The Mechanism of Microbiological Leaker Spoilage of Canned Foods: A Review

S ummary : This review summarizes the work on the subject carried out mainly in the authors'laboratories but also in the associated laboratories of Metal Box Co. Ltd., London, and Plat Manufaktor, Malmö, Sweden. Special attention is paid to the mechanism of bacterial reinfection and how it is influenced by deviations in can construction or can handling procedures. Methods of preventing bacterial reinfection at the most critical points in the canning operation are considered and certain guiding principles are derived.     

Environmental Life Cycle Assessment of a Canned Sardine Product from Portugal

This study aims to assess the environmental impacts of canned sardines in olive oil, by considering fishing, processing, and packaging, using life cycle assessment (LCA) methodology. The case study concerns a product of a canning factory based in Portugal and packed in aluminum cans. It is the first LCA of a processed seafood product made with the traditional canning method. The production of both cans and olive oil are the most important process in the considered impact categories. The production of olives contributes to the high environmental load of olive oil, related to cultivation and harvesting phases. The production of aluminum cans is the most significant process for all impact categories, except ozone depletion potential and eutrophication potential, resulting from the high energy demand and the extraction of raw materials. To compare to other sardine products consumed in Portugal, such as frozen and fresh sardines, transport to the wholesaler and store was added. The environmental cost of canned sardines is almost seven times higher per kilogram of edible product. The main action to optimize the environmental performance of canned sardines is therefore to replace the packaging and diminish the olive oil losses as much as possible. Greenhouse gas emissions are reduced by half when plastic packaging is considered rather than aluminum. Frozen and fresh sardines represent much lower environmental impacts than canned sardines. Nevertheless, when other sardine products are not possible, it becomes feasible to use sardines for human consumption, preventing them from being wasted or used suboptimally as feed.     

Spoilage Bacteria in Canned Foods: I. Flat Sour Spoilage Bacteria in Canned Asparagus and the Thermal Death Time

Bacillus stearothermophilus was found to be a cause of spoilage of asparagus canned in Taiwan. The F(250) and Z values of the isolates were 14.2 min and 17.8 F (-7.9 C), respectively.     

Spoilage Bacteria in Canned Foods: II. Sulfide Spoilage Bacteria in Canned Mushrooms and a Versatile Medium for the Enumeration of Clostridium nigrificans

Clostridium nigrificans was found to be a spoilage organism of canned mushrooms in Taiwan. A modified beef extract tryptone iron medium, both in broth and agar form, was designed for the detection and recovery of the organisms. A procedure of simple plate counting method of C. nigrificans was established.     

Kinetics of Chemical Reactions for Prediction of Quality of Canned Fish during Storage

Changes in a wide range of quality characteristics of canned fish were studied during storage at different temperatures. A number of biochemical parameters were found that undergo significant monotonic changes in the course of storage, correlating with organoleptic scores. It was demonstrated that simulation of thermal aging of canned fish on the basis of on the laws of chemical kinetics may be used for predicting quality changes and determining shelf life.     

Levels of Heavy Metals in Canned Bonito,Sardines, and Mackerel Produced in Turkey

Concentrations of selected metals were determined using ICP-MS in canned bonito, sardines and mackerel commercialized in Turkey. Thirty samples and two different brands were sampled for each fish species. The minimum and maximum concentrations of trace metals in canned bonito, sardines and mackerel were found as 0.000–34.742, 0.000–89.015, 0.000–28.725 mg/kg for iron, 2.388–26.620, 10.930–41.340, 4.778–29.270 mg/kg for zinc, 0.331–1.548, 0.599–2.242, 0.336–2.884 mg/kg for copper, 0.000–0.065, 0.000–0.113, 0.000–0.115 mg/kg for cadmium, 0.000–0.190, 0.000–0.158, 0.000–0.385 mg/kg for tin, 0.000–0.111, 0.000–0.223, 0.000–0.208 mg/kg for mercury and 0.000–3.046, 0.000–2.875, 0.000–3.529 mg/kg for lead, respectively. These levels are similar those found in other studies. Although the samples have concentrations within permissible limits for Zn, Cu, Sn and Hg, some of them contained Fe, Cd and Pb above these limits. Periodical controls of metals in canned fish are essential both to protect human health and to provide data on this subject.     

Bacteriological and Shelf-Life Characteristics of Canned, Pasteurized Crab Cake Mix

The bacteriological spoilage characteristics of a canned, pasteurized crab cake mix product stored at various temperatures were investigated. A large number of bacteria, both mesophilic and psychrophilic, survived the pasteurization process. Bacillus and Micrococcus were found to predominate when the product was stored at 30 C (86 F) and 18 C (64 F), whereas Alcaligenes predominated at 2 C (36 F). The product was found to be free of Escherichia coli. Bacterial counts, trimethylamine nitrogen, volatile reducing substances, and ammonia determinations were evaluated as indices of quality for the product. Close correlation was observed between bacterial counts, volatile reducing substance values, and organoleptic tests when the product was stored at 30 C (86 F). The shelf-life of the product was approximately 6 months at 2 C (36 F), 4 days at 18 C (64 F), and 27 hr at 30 C (86 F).     

PCR Detection of Thermophilic Spore-Forming Bacteria Involved in Canned Food Spoilage

Thermophilic bacteria that form highly heat-resistant spores constitute an important group of spoilage bacteria of low-acid canned food. A PCR assay was developed in order to rapidly trace these bacteria. Three PCR primer pairs were designed from rRNA gene sequences. These primers were evaluated for the specificity and the sensitivity of detection. Two primer pairs allowed detection at the species level of Geobacillus stearothermophilus and Moorella thermoacetica/thermoautrophica. The other pair allowed group-specific detection of anaerobic thermophilic bacteria of the genera Thermoanaerobacterium, Thermoanaerobacter, Caldanerobium and Caldanaerobacter. After a single enrichment step, these PCR assays allowed the detection of 28 thermophiles from 34 cans of spoiled low-acid food. In addition, 13 ingredients were screened for the presence of these bacteria. This PCR assay serves as a detection method for strains able to spoil low-acid canned food treated at 55°C. It will lead to better reactivity in the canning industry. Raw materials and ingredients might be qualified not only for quantitative spore contamination, but also for qualitative contamination by highly heat-resistant spores.     

The Detection of Microbial Spoilage in Canned Foods Using Thin-layer Chromatography

Thin-layer chromatography was investigated as an inexpensive alternative to traditional microbiological techniques for the detection of microbial growth in canned vegetables. It was compared with culture methods, pH determination and direct microscopy in batches of canned vegetables with a known incidence of spoilage.     

Polycyclic Aromatic Hydrocarbon Profiles of Some Brands of Canned Fish in the Nigerian Market

Concentrations and profiles of polycyclic aromatic hydrocarbons (PAHs) were determined in selected popular brands of canned fish (mackerel, sardine, and tuna) consumed in Nigeria with a view to providing information on the health risk associated with consumption of these products. The concentrations of PAHs were measured by gas chromatography equipped with flame ionization detection (GC-FID) after dichloromethane/hexane extraction and clean-up. The concentrations of Σ16 PAHs in these brands of canned fish varied from 174.6 to 350.8 μg/kg, 187.4 to 592.5 μg/kg, and 204 to 264.6 μg/kg for mackerel, sardine, and tuna, respectively. Benzo(a)pyrene was detected in 48% of the investigated brands at concentrations higher than the maximum tolerable limit of 5 μg/kg. The daily intake of PAHs from the consumption of any brand of these canned fish ranged from not detected (nd) to 54.3 ng BaP/kg bw/day, nd to 56.4 ng PAH2/kg bw/day, nd to 86.4 ng PAH4/kg bw/day, and nd to 153.7 ng PAH8/kg bw/day. The estimated margin of exposure (MOE) values (BaP-MOE, PAH2-MOE, PAH4-MOE, and PAH8-MOE) in a significant proportion of the brands was less than 10,000, which indicates a potential health risk for the consumers of these brands of canned fish.     

Role of Curing Agents in the Preservation of Shelf-stable Canned Meat Products

Experiments were conducted to gain a better understanding of the mechanism by which sodium chloride, sodium nitrate, and sodium nitrite supplement the action of heat in preserving canned cured meat products. Heated spores of putrefactive anaerobe 3679h were less tolerant of all three curing agents in the outgrowth medium than were unheated spores. When the curing agents were added to the heating menstruum, but not to the outgrowth medium, sodium chloride and sodium nitrate tended to protect the spores against heat injury, but sodium nitrite did not. When the spores were both heated and cultured in the presence of the curing agents: (i) nitrate and salt increased the apparent heat resistance at low concentrations (0.5 to 1%) but decreased it at concentrations of 2 to 4%; (ii) nitrite was markedly inhibitory, especially at pH 6.0. At the normal pH of canned luncheon meats (approximately 6.0), nitrite appears to be the chief preservative agent against spoilage by putrefactive anaerobes.