Staphylococcus aureus. Listeria spp. and Salmonella spp. were not detected in any treatment. Bacillus spp. incidence was 50% of the cheese, being B. cereus, B. cereus variety mycoides and B. pumilus. Bacillus cereus and Staphylococcus aureus grew at 4/20°C. Mesophilic aerobic bacteria were between 10⁴ and 10⁷ cfu/g. At 4/20°C counts decreased. At 4°C the behaviour was variable. Moulds were lower than 10⁴ cfu/g and yeasts were between 10⁴ and 10⁵ cfu/g. pH, moisture content and tritatable acidity ranges of samples were 5.5-6, 51-52.3% and 1.215-1.935 g/100 g of lactic acid, respectively. Manufacturing of this cheese includes a short heat treatment and starter culture addition; consequently, our results indicate that this processing may be insufficient for achieving hygienic cheese production. The storage at refrigeration temperature will not always guarantee the cheese safety and quality.     

Chemical and sensory changes in haddock and herring stored under modified atmosphere

The effectiveness of storage in atmospheres with increased proportions of CO₂ to extend the shelf-life of haddock and herring was examined. Using a 40: 30: 30/CO₂: O₂: N₂ atmosphere with haddock no useful extension of shelf-life was achieved at +5°C and only limited extension at 0°C. A more useful extension of shelf-life at 0°C was obtained by storing haddock in a 60: 20: 2O/CO₂: O₂: N₂ atmosphere and with herring in a 60:40/CO₂::N₂: atmosphere. Total volatile bases (TVB) and hypoxanthine values (Hx) correlated with the cooked flavour. There were no significant differences in drip-loss between the modified atmosphere packaging (MAP) stored samples and the controls. Peroxide values (PV) in herring were lower in MAP stored samples. Whole haddock and whole herring were found to have a longer shelf-life when stored in MAP at 0°C than when stored as fillets.     

Quality attributes of farmed eel (Anguilla anguilla) stored under air, vacuum and modified atmosphere packaging at 0 degrees C

The shelf life of fresh eel in various packaging conditions of atmospheric air, vacuum and modified atmosphere packaging (MAP) (40% CO(2), 30% N(2) and 30% O(2)) at 0 degrees C was investigated. All raw eel samples received acceptable sensory scores during the first 11+/-1 days of storage in atmospheric air, 11+/-1 days of storage in vacuum and finally 18+/-1 days of storage in MAP conditions. Using the microbial quality indicators the shelf life of eel packed in air, vacuum and MAP was estimated to be more than 18, 28 and 34 days, respectively. The main spoilage microorganisms under MAP conditions were lactic acid producing bacteria followed by Shewanella spp., pseudomonads, Enterobacteriaceae and yeasts. Chemical data revealed that pH, ammonia, glucose and lactate examinations might not be useful for monitoring eel quality differences.     

Microbiological quality and safety of fresh cultivated and wild mushrooms commercialized in Spain

402 samples of 22 species of cultivated and wild fresh mushrooms sold in retail markets and supermarkets in Zaragoza (Spain) were studied to quantify their microbial load (mesophilic aerobic microorganisms, Pseudomonas genus, Enterobacteriaceae, lactic acid bacteria, total and thermotolerant coliform bacteria, Escherichia coli, yeasts and moulds) and to investigate the presence of E. coli O157:H7, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus and Yersinia enterocolitica. The total microbial counts ranged from 4.4 to 9.4 log cfu/g, the genus Pseudomonas being the most prevalent with counts from 3.7 to 9.3 log cfu/g and Auricularia auricula-judae the species with the highest microbial load (9.4 log cfu/g). No significant differences (p > 0.05) were detected between mean counts of wild and cultivated species in all the microbial groups studied. The microbiological safety level of the cultivated mushrooms was excellent since no pathogens were isolated, and the microbial counts of indicator microorganisms were low, being detected in only half of the species. Salmonella spp, E. coli O157:H7 and S. aureus were not isolated from any sample, Y. enterocolitica was detected in only four samples of wild mushrooms whereas twenty-six (6.5%) were positive for L. monocytogenes, their occurrence being relatively high in Calocybe gambosa (40%), Hygrophorus limacinus (40%) and Tuber indicum (100%). These results suggest that a strategy to reduce bacterial populations, and to improve the microbiological safety of some species of fresh mushrooms, should be investigated.     

Microbiological and sensory quality of stored croissant‐type bakery products depending on external (sorbic acid) and internal (dough,aw value) conditions

The work presents some results from the evaluation of microbiological (total bacterial count, coliform bacteria, moulds and yeasts) and sensory (shape, odour, colour, taste, consistency, crust, soft inside, etc.) quality and of the a_w value and pH during the 90‐day storage (interval of 0, 30, 45, 60, 75 and 90 days) under laboratory conditions at 20 ± 2°C in eight types of the bakery croissant‐type product with the nougat cream differing by the type of dough (brioche, croissant( a_w value of the cream, and by the presence or absence of sorbic acid in the spirit spray applied onto the surface of products. The above‐indicated parameters were examined also in the nougat cream samples (on the zero and 90^th day of storage). The chosen quality parameters permitted the level of the durability influence of croissants depending on external (sorbic acid) as well as internal (recipe, a_w) conditions to be estimated.     

Microbiological and physicochemical properties of fresh retail cuts of beef packaged under an advanced vacuum skin system and stored at 4 degrees C

The effect of an advanced vacuum skin packaging system on the microbiological and physicochemical properties of fresh retail cuts of beef (including meat portions from six different anatomical regions) stored at 4 degrees C was compared with the effect of traditional vacuum packaging. The vacuum skin packaging system whose effect on meat quality was evaluated in this work displayed two remarkable features: (i) the instantaneous heating of the lower surface of the upper film of the package before the film descended over the meat surface and (ii) the tight disposition of the plastic film on the meat surface, which avoided wrinkles and purges. Throughout storage at 4 degrees C, rates of bacterial growth were statistically significantly slower in beef portions processed with the vacuum skin packaging system than in those processed with traditional vacuum packaging, with average differences of 2.07, 1.60, and 1.25 log CFU/g in counts of aerobic mesophiles, anaerobes, and lactic acid bacteria, respectively. pH values were statistically significantly lower for beef portions packaged with the vacuum skin system than for those that were vacuum packaged in the traditional manner, probably because of the relative predominance of lactic acid bacteria observed in such samples, which coincided with both higher meat firmness values and a slower meat tenderization process. The vacuum skin system prevented the appearance of undesirable coloration on the meat surface and also significantly improved the commercial color of the meat as determined on the basis of luminosity (L*) and the redness (a*). Overall, the quality (as determined by microbiological and physicochemical analyses and by visual examination) of fresh retail cuts of beef packaged with the vacuum skin system and stored at 4 degrees C was higher than that of meat samples processed with the traditional vacuum-packaging system.     

Combined effect of oregano essential oil and modified atmosphere packaging on shelf-life extension of fresh chicken breast meat, stored at 4 degrees C

The combined effect of oregano essential oil (0.1% and 1% w/w) and modified atmosphere packaging (MAP) (30% CO2/70% N2 and 70% CO2/30% N2) on shelf-life extension of fresh chicken meat stored at 4 degrees C was investigated. The parameters that were monitored were: microbiological (TVC, Pseudomonas spp., lactic acid bacteria (LAB), yeasts, Brochothrix thermosphacta and Enterobacteriaceae), physico-chemical (pH, TBA, color) and sensory (odor and taste) attributes. Microbial populations were reduced by 1-5 log cfu/g for a given sampling day, with the more pronounced effect being achieved by the combination of MAP and oregano essential oil. TBA values for all treatments remained lower than 1 mg malondialdehyde (MDA) kg(-1) throughout the 25-day storage period. pH values varied between 6.4 (day 0) and 5.9 (day 25). The values of the color parameters L*, a* and b* were not considerably affected by oregano oil or by MAP. Finally, sensory analysis showed that oregano oil at a concentration of 1% imparted a very strong taste to the product for which reason these lots of samples were not scored. On the basis of sensory evaluation a shelf-life extension of breast chicken meat by ca. 3-4 days for samples containing 0.1% oregano oil, 2-3 days for samples under MAP and 5-6 days for samples under MAP containing 0.1% of oregano oil was attained. Thus oregano oil and MAP exhibited an additive preservation effect.     

Effect of integrated application of gamma irradiation and modified atmosphere packaging on physicochemical and microbiological properties of shiitake mushroom (Lentinus edodes)

Shiitake (Lentinula edodes) mushrooms were packed in biorientated polypropylene (BOPP) bags and exposed to different doses of gamma irradiation (1.0, 1.5, and 2.0 kGy) within the packaging, heat sealed and stored at 4 °C for 20 d. Of the three doses, 1.0 kGy was most effective in maintaining a high level of firmness. Samples treated with 1.0 kGy also exhibited smaller initial declines in soluble protein, higher increases in total sugar content and lower levels of malondialdehyde accumulation. Furthermore, 1.0 kGy promoted the accumulation of phenolics compound and showed higher antioxidant ability during storage. At higher doses, 2.0 kGy resulted in a higher microbial reduction, but showed negative effects on texture, chemical properties and functional components. All the gamma irradiation were effective in retarding mushroom sensory deterioration. Thus, application of gamma irradiation in combination with MAP can extend the storage life of shiitake mushroom up to 20 d.     

Microbiological spoilage of vacuum and modified atmosphere packaged Vietnamese Pangasius hypophthalmus fillets

This study investigated the identity, growth and metabolite production of micro-organisms causing spoilage of Pangasius hypophthalmus fillets packaged in air, vacuum and modified atmospheres (MAP) (MAP 1: 50%CO(2)-50%N(2) and MAP 2: 50%CO(2)-50%O(2)) during storage at 4 °C. Based on the time it took for psychrotrophic total colony counts to exceed 7 log cfu g(-1), the shelf life of the fillets packaged in air, vacuum, MAP 1 and MAP 2 was estimated to be 7, 10, 12 and 14 days respectively. The longest lag phases were observed in the samples packaged in MAP 2 (50%CO(2)-50%O(2)). In the fillets packaged in air and under vacuum, the dominant flora identified by partial 16S rDNA sequencing at the end of the shelf life generally consisted of Gram-negative bacteria mostly belonging to the genera Serratia and Pseudomonas. In contrast, lactic acid bacteria (Carnobacterium maltaromaticum and Carnobacterium divergens) and Brochothrix thermosphacta were identified as the dominant spoilage flora in the samples packaged under the two MAPs investigated. By means of solid-phase microextraction gas chromatography mass spectrometry (SPME GC-MS) analysis, volatile organic compounds in the headspace of the samples at the end of the shelf life were identified for each packaging condition. Based on these results, a selective ion flow tube mass spectrometry (SIFT-MS) method was developed to quantify the production of volatile metabolites during storage of the fillets. The results of these analyses indicated that several compounds contributed to the bacterial spoilage of Pangasius fillets e.g., ethanol, 2,3-butanediol, diacetyl, acetoin, ethyl acetate, acetic acid and sulfur compounds. It also emerged that the production of these compounds was dependent on the packaging condition applied.     

Microbiological quality of ice creams commercialized in some cities in the state of Rio de Janeiro, Brazil

The microbiological quality of 60 ice cream samples of three commercial brands (A, B and C) of various flavours, commercialized in some towns in the State of Rio de Janeiro, Brazil, was evaluated. Total bacteria count (TCB), coliforms at 35°C (CT), coliforms at 44°C (CF) and presence of Staphylococcus aureus were performed on all samples. TCB ranged from 2.0 × 10 ² to 6.9 × 10 ⁵ cfu/mL, CT from < 3–≥ 2400 MPN/mL, CF from < 3–1100 MPN/mL and S. aureus from < 10–1.4 × 10 ⁶ cfu/mL. The level of bacterial contamination found in this study reflects the unhygienic conditions prevalent in manufacturing and storage of ice creams. Actions are thus necessary by the Brazilian regulatory agencies to require the ice cream processing plants to adopt quality guarantee systems, such as good manufacturing practices and hazard analysis and critical control points system.     

Quality of chilled ready-to-bake pizza stored in air and under modified atmospheres: Microbiological and sensory attributes

Modified atmosphere packaging (MAP) studies on microbiological and sensory analysis were conducted to extend the shelf life of ready-to-bake pizza stored at 7±1°C. The gas combinations used were: atm1: air (control), atm2: CO₂ (100%), atm3: N₂ (100%), atm4: 50% CO₂/50% N₂. Total plate count (TPC), yeasts/molds (Y/M), coliforms, lactic acid bacteria (LAB), psychrotrophs, and anaerobic spore formers were estimated at time intervals of 0, 5, 10, 15, and 20 days. TPC and LAB of pizza samples (atm1) reached 7.10 and 8.14 log CFU/g after 10 days of storage, respectively. Coliforms, psychrotrophs, and Y/M were significantly higher (p<0.05) for pizza samples stored in atm1 than other storage conditions of MAP. Finally, counts of anaerobic spore formers were low (<3 log CFU/g) irrespective of the packaging conditions throughout the entire storage period. It was concluded that among the 4 atmospheres examined, atm2 (100% CO₂) was the best, followed by atm4>atm3>atm1 respectively, in descending order. MAP conditions under this study may extend shelf life of pizza to considerable amount of time.     

Effect of high pressure on the microbiological quality of cooked chicken during storage at normal and abuse refrigeration temperatures

Vacuum-packaged cooked poultry meat was treated at a range of pressures (400–600 MPa) and hold times (1, 2 and 10 min), followed by storage at 4°, 8° or 12 °C for up to 35 days. Weissella viridescens was found to be the dominant microorganism in the pressure-treated meat, constituting 100% of the microflora identified at 500 and 600 MPa. None of the pressure-treated samples had obvious signs of spoilage during the 35 day storage period, even when the Weissella count was >7 log₁₀ cfu/g. Studies on a typical W. viridescens isolate showed it to be relatively pressure-resistant in poultry meat, with <1 log reduction in numbers after a treatment of 2 min at 600 MPa. Agar diffusion assays showed that the isolate also caused the inhibition of a number of Gram-positive and Gram-negative pathogens, including strains of Clostridium botulinum, Listeria monocytogenes, Bacillus cereus and Escherichia coli. The selection of a pressure-resistant organism, such as this Weissella sp. could be advantageous in extending the shelf-life, and also microbiological safety, of the cooked meat, as it could give protection in addition to the pressure treatment itself.     

Improvement of the overall quality of table grapes stored under modified atmosphere packaging in combination with natural antimicrobial compounds

ABSTRACT:  Consumers demand new means of preservation with absence of chemicals. In this work a package was developed (thermosealed baskets) with grapes wrapped with 2 distinct films (M and P) with different permeability (medium and high, respectively) without or with the addition of a mixture of eugenol, thymol, and carvacrol. Table grapes stored on air (control) lost their quality attributes very rapidly, manifested by accelerated weight loss, color changes, softening, and increase in soluble solids concentration and titratable acidity ratio (SSC/TA). The use of modified atmosphere packaging (MAP) alone retarded these changes, the effects being significantly greater when essential oils were added (especially for M film), although atmospheric composition was not affected by incorporating essential oils. In addition, microbial counts (molds and yeasts and mesophilic aerobics) were drastically decreased and accompanied by lower occurrence of berry decay. Although slight odor was detected after opening the packages, absence of the typical flavor of these compounds was found by trained panelists after tasting the berries. Thus, with this safe, simple, and innovative technology, the overall quality (sensory and safety) could be improved and considered as a toll alternative to the use of synthetic fungicides.     

Effects of temperature on Agrocybe chaxingu quality stored in modified atmosphere packages with silicon gum film windows

The effects of three storage temperatures (1, 3, and 5 °C) were determined on the quality of the edible mushroom Agrocybe chaxingu stored in modified atmosphere packages (MAP) with and without (control) silicon gum film windows. Results showed that the storage temperature had clear effects on headspace gas concentrations of O₂, CO₂ and ethylene, sensory characteristics, respiration rate, ascorbic acid content, soluble solid content and electrolyte leakage. The higher storage temperature (5 °C) resulted in more rapid changes in the different quality parameters for the stored mushroom except in the case of storage at 1 °C where chilling injury occurred. The MAP with silicon gum film windows at 3 °C provided the best atmosphere for mushroom A. chaxingu as shown by a fact that the MAP packs with windows at 3 °C had better quality than the control.     

Effects of modified atmosphere packaging (MAP) on the microbiological quality and shelf life of ostrich meat

Effects of various concentrations of O₂/CO₂ in modified atmosphere packaging on the microbiological quality and shelf-life of ostrich meat was investigated. Nine–12 months old ostriches were used. The iliofibularis muscle was cut into small cubes that were divided into five groups and then separately packaged under various gas mixes: air and O₂:CO₂:N₂ ratios of 80:20:0, 60:20:20, 60:40:0, and 40:40:20, using 2 different headspace ratios (1:1 and 3:1). The packaged meats were kept at 4 °C for 10 days and were analysed microbiologically, physico-chemically and sensorially. As a result, the meat quality and shelf-life of ostrich meat under various gas compositions were improved; microbial growth was delayed due to high CO₂ usage and shelf-life was increased by 5–7 days. However, an undesired loss of red colour of the ostrich meat may affect consumer acceptance.     

Relation of biogenic amines to microbial and sensory changes of precooked chicken meat stored aerobically and under modified atmosphere packaging at 4 °C

The formation of biogenic amines and their correlation to microflora and sensory characteristics of a precooked chicken meat product stored aerobically and under modified atmosphere packaging (MAP) (30% CO₂, 70% N₂) was studied. Putrescine was the main amine formed both in aerobically and MA-packaged chicken samples. For the rest of the biogenic amines, including tyramine, histamine, and cadaverine, a stepwise increase was recorded throughout the 23-day storage period under the above packaging conditions. Spermidine was found in higher amounts, as compared to spermine in both aerobically and MA-packaged chicken samples at 4 °C. Formation of these amines in precooked chicken stored either aerobically or under a 30% CO₂, 70% N₂ atmosphere followed an inconsistent trend during the entire storage period at 4 °C. Agmatine, β-phenyl-ethylamine, and tryptamine were not detected in precooked chicken. Of the bacterial groups monitored, lactic acid bacteria (LAB) became the dominant bacteria after day 8 of storage under MAP while LAB were the dominant population of natural microflora of precooked chicken stored both aerobically or under MAP, reaching 7.5 and 8.0 log cfu/g, respectively, on day 23 of refrigerated storage. Enterobacteriaceae populations in chicken meat were below the detection limit (<1 log cfu/g) by pour plating throughout the 23-day storage period, irrespective of packaging conditions. Based on sensory data, after ca. 8 days for the precooked chicken meat stored aerobically and after 12 days under MAP (time to reach initial decomposition stage, score of 2) the putrescine and tyramine content of chicken samples were ca. 14–19 and 1.4 mg/kg, values that may be proposed as the limit for spoilage initiation of precooked chicken meat (respective TVC for both aerobically and MA-packaged chicken meat were ca. 6.5 log cfu/g).     

Microbiological, physicochemical and organoleptic changes in dry-salted olives of Thassos variety stored under different modified atmospheres at 4 and 20 °C

Microbiological, physico-chemical and organoleptic changes were studied in dry-salted olives, cv. Thassos, stored under different atmospheres (100% carbon dioxide and nitrogen, 40% CO₂/30%O₂/30%N₂ and air) at 4 and 20 °C for 180 days. The initial microbial flora comprised of yeasts, no lactic acid bacteria, enterobacteria, pseudomonads or Staphylococcus aureus were detected, as the low water activity/high salt content does not favour their growth. At 4 °C, the population of yeasts declined steadily throughout storage but to a different extent depending on the gaseous atmospheres. At 20 °C, there was an initial decline in yeast counts in all samples followed by a steady increase until the end of the storage period. The CO₂ atmosphere was most effective at keeping the number of yeasts low at both storage temperatures. All gas atmospheres prevented fungal growth at both temperatures apart from the samples stored in air. The pH, a_w and salt content of the olives did not change significantly throughout the storage period. The prevailing yeast species was the salt tolerant Candida famata . The organoleptic characteristics did not differ significantly among differently treated olives. However, increased rancidity and reduced fruit colour was observed in the samples stored at 20 °C.