Flavour release from dried vegetables

The research described in this thesis was focused on the development of an in vitro model system for isolation of volatile compounds from dried vegetables under mouth conditions, such as volume of the mouth, temperature, salivation and mastication. Instrumental analysis of these volatile compounds by gas chromatography (GC), combined with mass spectrometry, flame ionisation detection (FID) and sniffing port detection (SP) was correlated with descriptive sensory analysis. Dried vegetables were subjected to these techniques in order to study three aspects. (1) Factors influencing flavour release from dried vegetables under mouth conditions. (2) Suitability of three types of the model system for simulation of flavour release in the mouth. (3) Characterisation of the flavours of rehydrated vegetables, as influenced by cultivar, origin, storage and rehydration conditions.Flavour perception, physical aspects of flavour release, flavour analysis and factors affecting the flavour of dried vegetables, including literature concerned were discussed briefly in Chapter 1 . The thesis was outlined at the end of this chapter.Three types of the mouth model system were introduced in Chapter 2 and compared for flavour release from rehydrated bell peppers. Release was largest in the 'purge-and-trap1system, followed by the 'dynamic headspace and mastication, (DHM) and dynamic headspace' system, respectively.Flavour release influenced by the composition of artificial saliva was studied for bell peppers in Chapter 3 and for French beans in Chapter 4 . Influence of saliva volume on the flavour release from French beans was studied in Chapter 4 as well. Saliva component mucin mainly decreased flavour release in both vegetables, because of flavour~ protein interactions, a similar effect showed α-amylase in bell peppers. Release in French beans was generally increased by α-amylase, probably due to degradation of inclusion complexes of starch. Decrease in flavour release from French beans by saliva volume was evaluated in a model study. GC/SP patterns of odour active compounds were hardly influenced by both saliva composition and volume.Chapter 5 revealed that flavour release from rehydrated French beans, red bell peppers and leeks in the DHM model system did not differ significantly from their release in the mouth of 12 assessors. These assessors released volatile compounds with different efficiencies, but they showed a statistically consistent efficiency in flavour release across the vegetables.The flavours of the three rehydrated vegetables mentioned above were characterised by GC/SP of volatile compounds released in the DHM model system and by descriptive sensory analysis (Chapter 6). A common odour profile was shown in the vegetables, comprising each of the odour active compounds present in French beans. correlation of rehydrated vegetables with sensory attributes and volatile compounds showed considerable contribution of volatile compounds to the flavour of rehydrated vegetables.The flavours of commercially dried bell peppers (origins Chile, Hungary and Turkey) were evaluated by GC/SP and descriptive and hedonic panels ( Chapter 7 ). Although the three origins differed substantially in FID patterns, GC/SP patterns and scores for 'odour' attributes in sensory analysis were hardly different. Differences in appreciation between Chilean and Turkish bell peppers are therefore expected to be due to differences in 'taste' attributes (sour, bitter, sharp and pungent).The influence of storage conditions (water activity (aw), temperature and light) on the flavour of dried French beans was studied in Chapter 8 . Elevated temperature at aw 0.3 and 0.5 resulted in an increase in the number of assessors perceiving chemical, rotten odours in GC/SP and in an increase in scores for 'chemical', 'burned', 'musty' and ,bitter, attributes in sensory analysis. Light exposure at aw 0.1 resulted in an increase in the number of assessors perceiving chemical odours at the sniffing port and in increased scores for 'chemical, and 'burned' attributes in sensory analysis. French beans stored at 200C were more appreciated by the hedonic panel than those stored at 400C (absence of light, aw 0.3). Relationships between differently stored French beans, sensory attributes and volatile compounds indicated the latter compounds to be responsible for the difference in flavour and appreciation of dried French beans by storage conditions.The flavour of French beans influenced by rehydration conditions was described in Chapter 9 . Extended rehydration resulted in GC/SP in increased intensity for 2-butenal, 2methyl -2 -butenal, 1-octen-3-one and one unknown compound and in increased intensities for chemical,, 'mealy', ,mushroom, and musty, attributes in sensory analysis. Both instrumental and sensory analysis of the texture revealed a gradual decrease with extended rehydration. Relationships between sensory attributes and volatile compounds showed major contribution of volatile compounds to the difference in flavour of French beans resulting from rehydration conditions.It can be concluded ( Chapter 10 ) that flavour release from rehydrated vegetables was influenced by both saliva composition and volume. Mouth model system DHM simulated flavour release in the mouth quite well. The flavours of dried vegetables were shown to be influenced by cultivar, origin, storage and rehydration conditions.