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Lipid-derived flavour and off-flavour possible upon food processing
Friday, 16 October, 2020, 08 : 00 AM [IST]
Dr Siddhant Bhargava
Flavour is a very significant aspect that determines the accessibility of both ethnic as well as functional foods. This can be favourable or unfavourable based on the chemical nature of the volatile compounds present, their effectiveness, and the incidence of non-volatile components in the edibles we consume.

Lipid, being a chief food constituent, tends to add to the formation of food flavour through the connections with other mechanisms or due to its own degradation during the process of food processing, cooking and storage. This is predominantly vital while dealing with functional consumables that may encompass a high percentage of highly unsaturated oils.

The lipid may be involved in the Strecker degradation and Maillard reaction, the two procedures that occur during food processing, and as a result, it leads to the formation of a myriad of volatile compounds. Lipoxygenases and autoxidation of unsaturated fatty acids also have an important role to play in the growth of volatile compounds.

Flavours tend to dominate the sensory characteristic of the overall food adequacy. While aroma volatiles tend to have a key impact on flavour, taste properties of high-molecular-weight components along with the contribution from non-volatile precursors should also be taken into consideration.

Other dynamics
Additionally, the effects of colours, consistency, juiciness, and temperature are among other dynamics that influence the overall sensory character of foods. In this case, a great emphasis has to be laid on functional and invigorated foods in which flavour of such products must bear a resemblance to those of their earthy equivalents.

The raw products often tend to have less aroma and only a mild taste, but they do serve as a rich pool of compounds coupled with taste demonstrative properties as well as aroma precursors and flavour enhancers. Once processed, edibles tend to develop a particular aroma.

For instance, the coffee upon roasting generates numerous volatile compounds that are accountable for the required flavour credited to coffee. Another example would be, meat when processed on heat, whether cooking, grilling, roasting, or frying tends to produce specific meaty flavours. Along with heating, the age-old process of fermentation also plays a crucial role in the development and enhancing of flavours in most edibles and beverages.

Autoxidation of unsaturated fatty acids
In general, the flavour of fats and oils coupled with lipid-containing foods is also influenced by their constituents which may be detrimental, such as those generated upon autoxidation of unsaturated fatty acids or be required as in the case of most lipoxygenase-derived lipid-based volatiles. Additionally, the non-volatile taste-active ingredients of muscle foods, comprising of poultry, red meat and seafood tend to cover free amino acids, decreased sugar content, vitamins and nucleotide, among others.

The interface of these mechanisms with each other or their degradation products via the Strecker degradation and Maillard reaction tends to produce a large number of intermediates and volatiles which add to the needed aroma of such foods upon thermal processing and heating process that is experienced during cooking, frying, and grilling.

Lipids also serve as a vital contributor to the overall flavour of meat and seafood and are in charge, at least in part, for diverse species-dependent aroma character and palate of muscle food. Undoubtedly, dietary regimes also tend to influence the flavour of red meat, seafood, and poultry.

Taking into consideration plant oils, based on their origin such as oilseeds, fruit oils and fruit seed oils, their fatty acid configuration, triacylglycerol profile, and the existence of negligible components, together with bioactive, and storage conditions edict their flavours and oxidative steadiness.

Flavour and off-flavour volatiles of functional foods like meat

The process of food processing makes way for the generation of a large number of compounds that are volatile in nature. Each of these compounds tends to have a diverse impact on the entire flavour sensation that it displays. For instance, a large number of compounds have been found in the ingredients of heat-processed edibles that include those of plant origin and muscle foods resultant from lipid degradation.

Among the volatile compounds that have been found in meat, hexanal is considered to be a dominant aldehyde and is usually present together with 2,3-octanedione. Generated from the oxidation of linoleic and arachidonic acids which are omega-6 fatty acids, Hexanal is formed directly from linoleic or arachidonic acids.

Warmed-over flavour (WOF) or the off-flavour note in meats, particularly poultry is of great interest in current times. The aroma profile for fresh meat that has been stored encompasses certain compounds that are qualitatively similar to the WOF of reheated meat but is present at different concentrations. Needless to say, WOF is a major concern for the domains of restaurant and foodservice. Moreover, with the consumption trends graduating towards ready-to-eat meals, WOF of reheated meat post chilled storage has taken a backseat.

Beany flavour in soybean products
Soybean is a legume that is used in several ways in edibles such as soymilk, oil, flour, fermented bean paste and tofu along with nutraceuticals and functional foods. However, on the ageing of the oil, a beany flavour is noted and this phenomenon is termed as a reversion. Additionally, the use of soy protein in food formulations has an ability to make an indirect contribution to flavour along with the occurrence of bioactive compounds. The isoflavones present in soy might impact the lipid steadiness and hence the whole impact on flavour has assessed soybean on the off-flavour generation.

Fishy or musty off-flavour in non-fish oils
The fishy odour often perceived is owing to the incidence and interaction of non-lipid components with lipid oxidation products. It has been researched that trimethylamine (TMA) formed from phosphatidylcholine (PC) is accountable for fishy off-flavour in non-fish oils like soybean oil when present together with other modules. This was chiefly perceived for rapeseed/canola oil due to the inconsistency of concentration of certain compounds like 2- and 3-methylbutanoic acid, 2-methoxy phenol, and ethyl 2-methyl butanoate.

Off-flavours in supplement capsules of omega-3 oils
Omega-3 is a polyunsaturated fatty acid (PUFAs) that has been known widely due to the various health advantages it offers. These elements are mainly present in omega-3 PUFAs - mainly in the blubber of aquatic mammals like whales and seals, the bodies of fatty fish such as salmon and mackerel.

However, omega-3 PUFAs are very vulnerable to corrosion due to their high degree of unsaturation, and readily form primary oxidation products which break down to secondary oxidation products. The fishy off-flavour present in the oxidised omega-3 oils is a result of the presence of secondary oxidation products, such as 2,4,7-decatrienals and other carbonyl compounds.

Lipids being a prime source of flavour in food, both required and undesirable it has been found that lipid-derived flavour and off-flavour may be produced upon food processing through the involvement of oxidisation processes. It is likely to regulate the development of off-flavour and to yield the desirable flavour by better comprehending the mechanisms involved and by the inclusion of bioactive or bioactive-containing components in the fabrication of traditional and novel functional foods.

(The author is fitness and nutritional scientist and co-founder of Food Darzee)
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