Modern analyses and binding studies of flavour volatiles with particular reference to dairy protein products

Food structure: Its formation and relationships with other properties

Food materials are complex in nature as it has heterogeneous, amorphous, hygroscopic and porous properties. During processing, microstructure of food materials changes which significantly affects other properties of food. An appropriate understanding of the microstructure of the raw food material and its evolution during processing is critical in order to understand and accurately describe dehydration processes and quality anticipation. This review critically assesses the factors that influence the modification of microstructure in the course of drying of fruits and vegetables. The effect of simultaneous heat and mass transfer on microstructure in various drying methods is investigated. Effects of changes in microstructure on other functional properties of dried foods are discussed. After an extensive review of the literature, it is found that development of food structure significantly depends on fresh food properties and process parameters. Also, modification of microstructure influences the other properties of final product. An enhanced understanding of the relationships between food microstructure, drying process parameters and final product quality will facilitate the energy efficient optimum design of the food processor in order to achieve high-quality food.

Binding of carbonyl flavours to canola, pea and wheat proteins using GC/MS approach

Interactions of homologous aldehydes (hexanal, heptanal, and octanal) and ketones (2-hexanone, 2-heptanone, and 2-octanone) to salt and alkaline-extracted canola and pea proteins and commercial wheat gluten were studied using GC/MS. Long-chain aldehyde flavours exhibited higher binding affinity, regardless of protein type and isolation method. Salt-extracted canola protein isolates (CPIs) revealed the highest binding capacity to all aldehydes followed by wheat gluten and salt-extracted pea protein isolates (PPIs), while binding of ketone flavours decreased in the order: PPIs>wheat gluten>CPIs. Two aldolisation products, 2-butyl-2-octenal and 2-pentyl-2-nonenal, were detected from the interactions between CPIs with hexanal and heptanal, respectively. Protein thermal behaviour in the presence of these compounds was analysed by differential scanning calorimeter, where decreased ΔH inferred potential conformational changes due to partial denaturation of PPIs. Compared to ketones, aldehyde flavours possessed much higher "unfolding capacity" (lower ΔH), which accounted for their higher binding affinities.

Characterization of volatile compounds of Indian cress absolute by GC-olfactometry/VIDEO-sniff and comprehensive two-dimensional gas chromatography

Indian cress (Tropaeolum majus L.) has been consumed in salad or soup for decades, but its odor's detailed molecular composition is still unknown. Here we report on the study of the odorant profile and odor-impact compounds of Indian cress absolute by GC-olfactometry/vocabulary-intensity-duration of elementary odors by sniffing (GC-O/VIDEO-Sniff) on an eight-way multiport system, combined with GCxGC-MS analyses for the identification of odorant trace constituents. Odor impact compounds of Indian cress absolute were determined by GC-O, and the overall influence of sulfury and fruity notes stood out. Forty-four odorant compounds were identified among which 22 (50% of the identified odorant molecules) were identified by using comprehensive two-dimensional GC coupled to a time-of-flight-mass spectrometer (TOFMS). These trace compounds were not detected by 1D-qMS or could only be found with specific searches once they were detected by comprehensive 2D-GC, although they were well perceived by the judges in GC-O. This was amongst others the case for the two molecules having the highest odor impact, (E)-hex-2-enal (fruity) and diethyl trisulfide (alliaceous, sulfury, cabbage). A powerful sulfur-containing odor compound whose first identification in cress was recently reported by the authors was detected by GC-O: O,S-diethyl thiocarbonate (fruity/red fruit and sulfury odor).

Chemical causes of the typical burnt smell after accidental fires

The components responsible for the typical burnt smell that occurs after accidental fires (e.g. in buildings) were identified. For this purpose, samples of odorous materials were taken from different real fire sites. Their volatile fractions were analysed by means of thermal desorption, headspace analysis and solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC/MS). Measurements performed with SPME gave the highest number of analytes as well as the highest signal intensities. A divinylbenzene/carboxen/polydimethylsiloxane SPME fibre was found to be the most suitable for this task. To distinguish the odour-active compounds from the ca. 1,400 identified volatiles concentrated by SPME, an olfactory detection port was attached to the GC/MS and the column effluent was assessed by panellists. The results revealed that eleven odorous compounds were present in most of the investigated samples: acetophenone, benzyl alcohol, 4-ethyl-2-methoxyphenol, 2-hydroxybenzaldehyde, 2-hydroxy-5-methylbenzldehyde, 2-methoxyphenol, 2-methoxy-4-methylphenol, 2-methylphenol, 3-methylphenol, 4-methylphenol and naphthalene. Their odour activities were confirmed in additional olfactory experiments, and the relative ratios of these eleven compounds were determined. Based on these ratios, standard solutions that presented an intense odour with typical characteristics of the burnt smell were produced.

Contribution of mass spectrometry to assess quality of milk-based products

The vast knowledge of milk chemistry has been extensively used by the dairy manufacturing industry to develop and optimize the modern technology required to produce high-quality milk products to which we are accustomed. A thorough understanding of the chemistry of milk and its numerous components is essential for designing processing equipment and conditions needed for the manufacture and distribution of high-quality dairy products. Knowledge and application of milk chemistry is also indispensable for fractionating milk into its principal components for use as functional and nutritional ingredients by the food industry. For all these reasons, powerful analytical methods are required. Because of the complexity of the milk matrix, mass spectrometry, coupled or not to separation techniques, constitutes a key tool in this area. In the present manuscript, we review the contribution and potentialities of mass spectrometry-based techniques to assess quality of milk-based products.

Comparison of different extraction methods: steam distillation, simultaneous distillation and extraction and headspace co-distillation, used for the analysis of the volatile components in aged flue-cured tobacco leaves

Steam distillation (SD), simultaneous distillation and extraction (SDE) and headspace co-distillation (HCD) were compared here for their effectiveness in the extraction of volatile compounds from tobacco. The different grades of aged flue-cured tobacco leaves extracted by the three methods respectively were analyzed using GC-MS. Mass spectra or authentic compounds were used to identify around 408 components in various volatile fractions. On the one hand, the qualitative comparison showed that more compounds were detected in HCD extract (391 components) than in SDE extract (377 components), and the approximately quantitative analysis showed that the total amount of volatile components in SDE extract (445.48 microg/g) was much more than that in HCD extract (315.72 microg/g). But on the other hand, HCD was the most efficient for nearly all the highly volatile compounds among the three methods. As to low-volatile compounds such as lactones, long chain aldehydes, ketones, alcohols, and esters, more was detected in SDE extract than in HCD extract. The SD method (322 components, total amount 228.42 microg/g) was the lowest sensitive to all compounds except semi-volatile fatty acids among the three methods.

Headspace techniques in foods, fragrances and flavors: an overview

Headspace techniques have traditionally involved the collection of volatiles in the vapor state under either dynamic or static conditions as a means of determining concentrations in the product of interest. A brief overview of contemporary headspace applications and recent innovations are presented from the literature and Chapters in this book. New approaches used to concentrate volatiles under static conditions such as solid phase micro extraction, SPME, are examined. Advances in purge and trap applications and automation are also presented. Innovative methods of evaluating headspace volatiles using solid state sensor arrays (electronic noses) or mass spectrometers without prior separation are referenced. Numerous food and beverage headspace techniques are also reviewed. Advantages, limitations and alternatives to headspace analysis are presented.

Applications of solid-phase microextraction in food analysis

Food analysis is important for the evaluation of the nutritional value and quality of fresh and processed products, and for monitoring food additives and other toxic contaminants. Sample preparation, such as extraction, concentration and isolation of analytes, greatly influences the reliable and accurate analysis of food. Solid-phase microextraction (SPME) is a new sample preparation technique using a fused-silica fiber that is coated on the outside with an appropriate stationary phase. Analyte in the sample is directly extracted to the fiber coating. The SPME technique can be used routinely in combination with gas chromatography (GC), GC-mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC) or LC-MS. Furthermore, another SPME technique known as in-tube SPME has also been developed for combination with LC or LC-MS using an open tubular fused-silica capillary column as an SPME device instead of SPME fiber. These methods using SPME techniques save preparation time, solvent purchase and disposal costs, and can improve the detection limits. This review summarizes the SPME techniques for coupling with various analytical instruments and the applications of these techniques to food analysis.