Potato Maillard reactions

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). 

CIC the earthy odour of fresh potatoes is represented by 2-isopropyl-3-methoxy pyrazine. This earthy note is supported by the mushroom character of l-octen-3-ol. The key component of boiled potatoes is 3-(methylthio)-propanal, balanced with dimethyl sulphide. The high reaction temperatures in baked and fried potatoes start the Maillard reaction to form mainly heterocyclic components 2-ethyl-3,5-dimethyl pyrazine, 2-ethyl-6-vinyl pyrazine, 5-methyl-6,7-dihydro-(5H)cyclopenta-pyrazine, 2-acetyl-l,4,5,6-tetrahydro-pyridine are responsible for the roasted, nutty cracker-like flavour. The heat-induced degradation of the potato lipids and the frying oil imparts a fatty, tallowy character to the french fried potatoes. (E,E)-2,4-Decadienal, 2-octenal, octanoic acid and decanoic acid are main contributors to this fatty note. 

Cooking starch in the presence of amino acids may favour the occurrence of Maillard reactions, lowering the bioavailability of lysine in the diet. 13C CPMAS was used to follow the effect of Maillard reactions on the bioavailability of potato starch.124 A loss of crystallinity was found for the three samples studied starch, amylopectin, and amylose, being more marked for amylose. A similar study on chestnut starch indicated that Maillard reactions do not influence significantly its digestibility.125 NMR was used to characterize some Maillard reaction products extracted from model reactive mixtures such as starch-glucose-lysine 126 and lactose-lysine.127... 

Saccharomyces cerevisiae was cultivated with potato protein liquor (PPL) and glucose (starch hydrolysate) as substrate. Before the start of the cultivation PPL was sterilized at various temperatures between 80 and 120 °C for different periods between 5 s and 30 min [27]. The foaminess of PPL was very low before the sterilization. The foaminess increased with the temperature and time during sterilization and, at 120 °C and 30 min, 2 was enlarged by a factor of 2x10. This effect is due to the denaturation of proteins [4] and the formation of Maillard reactions between reducing sugars and amino adds [28]. 

Nearly all foods are made up of a complex mixture of components, including carbohydrates, amino acids, and proteins. When these foods are heated, the Maillard reaction occurs resulting in the formation of a large variety of volatile flavor compounds (1-3). The Maillard reaction is responsible for both desirable and undesirable aromas in foods. The aroma of bread, chocolate, coffee, and meat are all examples of desirable aromas resulting from the Maillard reaction. The aromas of burned food, canned products, stale milk powder, cereal, and dehydrated potatoes are typical examples of the undesirable aspects of this reaction. 

Additional minor volatile compounds are found in both frying oils and in fried foods, including cis,trans- and trans,trans-2,4-decaderived from oxidized linoleate and 2,4-heptadienal derived from linolenate. The isomers of 2,4-decadienal impart a desirable fried food flavor in fried potatoes when present in small amounts, but excessive amounts of this aldehyde would be expected to cause undesirable rancid flavors. Furfural compounds may be derived from interactions between food sugars and proteins. Minor amounts of sulfur compounds and nitrogen-containing heterocyclic compounds (methyl pyrazine and 2,5-dimethylpyrazine in potatoes) may originate from Maillard reactions (Chapter 11). 

Expansion is desirable for snacks and breakfast cereals, but the increased surface area formed by the numerous air cells favors oxidation. However, antioxidants derived from Maillard reaction products may help reduce oxidation rates. Oatmeal cookies containing potato peels showed lower peroxide values than control cookies, and extruded peels had greater antioxidant activity than did non-extruded peels (Arora and Camire, 1994). 

Removal of glucose during the production of egg powder using glucose oxidase (cf. 11.4.3) prevents the Maillard reaction responsible for discoloration of the product and deterioration of its whippability. Similar use of glucose oxidase for some meat and protein products would enhance the golden-yellow color rather than the brown color of potato chips or French fries which is obtained in the presence of excess glucose. 

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