Ripening volatile compounds

The volatiles produced by the LOX pathway and autoxidation are typically volatile aldehydes and alcohols responsible for fresh and green sensorial notes. In the LOX pathway these volatile compounds are produced in response to stress, during ripening or after damage of the plant tissue. The pathway is illustrated in Scheme 7.2. Precursors of the LOX (EC 1.13.11.12) catalysed reactions are Cis-polyunsaturated fatty acids with a (Z,Z)-l,4-pentadiene moiety such as linoleic and a-linolenic acids that are typically oxidised into 9-, 10- or 13-hydro-peroxides depending on the specificity of the LOX catalyst. These compounds are then cleaved by hydroperoxide lyase (HPL) into mainly C, C9 and Cio aldehydes, which can then be reduced into the corresponding alcohols by alcohol dehydrogenase (ADH EC 1.1.1.1) (Scheme 7.2) [21, 22]. The production of volatile compounds by the LOX pathway depends, however, on the plants as they have different sets of enzymes, pH in the cells, fatty acid composition of cell walls, etc. 

The aroma of intact black currant fruit is mostly produced by anabolic pathways of the plant, and production of fruit volatiles occurs mainly during a short ripening period [112]. The aroma profile of black currant shares similarities with that of other berry fruits, although terpenes are more abundantly present in black currant [107]. Black currant is mainly used for the production of juice. Over 150 volatile compounds have been reported from either black currant berries and/or juice, of which the major groups are monoterpenes, sesquiterpenes, esters and alcohols [107]. Processing of berries to juice has been shown to lead to major changes in the aroma composition [113-118]. 

Engels, W. J. M., Dekker, R., de Jong, C., Neeter, R., and Visser, S. (1997). A comparative study of volatile compounds in water-soluble fraction of various types of ripened cheese. Inf. Dairy. 7, 255-263. 

Luning, P.A., Rijk, T., Withers, H.J. and Roozent, J.P. (1994) Gas chromatography, mass spectrometry, and sniffing port analyses of volatile compounds of fresh bell peppers (Capsicum annuum) at different ripening stages. Journal of Agricultural and Food Chemistry 42, 977-983. 

Andres, A.I., Cava, R. and Ruiz, J. (2002) Monitoring volatile compounds during dry-cured ham ripening by solid-phase microextraction coupled to a new direct-extraction device,/. Chromatogr. A, 963(1-2), 83-88. 

Aldehydes are by far the most numerous compounds identified as dry-cured ham odorants, with different odors (green, rancid, toasted) and thresholds in air ranging from 0.09 to 480 ng/L (Table 1). Most of them were identified in the first works focused on dry-cured ham volatile compounds (7,2). Aldehydes are essential for meat flavor (70), but large quantities in meat and meat products have been related to lipid oxidation and deterioration (77). The effect of several quality factors has been researched and it was found that the rearing system of pigs (S) and ripening conditions (7) influence on the contribution to odor and the content of some aldehydes. 

The largest values for the 14-days group matched with the largest scores for the rancid note (it ). In fact, pentanal and hexanal (two usual indicators of lipid oxidation in meat, 11) were much more abundant in the 14-days group. It is known that during ripening of hams an increase of lipid oxidation volatile compounds takes place, and it is also followed by a important decrease (2). The decrease in some compounds could be related to the decrease of lipid oxidation caused by the depletion of the oxygen available in the tubes and to the lost of odorants by reactions with other components. 

Arques, J.L., Garde, S., Femandez-Garcia, E., Gaya, R, and Nunez, M. 2007. Volatile compounds, odor, and aroma of La Serena cheese high pressure treated at two different stages of ripening. Journal of Dairy Science 90 3627-3639. 

Scarpellino, R., and Kosikowski, F. V. (1962). Evolution of volatile compounds in ripening raw and pasteurized milk Cheddar cheese observed by gas chromatography. J. Dairy Sci. 45, 343-348. 

Tressl R, Jennings WG (1972) Production of volatile compounds in the ripening banana. J Agric Food Chem 20 189-192... 

Soukoulis C, Cappellin L, Aprea E, et al. PTR-TOF-MS, a novel, rapid, high sensitivity and non-invasive tool to monitor volatile compound release during fruit post-harvest storage the case study of apple ripening. Food Bioprocess Tech. 2013 6 2831-43. 

The main role of propionic acid bacteria in cheese ripening consists in the utilization of lactate produced by lactic acid bacteria as an end product of lactose fermentation. Lactate is then transformed into propionic and acetic acids and CO2. The volatile acids provide a specific sharp taste and help preserve a milk protein, casein. Hydrolysis of lipids with the formation of fatty acids is essential for the taste qualities of cheese. The release of proline and other amino acids and such volatile compounds as acetoin, diacetyl, dimethylsulfide, acetaldehyde is important for the formation of cheese aroma. Carbon dioxide released in the processes of propionic acid fermentation and decarboxylation of amino acids (mainly) forms eyes, or holes. Propionic acid bacteria also produce vitamins, first of all, vitamin At the same time, an important condition is to keep propionibacteria from growing and producing CO2 at low temperatures, since this would cause cracks and fissures in cheese. 

The formation of typical aromas takes place during the ripening of fruit. In bananas, for example, noticeable amounts of volatile compounds are formed only 24 h after the climacteric stage has passed. The aroma build-up is affected by external factors such as temperature and day/night variations. Bananas, with a day/night rhythm of 30 °C/20 °C, produce about 60% more volatiles than those kept at a constant temperature of 30 °C. The synthesis of aroma substances is discussed in section 5.3.2. 

Volatile compounds play a fundamental role in food seience and technology. In part, this is because they are released when foods and drinks are consumed, and are hence involved in aroma and flavour which are intimately linked to our enjoyment, palatability and perception of food. Aroma volatiles that reach the olfactory epithelium, via orthonasal and retronasal pathways, play not only a major role in our enjoyment of food (and drink), but also allow us to assess food quality or to detect subtle changes in food products as a result of modifications in ingredients and production. Volatile organic compounds (VOCs) are also emitted directly from food which can, for example, give us information about ripening processes (e.g. cheese or fruits) and the effects of storage. 

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