[Changes in chemical composition of tomatoes during processing]

Reversed-phase ultra-high-performance liquid chromatography coupled to electrospray ionization-quadrupole-time-of-flight mass spectrometry as a powerful tool for metabolic profiling of vegetables: Lactuca sativa as an example of its application

Lettuce (Lactuca sativa), a leafy vegetal widely consumed worldwide, fresh cut or minimally processed, constitutes a major dietary source of natural antioxidants and bioactive compounds. In this study, reversed-phase ultra-high-performance liquid chromatography (RP-UHPLC) coupled to electrospray ionization-quadrupole-time-of-flight mass spectrometry (ESI-QTOF-MS) was applied for the comprehensive profiling of polar and semi-polar metabolites from three lettuce cultivars (baby, romaine, and iceberg). The UHPLC systems allowed the use of a small-particle-size C18 column (1.8 μm), with very fine resolution for the separation of up to seven isomers, and the QTOF mass analyzer enabled sensitive detection with high mass resolution and accuracy in full scan. Thus, a total of 171 compounds were tentatively identified by matching their accurate mass signals and suggested molecular formula with those previously reported in family Asteraceae. Afterwards, their structures were also corroborated by the MS/MS data provided by the QTOF analyzer. Well-known amino acids, organic acids, sesquiterpene lactones, phenolic acids and flavonoids were characterized, e.g. lactucin, lactucopicrin, caftaric acid, chlorogenic acid, caffeoylmalic acid, chicoric acid, isochlorogenic acid A, luteolin, and quercetin glycosides. For this plant species, this is the first available report of several isomeric forms of the latter polyphenols and other types of components such as nucleosides, peptides, and tryptophan-derived alkaloids. Remarkably, 10 novel structures formed by the conjugation of known amino acids and sesquiterpene lactones were also proposed. Thus, the methodology applied is a useful option to develop an exhaustive metabolic profiling of plants that helps to explain their potential biological activities and folk uses.

Quantitative studies and taste reconstitution experiments of the sour and lingering mouthful orosensation in a debittered extract of traditional Japanese dried and fermented skipjack tuna (hongarebushi)

Hongarebushi, Japanese dried skipjack tuna and a high quality ingredient of Japanese dashi, was investigated for its taste active composition. The recent investigation focused on a debittered fish fraction, which revealed a strong umami and salt impact accompanied with a pleasant and pronounced sourness. Whereas the umami and salt tastes could be correlated to monosodium glutamate (MSG), ribonucleotides, and mineral salts, the pleasant sourness was not exclusively induced by organic acids. The essential compound imparting the sour orosensation, persistence, and mouthfulness of the debittered skipjack tuna extract was investigated, and omission experiments emphasized the impact of N-acetylglutamic acid (NAG) on the overall taste sensation of the debittered fish extract. This metabolite, which is known to be present as a minor constituent in animal- and plant-derived foods, was quantified in this study for the first time in seafood, soybean products, dried shiitake mushrooms, and dried fish in notable amounts. Furthermore, it was described for the first time as an essential taste contributor to the nonvolatile profile of a foodstuff, in this case of a debittered extract of hongarebushi.

Taste modulating N-(1-methyl-4-oxoimidazolidin-2-ylidene) α-amino acids formed from creatinine and reducing carbohydrates

Recent investigations led to the discovery of N-(1-methyl-4-oxoimidazolidin-2-ylidene)aminopropionic acid as a taste modulator enhancing the typical thick-sour mouthdryness and mouthfulness imparted by stewed beef juice. In the present study, systematic model reactions were targeted toward the generation of a series of N-(1-methyl-4-oxoimidazolidin-2-ylidene)-α-amino acids by Maillard-type reactions between creatinine and ribose, glucose, methylglyoxal, or glyoxal, respectively. By application of a comparative taste dilution analysis on fractions isolated from thermally treated creatinine/carbohydrate mixtures by means of hydrophilic liquid interaction chromatography (HILIC), a total of nine N-(1-methyl-4-oxoimidazolidin-2-ylidene)-α-amino acids were identified by means of LC-MS, LC-TOF-MS, and 1D/2D NMR experiments. Six of the nine creatinine glycation products were previously not reported in the literature. Whereas creatinine exhibited a bitter taste, none of the N-(1-methyl-4-oxoimidazolidin-2-ylidene)-α-amino acids imparted any intrinsic taste activity up to levels of 10 mmol/L (in water). Depending strongly on their chemical structure, these N-(1-methyl-4-oxoimidazolidin-2-ylidene)-α-amino acids induced a thick-sour, mouthdrying orosensation and mouthfulness enhancement when evaluated in model broth with recognition thresholds ranging from 31 to >1000 μmol/L.

Tomato glycoalkaloids: role in the plant and in the diet

Tomatoes, a major food source for humans, accumulate a variety of secondary metabolites including phenolic compounds, phytoalexins, protease inhibitors, and glycoalkaloids. These metabolites protect against adverse effects of hosts of predators including fungi, bacteria, viruses, and insects. Because glycoalkaloids are reported to be involved in host-plant resistance, on the one hand, and to have a variety of pharmacological and nutritional properties in animals and humans, on the other, a need exists to develop a better understanding of the role of these compounds both in the plant and in the diet. To contribute to this effort, this integrated review presents data on the history, composition, and nutrition of tomatoes, with special focus on the assessment of the chemistry, analysis, composition, nutrition, microbiology, and pharmacology of the tomato glycoalkaloids comprising alpha-tomatine and dehydrotomatine; their content in different parts of the tomato plant, in processed tomato products, and in wild and transgenic tomatoes; their biosynthesis, inheritance, metabolism, and catabolism; plant-microbe relationships with fungi, bacteria, viruses, insects, and worms; interactions with ergosterol and cholesterol; disruption of cell membranes; tomatine-induced tomatinases, pantothenate synthetase, steroid hydroxylases, and cytokines; and inhibition of acetylcholinesterase. Also covered are tomato-human pathogen relationships and tomatine-induced lowering of plasma cholesterol and triglycerides and enhancement of the immune system. Further research needs in each of these areas are suggested. The overlapping aspects are discussed in terms of general concepts for a better understanding of the impact of tomato glycoalkaloids in the plant in general and in food in particular. Such an understanding can lead to the creation of improved tomatoes and to improved practices on the farm and in the consumption of tomatoes.

Formation of volatile compounds during heating of spice paprika (Capsicum annuum) powder

Spice paprika (red pepper; Capsicum annuum) is the most cultivated spice worldwide and is used mainly for its color and pungency. However, current research is also focusing on the flavor as an important parameter. This paper deals with the kinetics of the formation of those volatiles that indicate a decrease in spice paprika quality due to Maillard reaction, hydrolytic reactions, and oxidative degradation reactions of lipids such as fatty acids and carotenoids. Spice paprika volatiles were quantitatively analyzed by means of headspace gas chromatography (HS-GC) and solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS). The kinetics of their formation were investigated, and the respective activation energies determined. Strecker aldehyde, acetone, and methanol formation followed a pseudo-zero-order reaction kinetic, and formation of dimethyl sulfide (DMS) was characterized by a first-order kinetic. The activation energies determined were between 86.3 and 101.8 for the Strecker aldehydes acetaldehyde (AA), 2-methylpropanal (2-MP), 3-methylbutanal (3-MB), and 2-methylbutanal (2-MB), 130.7 for acetone, 114.2 for methanol, and 109.7 kJ/mol for DMS. The amounts of Strecker aldehydes formed were correlated to the concentrations of the corresponding free amino acids present in the samples. The formation of hexanal and 6-methyl-5-hepten-2-one in Capsicum annuum during processing was confirmed, and the formation of beta-ionone was probably described for the first time. During heating, the concentration of hexanal increased rapidly. The formation of 6-methyl-5-hepten-2-one confirms that Capsicum annuum fruits contain lycopene.

Enantioselective multidimensional gas chromatography-mass spectrometry in the analysis of urinary organic acids

Enantioselective multidimensional gas chromatography-mass spectrometry is a valuable tool for the enantioselective analysis of compounds from complex matrices. Samples are separated initially on a precolumn and selected substances then transferred on-line to a main-column coated with suitable chiral stationary phase for enantioselective analysis with subsequent mass selective detection. In this paper the method is used as an adjunct to urinary organic acid analysis to provide information in patients with suspected inborn errors of metabolism. Lactic acid, alpha-hydroxyisocaproic acid, 3-phenyllactic acid and 3-(4-hydroxyphenyl)-lactic acid are separated in a single run. In addition, the enantioselective analysis of pyroglutamic acid is presented. D-Enantiomers of amino acids and alpha-hydroxycarboxylic acids derived from amino acids, point to a bacterial origin whereas the L-enantiomer is predominantly of endogenous origin. Therefore the enantiomeric ratio of chiral metabolites is an important parameter for the understanding of metabolic processes.