# Effect of Processing on Volatile Organic Compounds Formation of Meat--Review
## 4 Thermal Processing
### Drying  
Common meat preservation treatments include salting and drying. It is known that the volatile compounds of dried meat products are formed by numerous and complex reactions. Most of these reactions occur during the maturation phase and originate mainly from carbohydrate fermentation and lipolytic and proteolytic processes. The liberated free fatty acids, amino acids, and peptides then serve as substrates for oxidation, and Strecker and Maillard reactions result in a wide variety of volatile compounds with distinct aromatic notes and/or odor thresholds [79]. The formation of VOCs during the application of preservative treatments is mainly influenced by time, temperature, drying method, or salt concentration. Drying methods include spray drying (SD) (a method used to create powders such as chicken [80]), vacuum drying (VD), microwave vacuum drying (MVD), infrared vacuum drying (IFVD), viz hot air drying (HD), vacuum freeze-drying (FD), among others. However, it was found that the drying methods (HD, VD, MVD, and FD) caused damage to 8-carbon (C8) compounds, especially to a significant extent for eight-carbon alcohols. Moreover, each drying method has been shown to generate greater amounts of volatile compounds belonging to different groups: HD contributes to the generation of more ester compounds, MVD contributes to the generation of more aldehyde compounds, FD contributes to the generation of more hydrocarbon compounds, and VD contributes to the generation of more ketone compounds for the test material chicken and white Hypsizygus marmoreus [80,81]. Depending on the duration, drying can also generate different levels and types of volatile compounds. Volatile compounds of dried deer loin after 30 days and after 60 days showed that the change in the profile of volatile compounds over time is determined by changes in the processes of lipolysis, proteolysis, and oxidation such as alcohols (1-hexanol, 1 ocen-3-ol), aliphatic aldehydes, branched aldehydes, and furans [71]. The drying temperature affects the composition of volatile compounds by altering biochemical reactions: it affects the oxidation of fatty acids, the growth of microorganisms (generation of hydrolases and oxidases), and the activity of endogenous enzymes. An increase in temperature contributes to an increase in VOCs belonging to the group of alcohols, aldehydes, and ketones [82]. The salting process prolongs the shelf life of meat products. Higher salt content slowed the formation of alcohols and branched-chain aldehydes from amino acids such as valine, isoleucine, and leucine formed on the Strecker degradation reactions, while it promoted the formation of aldehydes from fatty acids. Moreover, salt has the effect of reducing proteolysis activity by modifying the polarity of the protein surface. The increased amount of salt used may result in reduced formation of volatile flavor-active substances in dried turkey ham [83]. In addition, an analysis of the literature showed the occurrence of a positive correlation between salt content and total aldehydes, and a negative correlation with total alcohols, alkanes, and ketones. Salt-curing methods such as static brining, pulsed pressure salting, and vacuum tumbling curing also affect the formation of volatile compounds in meat products. Research conducted by [PERSON] et al. [84] showed that vacuum drying reduced the values of volatile compounds (especially 1-hexanol, 1-ocen-3-ol, hexanal, and 2,3-octanone) compared to the other methods. Due to the formation of unpleasant odors such as 1-hexanol and 1-ocen-3-ol, attention should be paid to the selection of curing methods in terms of the taste of processed meat products and human health. Nowadays, due to the trend of reducing NaCl in food products, various substitutes (KCl, flavor enhancers, CaCl\({}_{2}\)) are used; however, in the study, it was found that sodium substitutes had a more significant effect on the odor profile [85].