Volatiles produced by microorganisms isolated from refrigerated chicken at spoilage

Food Freshness Measurements and Product Distinguishing by a Portable Electronic Nose Based on Organic Field-Effect Transistors

Determination of food freshness, which is the most ancient role of the human sense of smell, is still a challenge for compact and inexpensive electronic nose devices. Fast, sensitive, and reusable sensors are long-awaited in the food industry to replace slow, labor-intensive, and expensive bacteriological methods. In this work, we present microbiological verification of a novel approach to food quality monitoring and spoilage detection using an electronic nose based on organic field-effect transistors (OFETs) and its application for distinguishing products. The compact device presented is able to detect spoilage-related gases as early as at the 4 × 10⁴ CFU g^-1 bacteria count level, which is 2 orders of magnitude below the safe consumption threshold. Cross-selective sensor array based on OFETs with metalloporphyrin receptors were made on a single substrate using solution processing leading to a low production cost. Moreover, machine learning methods applied to the sensor array response allowed us to compare spoilage profiles and separate them by the type of food: pork, chicken, fish, or milk. The approach presented can be used to monitor food spoilage and distinguish different products with an affordable and portable device.

Challenges and Opportunities for Printed Electrical Gas Sensors

Printed electrical gas sensors are a low-cost, lightweight, low-power, and potentially disposable alternative to gas sensors manufactured using conventional methods such as photolithography, etching, and chemical vapor deposition. The growing interest in Internet-of-Things, smart homes, wearable devices, and point-of-need sensors has been the main driver fueling the development of new classes of printed electrical gas sensors. In this Perspective, we provide an insight into the current research related to printed electrical gas sensors including materials, methods of fabrication, and applications in monitoring food quality, air quality, diagnosis of diseases, and detection of hazardous gases. We further describe the challenges and future opportunities for this emerging technology.

Non-Destructive Measuring Systems for the Evaluation of High Oxygen Stored Poultry: Development of Headspace Gas Composition, Sensory and Microbiological Spoilage

As poultry is known to be a perishable food, the use-by date is set in such a way that food safety is guaranteed even with a higher initial bacterial count. This means, however, that some products are wasted, even if they are still safe to eat. Therefore, non-destructive measurement devices might be a good opportunity for individual shelf-life prediction, e.g., in retail. The aim of this study was therefore to use non-destructive measurement devices based on fluorescence quenching (oxygen detection) and mid-infrared laser spectroscopy (carbon dioxide detection) for the monitoring of high-oxygen-packed poultry in different storage conditions. During 15 days of storage, the gas composition of the headspace was assessed (non-destructively and destructively), while total plate count was monitored and a comprehensive sensory evaluation was performed by a trained panel. We were able to demonstrate that in most cases, non-destructive devices have comparable precision to destructive devices. For both storage conditions, the sensory attribute slime was correlated with reaching the critical microbiological value of 107 CFU/g; the attribute buttery was also useful for the prediction of regularly stored poultry. The change in the gas atmosphere as a sign of premature spoilage, however, was only possible for samples stored in irregular conditions.

Effect of Adding Essential Oils of Caraway and Rosemary on Volatile Aroma Compounds Derived from Stored Vacuum Packaged Minced Turkey Meat

Changes in the odor of meat during its storage are one of the basic indicators affecting its assessment and possible disqualification. The aim of the study was to determine whether the addition of essential oils may affect the composition and concentration of volatile compounds included in the aroma of stored turkey meat. We investigated the effect of adding essential oil (EO) of caraway (0.02% v/w), rosemary (0.02% v/w) and a mixture of the two (0.01% each) on the composition of volatile compound fractions formed during 10-day storage of vacuum-packed minced turkey meat. The EOs used were also evaluated for their influence on microbial contamination (total viable count and lactic acid bacteria count), sensory quality (odor and taste) and the level of fat rancidity (acid value, peroxide value and p-anisidine value) and pH in chill-stored samples. In terms of sensory indicators, the greatest beneficial effect of adding EOs was noted in the odor of raw meat. Use of the HS-SPME/GC-MS (headspace-solid phase microextraction/gas chromatography-mass spectrometry) method showed that the addition of essential oils significantly reduced the amounts of benzeneacetaldehyde, 2-octenal and ethyl 2-methyloctanoate compared with the control sample. In addition, in the presence of essential oils of rosemary and caraway, decreases were noted in benzaldehyde and 9-octadecenal, respectively. These changes may potentially affect the reception of the odor. There was a beneficial effect of the EOs in reducing the levels of fat oxidation indicators, including peroxides. However, the oils at applied concentrations had no significant effect on the total viable count and LAB count.

High-throughput sequencing approach to reveal the bacterial diversity of traditional yak jerky from the Tibetan regions

A high-throughput sequencing approach was used to investigate the bacterial community diversity of traditional Tibetan yak jerky, which was collected from three different regions in Tibet and with different natural drying times. Tibetan yak jerky from different regions had different bacterial communities, which was mainly reflected in the relative abundance levels of unclassified Cyanobacteria, Psychrobacter and Acinetobacter. The unclassified Cyanobacteria was the dominant genus of Qamdo yak jerky, Acinetobacter was the dominant genus of Shigatse yak jerky, and Psychrobacteria was the dominant genus of Nyingchi yak jerky. With increasing natural drying time, the diversity of bacterial communities in yak jerky decreased, and unclassified Cyanobacteria become the dominant genus. Spearman's correlation analysis and canonical correspondence analysis revealed that physicochemical factors (moisture content, water activity, shear force and pH) were significantly correlated with bacterial community. Our results will be beneficial to improve and standardize the safety and quality of traditional Tibetan yak jerky.

Glass-Fabric Reinforced Ag Nanowire/Siloxane Composite Heater Substrate: Sub-10 nm Metal@Metal Oxide Nanosheet for Sensitive Flexible Sensing Platform

The development of flexible chemiresistors is imperative for real-time monitoring of air quality and/or human physical conditions without space constraints. However, critical challenges such as poor sensing characteristics, vulnerability under toxic chemicals, and weak reliability hinder their practical use. In this work, for the first time, an ultrasensitive flexible sensing platform is reported by assembling Pt loaded thin-layered (≈10 nm) SnO₂ nanosheets (Pt-SnO₂ NSs) based 2D sensing layers on Ag nanowires embedded glass-fabric reinforced vinyl-phenyl siloxane hybrid composite substrate (AgNW-GFRVPH film) as a heater. The thermally stable AgNW-GFRVPH film based heater is fabricated by free radical polymerization of vinyl groups in vinyl-phenyl oligosiloxane and phenyltris(dimethylvinylsiloxy)silane with Ag NW and glass-fabric, showing outstanding heat generation (≈200 °C), high dimensional stability (13 ppm °C^-1), and good thermal stability (≈350 °C). The Pt-SnO₂ NSs, which are synthesized by calcination of Sn precursor coated graphene oxide (GO) sheets and subsequent Pt functionalization, exhibit high mechanical flexibility and superior response (R_air/R_gas = 4.84) to 1 ppm level dimethyl sulfide. Taking these advantages, GO-templated oxide NSs combined with a highly stable AgNW-GFRVPH film heater exhibits the best dimethyl sulfide sensing performance compared to state-of-the-art flexible chemiresistors, enabling them as a superior flexible gas sensing platform.

Dimethyl disulfide produced by the naturally associated bacterium bacillus sp B55 promotes Nicotiana attenuata growth by enhancing sulfur nutrition

Bacillus sp B55, a bacterium naturally associated with Nicotiana attenuata roots, promotes growth and survival of wild-type and, particularly, ethylene (ET)-insensitive (35)S-ethylene response1 (etr1) N. attenuata plants, which heterologously express the mutant Arabidopsis thaliana receptor ETR1-1. We found that the volatile organic compound (VOC) blend emitted by B55 promotes seedling growth, which is dominated by the S-containing compound dimethyl disulfide (DMDS). DMDS was depleted from the headspace during cocultivation with seedlings in bipartite Petri dishes, and (35)S was assimilated from the bacterial VOC bouquet and incorporated into plant proteins. In wild-type and (35)S-etr1 seedlings grown under different sulfate (SO(4)(-2)) supply conditions, exposure to synthetic DMDS led to genotype-dependent plant growth promotion effects. For the wild type, only S-starved seedlings benefited from DMDS exposure. By contrast, growth of (35)S-etr1 seedlings, which we demonstrate to have an unregulated S metabolism, increased at all SO(4)(-2) supply rates. Exposure to B55 VOCs and DMDS rescued many of the growth phenotypes exhibited by ET-insensitive plants, including the lack of root hairs, poor lateral root growth, and low chlorophyll content. DMDS supplementation significantly reduced the expression of S assimilation genes, as well as Met biosynthesis and recycling. We conclude that DMDS by B55 production is a plant growth promotion mechanism that likely enhances the availability of reduced S, which is particularly beneficial for wild-type plants growing in S-deficient soils and for (35)S-etr1 plants due to their impaired S uptake/assimilation/metabolism.

Potential of electric discharge plasma methods in abatement of volatile organic compounds originating from the food industry

Increased volatile organic compounds emissions and commensurate tightening of applicable legislation mean that the development and application of effective, cost-efficient abatement methods are areas of growing concern. This paper reviews the last two decades' publications on organic vapour emissions from food processing, their sources, impacts and treatment methods. An overview of the latest developments in conventional air treatment methods is presented, followed by the main focus of the paper, non-thermal plasma technology. The results of the review suggest that non-thermal plasma technology, in its pulsed corona discharge configuration, is an emerging treatment method with potential for low-cost, effective abatement of a wide spectrum of organic air pollutants. It is found that the combination of plasma treatment with catalysis is a development trend that demonstrates considerable potential. The as yet relatively small number of plasma treatment applications is considered to be due to the novelty of pulsed electric discharge techniques and a lack of reliable pulse generators and reactors. Other issues acting as barriers to widespread adoption of the technique include the possible formation of stable oxidation by-products, residual ozone and nitrogen oxides, and sensitivity towards air humidity.

The microbiology of DFD fresh meats: A review

Muscle which is deficient in glycogen because of exercise or stress prior to slaughter produces dark, firm, dry (DFD) meat. Such meat is characterized by a high ultimate pH (>6·0) and deficiencies in glucose and glycolytic intermediates. These factors can result in bacterial spoilage becoming evident at an early stage of growth of the meat flora. Spoilage becomes apparent when bacteria attack amino acids. This does not occur under aerobic conditions until bacteria exhaust the glucose at the meat surface. However, since glucose is absent in DFD meat, amino acids are utilised without delay and spoilage becomes evident at lower cell densities than in normal meat. The absence of glucose also allows the anaerobic flora to produce spoilage odours at an early stage. Additionally, the high pH of DFD meat allows growth of potent spoilage organisms which are inhibited at the usual ultimate pH of meat. Early aerobic spoilage can be prevented by the addition of glucose, but prevention of early anaerobic spoilage requires the addition of a citrate buffer which reduces the surface pH, as well as providing a carbohydrate substrate which is utilised in preference to amino acids. Comparisons can be made between spoilage of DFD red meat and spoilage of white meats from poultry and fish, which normally have a high ultimate pH.

Monitoring of chicken meat freshness by means of a colorimetric sensor array

A new optoelectronic nose to monitor chicken meat ageing has been developed. It is based on 16 pigments prepared by the incorporation of different dyes (pH indicators, Lewis acids, hydrogen-bonding derivatives, selective probes and natural dyes) into inorganic materials (UVM-7, silica and alumina). The colour changes of the sensor array were characteristic of chicken ageing in a modified packaging atmosphere (30% CO(2)-70% N(2)). The chromogenic array data were processed with qualitative (PCA) and quantitative (PLS) tools. The PCA statistical analysis showed a high degree of dispersion, with nine dimensions required to explain 95% of variance. Despite this high dimensionality, a tridimensional representation of the three principal components was able to differentiate ageing with 2-day intervals. Moreover, the PLS statistical analysis allows the creation of a model to correlate the chromogenic data with chicken meat ageing. The model offers a PLS prediction model for ageing with values of 0.9937, 0.0389 and 0.994 for the slope, the intercept and the regression coefficient, respectively, and is in agreement with the perfect fit between the predicted and measured values observed. The results suggest the feasibility of this system to help develop optoelectronic noses that monitor food freshness.

Volatile mediated interactions between bacteria and fungi in the soil

Soil is one of the major habitats of bacteria and fungi. In this arena their interactions are part of a communication network that keeps microhabitats in balance. Prominent mediator molecules of these inter- and intraorganismic relationships are inorganic and organic microbial volatile compounds (mVOCs). In this review the state of the art regarding the wealth of mVOC emission is presented. To date, ca. 300 bacteria and fungi were described as VOC producers and approximately 800 mVOCs were compiled in DOVE-MO (database of volatiles emitted by microorganisms). Furthermore, this paper summarizes morphological and phenotypical alterations and reactions that occur in the organisms due to the presence of mVOCs. These effects might provide clues for elucidating the biological and ecological significance of mVOC emissions and will help to unravel the entirety of belowground' volatile-wired' interactions.

Inhibitory effects of enterococci on the production of hydrogen sulfide by hydrogen sulfide-producing bacteria in raw meat

AIMS

Applying competitive exclusion micro-organisms to control hydrogen sulfide (H₂S) gas produced by hydrogen sulfide-producing bacteria (SPB) in chicken meat.

METHODS AND RESULTS

Five SPB strains, isolated from animal by-products, were used for screening lactic acid bacteria (LAB) that can inhibit the production of H₂S by SPB in trypticase soy broth supplemented with L-cysteine (TSB-L-cys). A sensitive and accurate test strip method was developed for H₂S determination in real time. One LAB strain, isolate L86, from cheese whey, demonstrated the highest inhibitory activity against the production of H₂S by SPB. The isolate L86 was confirmed as Enterococcus faecium that does not possess genes encoding for vancomycin resistance based on PCR analysis. Enterococcus faecium strain L86 reduced (P < 0·05) the yield of H₂S upto 51·2% in 10 h at 35°C in TSB-L-cys medium. In fresh chicken meat, the yield of H₂S produced by the artificially inoculated SPB was reduced (P < 0·05) by 48·6, 49·7 and 69·8% in 10 h at 35, 30 and 25°C, respectively. Enterococcus faecium strain L86 also reduced (P < 0·05) by 53·8% on the yield of H₂S produced by the indigenous SPB in partially spoiled chicken meat at 35°C for 10 h.

CONCLUSIONS

Enterococcus faecium strain L86 is effective on inhibiting the production of H₂S by SPB.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of this biological agent to raw animal by-products will provide a safer working environment in rendering processing plants and produce higher-quality rendered products.

Volatile Compounds Associated with Spoilage of Vacuum-Packaged Sliced Luncheon Meat by Brochothrix thermosphacta

By using gas chromatography-mass spectrometry, seven volatile compounds were identified in vacuum-packaged sliced corned beef spoiled by Brochothrix thermosphacta under aerobic conditions. Acetoin and diacetyl appeared to be of major sensory significance.

DNA comet assay for the detection of time-temperature abuse during the storage of poultry

Effects of abusive storage conditions on the quality of fresh chicken were studied by detecting DNA damage to breast fillets and liver with the neutral comet assay. Chilled samples were kept at 4 degrees C for prolonged periods, whereas frozen samples were exposed to temperatures of 4 degrees C, representing inadvertent thawing, and 20 degrees C, representing extreme abuse in the distribution chain. Comets' mean tail moment distributions reflected the increasing patterns of DNA damage, but the differences of values between close levels of treatment were sometimes insignificant. The design of the DNA damage index, integrating the distribution of mean tail moments over three trials, provided values significantly different, which allowed a more precise discrimination between samples according to the treatment levels. Considering the background level of DNA damage in control cells, a DNA damage index value of 50 microm was set as a limit for the detection of abusive storage. Temperature abuse could be detected after 7 and 22 h of exposure at 4 degrees C for liver and breast, respectively. These durations were by far shorter (1.5 and 2.5 h, respectively) when the temperature was increased to 20 degrees C. As for chilled storage, its damaging effects could be detected after 1.5 and 2.5 days for liver and breast, respectively. Liver cells were more sensitive to abusive conditions than breast muscle cells. The comet assay's detection limit was applicable to samples that were still considered of good quality with regard to the microbiological shelf life, thereby showing its high sensitivity as a rapid test for assessing the quality of fresh chicken.

Odor compounds in waste gas emissions from agricultural operations and food industries

In the last decades, large-scale agricultural operations and food industries have increased. These operations generate numerous types of odors. The reduction of land areas available for isolation of agricultural and food processing industrial operations from the public area and the increase in sensitivity and demand of the general public for a clean and pleasant environment have forced all of these industries to control odor emissions and toxic air pollutants. To develop environmentally sound, sustainable agricultural and food industrial operations, it is necessary to integrate research that focuses on modern analytical techniques and latest sensory technology of measurement and evaluation of odor and pollution, together with a fundamental knowledge of factors that are the basic units contributing to the production of odor and pollutants. Without a clear understanding of what odor is, how to measure it, and where it originates, it will be difficult to control the odor. The present paper reviews the available information regarding odor emissions from agricultural operations and food industries by giving an overview about odor problems, odor detection and quantification, and identifying the sources and the mechanisms that contribute to the odor emissions. Finally, ways of reducing or controlling the odor problem are discussed.

Uptake of choline from salmon flesh and its conversion to glycine betaine in response to salt stress in Shewanella putrefaciens

When cultured in M63 minimal medium plus 0.6 M NaCl, the growth of Shewanella putrefaciens was strongly inhibited. The addition of an extract from smoked salmon to this medium restored the growth almost to the unstressed level. A comparison of the 13C NMR spectra of intracellular solutes extracted from S. putrefaciens cells cultured in both conditions revealed the accumulation of glycine betaine (GB) from the smoked salmon extract (SSE). Analysis of the osmoprotective properties of this extract for several strains of Escherichia coli (which differ from each other in their ability to accumulate GB (i) from the surrounding environment, and (ii) from its hydroxylated precursor choline), demonstrated the absence of GB in the SSE. From the overall results, we inferred that salt-stressed S. putrefaciens cells accumulated GB from choline present in the SSE. Furthermore, the use of [14C]-labeled betaines gave evidence that S. putrefaciens (i) oxidised choline to GB, (ii) accumulated GB as a non-metabolisable osmolyte (up to 1300 nmol (mg dw)(-1) when cultured in a medium containing 0.5 M NaCl and either 1 mM choline or 1 mM GB), and (iii) both choline and GB uptake activities were osmotically upregulated (both activities were increased more than 50-fold in media containing 0.4 to 0.6 M NaCl). In all, our results suggest that in salted smoked salmon, S. putrefaciens imports and oxidises choline, leading to the intracellular accumulation of GB.

Effects of packaging and storage conditions on volatile compounds in gas-packed poultry meat

Volatile compounds released by raw chicken legs packed in modified atmosphere packages were determined in order to develop a spoilage indicator for monitoring the shelf-life of raw chicken. Internal spoilage indicators would react with compounds released during chemical, enzymatic and/or microbial spoilage reactions. The effects of four packaging factors (headspace volume, oxygen transmission rate of the package, residual oxygen and carbon dioxide concentration) and three storage factors (temperature, illumination and storage time) on the amounts of volatile compounds in the headspace of gas packages containing two chicken legs were studied. Statistical experimental design was applied and a linear screening design comprising 18 experiments (fractional factorial) was utilized. Volatile compounds in package headspace were determined by gas chromatography--mass spectrometry using the dynamic headspace technique. The results were compared with the results of sensory evaluation and microbial determinations. The head-space of stored packages was dominated by the following compounds: butene, ethanol, acetone, pentane, dimethylsulphide, carbon disulphide and dimethyl disulphide. In modelling, some interaction terms and squared terms were needed in addition to linear terms. The main factors affecting the amounts of ethanol, dimethyl sulphide, carbon disulphide and dimethyl disulphide were storage time and temperature. Other factors had only minor importance, carbon dioxide concentration and headspace volume being the most significant package parameters. The same four factors also had the greatest effects on the odour of chicken legs.

Isolation and characterization by conventional methods and genetic transformation of Psychrobacter and Acinetobacter from fresh and spoiled meat, milk and cheese

Of 126 samples of fresh and spoiled meat and dairy products, 40% were positive for the presence of Moraxella-like bacteria and 64% of Acinetobacter; 279 and 466 strains, respectively, were isolated and a part of these were tested by biochemical methods and DNA transformation assays. In some cases, the Moraxellaceae in the samples examined reached considerable quantitative levels, but their percentage in the microflora was generally low. Moraxella-like bacteria were predominant in fresh meat, Acinetobacter in spoiled meat and milk. Most acinetobacters belonged to biotype lwoffii (sensu lato) and all 90 strains tested were positive for DNA transformation with an auxotrophic Acinetobacter. Moraxella-like bacteria were identified as Psychrobacter immobilis in 96% of 103 transformation assays. Moraxellaceae show lipolytic activity but they are considered of low incidence in food spoilage. Only 3.7% of acinetobacters from dairy sources was able to produce ropy milk. Unlike strains from clinical isolates, psychrobacters and acinetobacters isolated from food often do not grow at 37 degrees C.

Volatile compounds produced by meat pseudomonads and relate reference strains during growth on beef stored in air at chill temperatures

Volatile compounds produced by 31 strains of pseudomonads and by reference strains of Pseudomonas fragi and Ps. fluorescens biotype 1 during growth on beef stored at 6 degrees C in air were analysed by gas chromatography-mass spectrometry of headspace gases. Compounds of major sensory significance were ethyl and methyl esters of C2-C8 fatty acids and sulphur-containing compounds which included methane- and isopropanethiols and their related sulphides and thioesters but not hydrogen sulphide. Ester production was mainly associated with growth of some, but not all, Ps. fragi and related meat strains but sulphur-containing compounds were produced by all but a single meat strain. A minority of other meat strains produced greater amounts of methyl ketones, secondary alcohols and unsaturated hydrocarbons believed to be of lipid origin.

Volatile compounds associated with the aerobic growth of some Pseudomonas species on beef

Five strains representing four clusters of meat spoilage pseudomonads were grown on sterile beef at 5 degrees C. After 7 days incubation sensory assessments were made and the chemical composition of the headspace gases determined by gas chromatography-mass spectrometry. There was good correlation between odour descriptions and chemical data for three of the strains. The most numerous types of product were esters and sulphur-containing compounds. Of 45 compounds identified only 1-undecene was common to all the tested strains.

Identification of volatile organic compounds produced by fluorescent pseudomonads on chicken breast muscle

Four different fluorescent pseudomonads were isolated from spoiled, uncooked chicken breasts and were grown in pure culture on initially sterile chicken breast muscle at 2 to 6 degrees C for 14 days. The volatile compounds produced by each culture were concentrated on a porous polymer precolumn and separated and identified by high-resolution gas chromatography-mass spectrometry.