Non-thermal processing of pineapple (Ananas comosus [L.] Merr.) juice using continuous pressure change technology (PCT): HS-SPME-GC-MS profiling, descriptive sensory analysis, and consumer acceptance.

The effects of single and twofold continuous pressure change technology (PCT) applications on the volatiles and sensory characteristics of pineapple juice were studied. Fresh and thermally pasteurised juices were additionally characterised. 128 volatiles were tentatively assigned in the four juices. Thermal pasteurisation and a single PCT treatment caused substantial losses in total volatiles of 6 and 20%, respectively. A second PCT passage further reduced the volatiles (36%) and is thus not recommended. PCT-treated samples were clearly distinguished from the remaining juices by principal component analysis. The descriptive sensory profiles, assessed by trained panellists, were not substantially affected by thermal pasteurisation and non-thermal PCT. The fresh juice exhibited a significant fishy off-flavour. In the consumer acceptance test, the thermally pasteurised juice was highly rated compared to both PCT-treated and the fresh juice. This study highlights the potential of PCT to avoid the genesis of off-flavours in fresh-like pineapple juice.

Sodium Chloride and Its Influence on the Aroma Profile of Yeasted Bread.

The impact of sodium chloride (NaCl) concentration on the yeast activity in bread dough and its influence on the aroma profile of the baked bread was investigated. Key aroma compounds in the bread samples were analysed by two-dimensional high-resolution gas chromatography-mass spectrometry in combination with solvent-assisted flavour evaporation distillation. High-sensitivity proton-transfer-reaction mass spectrometry was used to detect and quantify 2-phenylethanol in the headspace of the bread dough during fermentation. The analyses revealed significant (p < 0.05) changes in the aroma compounds 2-phenylethanol, (E)-2-nonenal, and 2,4-(E,E)-decadienal. Descriptive sensory analysis and discriminating triangle tests revealed that significant differences were only determinable in samples with different yeast levels but not samples with different NaCl concentrations. This indicates that a reduction in NaCl does not significantly influence the aroma profile of yeasted bread at levels above the odour thresholds of the relevant compounds, thus consumers in general cannot detect an altered odour profile of low­salt bread crumb.

Quantification of cyclic dipeptides from cultures of Lactobacillus brevis R2Δ by HRGC/MS using stable isotope dilution assay.

Lactic acid bacteria (LAB) play an important role as natural preservatives in fermented food and beverage systems, reducing the application of chemical additives. Thus, investigating their antifungal compounds, such as cyclic dipeptides, has gained prominence. Previous research has primarily focussed on isolation of these compounds. However, their precise quantification will provide further information regarding their antifungal performance in a complex system. To address this, deuterated labelled standards of the cyclic dipeptides cyclo(Leu-Pro), cyclo(Pro-Pro), cyclo(Met-Pro) and cyclo(Phe-Pro) were synthesized, and stable isotope dilution assays were developed, enabling an accurate quantification of cyclo(Leu-Pro), cyclo(Pro-Pro), cyclo(Met-Pro) and cyclo(Phe-Pro) in MRS-broth and wort. Quantitative results showed that, in the Lactobacillus brevis R2Δ fermented MRS-broth, the concentrations of cyclo(Leu-Pro), cyclo(Pro-Pro) and cyclo(Phe-Pro) were significantly higher (P < 0.05), than in wort for cyclo (Leu-Pro) when compared with their controls. This indicates that the formation of these three cyclic dipeptides is related to L. brevis R2Δ metabolism. Furthermore, this represents the first report of cyclic dipeptides quantification using stable isotope dilution assays in LAB cultures both in vitro and in a food system.

Influence of dextran-producing Weissella cibaria on baking properties and sensory profile of gluten-free and wheat breads.

Breads based on gluten-free buckwheat, quinoa, sorghum and teff flours were produced with addition of 20% sourdough fermented with exopolysaccharide (EPS) producing Weissella cibaria MG1. Wheat bread was baked as a reference. Dough rheology, bread quality parameters and sensory properties of the sourdough-containing breads were compared to sourdough non-containing control breads of the respective flour. The specific volume remained unaffected by sourdough application. In buckwheat, sorghum, teff and wheat sourdough breads acidification increased crumb porosity compared to control breads. Crumb hardness was significantly reduced in buckwheat (-122%), teff (-29%), quinoa (-21%) and wheat sourdough breads (-122%). The staling rate was significantly reduced in buckwheat, teff and wheat sourdough breads. Water activity of the sourdough containing bread crumb was not influenced by the presence of EPS. Due to the presence of exopolysaccharides (EPS) and influence of acidification, the dough strength, AF, as measured by oscillation tests decreased significantly in sourdough-containing buckwheat, sorghum and wheat dough, but increased in sourdough-containing quinoa and teff dough. Microbial shelf-life was significantly prolonged neither for gluten-free sourdough nor for wheat sourdough breads. Scanning electron microscopy of control and sourdough bread crumbs did not show differences concerning structural starch features. In addition, the aroma of most bread was not improved by sourdough addition.

The influence of molecular structure on odor qualities and odor detection thresholds of volatile alkylated phenols.

The relationship between chemical structure and odor characteristics of aroma compounds is interesting in terms of establishing a fundamental understanding and, in the long term, a perspective for the prediction of odor qualities and intensities of unknown compounds; on the other hand, such studies provide a useful tool to analytically elucidate compounds that are exceptionally potent odor contributors to a specific smell. In this respect, a broad knowledge of compounds with regard to their odor threshold and smell specificities compiled in a comprehensive odor library would drastically simplify the chemoanalytical process in identifying aromas and smells. Whereas numerous odor-active substance classes have been investigated intensively, such relationships and fundamental data have hitherto not been established for volatile phenols. In this study, a homologous series and isomers of 30 volatile phenols, including monoalkylated phenols and di- and trimethylphenols, were evaluated by determining their aroma attributes and their odor detection thresholds in air. The investigation demonstrates that the odor qualities, among them leather-like, horse stable-like, and medicinal, as well as the respective threshold values clearly depend on the arrangement of the alkyl substituents at the phenol ring. In particular, phenols with monoalkyl groups in the meta-position were found with very low odor detection thresholds of <1 ng/L air. A comparison of some selected phenols and their corresponding toluenes, which were found to be almost odorless, showed in addition that the phenolic hydroxyl group is obviously an important factor for the odor characteristic of this substance class.

Odor-active compounds in cardboard.

The odor-active compounds of cardboard were identified by aroma extract dilution analysis and HRGC-MS analysis. In total, 36 compounds were detected with medium to high intensities during HRGC-olfactometry. The highest odor intensities were evaluated for vanillin, (E)-non-2-enal, (R/S)-gamma-nonalactone, 2-methoxyphenol, (R/S)-delta-decalactone, p-anisaldehyde, 3-propylphenol, and a woody-smelling unknown compound. Most of the identified compounds were described as odor-active cardboard constituents for the first time. Sensory experiments demonstrated that extensive release of odor-active compounds occurred upon moistening of the cardboard. Accordingly, data indicated that the odorants are present in cardboard in relatively high amounts. In a further sensory study, a transfer of the released odor to food was demonstrated in a model experiment showing that cardboards with high odor potential can cause unwanted flavor changes in foods.

Quantification of phenyllactic acid in wheat sourdough using high resolution gas chromatography-mass spectrometry.

In this study, high-resolution gas chromatography-mass spectrometry (HRGC-MS) was successfully used to quantify the level of phenyllactic acid produced by Lactobacillus plantarum strains during sourdough fermentation. Investigation of samples collected during fermentation revealed that the production of phenyllactic acid occurs throughout the growth of L. plantarum in sourdough, but the highest production rate was observed during the logarithmic growth phase. The highest amount, that is, 33.47 mg of phenyllactic acid/kg of dough, was measured in sourdough fermented by the antifungal strain L. plantarum FST 1.7. Sourdoughs fermented by different L. plantarum strains contained different amounts of phenyllactic acid, thus indicating that the production is strain-dependent. Phenylacetic acid was also detected during sourdough analysis, thus showing that the HRGC-MS protocol developed is suitable for the detection not only of phenyllactic acid, but also of a broader range of phenolic acids that are highly relevant, but present in very low amounts in sourdough.

Changes in key odorants of raw coffee beans during storage under defined conditions.

During storage of raw coffee beans (green coffee) atypical odors may develop, which are suggested to influence the aroma of particularly the coffee beverage. To gain insight into the aroma compounds responsible for such odor changes, a comparative aroma extract dilution analysis was applied on unstored, raw Arabica coffee beans from Colombia (water content=11.75%) and on the same beans with a water content of 13.5%, which were stored for 9 months at 40 degrees C. In combination with the flavor dilution (FD) factors, the results of the identification experiments showed strong increases in (E)-beta-damascenone (cooked apple-like), 2-methoxy-4-vinylphenol (clove-like), and methyl 2-methyl- and methyl 3-methylbutanoate (fruity), whereas others, such as the earthy smelling 3-isopropyl-2-methoxypyrazine as well as 2-phenylethanol and 3-methoxyphenol, remained unchanged during storage. In addition, the previously unknown coffee odorant 2-methoxy-5-vinylphenol (intense smoky odor) increased significantly during storage. Quantitative measurements performed on raw coffee samples stored at various temperatures, water contents, and oxygen availabilities indicated that the significant increase of, in particular, the methyl esters of 2- and 3-methylbutanoic acid were responsible for the pronounced and fruity odor quality perceived in the stored green coffee, whereas the higher concentrations of 2-methoxy-4-vinylphenol and 2-methoxy-5-vinylphenol led to the more pronounced smoky, clove-like odor quality. On the basis of the results obtained, in particular the reduction of the water content in combination with lower temperatures can be suggested to avoid aroma changes in raw coffee beans caused by storage.

Important aroma compounds in freshly ground wholemeal and white wheat flour-identification and quantitative changes during sourdough fermentation.

An investigation on the odor-active compounds of wholemeal (WWF) and white wheat flour (WF 550) by aroma extract dilution analysis (AEDA) and by quantitative studies using stable isotope dilution assays (SIDA) revealed a significant number of odor-active compounds, such as (E)-2-nonenal, (E,Z)- and (E,E)-2,4-decadienal, (E)-4,5-epoxy-(E)-2-decenal, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, and vanillin, with high odor activities in both wheat flours. The amounts and, consequently, the aroma potencies of vanillin, (E,E)-2,4-decadienal, and 3-(methylthio)propanal were much higher in the WWF than in the WF 550 samples. Fermentation of suspensions of both flours with lactic acid bacteria did not generate new odorants; however, many compounds, such as acetic acid or 3-methylbutanal, were increased, whereas aldehydes (formed from the degradation of unsaturated fatty acids) were decreased. Comparing the odorant concentrations present before and after fermentation gave evidence that the main influence of the microorganisms on sourdough aroma is to either enhance or decrease specific volatiles already present in the flour. A comparison with literature data indicated that most of these odorants are also important for the bread crumb aroma present after baking of the dough.