LOW ODOUR

Nylon film has been used increasingly for packaging applications for foodstuffs and pharmaceutical products. The value of nylon in this application is due to low odour transmission and to some extent in the ability to boil-in-the-bag. Film of high brilliance and clarity, particularly from nylon 11, is available for point-of-sale displays. 

Some materials possess low odour thresholds their smell gives warning of impending danger. Others possess odour thresholds well in excess of the hygiene standard. Examples are included in Table 5.12. 

Some materials with low odour duesholds may paralyse die olfactory nerves and cause the sense of smell to be lost within minutes (e.g. hydrogen sulphide). 

Distilled bergimot oil, oblaiued by distilling the residues from the expression proerss, is of very low odour value, liaving a specific gravity as low as 0 865 aud an ester content which may fall as low as b per cent. 

Combined with the above requirements, the product should control/eliminate scale formation, contain surfactants to clean the system and be low-foaming. Toilet sanitisers are required to control odour whilst being of relatively low odour themselves. Although rapid bacteria kill is essential, the discharged product must be treatable in a domestic sewage system without interfering with its efficiency. 

Geosmin, 2-Methyl isobomeol (MIB) and 2-isopropyl methoxy pyrazine are known to be produced by various types of actinomycete cultures (10-15). Geosmin and MIB are saturated tertiary alcohols and resist oxidation. The steric configuration of the hydroxyl and methyl groups in both compounds are believed to interact with receptors in the nose, imparting their characteristic earthy odour (16). The four compounds itemised as the key osmogenes in this odorous emission have extremely low odour threshold concentrations. Their occasional occurence in drinking water can lead to widespread complaints and are routinely monitored for within this Authority. 

The most difficult problem in flavour research is to interpret the results of the volatile analysis, which gives information on the identity and the quantity of the volatile compounds collected from a given product. Many volatile compounds are not flavour-active, i.e. they cannot be detected in the olfactory system, while others may even in trace amounts have significant effects on flavour owing to their low odour-threshold values that is defined as the minimum concentration needed to produce an olfactory response. Consequently, the most abundant volatiles are not necessarily the most important contributors to flavour. Much... 

Ethyl 2-methylbutanoate, 2-methylbutyl acetate and hexyl acetate contribute most to the characteristic aroma of Fuji apples [49]. In Red Delicious apples, ethyl butanoate, ethyl 2-methylbutanoate, propyl 2-methylbutanoate and hexyl acetate contribute to the characteristic aroma as determined by Charm-Analysis and/or AEDA [50, 51]. In a comparative study of 40 apple cultivars, the highest odour potency or Charm value was found for -damascenone [52]. This compound usually occurs in a glycosidically bound form and is present primarily in processed products owing to hydrolysis of the glycoside bond after crushing fruit cells [53]. -Damascenone has a very low odour threshold with a sweet, fruity, perfumery odour and is not typical of apple aroma in gen-... 

Table 10.2 presents a summary of odour qualities, odour thresholds in water, and concentrations of some selected volatile compounds, which are characteristic flavour impact compounds, owing to their typical flavour quality and their rather low odour thresholds. These compounds are not formed during fermentation but originate from the raw material and contribute significantly to the typical flavour of a fruit. The components summarised in Table 10.2 are important compounds in wine and different fruits and are discussed later. 

A number of furans with thiol, sulphide or disulphide substitution have been reported as aroma volatiles, and these are particularly important in meat and coffee. In the early 1970s, it was shown that furans and thiophenes with a thiol group in the 3-position possess strong meat-like aromas and exceptionally low odour threshold values [50] however, it was over 15 years before such compounds were reported in meat itself In 1986,2-methyl-3-(methylthio)furan was identified in cooked beef and it was reported to have a low odour threshold value (0.05 pg/kg) and a meaty aroma at levels below 1 pg/kg [51]. Gasser and Grosch [52] identified 2-methyl-3-furanthiol and the corresponding disulphide, bis(2-methyl-3-furanyl) disulphide, as major contributors to the meaty aroma of cooked beef. The odour threshold value of this disulphide has been reported as 0.02 ng/kg, one of the lowest known threshold values [53]. Other thiols which may contribute to meaty aromas include mercaptoketones, such as 2-mercapto-pentan-3-one. 2-Furylmethanethiol (2-furfurylmercaptan) has also been found in meat, but is more likely to contribute to roasted rather than meaty aromas. Disulphides have also been found, either as symmetrical disulphides derived from two molecules of the same thiol or as mixed disulphides from two different thiols [54]. 

The chemical is used both in flavours and fragrances, but owing to its very strong smell and low odour threshold value the volume is limited. 

Low odour monomer with good film properties. 

A low odour monomer with good cure response and adhesion characteristics. 

Low-odour inks for food packaging are based on odour and taint-free substances, for example, aromatic free solvents and maleic resins. So called semi-drying oils are also used. These are slow to oxidise and therefore do not develop malodorous aldehydes as they dry. However, some smell may be noticed after a long period of time as oxidation proceeds. Other solvents, such as tung oil, develop quite some odour during drying but if properly... 

Self-emulslfiable. Low odour, low volatility carrier for the dyeing of polyester and its blends at atmospheric boil and also at elevated temperatures. Promotes migration and has excellent levelling properties. 

Possibility of manufacturing low-odouring and non-toxic coatings due to the substantial absence of volatility of the polymeric systems as well as the reduced release of photofragments, most of which remain linked to the polymer matrix. 

Oligomeric benzil ketals (DTGPA), prepared by reaction of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) with triethyleneglycol, in the presence of p-toluen-sulphonic acid, are reported [88] to be efficient in the UV curing of styrene/ unsaturated polyester formulations giving rise to coatings with very low odour. 

A novel class of low-odouring and non-yellowing polymeric photoinitiators, based on side-chain hydroxyalkylphenone moieties, is reported [89-91] to be very active for UV curable clear acrylic coatings. Due to low volatility and affinity for the organic phase, these photoinitiators are also claimed to be very effective in the curing of water-based acrylic emulsions in which water must be evaporated before the exposure to UV light. These commercial polymeric systems (KIP) are prepared by functionalization of a-methylstyrene prepolymers. 

KIP, by contrast, due to the formation of a polymer-anchored benzoyl radical (Scheme 22), caimot release benzaldehyde after photocleavage, thus allowing production of non-yellowing and low-odour coatings [89,91], especially required in the field of food packaging. 

Finally, although KIP is found to be as active as HIPK in film matrix [89,91], its better compatibility and low-odour properties make the polymeric system superior. 

Initiator or chain transfer agent Many available, including low odour Unusual, complicated system Novel thioesters strong colour and odour... 

Water-dispersible Low viscosity low odour non-flammable easy to clean good adhesion, especially to damp concrete good abrasion resistance Primarily concrete coatings, e.g. food factories, showrooms, laboratories, hospitals, nuclear power stations, breweries, etc. adhesives... 

Methacrylates used in the construction industry are low-viscosity, low-odour, high-flash-point liquids which can be chemically converted into tough, solid polymers by the addition of a catalyst (Figure 5.2). 

High molecular weight methacrylate monomers provide advanced technology for polymer concretes and crack sealers. These systems have the advantage of, for example, low odour, low-level toxicity and low shrinkage. 

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