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.     

Effect of thyme essential oil and packaging treatments on fresh Mediterranean swordfish fillets during storage at 4 °C

The present study evaluated the effect of thyme essential oil and packaging on fresh Mediterranean swordfish fillets during storage at 4 °C. Treatments in the present study included the following: air (A), modified atmosphere packaging (M), air with thyme oil (AT) and MAP with thyme oil (MT). Of the physicochemical parameters examined, TBA values for A and M swordfish samples were variable, indicative of no specific oxidative rancidity trend, whereas MT treatment inhibited lipid oxidation in swordfish samples during storage. On the basis of microbiological and sensory data, TMA-N and TVB-N limit values of acceptability for Mediterranean swordfish, of ca. 3.72 and 24.5 mg N/100 g, for the initiation of fresh Mediterranean swordfish spoilage, may be proposed. Of the treatments used in the present study, MT and M were the most effective for the inhibition of pseudomonads and H₂S-producing bacteria in swordfish. Lactic acid bacteria and Enterobacteriaceae (to a lesser extent) were also found to be part of the natural microbial flora of swordfish, irrespective of packaging treatment. Based primarily on sensory data, the shelf-lives of fresh refrigerated Mediterranean swordfish were 8 and 13 days under aerobic and MAP conditions, respectively. Addition of 0.1% thyme essential oil extended the product’s shelf-life under aerobic conditions by 5 days, whereas the combination of MAP and thyme oil resulted in a significant shelf-life extension of the swordfish fillets, i.e. by approximately 7½ days, according to sensory data, as compared to the control sample.     

Fate of Escherichia coli O157:H7, Salmonella and Listeria innocua on minimally-processed peaches under different storage conditions

Consumption of fresh-cut produce has sharply increased recently causing an increase of foodborne illnesses associated with these products. As generally, acidic fruits are considered ‘safe’ from a microbiological point of view, the aim of this work was to study the growth and survival of Escherichia coli O157:H7, Salmonella and Listeria innocua on minimally-processed peaches. The three foodborne pathogens population increased more than 2 log₁₀ units on fresh-cut peach when stored at 20 and 25 °C after 48 h. At 10 °C only L. innocua grew more than 1 log₁₀ unit and it was the only pathogen able to grow at 5 °C. Differences in growth occurred between different peach varieties tested, with higher population increases in those varieties with higher pH (‘Royal Glory’ 4.73 ± 0.25 and ‘Diana’ 4.12 ± 0.18). The use of common strategies on extending shelf life of fresh-cut produce, as modified atmosphere packaging and the use of the antioxidant substance, ascorbic acid (2% w/v), did not affect pathogens’ growth at any of the temperatures tested (5 and 25 °C). Minimally-processed peaches have shown to be a good substrate for foodborne pathogens’ growth regardless use of modified atmosphere and ascorbic acid. Therefore, maintaining cold chain and avoiding contamination is highly necessary.     

Effect of marinating process on the microbiological quality of Pacific saury (Cololabis saira) during vacuum-packaged storage at 4 °C

This study was carried out to evaluate the microbiological quality of Pacific saury ( Cololabis saira ) treated with marinating solutions containing either 12% NaCl + 2% acetic acid or 12% NaCl + 3% acetic acid, followed by vacuum packaging and storage at 4 °C for 90 days. The fish-to-marinating-solution ratio was 1:1.5. The growth rate of aerobic, halophilic, lactic acid bacteria and Pseudomonas spp. were significantly ( P  < 0.05) reduced in marinated vs. brined (12% NaCl + 0% acetic acid) fillets. Complete inhibition in the growth of both Enterobacteriaceae and Staphylococcus aureus was detected in fillets marinated in 3% and 2% acetic acid by the days 30 and 50 of storage, respectively. Both marinating conditions resulted in shelf life extension of the product to more than 90 vs. 60 days only for the brined fillets. Listeria monocytogenes , Vibrio parahaemolyticus and Salmonella spp. could not be detected in any of the analysed raw or treated samples.     

Chemical quality and sensory attributes of marinated Pacific saury (Cololabis saira) during vacuum-packaged storage at 4 °C

This study was carried out to evaluate the chemical changes and sensory attributes of Pacific saury (Cololabis saira), brined (12% NaCl brine solution) or marinated (12% NaCl + 2% acetic acid; or 12% NaCl + 3% acetic acid solutions) followed by vacuum-packaging and storage at 4 °C for 90 days. The chemical analysis revealed a significant reduction in the pH value, total volatile bases nitrogen (TVBN), and trimethylamine (TMA) contents in marinated versus brined fillets. Lipid oxidation, as indicated by the 2-thiobarbituric acid (TBA) values, was significantly delayed in marinated fillets in comparison with the brined fillets. The growth rate of psychrotrophic bacteria was significantly (P < 0.05) reduced in marinated versus brined fillets. No significant differences were detected for the sensory attributes between the two marinating conditions although the overall acceptability was significantly higher in marinated versus brined fish. Both conditions of the marinating process resulted in an extension of the shelf life of the product to more than 90 days versus only 60 days for the control brined fillets. The study concluded that marination of Pacific saury can delay the undesirable chemical changes, retard lipid oxidation, improve the sensory attributes and extend the shelf life of the product during refrigerated storage.     

Loss of viability of Listeria monocytogenes in contaminated processed cheese during storage at 4, 12 and 22 °C

The behaviour of Listeria monocytogenes in a processed cheese product was evaluated over time by inoculating the product with three different L. monocytogenes strains (Scott A, CA and a strain isolated from processed cheese) at three different inoculation levels (ca. 6 × 10⁵, ca. 6 × 10³ and 10² CFU/g of cheese or less) and after storage of the contaminated products at 4, 12 or 22 °C. Growth of L. monocytogenes was not observed in any of the experimental trials (experiments involving different combinations of strain, inoculum level and storage temperature) throughout the storage period. L. monocytogenes populations decreased over time with a rate that was strain- and storage temperature-dependent. Nonetheless, for cheeses that had been inoculated with the higher inoculum and stored at 4 °C viable populations of L. monocytogenes could be detected for up to nine months post-inoculation. The L. monocytogenes survival curves obtained from the different trials were characterised by a post-inoculation phase during which the populations remained essentially unchanged (lag phase) followed by a phase of logarithmic decline. The duration of the lag phase and the rate of inactivation of L. monocytogenes in the different trials were estimated based on data from the linear descending portions of the survival curves. In addition, a non-linear Weibull-type equation was fitted to the data from each survival curve with satisfactory results. The results of the present study emphasize that, according to the definition laid down in the European Union Regulation 1441/2007, the processed cheese product tested in this work should be considered and classified as one that does not support the growth of L. monocytogenes under reasonable foreseeable conditions of distribution and storage. However, post-processing contamination of the product should be austerely avoided as the pathogen can survive in the product for extended periods of time, particularly under refrigerated storage (4 °C).     

Survival of Salmonella enteritidis and changes in pH and organic acids in grated carrots inoculated or not with Lactobacillus sp and stored under different atmospheres at 4 °C

The fate of Salmonella enteritidis in grated carrots stored in air, modified atmosphere and vacuum at 4 °C was investigated with the coexistence or not of Lactobacillus sp. The population of Salmonella survived in all cases despite the presence of Lactobacillus and irrespective of the size of its inoculum. Lactic acid bacteria grew in all cases and a pH reduction was noted in all samples inoculated with Lactobacillus sp, while no such reduction occurred in sterile carrot tissue inoculated or not with S enteritidis. Sterile carrots exhibited minimum organic acid profile alterations compared to samples inoculated with Lactobacillus sp. Among these acids, lactate production was favoured under reduced oxygen conditions, in contrast to acetic acid, whose production required the presence of oxygen. These acids may act as an additional hurdle to control this pathogen under both aerobic and modified atmosphere packaging storage conditions. © 2002 Society of Chemical Industry     

Combined effect of vacuum-packaging and oregano essential oil on the shelf-life of Mediterranean octopus (Octopus vulgaris) from the Aegean Sea stored at 4 °C

The present study evaluated the use of vacuum packaging (alone) or with addition of oregano essential oil (EO), as an antimicrobial treatment for shelf-life extension of fresh Mediterranean octopus stored under refrigeration for a period of 23 days. Four different treatments were tested: A, control sample; under aerobic storage in the absence of oregano essential oil; VP, under vacuum packaging in the absence of oregano essential oil; and VO1, VO2, treated samples with oregano essential oil 0.2 and 0.4% (v/w), respectively, under VP. Of all the microorganisms enumerated, Pseudomonas spp., H₂S-producing bacteria and lactic acid bacteria (LAB) were the groups that prevailed in octopus samples, irrespective of antimicrobial treatment. With regard to the chemical freshness indices determined, thiobarbituric acid (TBA) values were low in all octopus samples, as could have been expected from the low fat content of the product. Both trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) values of oregano treated under VP octopus samples were significantly lower compared to control samples during the entire refrigerated storage period. Based primarily on sensory evaluation (odor), the use of VP, VO1 and VO2 extended the shelf-life of fresh Mediterranean octopus by ca. 3, 11 and 20 days, respectively.     

The effect of holding live sea urchins (Evechinus chloroticus) in air prior to gonad removal on gonad adenine nucleotide profiles during storage at 4 °C

Sea urchin gonads are usually sold as a fresh chilled product. Thus, to evaluate the effect of live urchin’s post-harvest conditions on gonad shelf-life, gonads were extracted either immediately after harvesting or after holding urchins in air at either 4 or 15 °C for 144 and 72 h, respectively. Gonads were subsequently washed in brine and stored at 4 °C for 10 days prior to adenine nucleotide (nmol/g w/w) profile determination. A decline in ATP (control: 376.16; urchins held in air: 231.58 and 245.16) and build-up of its degradation products, mainly inosine (control: 13.25; urchins held in air: 82.87 and 52.95), was observed in gonads recovered from urchins held in air. A faster increase in ATP degradation products was detected during storage of gonads recovered from urchins held in air, with final K-values (%) of 59.34 and 48.18 being significantly higher than K-values obtained from the controls (29.69, p < 0.05), suggesting that post-harvest handling can negatively impact on gonad shelf-life.     

Changes of radical-scavenging capacity and ferrous reducing power in chub mackerel Scomber japonicus and Pacific saury Cololabis saira during 4 °C storage and retorting

To clarify the effects of freshness of raw fishes and boil-retort process on the antioxidant activities, we determined stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging capacity and ferrous reducing power in the ethanol extract solution of chub mackerel Scomber japonicus and Pacific saury Cololabis saira meat before and after retort process (115 °C for 80 min). The antioxidant activities in boiled (mizu-ni) and canned fish were also investigated. The mizu-ni can products contain only fish meat and little salt. The radical-scavenging capacity was increased about ten times in chub mackerel and about six times in Pacific saury by the retort treatment. Both antioxidant activities of raw chub mackerel meat increased during 10 days storage at 4 °C. On the other hand, the increasing of antioxidant activity in the stored and retorted meat was observed until four days storage. In the case of mizu-ni canned products, the antioxidant activities were high in common-grade cans rather than high-grade cans. Almost the antioxidant activities shown in this study were correlated with absorbance at 245 nm. We consider that the results about differences of antioxidant activities between raw and retorted fishes or fresh and several day stored fishes are useful for the food functions and safeties.     

APC values and volatile compounds formed in commercially processed,raw chicken parts during storage at 4 and 13 °C and under simulated temperature abuse conditions

Skinless chicken breast fillets, thighs, wings and boneless breast with skin were selected from the production line of a commercial processor. Samples were evaluated over time in storage at 4 and 13 °C and under temperature abuse conditions for microbial proliferation and production of volatile compounds (VCs). Aerobic plate counts (APCs) were enumerated and VCs quantitated at 24 h storage intervals; however, APC increases were not reflected by significant correlations with headspace VCs. Compounds isolated from sample headspaces by solid phase microextraction (SPME) and direct headspace sampling and then analysed by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS) and gas chromatography/chemiluminescence detection (GC/SCD) were hydrogen sulphide, methanethiol, ethanol, acetone, C5, C6 and C7 hydrocarbons, dimethyl sulphide, methyl ethyl ketone, carbon disulphide, 1‐propanol, ethyl acetate, 1‐butanol, S‐methyl thioacetate, 3‐methyl‐1‐butanol, dimethyl disulphide and dimethyl trisulphide. Compounds appearing in the samples with any degree of consistency and therefore considered pertinent for these analyses were ethanol, acetone, methyl ethyl ketone, ethyl acetate, hydrogen sulfide, dimethyl sulphide and carbon disulphide. Elevated APCs and VC diversity occurred more prevalently in those samples from higher‐temperature storage. Published in 2000 for SCI by John Wiley & Sons, Ltd.     

Raman spectroscopic analysis and rheological measurements on natural actomyosin from haddock (Melanogrammus aeglefinus) during refrigerated (4 °C) and frozen (−10 °C) storage in the presence of trimethylamine-N-oxide demethylase from kidney of lizardfish (Saurida tumbil)

Changes in viscoelasticity and structure of haddock natural actomyosin (NAM) treated with partially purified trimethylamine-N-oxide demethylase (TMAOase) in the presence of cofactors (FeCl₂, ascorbate and cysteine), after refrigerated storage (4 °C) for 15 days or after frozen storage (−10 °C) for eight weeks, were elucidated using FT-Raman spectroscopy and dynamic viscoelastic measurement. Greater increases in the final storage modulus (G′) and loss modulus (G″), reflecting protein aggregation, were observed in the simulated NAM systems, containing NAM, trimethylamine oxide (TMAO) and cofactors, stored at −10 °C, compared to those stored at 4 °C, particularly in the system with a higher concentration of TMAOase (p < 0.05). Raman spectroscopy revealed that amide I and amide III bands of NAM were affected by TMAOase added as well as by storage temperature. The decrease in the CH₂ bending region near 1450 cm⁻¹, in the presence of TMAOase upon storage, suggested an increase in hydrophobic interactions of aliphatic residues. Changes in a doublet near 830 and 850 cm⁻¹ indicated an involvement of tyrosine residues as hydrogen bond donors in the system containing TMAOase after storage at both temperatures. The systems stored at −10 °C generally showed greater structural alteration than those kept at 4 °C, especially in the presence of 15 units of TMAOase/g. Therefore, TMAOase played an important role in the structural alteration and aggregation of haddock muscle proteins, mainly by the induction of formaldehyde formation.