Influence of growth conditions on heat-stable phospholipase activity in Pseudomonas

Cold-atmospheric-plasma activated-ice as a cooling medium with antimicrobial properties: Case study on fish fillet preservation

The efficacy and applicability of Plasma Activated Ice (PAI) -produced by cold atmospheric plasma (CAP) technology- on microorganisms and quality characteristics of perishable fresh sea bream (Sparus aurata) fillets, were evaluated. The changes in microbiological load and quality characteristics of fish fillets were investigated during storage with ice from deionized water (Control), PAI and ice from artificially produced water (Artificial) of H₂O₂ concentrations equal to those of PAI. Fresh sea bream fillets were packed under ice flakes (produced from PAI or Artificial or Control) on layers (as typically done in the relevant industry) and stored at 0.5 °C for 27 days. PAI application inhibited significantly the growth of microbial load of the fillets resulting in reduced growth rates while simultaneously significantly retarded the quality deterioration compared to the other disinfectant media. The use of PAI (with 10 mg/L H₂O₂) led to a 11-day and 6-day extension, i.e., 2-fold and a ∼ 1.5-fold extension, of the fillets shelf-life compared to the samples treated with Control and Artificial ice, respectively. The results proved the efficiency of PAI in extending the shelf-life of perishable foods during storage (or/and transportation), by validating its antimicrobial properties and cooling capacity.

Off-flavors generated during long-term ambient storage of pasteurized drinking yogurt from skim milk

Few studies have examined sensory quality changes during the storage of pasteurized drinking yogurt (PDY), and the cause of off-flavor development is unclear. Off-flavors generated during 90-d ambient storage (25 °C) of PDY from reconstituted skim milk were investigated by sensory evaluation, volatile component analysis with gas chromatography-mass spectroscopy, and gas chromatography-olfactometry. Rancid off-flavor was induced by increased fatty acid concentration due to fat decomposition by heat-stable lipase. Masking of off-flavors was inhibited by degradation of diacetyl, which originally contributed to yogurt-like flavors. Maillard reaction particular to ambient storage of PDY resulted in changes in the furaneol and sotolon levels, which may be involved in enhancement of off-flavors. Finally, our findings indicated that production of 4-vinylguaiacol may be involved in off-flavor development. The results of this study will contribute to the development of PDY with a longer shelf life and superior flavor.

Effect of an Olive Vegetation Water Phenolic Extract on the Physico-Chemical, Microbiological and Sensory Traits of Shrimp (Parapenaeus longirostris) during the Shelf-Life

The aim of this study was to evaluate the effects of phenolic extract derived from olive vegetation water (PEOVW) in deep-water rose shrimps (Parapenaeus longirostris) at the day of packaging (D0) and after three (D3), six (D6) and eight (D8) days of refrigerated storage. Freshly caught shrimps were randomly divided into four groups: the phenolic extract (PE) group (2 g/L of phenols); the sulfites (S) group (0.5% sodium metabisulfite solution); the phenolic extract + sulfites (PE + S) group (0.25% sodium metabisulfite solution with 1 g/L of phenols), and the control (CTRL) group (tap water). Concerning color coordinates, there were no variations either between groups or over time, while it is important to highlight that phenolic extract (PE group) led to a significant reduction in total volatile basic nitrogen (TVB-N; p < 0.001) and thiobarbituric reactive substances (TBARS; p < 0.001) values. Furthermore, PE also had a relevant effect in reducing bacterial counts and decreasing the microbial development. Finally, as concerns melanosis, the effect of phenolic extract alone was marginal, but when combined with half a dose of sodium metabisulfite, it was as effective as the shrimps treated with only sodium metabisulfite in delaying black spots (p < 0.05). These results are very promising with a view to commercializing additive-free shrimps.

A chitosan-based edible film with clove essential oil and nisin for improving the quality and shelf life of pork patties in cold storage

This study assessed chitosan (CS)-based edible films with clove essential oil (CO) and nisin (NI) singly or in combination, for improving quality and shelf life of pork patties stored in cold conditions. The treatments were control (without chitosan film coating), CS, CS-CO, CS-NI, and CS-CO-NI, and these were tested for physicochemical, microbiological and sensory qualities for 15 days (3 days per interval) on samples in cold storage (4 ± 2 °C). Overall, the results showed that the lightness (L* value) (53.47 to 67.58), yellowness (b* value) (1.32 to 2.88), pH (5.31 to 7.98), metmyoglobin (MetMb) content (54.10 to 63.36%), free fatty acid (FFA) (0.67 to 3.17%), peroxide value (PV) (0.80 to 3.67 milliequivalent/100 g), thiobarbituric acid reactive substances (TBARS) (0.69 to 3.27 mg MDA per kg), total viable count (TVC) (2.97 to 7.63 log CFU g-1), psychotrophic bacteria count (psychrotrophs) (2.94 to 6.59 log CFU g-1), Enterobacteriaceae (2.59 to 6.57 log CFU g-1), lactic acid bacteria (LAB) (2.53 to 6.81 log CFU g-1) and sensory scores (red non-discolored part (1 to 4.70), discoloration (1 to 4.40) and off-odor (1 to 5.00)) were gradually increased during storage and whereas redness (a* value) (16.43 to 8.62) and redness index (12.54 to 3.01) were decreased. However, the quality changes were minimal in the pork patties treated with CS-CO-NI. Based on sensory and microbiological evaluations, the shelf life of treated pork patties was 6 days for control, 9 days for CS and CS-NI, and 12 days for CS-CO and CS-CO-NI.

Effects of lysozyme combined with cinnamaldehyde on storage quality of olive flounder (Paralichthys olivaceus) fillets

Effects of lysozyme (LYS) combined with cinnamaldehyde (CA) on quality enhancement of olive flounder (Paralichthys olivaceus) fillets during refrigerated storage at 4 °C for 20 days were assessed. Changes of total viable count (TVC), K-value, total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), texture profile analysis (TPA), and trichloroacetic acid-soluble peptide (TCA-soluble peptide) in samples were determined periodically. Results demonstrated that the combination of LYS and CA treatment enhanced the antibacterial activity against S. putrefaciens and P. fluorescens, and lowered TVC values. Meanwhile, LYS combined with CA significantly retarded the increases of TBA value, TVB-N, K-value, and TCA-soluble peptide content compared to the control. Furthermore, the combined treatment also effectively maintained the texture properties of flounder fillets during the storage period. The efficiency was better than that of LYS or CA treatment alone. Thus, LYS combined with CA is promising in olive flounder shelf life extension.

Effect of spice-incorporated starch edible film wrapping on shelf life of white shrimps stored at different temperatures

BACKGROUND

White shrimps (Litopenaeus vannamei) are a major aquaculture product in the world fishery market. The main aim of this study was to investigate the effect of clove- and cinnamon-assimilated starch edible films on the shelf life of white shrimps in terms of maintaining their freshness and other organoleptic properties. Physical, chemical, microbial and sensory qualities of edible film-wrapped white shrimps were studied until they reached their limit of acceptability during storage at different temperatures (10 and 4 °C).

RESULTS

Shrimp samples wrapped with spice-assimilated edible films showed lower bacterial counts. Shelf life extension of edible film-wrapped white shrimps was estimated to be 14 and 12 days for storage at 10 and 4 °C respectively. Reduced lipid oxidation and release of nitrogen base compounds were noted for edible film-wrapped shrimp samples. Good consumer acceptance was noted for edible film-wrapped shrimp samples through sensory evaluation.

CONCLUSION

The results of this study show that spice-fused edible films were effective in inhibiting the growth of microbial populations. Reductions in lipid oxidation and total volatile base nitrogen were also achieved through edible film wrapping of shrimps, which increased their consumer acceptance during sensory evaluation. © 2016 Society of Chemical Industry.

Shelf-life extension of refrigerated sea bass slices wrapped with fish protein isolate/fish skin gelatin-ZnO nanocomposite film incorporated with basil leaf essential oil

Microbiological, chemical and sensory changes of sea bass slices wrapped with fish protein isolate (FPI)/fish skin gelatin (FSG) films incorporated with 3 % ZnO nanoparticles (ZnONP) (w/w, based on protein content) and 100 % basil leaf essential oil (BEO) (w/w, based on protein content) during storage of 12 days at 4 °C were investigated. Sea bass slices wrapped with FPI/FSG-ZnONP-BEO film had the lowest growth of psychrophilic bacteria, lactic acid bacteria and spoilage microorganisms including Pseudomonas , H2S-producing bacteria and Enterobacteriaceae throughout storage of 12 days in comparison with those wrapped with FPI/FSG-BEO, FPI/FSG-ZnONP, FPI/FSG film, polypropylene film (PP film) and the control (without wrapping), respectively (P < 0.05). Lowered increases in pH, total volatile base, peroxide value and TBARS value were found in FPI/FSG-ZnO-BEO film wrapped samples, compared with others (P < 0.05). Sensory evaluation revealed that shelf-life of sea bass slices was longest for samples wrapped with FPI/FSG-ZnONP-BEO film (12 days), as compared to the control (6 days) (P < 0.05).

Evaluation of microbial survival post-incidence on fresh Mozzarella cheese

Commercial fresh Mozzarella cheese is made by direct acidification and is stored dry or in water without salt addition. The cheese has a shelf life of 6 wk, but usually develops an off-flavor and loses textural integrity by 4 wk, potentially due to the lack of salt and high moisture that allow the outgrowth of undesirable bacteria. To understand how microbial incidence affects cheese quality and how incident pathogen-related bacteria are limited by salt level during refrigerated storage, we made fresh Mozzarella cheese with high (2%) and low (0.5%) salt. The high-salt cheese was packaged and stored dry. The low-salt cheese was packaged and stored either dry or in 0.5% salt brine. One portion of cheeses was evaluated for surviving incident microbes by aerobic plate counts, coliform counts, and psychrophilic bacterial counts, of which coliforms and psychrophiles were not detected over 9 wk. Aerobic plate counts remained at 100 to 300 cfu/g up to 2 wk but increased by 1,000- to 10,000-fold between 4 and 6 wk at all salt levels and storage conditions. Other portions of cheeses were inoculated with either Escherichia coli or Enterococcus faecalis, both of which increased by 100-fold over 90 d of storage. Interestingly, E. coli added to the cheese brine first grew in the brine by 100-fold before attaching to the cheese, whereas Ent. faecalis attached to the cheese within 24h and grew only on the cheese. We conclude that incident bacteria, even from similar environments, may attach to cheese curd and survive differently in fresh Mozzarella cheese than in brine. Overall, 2% salt was insufficient to control bacterial growth, and slow-growing, cold- and salt-tolerant bacteria may survive and spoil fresh Mozzarella cheese.

Effect of ethanolic extract of clove on the keeping quality of fresh mutton during storage at ambient temperature (25 ± 2 °C)

Antimicrobial potential of ethanolic extract of clove (Eugenia caryophyllata) on fresh mutton during storage at 25 ± 2 °C was evaluated. The extract inhibited spoilage and pathogenic microflora of mutton previously treated with acidulants to reduce surface microbial load and the surface pH, up to 4 days without any deleterious change in sensory and physical qualities. Biomarker cadaverine, an indicator of spoiling/spoiled mutton, was present in 1 day stored control samples and absent up to 4 days in treated mutton. The levels of other biomarkers like biogenic amine index (0.31 mg/100 g) and free fatty acids (1.52%) were lower in 4 days stored treated samples than 1 day stored control samples (3.6 mg/100 g and 2.4%, respectively). Thus, ethanolic extract of clove can be effectively used to improve the keeping quality of fresh mutton up to 4 days at 25 ± 2 °C.

Molecular analysis of bacterial communities in raw cow milk and the impact of refrigeration on its structure and dynamics

The impact of refrigeration on raw cow milk bacterial communities in three farm bulk tanks and three dairy plant silo tanks was studied using two methods: DGGE and cloning. Both methods demonstrated that bacterial taxonomic diversity decreased during refrigeration. Gammaproteobacteria, especially Pseudomonadales, dominated the milk after refrigeration. Farm samples and dairy plant samples differed in their microbial community composition, the former showing prevalence of Gram-positive bacteria affiliated with the classes Bacilli, Clostridia and Actinobacteria, the latter showing prevalence of Gram-negative species belonging to the Gammaproteobacteria class. Actinobacteria prevalence in the farm milk samples immediately after collection stood at about 25% of the clones. A previous study had found that psychrotolerant Actinobacteria identified in raw cow milk demonstrated both lipolytic and proteolytic enzymatic activity. Thus, we conclude that although Pseudomonadales play an important role in milk spoilage after long periods of cold incubation, Actinobacteria occurrence may play an important role when assessing the quality of milk arriving at the dairy plant from different farms. As new cooling technologies reduce the initial bacterial counts of milk to very low levels, more sensitive and efficient methods to evaluate the bacterial quality of raw milk are required. The present findings are an important step towards achieving this goal.

Xenorhabdus nematophila lrhA is necessary for motility, lipase activity, toxin expression, and virulence in Manduca sexta insects

The gram-negative insect pathogen Xenorhabdus nematophila possesses potential virulence factors including an assortment of toxins, degradative enzymes, and regulators of these compounds. Here, we describe the lysR-like homolog A (lrhA) gene, a gene required by X. nematophila for full virulence in Manduca sexta insects. In several other gram-negative bacteria, LrhA homologs are transcriptional regulators involved in the expression (typically repression) of virulence factors. Based on phenotypic and genetic evidence, we report that X. nematophila LrhA has a positive effect on transcription and expression of certain potential virulence factors, including a toxin subunit-encoding gene, xptD1. Furthermore, an lrhA mutant lacks in vitro lipase activity and has reduced swimming motility compared to its wild-type parent. Quantitative PCR revealed that transcript levels of flagellar genes, a lipase gene, and xptD1 were significantly lower in the lrhA mutant than in the wild type. In addition, lrhA itself is positively regulated by the global regulator Lrp. This work establishes a role for LrhA as a vital component of a regulatory hierarchy necessary for X. nematophila pathogenesis and expression of surface-localized and secreted factors. Future research is aimed at identifying and characterizing virulence factors within the LrhA regulon.

Culturable psychrotrophic bacterial communities in raw milk and their proteolytic and lipolytic traits

During cold storage after milk collection, psychrotrophic bacterial populations dominate the microflora, and their extracellular enzymes, mainly proteases and lipases, contribute to the spoilage of dairy products. The diversity, dynamics, and enzymatic traits of culturable psychrotrophs in raw milk from four farms were investigated over a 10-month period. About 20% of the isolates were found to be novel species, indicating that there is still much to be learned about culturable psychrotrophs in raw milk. The psychrotrophic isolates were identified and classified in seven classes. Three classes were predominant, with high species richness (18 to 21 species per class) in different seasons of the year: Gammaproteobacteria in spring and winter, Bacilli in summer, and Actinobacteria in autumn. The four minor classes were Alphaproteobacteria, Betaproteobacteria, Flavobacteria, and Sphingobacteria. The dominant classes were found in all four dairies, although every dairy had its own unique "bacterial profile." Most but not all bacterial isolates had either lipolytic or both lipolytic and proteolytic activities. Only a few isolates showed proteolytic activity alone. The dominant genera, Pseudomonas and Acinetobacter (Gammaproteobacteria), showed mainly lipolytic activity, Microbacterium (Actinobacteria) was highly lipolytic and proteolytic, and the lactic acid bacteria (Lactococcus and Leuconostoc) displayed very minor enzymatic ability. Hence, the composition of psychrotrophic bacterial flora in raw milk has an important role in the determination of milk quality. Monitoring the dominant psychrotrophic species responsible for the production of heat-stable proteolytic and lipolytic enzymes offers a sensitive and efficient tool for maintaining better milk quality in the milk industry.

Phenotypic characterization of raw milk-associated psychrotrophic bacteria

Among the 68 isolates, selected from 13 raw-milk samples in Finland (that originate from farm, truck or silo tanks), 60 (88%) were psychrotrophs. All the isolates were characterized by the determination of their spoilage and phenotypic features: proteolytic and lipolytic activities, the production of lecithinases and hemolytic factors were considered. Phenotypic characterization of the isolates was mainly performed with API 20NE and BIOLOG GN2 identification systems; the results were system-dependent, although the presence of representatives of the Pseudomonas genus (for the majority of the isolates) was suggested by both systems. The results of the numerical profile analyses by API 20NE proposed that some strains might be members of Stenotrophomonas, Burkholderia and Acinetobacter genera; however, the identity of many isolates remained doubtful or controversial.