Sensory Rejection Research Articles

Quality Evaluation of Grated Graviera Cheese Stored at 4 and 12°C using Active and Modified Atmosphere Packaging

AbstractThe effect of active [oxygen absorber (OA) combined with an ethanol emitter (EE)] and modified atmosphere (100% Nitrogen) packaging in combination with a high barrier experimental polyethylene terephthalate‐silicon oxides//low density polyethelene film on shelf‐life extension of grated Graviera cheese stored at 4 and 12°C was investigated. Microbiological (total viable counts, Pseudomonads, lactic acid bacteria, Enterobacteriaceae and Yeasts/Moulds), physico‐chemical (pH, thiobarbituric acid and colour) and sensory (odour and taste) changes occurring in the product were monitored as a function of treatment and storage time (10 weeks). Sensory shelf‐life was approximately 1, 1.5, 4.5, 6, 9 and at least 10 weeks for control samples (12 and 4°C), for N2 packaged samples (12 and 4°C) and samples packaged with the OA + EE (12 and 4°C), respectively. At the point of sensory rejection, yeasts and moulds increased from 2.00 to 3.60 and 5.55 log CFU/g for control samples stored at 4 and 12°C, respectively. Similarly, for samples stored under nitrogen, yeasts and moulds reached 2.00 and 2.32 log CFU/g at 4 and 12°C, respectively. Yeasts and moulds in samples with the OA + EE remained below 2 log CFU/g throughout the entire storage period, irrespective of storage temperature. pH varied between 5.72 and 6.49 depending on specific treatment. Malondialdehyde absorbance ranged between 0.05 for fresh samples and 0.79 mg/kg at the time of sensory rejection of samples. Light parameters L and b decreased while parameter a increased during storage, reflecting a gradual discolouration of all samples and especially those stored at 12°C.

Effect of reduced oxygen atmosphere and sodium acetate treatment on the microbial quality changes of seer fish ( Scomberomorus commerson) steaks stored in ice

The effect of reduced oxygen atmosphere and sodium acetate treatment on the microbial quality of seer fish ( Scomberomorus commerson) steaks was determined during chilled storage (1–2 °C). The O 2 absorber reduced the oxygen content in the pack to less than 0.01% corresponding to 99.96% reduction within 24 h. The use of O 2 absorber with sodium acetate dip treatment (2% w/v) extended the sensory shelf life up to 25 days compared to only 12 days for control air packs and 20 days for untreated samples with O 2 absorber. A prominent lag phase was observed for many bacterium studied, particularly for the sodium acetate treated samples with O 2 absorber. On the day of sensory rejection, both the total mesophilic and psychrotrophic counts reached 7.7–8.1 and 7.1–7.9 log cfu/g, respectively. The sodium acetate treatment and reduced O 2 atmosphere affected the type of major spoilers. In air packed samples, H 2S-producers predominated followed by Brochothrix thermosphacta, Pseudomonas spp., where as in the untreated samples with O 2 absorber, H 2S-producers predominated the microbial flora followed by Lactobacillus spp. For treated samples with O 2 absorber, B. thermosphacta formed the major micro-flora followed by Lactobacillus spp. The use of O 2 absorber inhibited the growth of Pseudomonas spp., and total Enterobacteriaceae.

Applicability of a microbial Time Temperature Indicator (TTI) for monitoring spoilage of modified atmosphere packed minced meat

The applicability of a microbial Time Temperature Indicator (TTI) prototype, based on the growth and metabolic activity of a Lactobacillus sakei strain developed in a previous study, in monitoring quality of modified atmosphere packed (MAP) minced beef was evaluated at conditions simulating the chill chain. At all storage temperatures examined (0, 5, 10, 15 °C), the results showed that lactic acid bacteria (LAB) were the dominant bacteria and can be used as a good spoilage index of MAP minced beef. The end of product's shelf life as revealed by the sensory evaluation coincided with a LAB population level of 7 log 10 CFU/g. For all temperatures tested, the growth of L. sakei in the TTI resembled closely the growth of LAB in the meat product, with similar temperature dependence of the μ max and thus similar activation energy values calculated as 111.90 and 106.90 kJ/mol, for the two systems, respectively. In addition, the end point of TTI colour change coincided with the time of sensory rejection point of the beef product during its storage under isothermal chilled temperature conditions. The estimated activation energy, E α, values obtained for parameters related to the response of Δ E (total colour change of the TTI) describing the kinetics of colour change of the TTI during isothermal storage (i.e. the maximum specific rate of Δ Ε evolution curve, μ Δ Ε , and also the reciprocal of t i, time at which half of the maximum Δ Ε is reached), were 112.77 and 127.28 kJ/mol, respectively. Finally, the application of the microbial TTI in monitoring the quality deterioration of MAP minced beef due to spoilage was further evaluated under dynamic conditions of storage, using two separate low temperature periodic changing scenarios, resembling the actual conditions occurring in the distribution chill chain. The results showed that the end point of TTI, after storage at those fluctuating temperature conditions, was noted very close to the end of product's sensorial shelf life. This finding points to the applicability of the developed microbial TTI as a valuable tool for monitoring the quality status during distribution and storage of chilled meat products, which are spoiled by lactic acid bacteria or other bacteria exhibiting similar kinetic responses and spoilage potential.

Bacillus cereus in refrigerated milk submitted to different heat treatments.

The possibility of the survival, germination, and multiplication of Bacillus cereus in extended-shelf-life milk prompted research into the occurrence of the bacteria in refrigerated milk submitted to different heat treatments. Samples were submitted to ultrapasteurization (138 degrees C for 2 s), "superpasteurization" (96 degrees C for 13 s), and pasteurization (74 degrees C for 15 s) and stored under refrigeration at 4 +/- 2 degrees C for up to 6 weeks. The milk was analyzed for its sensory quality and for the quantitative determination of mesophilic and psychrotrophic B. cereus in the vegetative form at incubation temperatures of 7 and 30 degrees C, in addition to standard plate counts and psychrotrophic counts. In the three experimental trials, the psychrotrophic B. cereus counts were below the detection limit of the methodology (<10 CFU/ml) in all of the samples analyzed, independent of the heat treatment and storage period. The count of mesophilic B. cereus was restricted to samples of superpasteurized and pasteurized milk from a single trial, reaching 4.0 x 10(1) and 7.0 x 10(5) CFU/ml, respectively. Although the pasteurized milk had higher populations of mesophilic B. cereus after the second week of storage, flavor defects resulting in sensory rejection of the product did not appear before the fourth week of storage. The results of this research indicate that superpasteurization and ultrapasteurization are adequate for maintaining the product at refrigeration temperatures for 6 weeks. Pasteurized milk produced under clean conditions should have a shelf life limited to less than 2 weeks.

Combined effect of an oxygen absorber and oregano essential oil on shelf life extension of rainbow trout fillets stored at 4 °C

In the present study the combined effect of an O 2 absorber and oregano essential oil (0.4% v/w) on shelf life extension of rainbow trout fillets ( Onchorynchus mykiss) stored under refrigeration (4 °C) was investigated. The study was based on microbiological [TVC, Pseudomonas spp., Lactic Acid Bacteria, H 2S-producing bacteria including Shewanella putrefaciens, Enterobacteriaceae and Clostridium spp.), physicochemical (pH, PV, TBA, TVBN and Drip loss) and sensory (odor, taste) changes occurring in the product as a function of treatment and storage time. Aerobically-packaged rainbow trout fillets stored at 4 °C were taken as control samples. Results showed that TVC exceeded 7 log cfu/g on day 4 of storage for control samples, day 7–8 for samples containing oregano oil, day 9 for samples containing the O 2 absorber and day 12–13 for samples containing the O 2 absorber and oregano oil. Pseudomonas spp., Enterobacteriaceae and LAB were only partially inhibited by the O 2 absorber and/or the oregano oil. In all cases the inhibition effect was more pronounced when the combination of O 2 absorber with oregano essential oil was used. pH decreased from an initial value of 6.65–6.09 and subsequently increased to 6.86 due to formation of protein decomposition products. % Drip loss ranged between 7% and 11–12% at the end of the product shelf life. PV values ranged between 11.4 and 27.0 meq O 2/kg oil while malondialdehyde (MDA) ranged between 9.6 and 24.5 mg/kg. TVBN ranged between 10.6 and 54.6 mg/kg at the time of sensory rejection. Sensory shelf life was 4 days for the control samples, 7–8 days for samples containing oregano oil, 13–14 days for samples containing the O 2 absorber and 17 days for samples containing the O 2 absorber plus oregano oil.

Combined effect of an O2 absorber and oregano essential oil on shelf-life extension of Greek cod roe paste (tarama salad) stored at 4 °C

Abstract In the present study the combined effect of an O2 absorber and oregano essential oil (0.1% v/w) on shelf life extension of Greek cod roe paste (tarama salad) stored under refrigeration (4 °C) was investigated. The study was based on microbiological [Total viable count (TVC), Lactic Acid Bacteria (LAB), Enterobacteriaceae, H2S-producing, yeast and molds and Clostridium spp.), physicochemical (pH, fatty acid composition, thiobarbituric acid (TBA), and color) and sensory (color, odor, and taste) changes occurring in the product as a function of treatment and storage time. Aerobically packaged tarama salad stored at 4 °C was taken as the control sample. Results showed that TVC exceeded 7 log cfu/g on day 12–13 of storage for control samples and day 31–32 for samples containing oregano oil. Samples containing either the O2 absorber or the O2 absorber plus oregano oil never reached 7 log cfu/g during the 60 day storage period. LAB were only partially inhibited by the oregano oil and/or the O2 absorber. Yeasts and molds were totally inhibited by the O2 absorber. Enterobacteriaceae populations were below the method detection limit (2 log cfu/g) H2S-producing bacteria were the dominant spoilage microorganisms. Clostridum spp. was absent in 25 g sample. pH decreased from an initial value of 4.36 to 3.03 depending on specific treatment. Color parameters L⁎ and b⁎ increased and a⁎ decreased in control samples as well as in samples containing oregano oil. Color parameters remained unaffected in samples containing the O2 absorber. TBA expressed as malondialdehyde (MDA) values increased from 1.5 mg/kg to 3.4, 3.2 and 2.9 mg/kg for samples containing oregano oil, the O2 absorber and O2 absorber plus oregano oil at the point of sensory rejection, respectively. Saturated fatty acids (SFA) increased during storage with a respective decrease in monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) both in control samples and samples containing oregano oil. Fatty acid composition remained unaffected in all samples containing the O2 absorber. Sensory shelf life was 24 days for the control samples, 32 days for samples containing oregano oil, 60 days for samples containing the O2 absorber and at least 60 days for samples containing the O2 absorber plus oregano oil. Industrial relevance Oxygen absorbers as well as plant essential oils are considered natural means of preservation and may substantially extend the shelf life of foodstuffs while maintaining desirable sensory attributes (taste, odor and color).

Nucleotide breakdown products of seer fish (Scomberomorus commerson) steaks stored in O2 scavenger packs during chilled storage

Abstract Freshness of seer fish ( Scomberomorus commerson ) steaks packed with and without O 2 scavenger was assessed by sensory and chemical methods. O 2 scavenger used in the present study reduced the O 2 level in the pack to less than 0.01% within 24 h. Samples in air packs were sensorily acceptable only up to 12 days compared to 20 days in O 2 scavenger packs. TVB-N levels were 37 and 34 mg N 2 /100 g and TMA-N levels were 16.4 and 15.2 mg N 2 /100 g on the day of sensory rejection for air and O 2 scavenger packs, respectively. IMP decrease and Hx increase was significantly ( P 2 scavenger packs. On sensory rejection day, the average K, Ki , P and H values were 63–65%, Fr value was 34% and G value was 178% for O 2 scavenger packed samples compared to 81%, 18% and 443% for air packed samples, respectively. Industrial relevance The O 2 scavenger is an innovative active packaging technique, which is highly effective in reducing the O 2 present inside the pack. This can be used in place of traditional vacuum packaging for extending the shelf life of fish products, which reduces the use of vacuum packaging equipments thereby making the process cost effective.

The effects of soluble gas stabilisation on the quality of packed sardine fillets (Sardina pilchardus) stored in air, VP and MAP

SummarySardine (Sardina pilchardus) is a species that for its abundance assumes great importance in the Portuguese fishing sector. In order to contribute for a better utilisation of this species, the aim of this study was to investigate the effect of the pre‐treatment with soluble gas stabilisation (SGS) (100% CO2 at 2 bar, during 15 and 30 min) on the quality and shelf‐life of sardine fillets, packed in air (AP), vacuum (VP) and modified atmosphere (MAP: 5% O2/35% CO2/60% N2). During the chilled storage, the quality changes were evaluated by sensory evaluation, chemical and microbiological analysis. The total volatile basic nitrogen content remained almost constant, between 16 and 19 mg N/100 g muscle, during the storage period, for all samples. The TBARs values increased with storage time, for all batches and storage conditions. The application of SGS treatment to sardine fillets, resulted in a bacteriostatic effect, contributing to the improvement of the microbiological quality of fillets. Considering a sensory criteria, the shelf‐life of SGS pre‐treated sardine fillets was found to be 5 days in AP and MAP while in VP‐treated fillets a shelf‐life of 8 days was reported. At sensory rejection, sardine fillets presented a K‐value of 30% in AP and MAP batches and 40% in VP batch.

Modelling spoilage of fresh turbot and evaluation of a time–temperature integrator (TTI) label under fluctuating temperature

Kinetic models were developed to predict the microbial spoilage and the sensory quality of fresh fish and to evaluate the efficiency of a commercial time–temperature integrator (TTI) label, Fresh Check®, to monitor shelf life. Farmed turbot ( Psetta maxima) samples were packaged in PVC film and stored at 0, 5, 10 and 15 °C. Microbial growth and sensory attributes were monitored at regular time intervals. The response of the Fresh Check® device was measured at the same temperatures during the storage period. The sensory perception was quantified according to a global sensory indicator obtained by principal component analysis as well as to the Quality Index Method, QIM, as described by Rahman and Olley [Rahman, H.A., Olley, J., 1984. Assessment of sensory techniques for quality assessment of Australian fish. CSIRO Tasmanian Regional Laboratory. Occasional paper n. 8. Available from the Australian Maritime College library. Newnham. Tasmania]. Both methods were found equally valid to monitor the loss of sensory quality. The maximum specific growth rate of spoilage bacteria, the rate of change of the sensory indicators and the rate of change of the colour measurements of the TTI label were modelled as a function of temperature. The temperature had a similar effect on the bacteria, sensory and Fresh Check® kinetics. At the time of sensory rejection, the bacterial load was ca. 10 5–10 6 cfu/g. The end of shelf life indicated by the Fresh Check® label was close to the sensory rejection time. The performance of the models was validated under fluctuating temperature conditions by comparing the predicted and measured values for all microbial, sensory and TTI responses. The models have been implemented in a Visual Basic add-in for Excel called “Fish Shelf Life Prediction (FSLP)”. This program predicts sensory acceptability and growth of spoilage bacteria in fish and the response of the TTI at constant and fluctuating temperature conditions. The program is freely available at http://www.azti.es/muestracontenido.asp?idcontenido=980&content=15&nodo1=30&nodo2=0.

Effects of Modified Atmosphere Packaging on Toxin Production by Clostridium botulinum in Raw Aquacultured Summer Flounder Fillets (Paralichthys dentatus)

Packaging fishery products under vacuum atmosphere packaging (VAC) and modified atmosphere packaging (MAP) conditions can significantly extend the shelf life of raw, refrigerated fish products. There is considerable commercial interest in marketing VAC and MAP refrigerated (never frozen) raw fish fillets. The objective of this study was to determine if Clostridium botulinum toxin development precedes microbiological spoilage in raw, refrigerated flounder fillets. Aquacultured flounder (Paralichthys dentatus) individual fish fillets either were packed with a film having an oxygen transmission rate (OTR) of 3,000 cm3 m−2 24 h−1 at 22.8°C or were vacuum packaged or packaged under 100% CO2 with a film having an OTR of 7.8 cm3 m−2 24 h−1 at 21.1°C and were stored at 4 and 10°C. Samples were analyzed by aerobic plate count (APC) for spoilage and qualitatively for botulinum toxin with a mouse bioassay. The results demonstrate that flounder fillets (4°C) packaged with a film having an OTR of 3,000 were microbiologically spoiled (APC, >107 CFU/g) on day 15, but there was no toxin formation, even after 35 days of storage. However, at 10°C, toxin production occurred (day 8), but it was after microbial spoilage and absolute sensory rejection (day 5). Vacuum-packaged fillets and 100% CO2 fillets (4°C) packaged with a film having an OTR of 7.8 were toxic on days 20 and 25, respectively, with microbial spoilage (APC, >107 CFU/g) not occurring during the tested storage period (i.e., >35 days). At 10°C, in vacuum-packaged flounder, toxin formation coincided with microbiological spoilage (days 8 to 9). In the 100% CO2-packaged fillets, toxin formation occurred on day 9, with microbial spoilage occurring on day 15. This study indicates that films with an OTR of 3,000 can be used for refrigerated fish fillets and still maintain the safety of the product.

Microbiological quality of maatjes herring stored in air and under modified atmosphere at 4 and 10 °C

Microbiological and sensory changes of maatjes herring stored in air (experiment I) and under modified atmosphere (MAP) (experiments II and III) were evaluated during storage at 4 and 10 °C. Microbial (total and psychrotrophic viable bacteria, lactic acid bacteria and Enterobacteriaceae) counts and chemical analyses (chloride content, fat content, dry matter, ash and pH) were performed. A Quality Index Method (QIM) scheme developed for maatjes herring was used for sensory evaluation. The main reasons for sensory rejections at both storage temperatures were a strong rancid taste for herring stored in air (Experiment I) and a sour, bitter, rotten taste and an aftertaste like old flower water for MAP herring (Experiments II and III). A soft texture of freshly produced samples (Experiment II) was noticed. The sensory shelf-life of maatjes herring stored in air (Experiment I) was three days at both 4 and 10 °C. The MAP herring in Experiments II and III had a shelf-life of 5 and 6 days, respectively, at both storage temperatures. Rancidity due to oxidation of fat was the main spoilage indicator for air-stored maatjes herring. Autolytic enzymes may affect textural deterioration. The characteristic off-odour and off-taste in the MAP herring (Experiments II and III) were may well be attributable to microbial metabolism. On the day of sensory rejection, total viable counts for herring in all three experiments (Experiments I–III) stored at 4 °C did not reach 10 6 cfu/g, which is considered the limit of acceptability for maatjes herring given by the Dutch fishery authorities. It appears that total viable counts have minor significance in the sensory assessment of maatjes herring.

Nucleotide degradation of sodium acetate and potassium sorbate dip treated and vacuum packed Black Pomfret ( Parastromateus niger) and Pearlspot ( Etroplus suratensis) during chill storage

Quality changes of vacuum packed Black Pomfret ( Parastromateus niger) and Pearlspot ( Etroplus suratensis) treated with sodium acetate and potassium sorbate, respectively, and subsequently stored in vacuum packs in ice during chill storage were evaluated by measuring the volatile base nitrogen values, K-values and sensory parameters. The effects of sodium acetate (2% w/v) and potassium sorbate (2% w/v) dip treatments on vacuum packed Black Pomfret and Pearlspot were also examined. Total volatile base nitrogen values were found to increase slowly with time, whereas the K-values were found to increase linearly with time in samples of both the species and exceeded the acceptability limit on the day of sensory rejection. The K-values, representing the ratio between the sum of inosine and hypoxanthine to the sum of all other ATP breakdown products, was found to be a more reliable method for estimation of the quality of fresh/preserved fish. Sodium acetate/potassium sorbate dip treated and vacuum packed Black Pomfret and Pearlspot exhibited lower K-values compared to untreated samples. Treated vacuum packed samples of Black Pomfret were found to be in good and acceptable condition up to 16 days whereas treated vacuum packed samples of pearlspot remained in good condition up to 15 days compared to vacuum packed and air packed samples which were acceptable only up to 10 and 8 days, respectively. The sensory characteristics correlated well with the K-values for both the species.

Influence of storage temperature on microbial spoilage characteristics of haddock fillets ( Melanogrammus aeglefinus) evaluated by multivariate quality prediction

The proliferation of specific spoilage organisms (SSO) and quality changes were evaluated in haddock fillets stored in styrofoam boxes at 0, 7 and 15 °C and under temperature fluctuations. A rapid electronic nose technique was used to monitor different classes of compounds, representing microbial metabolites that were characteristic for the onset of spoilage odors. Photobacterium phosphoreum predominated among the spoilage bacteria and high levels of TVB-N were observed at sensory rejection. Pseudomonas spp. appeared to be responsible for the development of sweet, fruity spoilage odors in haddock fillets coinciding with increasing response of the electronic nose CO sensor. H 2S-producing bacteria, most likely Shewanella putrefaciens, were associated with the H 2S sensor's response at abusive temperature conditions. Partial Least Squares Regression (PLSR) was used as an explorative tool to provide a better understanding of the spoilage potential of SSOs, by evaluating models based on electronic nose responses and counts of specific spoilage organisms to predict sensory quality (Torry scores). The best prediction of the sensory quality was obtained by PLSR models based on five variables: the electronic nose sensors (CO, NH 3 and H 2S), pseudomonads counts and a time–temperature variable. Good agreement between the predicted and experimental data indicates that these variables characterize the sensory quality of haddock fillets stored under different temperatures.

Relation of Biogenic Amines' Formation with Microbiological and Sensory Attributes in Lactobacillus-Inoculated Vacuum-Packed Rainbow Trout (Oncorhynchus mykiss) Fillets

The biogenic amine (BA) content of vacuum-packed filleted rainbow trout (Oncorhynchus mykiss) inoculated or not with two different Lactobacillus strains, individually or in combination, was monitored during refrigerated storage for 20 days and related to respective bacteriological and sensory changes occurring during the same period. Eight amines, namely putrescine, cadaverine, tyramine, tryptamine, beta-phenylethylamine, histamine, spermine, and spermidine, were determined, whereas agmatine was not detected in any of the samples. In all cases, BA concentration was higher (P < or = 0.05) in the controls compared to all inoculated treatments, whereas the trend with regard to the bacterial populations (Enterobacteriaceae, pseudomonads, and H2S-producing bacteria) and the off-odor scores was similar. Inoculation with Lactobacillus sakei CECT 4808 showed the best preservative effect among inoculated treatments. Concentrations of putrescine and cadaverine, the main BAs formed, correlated well with both spoilage bacterial counts and off-odor scores and can be useful indicators of shelf life. Spermine and spermidine contents decreased during storage, while levels of the other determined BAs remained below 10 mg/kg even after sensory rejection.

Effects of sodium acetate dip treatment and vacuum-packaging on chemical, microbiological, textural and sensory changes of Pearlspot ( Etroplus suratensis) during chill storage

The effects of sodium acetate dip treatment, followed by vacuum-packaging, on the shelf life of beheaded, scaled and gutted Pearlspot ( Etroplus suratensis) during chill storage were examined. Sodium acetate (2%, w/v) solution was used for the dip treatment. Pouches (size: 15 × 22 cm) made of 12μ-polyester laminated with 300 gauge low-density polyethylene were used for packing fish. After packing, all the packs were iced with flake ice in the ratio (1:1) fish: ice in an insulated box and were kept in a cold room maintained at 0–2 °C. The control and the treated packs were analysed periodically for chemical (pH, TBA, TMA, TVB-N), microbiological (total viable count), textural and sensory characteristics. Changes in Staphylococcus aureus, Enterobacteriacea and Feacal streptococci were determined for fresh fish and for fish samples at the time of sensory rejection. Air packed samples were found to have a shelf life of about 8 days; vacuum-packed samples were found to be acceptable up to 10 days, whereas sodium acetate-treated vacuum packed samples were found to be acceptable up to 15 days. Thus, vacuum-packaging, in combination with sodium acetate, was found to delay the spoilage, thereby significantly extending the shelf life of Pearlspot at refrigeration temperatures.

Effects of temperature, oxygen exclusion, and storage on the microbial loads and pH of packed ostrich steaks

Ostrich steaks (96) were packed (air or vacuum) and stored at 4 °C or 10 °C. Microbiological loads (total viable counts – TVC, psychrotrophic, Enterobacteriaceae, lactic acid bacteria – LAB, Pseudomonas and fluorescent Pseudomonas) and pH values were determined at 0, 3, 6 and 9 days. High counts (8.0–10.2 log 10 cfu TVC/g) were observed at day 9, possibly as a consequence of the initial high microbial load (range 4.9–5.4 log 10 cfu TVC/g) and pH (average 6.7). Temperature and sampling day significantly influenced all microbial counts. Gas atmosphere had a small or negligible influence on levels of Enterobacteriaceae and LAB. For most microbial groups temperature significantly influenced bacterial levels up to day 6 of storage, while gas atmosphere had a significant effect at days 6 and 9. Both effects (temperature and gas atmosphere) were significant factors from day 0 for fluorescent Pseudomonas. Samples vacuum-packed and stored at 4 °C showed the lowest microbial loads at day 9. Only for these samples was no sensory rejection observed at the end of the experiment.

Evaluation of Shelf Life of Superchilled Cod (Gadus morhua) Fillets and the Influence of Temperature Fluctuations During Storage on Microbial and Chemical Quality Indicators

ABSTRACTQuality changes of aerobically packed cod fillets stored under superchilling and abusive temperature conditions were characterized by the growth of specific spoilage organisms (SSO) and the production of microbial metabolites measured by an electronic nose along with traditional sensory and chemical analysis (total volatile basic nitrogen [TVB‐N], pH). A new process based on quick contact freezing and cold air blasting was used to achieve superchilling of fillets before chilled (0.5 °C) or superchilled (‐1.5 °C) storage. Photobacterium phosphoreum dominated under temperature abusive conditions coinciding with high levels of TVB‐N and increased electronic nose responses indicating increased levels of alcohols and aldehydes at sensory rejection. Dominating growth of Pseudomonas spp. in 1 batch was associated with the origin, the catching method, and the cooling conditions during processing. The superchilling process followed by superchilled storage (‐1.5 °C) extended the sensory shelf life of the fillets for at least 3 d compared with traditional process, resulting in a total shelf life of 15 d. High content of TVB‐N was observed in superchilled fillets at sensory rejection. P. phosphoreum counts were lower under superchilling conditions (6.0 to 6.8 log colony‐forming units [CFU]/g), compared with the traditionally processed chilled fillets (7.2 log CFU/g). However, H2S‐producing bacteria appeared to grow steadily under superchilling conditions reaching counts as high as 7.6 log CFU/g at sensory rejection.

The interaction of the non-bacteriocinogenic Lactobacillus sakei 10A and lactocin S producing Lactobacillus sakei 148 towards Listeria monocytogenes on a model cooked ham

Two lactic acid bacteria, Lactobacillus sakei subsp. carnosus (10A) and lactocin S producing Lactobacillus sakei 148 (LS5), were examined for their usefulness as protective culture in the biopreservation of cooked meat products. Co-culture experiments on a model cooked ham (MCH) between 10A or LS5 and a cocktail of three Listeria monocytogenes strains were performed to examine the influence of inoculum level (10(5) vs. 10(6)cfu/g), storage temperature (4 vs. 7 degrees C) and packaging type (vacuum-packaging vs. modified atmosphere-packaging). At 7 degrees C, applying Lactobacillus sakei 10A at 10(6) cfu/g limited the growth of Listeria monocytogenes to <1 log(10) cfu/g during 27 days, whilst an application level of 10(5) cfu/g failed to prevent growth to unacceptable levels. Lactobacillus sakei LS5 did not demonstrate an antagonistic effect towards Listeria monocytogenes. Lowering the temperature to 4 degrees C or switching from vacuum-packaging to modified atmosphere packaging (MAP) did not influence the ability of strain 10A to grow on the MCH, as its dominance did not change. A combination of strain 10A and 4 degrees C or a MAP containing 50% CO(2) completely inhibited the growth of Listeria monocytogenes. Sensory assessments and pH measurements confirmed that 10A, even when present at a high level for prolonged storage times, did not acidify the cooked ham to a point of sensory rejection.

Characterization of Volatile Compounds in Chilled Cod (Gadus morhua) Fillets by Gas Chromatography and Detection of Quality Indicators by an Electronic Nose

Volatile compounds in cod fillets packed in Styrofoam boxes were analyzed during chilled storage (0.5 degrees C) by gas chromatography (GC)-mass spectrometry and GC-olfactometry to screen potential quality indicators present in concentrations high enough for detection by an electronic nose. Photobacterium phosphoreum dominated the spoilage bacteria on day 12 when the fillets were rejected by sensory analysis. Ketones, mainly 3-hydroxy-2-butanone, were detected in the highest level (33%) at sensory rejection, followed by amines (TMA) (29%), alcohols (15%), acids (4%), aldehydes (3%), and a low level of esters (<1%). The electronic nose's CO sensor showed an increasing response with storage time coinciding with the production of ethanol and 2-methyl-1-propanol that were produced early in the storage, followed by the production of 3-methyl-1-butanol, 3-methyl-butanal, 2,3-butandiol, and ethyl acetate. Lipid-derived aldehydes, like hexanal and decanal, were detected in similar levels throughout the storage time and contributed to the overall sweet odors of cod fillets in combination with other carbonyls (3-hydroxy-2-butanone, acetaldehyde, 2-butanone, 3-pentanone, and 6-methyl-5-heptene-2-one).

Effect of Vacuum and Modified Atmosphere Packaging on the Shelf‐life of Liquid‐smoked Swordfish (Xiphias gladius) Slices

ABSTRACT: Swordfish fillets, dry‐salted and treated with liquid smoke, were sliced and packed in vacuum conditions and under modified atmosphere (MA) (5% O2,45% CO2, 50% N2) and stored at chilled temperature (4°C) to determine the effect of different packaging on shelf‐life. Sensory attributes, total volatile basic nitrogen (TVB‐N), pH, lipid oxidation by thiobarbituric acid test, and microbiological counts were monitored during 45 d of storage. The TVB‐N increased to levels recommended by European regulation at the time of sensory rejection, resulting as the most reliable parameter of quality decay. Lipid oxidation was low and microbial counts could not be correlated with quality decay. Sensory rejection (at least 50% of the assessors scoring =5 in a scale from 1 to 9) was sooner for MA‐packed samples (12d) than for vacuum‐packed ones (42d).