Process flavours

Process flavours or process flavours play a key role in those food products which have been exposed thermal treatment during processing and final preparation, where heating steps during preparation are applied. 

Since process flavours are generated by the interaction of raw materials like protein derivatives (amino acids) and reducing sugars (Maillard reaction), it is obvious that a large number of prepared food products are affected  

Meat products, e.g. beef, chicken, pork, lamb Vegetables, e.g. onions, potatoes, garlic Roasted products, e.g. coffee, cocoa, roasted nuts, popcorn Cereal products, e.g. biscuits, bread, extrudates Beverages, e.g. beer, wine, whiskey 

The generation of non-volatile components plays an important role because important attributes like umami, mouthfeel, texture, etc. can be given to the final products. 

Besides the well-known Maillard reaction, additional reactions like sugar degradation, fat oxidation and interaction of Maillard intermediates are major sources for powerful flavour materials. 

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Flavourings may contain flavouring substances, flavouring preparations, process flavourings, smoke flavourings and flavouring adjuvants. 

Cysteine can be obtained by hydrolysis from cysteine-rich proteins in hair or feathers or from petrochemical sources. Cysteine is an important raw material in Maillard reactions for the preparation of process flavours, but it can also serve as a source of ammonia and hydrogen sulfide for the preparation of flavour chemicals, such as the terpene sulfur compounds mentioned in Sect. 13.2.4 and furfuryl mercaptan mentioned in Sect. 13.4.2.4. 

Methionine can be obtained from enzymatic protein hydrolysates or from petrochemical sources. To a lesser extent than cysteine, it is a raw material in Maillard reactions for the preparation of process flavours and it can also be utilised as a precursor for the chemical preparation of the sulfide methional, which is an important flavour constituent for potato, malt, seafood and many other flavours. Methional can be reduced to methionol, which can be esterified with organic acids to, for instance, methionyl acetate and methionyl butyrate, which are useful compounds for pineapple and other fruit flavours (Scheme 13.16). 

For the production of process flavours, heat has to be applied to the raw materials for the thermal processing. This offers different possibilities for the production process ... 

The maximum permitted temperature for the production of process flavours is around 180 °C, as defined by legal regulations, but in general, the temperatures actually used are much lower in order to be able to reach a broad variety of different flavour profiles, such as cooked, boiled, fried, roasted and shallow-fried notes. The pressure during the reaction is usually below 10 bar (10,000 hPa). 

In the modern production of process flavours, the following topics are coming more and more into focus ... 

Flavorzyme is a commercially available proteolytic enzyme preparation by Novo Nordisk Bioindustrials. It can be used to obtain a meat-like process flavouring from defatted soybean meal. With the help of aroma extract dilution analysis, Wu and Cadwallader [61] showed in their study of 2002 the presence of key aroma compounds of roasty, meat-like aroma in the enzymatically hydrolysed and heated hydrolysed protein, e.g. maltol, furaneol, methanethiol and furanthiol derivatives. 

Concentrated preparation, with or without flavour adjuncts, used to impart flavour, with the exception of only salty, sweet or acid tastes. It is not intended to be consumed as such. Flavouring means flavouring substances, flavouring preparations, process flavourings, smoke flavourings or mixtures thereof. Flavourings may contain foodstuff as well as other substances ... 

Table 3.3 lOFI and Council of Europe definitions of flavouring substance, flavouring preparation, process flavouring, and smoke flavouring [5, 6]... 

A product or mixture prepared for its flavouring properties which is produced from ingredients or mixtures of ingredients which are themselves permitted for use in foodstuffs, or are present naturally in foodstuffs, or are permitted for use in process flavourings, by a process for the preparation of foods for human consumption. Flavour adjuncts may be added... 

Process flavourings are typically used at a level of 0.1-2% in culinary products such as bouillons, sauces, but also in snacks, desserts and confectionery. The aimual production is estimated at 6750 tons in the USA [3] and about 4500 tons in Europe [4], Process flavourings have been reviewed amongst others by van den Ouweland [5], May [6], Salzer [7], Manley [8, 9], Manley and Ahmedi [3] and Kerler and Winkel [10]. 

A thermal process flavouring is a product prepared for its flavouring properties by heating food ingredients and/or ingredients which are permitted for use in foodstuffs or in process flavourings [2]. 

Process flavourings are more related to cooking than to chemical synthesis. The reactions that occur are chemically very complex with hundreds of volatiles and nonvolatiles being formed. The final process flavouring is defined by the sum of the sensory effects of all aroma-active volatiles and taste-active compounds. 

Model reaction trials and modem analytical methods (gas chromatography/mass spectrometry (GC/MS), gas chromatography/olfactometry (GC/0)) permitted the identification of key mechanisms responsible for flavour generation in process flavourings and some of the most important ones are detailed below. Often chemically complex precursor raw materials (vegetables such as onions, spices, yeast extracts, animal products) are used. Research work on these complex reactions is rare but necessary and allows the discovery of new key odorants and formation pathways. For example, Widder and co-workers [13] discovered a new powerful aroma compound, 3-mer-capto-2-methylpentan-l-ol in a complex process flavour based on onion. 

Without any doubt the Maillard reaction and the Strecker reaction play an outstanding role in thermal aroma generation [ 15-20] and in particular in process flavourings. 

Fats or raw materials that serve as a source for fatty acids are frequently employed in process flavourings. During the flavour reaction, thermal peroxidation of lipids such as triglycerides, fatty acids and phospholipids occurs. This non-enzymatic lipid oxidation, also called autoxidation, leads to a very complex mixture of reaction products, and has to be regarded separately from the enzymatic lipid oxidation which occurs at low temperature and is catalysed by lipoxygenases. 

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