Off-flavour production

Table 1.1 lists 12 symptoms of nonenzymic browning and shows how these develop in relation to the three stages of it. Note in particular that, as far as browning itself is concerned and also off-flavour production, there is an induction period. 

Grbin, P. R., Henschke, P. A. (2000) Mousy off-flavour production in grape juice and wine by Dekkera and Brettanomyces yeasts. Australian Journal of Grape and Wine Research, 6, 255-262. 

Studies of autoxidation and rancidity in relation to off-flavour production in foods cannot be overemphasized. Rancidity development in food products such as milk, meat, dehydrated food, potato chips, fruits and vegetables is a prime concern of food chemists. The process of autoxidation and rancidity not only involves cis to trans isomerization but also production of many other compounds, such as peroxides and hydroperoxides. IR spectroscopy has been used sucessfully to follow the autoxidation process qualitatively and quantitatively. Bands at 2.93, 3.2, 5.72 and 10 to 11 have been associated quantitatively with hydroperoxides, free acid, C=0, and cis to trans isomerization, respectively. Analysis by IR absorption was found to be more sensitive to changes than a qualified taste panel and considerably more sensitive than determination of peroxide values (O Connor, 1956). 

The cardboard like flavour that occurs in stale beer is thought to arise fi-om the fi ee radical mediated oxidation of various constituents in beer. The characteristic odour and taste are caused by decomposition products finm the free radical process. Similar processes occur in many foods, but in beer, these off-flavour products can be detected by the consumer even at very low concentrations. 

Lipid hydroperoxides are either formed in an autocatalytic process initiated by hydroxyl radicals or they are formed photochemically. Lipid hydroperoxides, known as the primary lipid oxidation products, are tasteless and odourless, but may be cleaved into the so-called secondary lipid oxidation products by heat or by metal ion catalysis. This transformation of hydroperoxides to secondary lipid oxidation products can thus be seen during chill storage of pork (Nielsen et al, 1997). The secondary lipid oxidation products, like hexanal from linoleic acid, are volatile and provide precooked meats, dried milk products and used frying oil with characteristic off-flavours (Shahidi and Pegg, 1994). They may further react with proteins forming fluorescent protein derivatives derived from initially formed Schiff bases (Tappel, 1956). 

SKIBSTED L H, MiKKELSEN A and BERTELSEN G (1998) Lipid-derived off-flavours in meat, in Shahidi F Flavour of Meat, Meat Products and Seafoods, Blackie Academic Professional, London, 217-56. 

The enzymes present in soy bean flour are not desirable in all products because they interact with the fat phase and can cause beany off-flavours. Enzyme inactive soy flour is made for these products. 

Other compounds, such as 2,4,6-trichloroanisole (TCA), 2-isopropyl-3-methoxypyrazine and 2-isobutyl-3-methoxypyrazine, were found downstream of a pulp mill effluent, and were considered as off-flavours. These compounds are by-products of chlorination, or can be produced by actinomycetes or other biota [74]. 

In case there is a significant difference between the stressed and the nonstressed sample, off-flavours or strong sensorial deviations are monitored. As a next step, further analytical evaluations, e.g. GC-MS, are performed for the identification of relevant degradation products. 

Also on the positive side, severe heat treatment of cream improves the oxidative stability of butter produced therefrom due to the exposure of antioxidant sulphydryl groups. As discussed in section 9.2.2, lactones formed from hydroxyacids are major contributors to the desirable cooking quality of milk fats but contribute to off-flavours in other heated products, e.g. milk powders. 

Riboflavin absorbs light maximally at about 450nm and in doing so can be excited to a triplet state. This excited form of riboflavin can interact with triplet 02 to form a superoxide anion OJ (or H202 at low pH). Excited riboflavin can also oxidize ascorbate, a number of amino acids and proteins and orotic acid. Riboflavin-catalysed photo-oxidation results in the production of a number of compounds, most notably methional (11.1) which is the principal compound responsible for the off-flavour in milk exposed to light. 

Shahidi, F. 1994. Assessment of lipid oxidation and off-flavour development in meat and meat products. In Flavour of Meat and Meat Products (F. Shahidi, ed.) pp. 247-266. Chapman and Hall, Glasgow, U K. 

Marchsan, M. and Morran, J. (2002). Tastes associated with products in contact with drinking water. Abstract from the Sixth IWA Symposium on Off-Flavours in the Aquatic Environment. Barcelona, Spain, October 7-10. 

The gingerols can undergo a retro aldol reaction at the P-hydroxy ketone group to yield zingerone and aliphatic aldehydes, such as hexanal. This reaction can occur by base catalysis or by the action of heat, and with oleoresins it proceeds rapidly at temperatures above 200°C. The process is detrimental not only because of reducing the pungency level, but also from the production of off-flavours by the liberated aldehydes. 

Rauhut, D., Kiirbel, H. (1994) The production of H2S from elemental sulfur residues during fermentation and its influence on the formation of sulfur metabohtes causing off-flavours in wine. Viticultural and Enological Science, 49, 27-36. 

Grbin et al. 2007). ATHP reduction may lead to EHTP. As ethanol is a precursor, mousy off-flavour occurs after alcoholic fermentation, preferably after lactic acid bacteria activity. It seems that the formation of mousiness may be induced by oxidation but it is not clear if the effect is on the microorganisms or in any chemical reaction stimulated by the redox potential. Other agents claimed to affect its production (high pH, low sulphite, residual sugar content) (Lay 2004 Snowdon et al. 2006 Romano et al. 2007) are also stimulators of microbial activity and so the true mechanisms are not yet clarified, but the non-enzymatic chemical synthesis has been ruled out in D. anomala (Grbin et al. 2007). 

Before a sheet filter is used for the first time, the filter sheets should be rinsed for about 15 min with water, to make sure that the product does not have any off-flavour due to the sheets (paper or diatomaceous earth flavour). For this rinsing operation the flow rate should be high and the filter sheet pack should not be tightened. 

The vocabulary varies. Off-flavour is an atypical flavour often associated with deterioration of the product. Taint is often used as a synonym for off-flavour. 

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