Aldehyde sensory property

As mentioned before, the sensory properties of the various heterocyclic compounds discussed in this contribution are one of the important factors determining food quality. The data on sensory characteristics of the various numerous compounds formed through the reaction of aldehydes with ammonia or ammonium sulfide, in the presence or in the absence of acetoin, are scattered in the literature (57) and thus are not easy to find. At the same time, information on sensory characteristics of compounds of this type is of primary importance to food chemists. Sultan (29) has compiled much of this information which is presented here in Table IV where also the appropriate references to the original literature are given. 

The aroma volatiles of some melon species consist of a complex mixture of esters together with other components, including C9 unsaturated aldehydes, alcohols, and acetates whose sensory properties have been described as melonlike [10,31-33,35]. Several esters and alcohols were described among the volatiles of muskmelons [33, 34]. 

Lipoxygenases play an important role in determining oil quality. The aromas typical of olive oil are due to complex mixtures of volatile compounds those especially abundant are saturated and unsaturated six carbon atom aldehydes, alcohols, and the esters of alcohols, the cited aldehydes and alcohols having sensory properties responsible for the so-called green odour (Hatanaka, 1996). 

As a result of acid-catalysed reactions during steam distillation, a number of terpenes and sesquiterpenes [66] of the native cold-pressed oils undergo transformation /9, 67-69]. This applies mainly to the pinenes, sabinene, thujene and some sesquiterpenes. While cold-pressed lime oils contain up to 2.3% of the reactive germacrenes, only traces of germacrene B can be found in distilled oils ]70]. When compared to their educts, the newly formed constiments, mainly alcohols, such as a-terpineol or fenchyl alcohol, possess completely different sensory properties. Additionally, cyclisations and hydratisations of aldehydes result in a reduced presence of these constituents in distilled products. Many compounds which characterise the flavour of distilled lime are formed during production. The extremely different composition of cold-pressed and distilled oils accounts for their completely different flavour profile and they, therefore, have to be considered as a reaction flavouring. 

Some aldehydes are the same (see Fig. 5.13), but a significant number reacts chemically with amino groups in the protein molecules (Fig. 5.16) [1,6,11,16,33,46]. This binding is irreversible due to subsequent reactions, and the part of the aldehyde which has reacted chemically is lost as far as sensory properties are concerned. In this way, for instance, hexanal reacts easily with amino groups of the arginine residues in soy protein and in casein ]11]. 

Sensory Properties. This mixture showed a very strong onion and leek-like aroma. All components can be sensorially characterized by GC-0. The sensory characteristics of the 1,3,5-dithiazines from isobutanal and ethanal used as starting aldehydes have already been reported earlier 17). 

ES-Safi N. Cheynler V. Moutounet, M. Role of aldehydic derivatives in the condensation of phenolic compounds with emphasis on the sensorial properties of fruit-derived foods. J. Agric. Food Chem. 2002, 50, 5571-5585. 

During lipid oxidation, the primary oxidation products that are formed by the autoxidation of unsaturated lipids are hydroperoxides, which have little or no direct impact on the sensory properties of foods. However, hydroperoxides are degraded to produce additional radicals which further accelerates the oxidation process and produce secondary oxidation products such as aldehydes, ketones, acids and alcohols, of which some are volatiles with very low sensory thresholds and have potentially significant impact on the sensory properties namely odor and flavor [2, 3]. Sensory analysis of food samples are performed by a panel of semi to highly trained personnel under specific quarantined conditions. Any chemical method used to determine lipid oxidation in food must be closely correlated with a sensory panel because the human nose is the most appropriate detector to monitor the odorants resulting from oxidative and non-oxidative degradation processes. The results obtained from sensory analyses provide the closest approximation to the consumers approach. Sensory analyses of smell and taste has been developed in many studies of edible fats and oils and for fatty food quality estimation [1, 4, 5]. 

Characterization of essential oils must include three kinds of analysis sensory analysis determination of physicochemical properties such as specific gravity (20°C), refractive index, optical rotation, aldehyde and carotenoid contents and solubility spectroscopic properties (UV and IR) and chromatographic analysis. In Table 5.10, the main analytical determinations that can be carried out in the quality control of essential oils are summarized. The ranges of values for each analytical parameter of essential oils from oranges are also shown. 

A careful organoleptic evaluation of the a,p-unsaturated aldehyde (17) which was detected in various food products such as carrot root oil (72), tomato (74), beef (342) and cranberry (17) has shown that this aldehyde has some remarkable flavor properties. Above the threshold concentration of about 0.1 ppb (72), for example at 0.4 to 2 ppb in water, ( )-2-nonenal (17) possesses a woody character (470). Above 8 ppb the sensory impression turns into a fatty one which becomes unpleasant above 30 ppb. Finally, an aqueous solution of 1,000 ppb of aldehyde (17) has a strong taste of cucumber. The fresh-brew woody note of roasted and ground coffee as well as the woody effect in bell peppers is due to the presence of this compound (470). Addition of (jE)-2-nonenal (17) to cranberry juice at a level of 1 ppb causes a considerable reduction in the normal astringent character of the juice (470) without any change of the original odor impression. An antagonistic effect of (17) is observed on the flavor of (Z)-3-hexenal (5) (375). Above 2 flavor units (E) 2 nonenal (17) causes the stale flavor of spoiled beers (381). 

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