A. J. Taylor

Atmospheric pressure chemical ionisation mass spectrometry for in vivo analysis of volatile flavour release

Abstract To follow volatile flavour release in the expired air of people during eating, several physiological and analytical constraints must be observed to obtain good quality data. An interface has been developed to sample air from the nose and ionise the volatile compounds contained therein by atmospheric pressure chemical ionisation. The ions formed are detected in a quadrupole mass spectrometer. The interface design overcomes many of the constraints and allows volatile detection in the 100–10 ppbv range, depending on the nature of the volatile compound to be analysed. The principles and operating parameters of the interface are described. Control of the ionisation process is effected through the operating conditions within the interface. Since many compounds are introduced simultaneously into the interface, it is preferable to minimise fragmentation otherwise the spectra are extremely complex and it is difficult to assign ions to compounds unequivocally, with the result that quantification is imprecise. The ionisation parameters are set to favour formation of the protonated molecular (MH + ) ion from the compounds and minimise formation of cluster ions, which can also confuse the spectra. The sensitivity and linearity of the technique is demonstrated for a range of flavour volatiles with a dynamic range of three orders of magnitude. The lower limit of sensitivity is determined by the signal to noise ratio whereas the upper limit occurs when all the available charge is exhausted. The technique was designed primarily to monitor real-time changes in the concentration of known volatiles during eating and has limited identification power. However, for reliable quantification, it is necessary to assign the ions monitored in-nose with the volatile compounds present in the food. Besides assignments made on nominal mass, isotopic ratio analysis and accurate mass measurements have also been used to determine the contribution of certain compounds to a particular ion intensity.

A review of the methodology of the 2-thiobarbituric acid test

Abstract The 2-thiobarbituric acid (TBA) test for the measurement of lipid oxidation was discovered over 40 years ago. Since then it has been widely used for the measurement of the oxidative state of biological and food materials. Despite copious literature references and its widespread usage there are still uncertainties over the exact chemistry of the reaction and its applicability. This review attempts to draw together the relevant publications and discuss the merits of the TBA test, particularly in the analysis of foods.

The potential of bambara groundnut (Vigna subterranea) in vegetable milk production and basic protein functionality systems

Abstract Bambara groundnut is an underutilized African legume which provides security for many farmers as it shows considerable drought resistance. The possibility of producing a vegetable milk for local use or an extracted protein with functional properties for use in food processing applications was studied. Milks were made by soaking bambara groundnut overnight, homogenizing and removing insoluble material to give a milky liquid. The beany taste could be removed by dry-frying the beans after soaking but before homogenization. Milks produced in this way were preferred by the taste panel (composed largely of Africans). A comparison of bambara groundnut milk and milks prepared from cowpea, pigeonpea and soybean was made using sensory and instrumental analysis. Sensory analysis showed all milks were acceptable with bambara groundnut ranked first in the preference trial. The lighter colour of bambara groundnut milk was more acceptable to the taste panel but there was no correlation between viscosity measured on a viscometer and viscosity perceived by the taste panel. A crude protein isolate (76% protein) from bambara groundnut was subjected to standard protein functionality tests but it was inferior to the standard used (egg albumen and soy isolate). It did not show any useful properties in emulsification, foam stabilization, or gelation or in a model cake system.

Simultaneous instrumental and sensory analysis of volatile release from gelatine and pectin/gelatine gels

Abstract Release of volatiles from gels during eating was measured by monitoring the volatile composition of breath, using on-line atmospheric pressure chemical ionisation–mass spectroscopy (APCI–MS), and by simultaneous sensory time–intensity (TI) evaluation. The time–release (TR) and TI curves were very similar, suggesting a simple relationship between changes in volatile concentration over the eating time course and the intensity of volatile perception. Analysis of the T max values (time to maximum intensity) showed that the ratio between the T max for the sensory and instrumental data (sensory T max /instrumental T max ) varied with the instrumental T max , such that at low T max values the ratio was >1.0 and, as T max increased, the ratio decreased to below 1.0. This trend suggested that with short eating events there may be a lag in perception after the maximum breath stimulus concentration. Conversely if the eating process took longer, sensory adaptation might occur. ©

Variations in cyanogen content of cassava during village processing in Cameroon

Abstract A study of the traditional processing of two cassava foods, ‘farine de manioc’ and ‘baton de manioc’, was undertaken in Cameroon. The influences of various stages of the processes on the amounts of the different cyanogenic components (cyanogenic glucosides, cyanohydrins and hydrogen cyanide) were studied. The traditional water fermentation, followed by pressing and sun-drying or boiling, reduced the amount of total cyanogens in fresh roots (91–1515 mg kg −1 ) to more acceptable levels (0.0–11.3 mg kg −1 ) in foods ready for consumption. Fermentation temperature and the extent of root comminution increased the rates of glucoside hydrolysis giving a temporary increase in the levels of the intermediate product, cyanohydrin. Despite the low pH in the fermentations, hydrolysis of cyanohydrins to hydrogen cyanide was still in evidence in the later stages of fermentation, the latter compound being removed during pressing, sun-drying and cooking.

In vivo measurement of flavour release from mixed phase gels

Flavour release was investigated from pure gelatin, pure agarose and mixed gelatin-agarose gels, all containing 25% sucrose and flavoured with p-cymene, ethyl butyrate, pyrazine and ethanol. Gels were characterised by optical microscopy, and rheological techniques to determine phase separation, elastic modulus and melting temperature. Volatile release was measured by monitoring the four volatiles in the expired air from one individual eating the gels, using Atmospheric Pressure Chemical Ionisation-Mass Spectrometry. The release pattern of p-cymene was not affected by gel type. The release of ethanol, ethyl butyrate and pyrazine was affected to different extents by the matrix suggesting that both the properties of the volatile and the matrix determine volatile release in vivo.

Potential of oxidised phenolics as food colourants

Abstract A range of phenolic compounds was oxidized using the enzyme polyphenoloxidase (E.C. 1.14.18.1). Mixtures of phenolics and mixtures of phenolics with amino acids and peptides were also oxidised. The oxidised products exhibited red, yellow, blue, green and orange colours but many of them turned to brown or black as further reactions occurred. The colours were measured in terms of Hunter l ,a,b coordinates and the stability of the colours to heat, pH and sulphur dioxide was measured. The majority of colours had insufficient stability or tinctorial power to be considered for use as food colourants. The exceptions were the orange products formed on oxidation of catechin and the yellow products from dihydroquercetin.

Extraction and ESI–CID–MS/MS analysis of myoglobins from different meat species

Abstract Meat speciation methods for raw meats are available but are not always effective in cooked products. The globin protein from myoglobin is heat stable, shows different molecular weights for each species and electrospray mass spectrometry (ESI–MS) can partially differentiate some species. To improve the analysis, the heat stable globin protein was extracted and subjected to fragmentation by ESI–CID–MS/MS. The [M+16H] 16+ and [M+17H] 17+ ions were chosen as precursor ions and fragmented by collision-induced dissociation (CID). Fragmentation occurred at proline residues with cleavage either side of the peptide bond leading to the typical pattern of peptide ions. The patterns were dominated by a series of y ″ n fragments of which the fragments from cleavage of the His/Pro residues at 119/120 ( y ″ 34 and y ″ 35 ) were relatively intense. A strategy for differentiating the four species by ESI–MS and ESI–CID–MS/MS is discussed.

Understanding flavour release: the key to better food flavour?

The flavour of food is one of the key factors determining food quality and acceptance. When food is eaten, flavour compounds are released at different rates, depending on the physical properties of the molecules themselves and on the physical and chemical properties of the food matrix. When foods are reformulated to meet dietary goals (e.g. low sugar or fat, high fibre) there is a change in flavour release properties which adversely affects the perceived flavour. Flavour analysis has generally ignored the temporal aspects of flavour release but this parameter may help explain subtle differences in flavour perception. Methods for measuring sensory changes with time (time intensity analysis) are well established but methods for measuring the flavour volatiles delivered to the olfactory receptors have recently developed to the stage where detection at the ug/kg (ppb) level is achievable. Results from these measurements have been used to study flavour release from a range of foods. One application of this technique is to determine the differences in flavour release between regular and low‐fat foods. The information obtained can be used to reformulate flavours in a systematic manner to improve the flavour of low‐fat products.

Flavour volatile compound analysis in strawberry (Fragaria x ananassa Duch.) fruits: comparison of two mass spectrometer techniques for identifying volatile compounds

Strawberry fruits (Fragaria x ananassa Duch.) cv. Elsanta were harvested at the ideal stage of maturity and their volatile compound profile was analysed using both Atmospheric Pressure Chemical Ionisation–Mass Spectrometry (APCI–MS) and Gas Chromatograph–Mass Spectrometry (GC–MS). The APCI–MS was run simultaneously with GC–MS so that after identification of the most abundant compounds by APCI–MS, GC–MS could separate the ions and compare them with a Masslynx library to enable their identification. There was good agreement on the compound identity using the two techniques for nine out of fourteen selected volatile compounds. However the GC–MS gave a different identity to five of the selected compounds. The APCI–MS offers a rapid method of compound analysis while the GC–MS is slow but can differentiate between stereo-isomers.