Monitoring of taints related to printed solid boards with an electronic nose.

The main objectives were to combine knowledge gathered from the electronic nose (EN) with traditional analytical reference methods for measuring volatile compounds, such as sensory and headspace methods. The impacts of different colouring agents on the sensory properties of packaging materials when analysed by EN were determined. The first step in investigations using the EN was optimization of sample treatment and analysis parameters for the samples. The best resolution was achieved at 60 degrees C in 20 min, and the effect of humidity on the EN sensors was confirmed. A comparison was made of three sensory methods for analysing taints of packaging materials. The study showed that the odour of the packaging itself was often not a reliable indication of the taint perceived in the packed foodstuff and should be regarded only as indicative. Taints caused by pigments of printed solid boards were analysed by EN. Twenty samples were studied, representing unprinted solid board, lacquered solid board, offset printed solid board with 14 different colours and offset printed, lacquered solid board with four colours. The EN succeeded in grouping these materials according to their colouring agents or lacquering, despite slight overlapping of replicates, and the results appeared to reflect at least to some extent the off-flavours perceived in sensory evaluation. The results of this study are only indicative, because the analysis of results from different sources or equipment requires more extensive use of statistical methods.

Inhibition of growth of nonproteolytic Clostridium botulinum type B in sous vide cooked meat products is achieved by using thermal processing but not nisin.

The safety of refrigerated processed foods of extended durability (REPFEDs) with respect to nonproteolytic Clostridium botulinum is under continuous evaluation. In the present study, mild (P7.0(85.0) values 0 to 2 min [P, pasteurization value; z-value 7.0 degrees C; reference temperature 85.0 degrees C]) and increased (P7.0(85.0) values 67 to 515 min) heat treatments were evaluated in relation to survival of nonproteolytic C. botulinum type B spores in sous vide processed ground beef and pork cubes. The use of two concentrations of nisin in inhibition of growth and toxin production by nonproteolytic C. botulinum in the same products was also evaluated. A total of 96 samples were heat processed and analyzed for C. botulinum by BoNT/B gene-specific polmerase chain reaction and for botulinum toxin by a mouse bioassay after storage of 14 to 28 days at 4 and 8 degrees C. Predictably, after mild processing all samples of both products showed botulinal growth, and one ground beef sample became toxic at 8 degrees C. The increased heat processing, equivalent to 67 min at 85 degrees C. resulted in growth but not toxin production of C. botulinum in one ground beef sample in 21 days at 8 degrees C: in the pork cube samples no growth was detected. The increased heating of both products resulted in higher sensory quality than the milder heat treatment. Nisin did not inhibit the growth of nonproteolytic C. botulinum in either product; growth was detected in both products at 4 and 8 degrees C, and ground beef became toxic with all nisin levels within 21 to 28 days at 8 degrees C. Aerobic and lactic acid bacterial counts were reduced by the addition of nisin at 4 degrees C. The study demonstrates that the mild processing temperatures commonly employed in sous vide technology do not eliminate nonproteolytic C. botulinum type B spores. The intensity of each heat treatment needs to be carefully evaluated individually for each product to ensure product safety in relation to nonproteolytic C. botulinum.

Chitosan disrupts the barrier properties of the outer membrane of gram-negative bacteria.

The mode of antimicrobial action of chitosan (polymeric beta-1,4-N-acetylglucosamine) on gram-negative bacteria was studied with special emphasis on its ability to bind to and weaken the barrier function of the outer membrane (OM). Chitosan (250 ppm) at pH 5.3 induced significant uptake of the hydrophobic probe 1-N-phenylnaphthylamine (NPN) in Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium. The effect was reduced (E. coli, salmonellae) or abolished (P. aeruginosa) by MgCl2. No NPN uptake was observed during exposure of the salmonellae to chitosan at pH 7.2. Chitosan also sensitized P. aeruginosa and the salmonellae to the lytic effect of sodium dodecyl sulfate (SDS); such sensitization was not blocked by MgCl2 and was reversible by washing chitosan-treated cells prior to SDS exposure. Chemical and electrophoretic analyses of cell-free supernatants of chitosan-treated cell suspensions showed that interaction of chitosan with E. coli and the salmonellae involved no release of lipopolysaccharide (LPS) or other membrane lipids. However, chitosan rendered E. coli more sensitive to the inhibitory action of dyes and bile acids used in selective media. Highly cationic mutants of S. typhimurium were more resistant to chitosan than the parent strains. Electron microscopy showed that chitosan caused extensive cell surface alterations and covered the OM with vesicular structures. Chitosan thus appeared to bind to the outer membrane, explaining the loss of the barrier function. This property makes chitosan a potentially useful indirect antimicrobial for food protection.

Safety evaluation of sous vide-processed products with respect to nonproteolytic Clostridium botulinum by use of challenge studies and predictive microbiological models.

Sixteen different types of sous vide-processed products were evaluated for safety with respect to nonproteolytic group II Clostridium botulinum by using challenge tests with low (2. 0-log-CFU/kg) and high (5.3-log-CFU/kg) inocula and two currently available predictive microbiological models, Food MicroModel (FMM) and Pathogen Modeling Program (PMP). After thermal processing, the products were stored at 4 and 8 degrees C and examined for the presence of botulinal spores and neurotoxin on the sell-by date and 7 days after the sell-by date. Most of the thermal processes were found to be inadequate for eliminating spores, even in low-inoculum samples. Only 2 of the 16 products were found to be negative for botulinal spores and neurotoxin at both sampling times. Two products at the high inoculum level showed toxigenesis during storage at 8 degrees C, one of them at the sell-by date. The predictions generated by both the FMM thermal death model and the FMM and PMP growth models were found to be inconsistent with the observed results in a majority of the challenges. The inaccurate predictions were caused by the limited number and range of the controlling factors in the models. Based on this study, it was concluded that the safety of sous vide products needs to be carefully evaluated product by product. Time-temperature combinations used in thermal treatments should be reevaluated to increase the efficiency of processing, and the use of additional antibotulinal hurdles, such as biopreservatives, should be assessed.

The storage life of packed shredded Iceberg lettuce dipped in glycine betaine solutions.

The effects of glycine betaine dip, packaging method, and storage time on the sensory quality of shredded Iceberg lettuce were first modeled using a statistical experimental design, followed by a second storage test verifying the effect of the glycine betaine treatment. Shredded lettuce was dipped in 0 to 100 mg/liter active chlorine solution and then in 0 to 1.0 mol/liter glycine betaine solution, packed in 25 microm oriented polypropylene film, 250 g per package, and stored at 5 degrees C for 8 days. Models with good predictability were created suggesting that the glycine betaine dip helped retain sensory quality, especially appearance (P < 0.05). The models also suggested that washing periods over 60 s were not needed and that the microperforation of packages should not exceed 0.31 mm2 per package. The modeled positive effect on sensory quality was verified in the second storage test (P < 0.05). The optimum glycine betaine concentration was 0.2 mol/liter. Chlorination of the first dip particularly retained appearance of packed lettuce.

Shelf life of sliced raw potatoes of various cultivar varieties--substitution of bisulfites.

The effects of potato variety (Van Gogh, Bintje and Fambo), washing with browning prevention chemicals in place of sodium bisulfite, percentages of CO2, O2, and N2 in the package headspace, and storage time (1, 4, and 7 days) on the sensory and microbiological quality of potato slices were examined. Citric acid and ascorbic acid (at 0.1% each and at 0.5% each) were used as browning prevention chemicals. In the packaging atmosphere the percentage of N2 was 75 or 80%, the percentage of O2 was 5 or 0%, and the percentage of CO2 was 20% at the beginning of storage. Packed potato slices were stored in the dark at 5 degrees C. Darkening was the most important factor limiting the sensory quality of raw potato slices. Darkening occurred quickly with Fambo slices; it seems that Fambo is not a suitable potato variety if slices are to be stored. Water-washed and cooked Van Gogh slices were still acceptable for retailing after a storage period of 7 days. After 7 days of storage the best sensory quality of both raw and cooked Bintje slices was obtained with washing solutions containing 0.1 to 0.5% citric and ascorbic acids and with the gas mixture containing 20% CO2 and 80% N2. The number of microorganisms was higher in samples stored in the atmosphere containing 5% O2 than samples stored in the atmosphere containing 0% O2. Washing of potato slices with browning prevention chemicals decreased the number of microorganisms compared to potato slices not washed or potato slices washed with water after 7 days of storage.

A nondestructive leak detection method for flexible food packages using hydrogen as a tracer gas.

A nondestructive leak detection method developed at Technical Research Centre of Finland (VTT) was tested for both gas-flushed and vacuum flexible packages. In the method, a gas package containing 0.5 to 5.0% (vol/vol) hydrogen in nitrogen was positioned in a test chamber, a controlled vacuum was pulled in the chamber through a pipe connected to a hydrogen sensor, and leaking packages were detected by the sensor as increased H2 concentration. The H2 tracer gas (0.5 to 5.0%) was introduced into leaking finished vacuum packages at 200 kPa pressure. Within 1 to 4 s the developed test method was able to detect leaks down to 10 to 15 microns and 20 to 30 microns in diameter in commercially manufactured gas-flushed packages filled with roasted meat balls and vacuum packages filled with ground coffee, respectively. Before leak testing, the vacuum packages were charged with H2 for 30 s. The sensitivity and leak detection time of the test method were improved when the H2 concentration in the package was increased and when the free space in the test chamber was decreased. The evaluated H2 concentrations did not affect the sensory or microbiological quality of the roasted meat balls. This study clearly demonstrated that the hydrogen tracer gas leak detection method has potential to be further developed as a fast, nondestructive, on-line leak testing apparatus for flexible packages with or without a headspace.

Shelf-life of prepeeled potato cultivated, stored, and processed by various methods.

The effects of cultivation conditions, winter storage, peeling method, browning prevention chemicals replacing sodium bisulfite, and packing methods on the sensory, nutritional and microbiological quality of pre-peeled potato were examined. Two different cultivation lots of the potato variety Van Gogh were used. Cultivation and harvesting conditions and peeling method were the most important facts reducing the sensory quality, especially the appearance, of prepeeled and sliced potatoes. Cooking and baking of potatoes decreased the appearance defects detected in raw potatoes. The levels of vitamin C in packaged samples decreased during winter storage. Cooking for 10 min and keeping potatoes at 60 degrees C for 1 h after cooking also decreased the content of vitamin C. In potato samples immediately after treatments aerobic bacteria were present at levels of 400 to 2,950 CFU/g and lactic acid bacteria at levels of 8 to 16 CFU/g. The number of aerobic bacteria did not increase during storage, and the number of lactic acid bacteria increased at the most to 90 CFU/g. Peeling, washing and packaging methods, cultivation conditions, and winter storage did not have important effects on the number of microbes present.

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.

Active and smart packaging for meeting consumer demands for quality and safety.

Over the past few decades, many new packaging techniques have been introduced in the quest for natural preservation of foods and on-time quality monitoring of packaged food to ensure good product quality and safety for the consumer. This paper discusses scientific, technological, commercial and legislative development, as well as consumer aspects and acceptance of the active and smart food packaging techniques with current or potential commercial value, and the elements that both the manufacturers of these packaging systems and the food industry should take into account before launching products using these techniques.

Preincubation time and the use of oxygen indicators in determining the microbiological quality of aseptically packed pea and tomato soup.

In order to get accurate information about the preincubation time needed for viscous aseptic products, the growth characteristics of three food poisoning organisms Staphylococcus aureus, Clostridium perfringens and Bacillus cereus in pea soup, and one spoilage organism, Lactobacillus plantarum, in tomato soup, were followed during a preincubation period at 30 degrees C for 14 days. The sterile food packs were sealed into polyamidepolyethylene laminate bags containing different headspace gas concentrations (21% oxygen + 80% nitrogen, 5% oxygen + 95% nitrogen and 100% nitrogen). Bacterial growth was followed every second day by counting the number of colony forming units and following the headspace oxygen and carbon dioxide concentrations. The bacterial strains differed in their growth characteristics, especially in their ability to consume oxygen from the headspace, and also in their ability to produce carbon dioxide. The headspace oxygen concentration was also followed by oxygen indicators in order to determine the correlation with the oxygen concentration of the headspace and the growth of bacteria. The bacterial growth followed more closely the concentration of carbon dioxide than the concentration of oxygen. It was concluded that further studies are needed to determine the preincubation period for viscous aseptic products in order to furnish accurate data on the growth characteristics of low numbers of bacteria in aseptic foods at different headspace gas compositions.