8 - Flavors PDF

11/13/2024 8 - Flavors NUT312 - Food Chemistry 1 Introduction  Although nutritionists may wish otherwise, it is the flavour and appearance of food rather than it...

11/13/2024 8 - Flavors NUT312 - Food Chemistry 1 Introduction  Although nutritionists may wish otherwise, it is the flavour and appearance of food rather than its nutrients that win the compliments at the dinner table ◦ Taste and odor are collectively referred to as flavour  Taste is the property of liquids, solids or gases in solution that is detected by receptor cells in the taste buds on the tongue and elsewhere in the oral cavity  Odor (or aroma, or smell) is the property of volatile substances detected by the receptor cells of the olfactory systems 2 1  11/13/2024 Introduction  The food chemist faces a number of difficulties in investigating flavour 1. There is no physical or chemical detection probe  The skill of a trained taste panel or the nose of an experimenter are used 2. A food flavour rarely depends on a single substance  When the mixture of substances involved in a particular flavour is revealed and then reconstituted, the original flavor cannot be obtained  This is because some substances present in exceedingly small proportions have great influence on the total flavour of the food 3 Taste  Taste substances are usually water- soluble and non-volatile ◦ Four primary taste sensations: 1. Sweet 2. Salty 3. Sour 4. Bitter ◦ A fifth one, umami(meatiness), is described as a savory and delicious sensation 4 2  11/13/2024 Sweetness  Sweetness has received the most attention from research ◦ It is the special characteristic of sugars ◦ Most sugars are less sweet than sucrose (reference sugar) 5 Sugar Derivatives: Sugar Alcohols  Obtained from their parent mono- or dissaccharide by reduction of the carbonyl group to a hydroxyl ◦ Isomalt is made by a bacterium  A little less sweet than sucrose  Unabsorbed by the small intestine; contribute little to the caloric intake ◦ Excess consumption: osmotic diarrhea 6 3  11/13/2024 Artificial Non-sugar Sweeteners 8 4  11/13/2024 1. Saccharin  Advantages: 1. x300 sweeter than sucrose 2. Stable to processing procedures 3. Low price 4. Zero ‘calories’ 5. Non-cariogenic  Disadvantages: 1. Unpleasant metallic after-taste (that is why used usually with sucrose) 2. Questionable safety slightly (banned in Canada) 9 2. Sodium Cyclamate and Acesulphame K  Sodium cyclamate: ◦ x30 sweeter than sucrose ◦ Masks off-flavors (synergistic enhancement with saccharin) ◦ Good thermal stability ◦ Highly soluble ◦ Banned for use in USA  Acesulphame K: ◦ x200 sweeter than sucrose ◦ Stable over a wide range of temperatures and pH ◦ Easily soluble 10 5  11/13/2024 3. Aspartame  L-aspartyl-L-phenylalanine methyl ester (Aspartame) was discovered by chance, following a gap of laboratory hygiene ◦ It has a clean sucrose-like flavour that has made it extremely popular with soft-drink manufacturers (x180) ◦ Its main drawback is its instability outside the pH range 3-6 and at temperatures above 70oC ◦ Health concerns for PKU patients  PKU: impaired capacity to cope with an excess of phenylalanine; hence the need for a warning on the label 11 4. Neohesperidine Dihydrochalcone (DHC)  Neohesperidine DHC is obtained by chemically converting naringin (source of the bitterness of grapefruit) ◦ x1500-1800 sweeter than sucrose ◦ Very expensive; not used alone in food products ◦ It masks the bitterness of other substances, making it attractive for pharmaceutical products 12 6  11/13/2024  5. Sucralose ◦ Brand: Splenda ◦ x600 sweeter than sucrose ◦ The only artificial sweetener made from sucrose  Chlorinated sucrose derivative  Safe to use  Heat stable  Long shelf-life  6. Alitame ◦ Formed from L-aspartic acid and D-alanine ◦ x2000 sweeter than sucrose ◦ Promotes Maillard browning 13 Plant-derived Sugar Substitutes 14 7  11/13/2024 1. Glycyrrhizin  X50-100 sweeter than sucrose  Derived sugar from the liquorice root  Widely used in Far East for flavoring and sweetening foods and drinks, medicines and tobacco  Anti-allergenic, anti-inflammatory and expectorant are beneficial, but bad for kidney and blood pressure 15 2. Stevioside (Stevia) ◦ Extracted from the leaves of Stevia rebaudiana cultivated in Far East and South America ◦ 300x sweeter than sucrose ◦ Recently approved for use in the USA and the EU 3. Thaumatin ◦ Obtained from a West African tree and marketed under the name Talin ◦ Extremely sweet (x2000) ◦ Resistant to thermal treatment 16 8  11/13/2024 Sweetness Intensity of Commercial Artificial Sweeteners 17 Bitterness  Studies with the metal halides have suggested that the structural criterion that distinguishes saltiness from bitterness is simply size ◦ When the ionic diameters is below that of potassium bromide (0.658 nm), which tastes both salty and bitter, then the salty taste predominates  Sodium chloride (0.556 nm): salty  Potassium iodide (0.706 nm): bitter  Magnesium chloride (0.850 nm): bitter 18 9  11/13/2024 Bitterness  Phenolic substances in the form of flavonoids (vitamin P) are important sources of bitterness in fruit juices ◦ Naringin in grapefruit and oranges ◦ Limonin in citrus juices  Both have anti-cancer properties  Bitterness is desirable in beer ◦ This is achieved by adding dried hops that are rich in bitter resins 19 Bitterness  The ability to perceive bitterness protected animals from dangerous bitter alkaloids present in many plants ◦ Alkaloids are organic compounds having nitrogen in a heterocyclic ring ◦ They include nicotine, caffeine, cocaine and quinine  Quinine is used as a bittering agent in soft drinks such as ‘bitter lemon’ and ‘tonic water’ (Perrier)  Quinine was the first effective treatment for malaria 20 10  11/13/2024 Saltiness Saltiness is easily detected on the side tip of the tongue and is elicited by inorganic salts like NaCl 21 Saltiness  We add salt to enhance the food flavour, but Na ions, naturally present in many foods, have a major role in their flavour ◦ When Na ions were eliminated from a mixture of amino acids, sugars, organic acids, and other compounds that mimics the flavour of crab meat, the mixture was totally lacking in crab-like character ◦ Salt decreases the sweetness of sugars 22 11  11/13/2024 Sourness  Sourness is assumed to be a property of solutions of low pH, but H+ is much less important for taste than organic acids that occur in acidic foods ◦ Citric acid and malic acid: most fruit and fruit juices ◦ Tartaric acid: grapes ◦ Isocitric acid: blackberries ◦ Acetic acid: vinegar ◦ Lactic acid: pickles and yogurt 23 Astringency  Astringency (dry feeling) is registered within the oral cavity generally as well as on the tongue ◦ It is a ‘mouth-feel’ and it is regarded as sensation not taste ◦ It results from reactions of proteins in the saliva or tongue surface with the polyphenolic substances in foods ◦ It is usually regarded as a desirable characteristic of red wine and tea  In both these beverages, it is associated with the high content of tannins, which are also involved in color  Tannins are anti-nutritional since they bind Fe and Ca 24 12  11/13/2024 Astringency  When we drink black tea, we normally seek to moderate the astringency 1. Lemon juice is added  This lowers the pH and astringency 2. Milk is added  Milk proteins compete with the proteins of the mouth for the polyphenolics 25 Pungency  Pungency, ‘hotness’, is another sensation experienced by the entire oral cavity ◦ It is the essential characteristic of spices, ginger and red/green chillies  The active components are capsaicinoids (capsaicin and dihydrocapsaicin) 26 13  11/13/2024 Pungency  Another group of pungent components are glucosinolates found in cabbage, broccoli, mustards and radish ◦ Glucosinolates themselves are not pungent, but when the plant tissue is chopped, they bind to the enzyme myrosinase resulting in pungent isothiocyanates (or mustard oil) production  Glucosinolates have cancer fighting properties  When cabbage is cooked, myrosinase denatures; isothiocyanates are not formed ◦ Instead, sulfur compounds arise, which give characteristic unattractive odor 27 Cooling  It is a minor sensation associated with some products such toothpaste, mouthwash etc. ◦ The best known cooling substance is menthol  Dominant component of peppermint oil 28 14  11/13/2024 Meatiness or Umami  Described as a savory and delicious sensation that is associated with:  Inosine monophosphate, IMP  Monosodium glutamate, MSG  Alone, neither of these substances has a strong taste; but, when together, they show a remarkable synergism ◦ A mixture of equal proportions of IMP and MSG tastes some 20 times stronger than the same total amount of one alone ◦ The addition of a small amount of MSG to a food product that naturally contains modest amounts of IMP will have a dramatic effect on the flavour 29 Meatiness or Umami  Glutamic acid, as MSG, is naturally present at low levels in muscles, but in meat, it is derived mostly from protein breakdown that occurs during the ageing process (hence aged meat is more flavorful)  IMP is a breakdown product of the AMP, that accumulates as ATP is utilized in the muscle post- mortem  While IMP and MSG provide the basic umami of meat, the difference in flavour between different meats depends on variations in their proportions ◦ For example, the IMP contents of beef and pork are roughly similar, but beef has twice as much MSG 30 15  11/13/2024 Odor  While taste enables us to make some broad assessment of the nature of a potential foodstuff, it is the odor that fills in the detail ◦ Counting the number of different substances that we can detect is impossible ◦ It is also impossible to draw a line between food odors and smells that we encounter every day that have nothing to do with food ◦ The sensitivity of olfactory receptors to stimulus molecules is much greater than in taste 31 Meat  There are three major groups of compounds that contribute to the flavour of meat: 1. MSG and IMP 2. Dipeptides 3. Compounds derived from the Maillard reaction during cooking 4. Unsaturated fatty acid breakdown products during cooking 32 16  11/13/2024 Fruit  The flavour of fruit is a blend of taste and odor ◦ The taste, an aggregate of sweetness (sugars), sourness (organic acids) and sometimes astringency (polyphenolics) ◦ A solution of just sucrose and citric acid tastes ‘fruity’ to most people  However, to distinguish between different fruits, we rely on the distinctive odors of the fruits’ 200 volatile components  Citrus fruits: terpenoids  In many fruits: aldehydes and ketones 33 Vegetables  Many vegetables owe their flavour to the enzyme lipoxygenase ◦ During harvesting, if vegetables are physically damaged, the enzyme reacts with unsaturated fatty acids from the cell membranes to give off-flavours  Blanching, a short-heat treatment, inactivates lipoxygenase 34 17  11/13/2024 Onion and Garlic  Just as in cruciferous plants, the compounds that occur in the raw, undamaged onion and garlic are odorless  It is only when the garlic is crushed or the onion is sliced that the enzyme alliinase gains access to its substrates and the flavour becomes obvious  In onions, formation of thiopropionaldehyde S-oxide is the source of onion’s lachrymatory effects 35 Garlic and Health  Reductions in blood cholesterol levels when fresh garlic is consumed daily for 2-3 months  Allicin, a garlic sulfur compound, is a potent antibacterial, antithrombotic and anticancerogenic  ‘Odor free’ capsules of garlic oil popular as ‘alternative’ medicines 36 18  11/13/2024 Synthetic Flavorings  In recent years, a demand has built up in the food industry for flavorings outside the range of the traditional fruit flavours ◦ High demand for good-quality chocolate flavorings  Sulfides and pyrazines are implicated in the natural flavour of chocolate  A patented chocolate-flavoring formulation containing a representative pyrazine and sulfide is now available  A natural flavor is the essential oil which contains the flavoring constituents derived from a spice, fruit or fruit juice, vegetable or vegetable juice, herb, bark, root, leaf or similar plant material, meat, seafood, poultry, eggs, dairy products, or fermentation products thereof, whose significant function in food is flavoring rather than nutritional ◦ Artificial flavors are those that are made from components that do not meet this definition 37 19