Packaging microbial spoilage

Fruit juices and nectars are highly susceptible to fermentation and other forms of microbial spoilage and with few exceptions it is essential that some form of pasteurisation is employed when these products are packaged. The exceptions that are seen usually relate to freshly squeezed orange (or other) juices that are processed directly from fresh fruit and packaged immediately. These products have a very short shelf life, usually a few days, and are maintained by storage at temperatures between 0 and 5°C. 

The aseptically-processed concentrates retained sterility throughout the course of the study and were stored at 7.2° and 23.9°C. The samples in 6-oz. foil-lined composite cans and those cold filled into the 200-ml rectangular packages were stored only at -17.8°C because, they were not aseptically packed and were subject to microbial spoilage. 

The presence of oxygen in packaged foods has long been known to be a key problem of preservation and shelf-life, producing colour degradation, loss of nutrient, changes in flavour and odour, and microbial spoilage. 

The causes of microbial spoilage may be both diverse and multifactorial the quality of product preservation, the microbiological quality of the raw materials used - in particular production water microbe content, packaging and manufacture, and user contamination. 

GC-O is the method of choice for selecting those components that are responsible for aroma deviation in food, i.e., an off-flavor. In general, it can be applied to both foodbome off-flavor formation and off-flavor problems related to contamination. The latter is caused by odorants that normally do not belong to the overall aroma of the product, i.e., external contaminants (e.g., packaging) or compounds formed upon processing and storage (e.g., microbial spoilage). In both cases, the comparison of the off-flavor of the contaminated food with the reference product usually results in a limited number of sensory-relevant compounds, which reflect the difference in aroma profiles. Identification work can then be focused on these odorants. 

The package must also prevent the entry of organisms for example, packaging of sterile products must be microorganism proof—hence the continued use of glass ampules. For nonsterile products the preservative provides some protection, but continual microbial challenge will diminish the efficacy of the preservative, and spoilage or disease transmission may occur. 

The storage condition of raw materials, particularly hygroscopic substances, is important, and as a minimum water activity (Aw) of 0.70 is required for osmophilic yeasts, 0.80 for most spoilage moulds and 0.91 for most spoilage bacteria, precautions should be taken to ensure that dry materials are held below these levels. Some packaging used for raw materials, such as unlined paper sacks, may absorb moisture and may itself be subject to microbial deterioration and so contaminate the contents. For this reason polythene-lined sacks are preferable. Some liquid or semi-solid raw materials contain preservatives, but others such as syrups depend upon osmotic pressure to prevent the growth of os-mophiles, which are often present. With this type of material it is important that they are held at a con-... 

The first step in shelf life estimation is to determine the parameters controlling the loss of product quality. Shelf life may end for a product due to moisture uptake, oxidation, spoilage from microbial action, or a combination of these and other factors. Therefore, one must determine what is causing the end-point to occur. Having done that, calculations to estimate when that will occur in a package can be made. 

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