Microbial spoilage types

Lactic acid-producing bacteria associated with fermented dairy products have been found to produce antibiotic-like compounds caUed bacteriocins. Concentrations of these natural antibiotics can be added to refrigerated foods in the form of an extract of the fermentation process to help prevent microbial spoilage. Other natural antibiotics are produced by Penicillium wqueforti the mold associated with Roquefort and blue cheese, and by Propionibacterium sp., which produce propionic acid and are associated with Swiss-type cheeses (3). 

Lactic acid is generally present in spoiled canned, nonfermented vegetables, and it has been suggested that this can serve as a good indicator of microbial spoilage in this type of foods (Ackland and Reeder 1984). 

Bissett and Berry (76) reported on the ascorbic acid retention in orange juice as a function of container type. They stored FCOJ in fcil-lined cardboard, rectangular cartons and in polyethylene (PE)-lined fiber cylindrical cans for a year at -20.5°, -6.7°, and 1.1°C. At -20.5°C, the ascorbic acid retention was 93.5% in the foil-lined cartons and 91.5% in the PE-lined cans. Neither container proved effective above freezing due to microbial spoilage. The foil-lined carton was superior at 1.1°C, in that 89% of the ascorbic acid was retained after three months. In the PE-lined can, the retention was 44% after three months at 1.1°C. 

Flour acidity (ml of O.lmol/1 NaOH/lOg, titrated in the presence of phenolphthalein) depends upon the extraction rate of the flour and ranges between 2.0ml/g (flour type 450) and 5.5 ml/g (flour t)fpe 1800). Too low acidity often reflects poorly aged flour. Acidity above 7.0 suggests microbial spoilage. 

The alcoholic content of these wines prevents microbial spoilage, but flor yeasts spontaneously develop on the surface of the wine. After a certain degree of development, another tasting results in a new classification, determining the appropriate type of aging (crianza) for each bota biological or oxidative. 

It could be said that freshly pressed fruit juice provides the truly natural answer to all the requirements of a soft drink thirst quenching, fresh, healthy, flavour-some, nutritional and, of course, natural. So why should it have been necessary to look any further towards the creation of different flavour types and the myriad of drink var ieties that has appealed over the years in beverage markets around the world Necessity, being the mother of invention, has been the driving force in all this. In the early years of the industry there was a real necessity for soft drinks manufacturers, in order to stay in business, to control a major threat to their trade, that of microbial fermentation and spoilage of the bottled product. 

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-... 

A Bloodhound BH 114 electronic nose was used to differentiate between different types of bread spoilage [34]. Microbial and enzymatic spoilage caused by lipoxygenase can be differentiated from one another and from unspoilt bread after 48 hours by using cluster analysis. This is achieved before visible spoilage signs. Analysis of the bread samples with GC-MS identified the spoilage volatiles and the volatiles from the unspoilt bread. 

It is difficult to be specific about microbial damage in fruit and vegetables because there is usually a succession of micro-organisms and each commodity will differ. However, numerous different types of spoilage can be recognised. 

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