Off-odor

Dried Whole Egg and Yolk. Dried plain whole egg and yolk products are either dried as is, or have the glucose removed to improve stabiHty and shelf life of the product. Glucose is removed before drying by use of glucose oxidase or by yeast fermentation (see Yeasts). Bacterial fermentation is not used because of off-flavor and off-odor development. 

A review by Bailey and Swain ( ) cited several references which indicated nitrite was responsible for cured meat flavor. These same authors presented chromatograms of volatiles from cured and uncured hams and while the chromatograms were similar, some quantitative differences led to the conclusion that the major difference due to nitrite was its reactivity to retard lipid oxidation. Greene and Price ( ) suggested, however, that sodium chloride was the major factor responsible for cured meat flavor rather than sodium nitrite or an absence of lipid oxidation. It has been concluded from other recent work (2) that nitrite was necessary to produce a typical ham aroma and flavor as well as to retard the development of off-odors and flavors during storage of cooked cured meat. 

Fig. 21.9. Flame ionization gas chromatograms of the headspace of the acceptable and unacceptable flavor samples. (Reprinted/redrawn from J. Chromatogr., 351, R.A. Sanders, and T.R. Morsch, Ion profiling approach to detailed mixture comparison. Application to a polypropylene off-odor problem, 525-531, Copyright (1986) with permission from Elsevier.)...

Commentary This problem, like many other off-flavor and off-odor problems, was difficult because the offending compound was present at a very low level and was difficult to separate from another compound present in the sample. The two keys to this problem were the use of the handle (the off-flavor), detected with the sniff port, and the mass... 

Increase of shelf life under refrigeration and control of pathogenic nonsporeforming bacteria in fresh meat and poultry can be achieved by a 1-3 kGy dose. Doses for irradiation are selected under the consideration of threshold dose levels for sensory changes (off-odor), which depends on the type of animal meat (Table 7) [45]. Off-odor is due to the generation of volatile compounds from lipids and nitrogenous compounds formed by the reaction of these constituents with the reactive species produced by the radiolysis of water. 

Microoxygenation (MOX) is now widely applied for the maturation of red wines as an alternative to barrel aging. The proposed improvements in wine quality arising from MOX include color stabilization, removal of unwanted off-odors, and improvements... 

The impact of oxygen on wine aroma is likely to involve several oxidation mechanisms. One pathway involves pol) henol quinones, particularly in the case of the removal of unwanted sulfur-containing off-odors (RSH Mestres et ah, 2000), as illustrated in Fig. 4.4A. 

Nguyen, D. D., Dykes, S., Nicolau, L., and Kilmartin, P. A. (2010). Micro-oxygenation influence on reductive sulfur off-odors and colour development in a Cabernet Sauvignon wine. Am. ]. Enol. Vitic. 61 in press. 

Pure Yeast Culture. Recheck population periodically for purity. If a wild yeast population builds up significantly, discard the culture and begin again from a slant. Some wineries are using mass pitching techniques with dry or frozen yeast very successfully. This eliminates the need for any monitoring of culture population. Wild yeasts often cause unreliable and erratic fermentation rates, and this is often accompanied by off odors and off flavors in the wine. Erratic fermentations also often invite bacterial contamination. 

A problem associated with beef sterilized by irradiation at approximately room temperature is the production of an unpleasant flavor and aroma. This paper summarizes knowledge of the volatile components of enzyme-inactivated irradiated and nonirradiated beef, reviews the effects of concurrent and nonconcurrent irradiation procedures and of storage on these components, and presents evidence that methional (3-methylmercaptopropion-aldehyde), 1-nonanal, and phenylacetaldehyde are of primary importance to irradiation off-odor in beef thus processed. 

Selection of those components of primary importance in producing irradiation odor was aided by the observation that when all fractions eluted after 1-heptanal (Table IV) were collected together in a single trap, the trap exhibited irradiation off-odor, particularly when samples of distillate (0°C.) isolate were separated, though weak off-odor was recognized when traps isolates (—78°C.) were examined. An arbitrary decision was thus made to consider as potentially indispensable components only those compounds present in irradiated distillates eluted after 1-heptanal. This automatically eliminated hydrocarbons from consideration, though they were recognized as products of the irradiation process. 

Table V. Relative Proportions Of Possible Indispensable Off-Odor Components in Nonirradiated and Irradiated Beef...

The odor of the resulting synthetic irradiated beef slurries was compared with an equal quantity of freshly irradiated and slurried beef. Comparisons were made informally by persons experienced in sensory evaluation and familiar with irradiation off-odor. It was obvious almost immediately that some of the compounds contributed little or nothing to irradiation odor, while others affected it greatly. Trial and error mixing of compounds and concurrent odor evaluation led to the opinion that when added to a slurry of 100 grams of enzyme-inactivated beef in 75 ml. of distilled water, the following mixture caused very close approximation of irradiation off-odor. 

Higher concentrations of 1-nonanal were not tried since 7.6 p.p.m. was already much greater than the amount needed in a mixture with methional and phenylacetaldehyde to cause irradiation off-odor to be recognized. 

Oil-containing adhesives might emit fatty acid oxidation products like saturated and unsaturated aldehydes which can contribute to odor (Wilke, Jann and Brodner, 2004). Adhesives on a phenol resin base have been found responsible for odor annoyance in several office buildings in former East Berlin. Alkyl-substituted phenols, methyl, dimethyl and ethyl phenols, some of which have very low odor thresholds, have been detected in indoor air as well as in different floor samples and were most likely responsible for the off-odor (Kirchner and Pernak, 2004). 

The odor of plastics has hardly been investigated. The focus of most investigations is emission measurement of VOCs detectable by routine GC—MS analysis because emission limits have to be met by manufacturers to get approval for use of their material by authorities or by other companies which use the initial material for further processing. Examples of plastic off-odor analysis have been reported on certain occasions especially for food packaging materials regarding migration from the packaging into the food (Skjevrak et al, 2003). Other published data on the odor of plastic materials are rare for confidentiality reasons. A few selected examples of odorants found in certain plastic materials are mentioned below ... 

Thermoplastic Polyolefin (TPO) One batch of a thermoplastic polyolefin had a roasty off-odor. The important odorants 2,3-butandione, l-hexen-3-one, methional (3-methylthiopropanal), Z-2-nonenal, E-2-nonenal, l-octen-3-one, octanal, E,E-2,4-nonadienal, E,E-2,4-decadienal, and as the most important off-odorant 2-acetyl-l-pyrroline, could be identified (Mayer and Breuer, 2004b, 2006). 

Several operations may be employed to treat water prior to use. Aeration is used to drive off odorous gases, such as H2S, and to oxidize soluble Fe2+ and Mn2+ ions to insoluble forms. Lime is added to remove dissolved calcium (water hardness). A12(S04)3 forms a sticky precipitate of Al(OH)3, which causes very tine particles to settle. Various filtration and settling processes are employed to treat water. Chlorine, Cl2, is added to kill bacteria. Formation of undesirable byproducts of water chlorination may be avoided by disinfection with chlorine dioxide, C102, or ozone, 03. 

The sequence of strains following one another may produce distinctive results, depending on their individual characteristics and on prevailing conditions. Occasionally, these consequences may be undesirable, contributing to off-odor production and inducing color loss by adsorption. This is particularly a problem when fermentations are prolonged. 

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