Food Aroma Compounds Research Articles

Role of Microbial Fermentation in the Bio-Production of Food Aroma Compounds from Vegetable Waste

Flavour is a key driver of consumer preferences and acceptability of foods, and the food industry has made food aroma compounds a crucial area of research. At present, about 80% of food aroma compounds are produced by chemical synthesis; however, alternative production approaches have been explored to meet consumers’ demand for “clean label” food products and “natural” aromas. Bio-production of food aroma compounds from vegetable wastes through fermentation has emerged as a promising alternative. This review showed that fungi and yeasts, and also lactic acid bacteria, can be used to produce aroma compounds through the fermentation of vegetable waste. The produced compounds were mostly responsible for sweet, fruity, and floral notes. Other molecules imparting cheesy/buttery, creamy, green, herbal, grass notes were also obtained through the fermentation of vegetable food waste. Substrates varied from agricultural waste such as rice bran to by-products and waste from the fruit supply chain, in particular pomace, peels, pods. During the study, challenges and limitations for the scale-up of the process emerged. The production of aromas is still strongly strain and waste dependent. Certain aspects thus still require attention to avoid that a joint occurrence of technical challenges may cause the failure of the process.

3-Alkyl-2-methoxypyrazines: Overview of Their Occurrence, Biosynthesis and Distribution in Edible Plants.

Pyrazines are ubiquitous in nature - biosynthesized by microorganisms, insects, and plants. Due to their great structural diversity, they own manifold biological functions. Alkyl- and alkoxypyrazines for instance play a key role as semiochemicals, but also as important aroma compounds in foods. Especially 3-alkyl-2-methoxypyrazines(MPs) have been of great research interest. MPs are associated with green and earthy attributes. They are responsible for the distinctive aroma properties of numerous vegetables. Moreover, they have a strong influence on the aroma of wines, in which they are primarily grape-derived. Over the years various methods have been developed and implemented to analyse the distribution of MPs in plants. In addition, the biosynthetic pathway of MPs has always been of particular interest. Different pathways and precursors have been proposed and controversially discussed in the literature. While the identification of genes encoding O-methyltransferases gave important insights into the last step of MP-biosynthesis, earlier biosynthetic steps and precursors remained unknown. It was not until 2022 that in vivo feeding experiments with stable isotope labeled compounds revealed L-leucine and L-serine as important precursors for IBMP. This discovery gave evidence for a metabolic interface of the MP-biosynthesis and photorespiration.

Traditional Fermented Foods from Ecuador: A Review with a Focus on Microbial Diversity.

The development of early civilizations was greatly associated with populations’ ability to exploit natural resources. The development of methods for food preservation was one of the pillars for the economy of early societies. In Ecuador, food fermentation significantly contributed to social advances and fermented foods were considered exclusive to the elite or for religious ceremonies. With the advancement of the scientific research on bioprocesses, together with the implementation of novel sequencing tools for the accurate identification of microorganisms, potential health benefits and the formation of flavor and aroma compounds in fermented foods are progressively being described. This review focuses on describing traditional fermented foods from Ecuador, including cacao and coffee as well as less popular fermented foods. It is important to provide new knowledge associated with nutritional and health benefits of the traditional fermented foods.

Preparation of Pickering emulsions based on soy protein isolate-tannic acid for protecting aroma compounds and their application in beverages

In the present study, soy protein isolate was modified by tannic acid and used as a stabilizer for Pickering emulsions loaded with aroma compounds. The nanoparticles with tannic acid concentrations above 2 mg/mL were found to show great antioxidant properties. Essential oils, aroma compounds, and flavours can be stabilized by nanoparticles to form Pickering emulsions with a droplet diameter of<600 nm. E-nose analysis shows that nanoparticles provide outstanding protective functionalities for the 6 essential oils at 37 °C for 30 days. Further study of limonene and citral indicates that the nanoparticles afford nearly 60% protection against loss with a tannic acid concentration of 10 mg/mL. Furthermore, the nanoparticles also maintain the aroma of the beverages and lengthen the five-day shelf life. Overall, this research provides a sustainable, low-cost, and quickly prepared stabilizer for aroma compounds in foods.

Effect of lipids on food palatability: holding effect for aroma compounds and enhancement effect of Koku attributes

Lipids in foods play important roles in the improvement of their palatability as well as the supply of nutrition for energy. Lipids improve the food property which is decided by lots of factors such as taste, aroma, texture and so on involved in food palatability. In the case of taste, lipids enhance the intensity of sweetness and umami taste of foods, while they suppress their bitterness. Lipids also affect the food palatability related to aroma through the lipid oxidation in foods or the precursor of the aroma compounds such as linoleic acid and linolenic acid. In the case of texture, lipids in foods make them more tender and juicier. Recently, lipids were found to hold aroma compounds in foods and enhance the complexity, mouthfulness, and lingerngness in Koku attributes. Aroma compounds in foods are released from their lipids during chewing foods in oral cavity, and they enhance Koku attributes.

Electronic Nose for Monitoring Odor Changes of Lactobacillus Species during Milk Fermentation and Rapid Selection of Probiotic Candidates.

Probiotic bacteria have been associated with a unique production of aroma compounds in fermented foods but rapid methods for discriminating between foods containing probiotic, moderately probiotic, or non-probiotic bacteria remain aloof. An electronic nose (e-nose) is a high-sensitivity instrument capable of non-invasive volatile measurements of foods. In our study, we applied the e-nose to differentiate probiotic, moderately probiotic, and non-probiotic Lactobacillus bacteria strains at different fermentation time points (0th, 4th, and 11th) of milk fermentation. The pH of the changing milk medium was monitored with their corresponding increase in microbial cell counts. An e-nose with two gas chromatographic columns was used to develop classification models for the different bacteria groups and time points and to monitor the formation of the aromatic compounds during the fermentation process. Results of the e-nose showed good classification accuracy of the different bacteria groups at the 0th (74.44% for column 1 and 82.78% for column 2), the 4th (89.44% for column 1 and 92.22% for column 2), and the 11th (81.67% for column 1 and 81.67% for column 2) hour of fermentation. The loading vectors of the classification models showed the importance of some specific aroma compounds formed during the fermentation. Results show that aroma monitoring of the fermentation process with the e-nose is a promising and reliable analytical method for the rapid classification of bacteria strains according to their probiotic activity and for the monitoring of aroma changes during the fermentation process.

Characterization of the Key Aroma Compounds in Dog Foods by Gas Chromatography-Mass Spectrometry, Acceptance Test, and Preference Test.

Gas chromatography-mass spectrometry (GC-MS) coupled with the acceptance test, partial least-squares regression (PLSR) analysis, validation experiment, and preference test was used to identify the key aroma compounds in dog foods (DFs). Six DFs were evaluated by spraying six palatability enhancers onto a basal DF. The differently flavored palatability enhancers were prepared by the Maillard reaction using different protein sources and reaction conditions. The intake ratios of the six DFs were tested by six adult beagle dogs and were classified into high, medium, and low levels. A total of 55 volatile compounds were identified using headspace solid-phase microextraction (HS-SPME) GC-MS. Correlation analysis of the volatile compounds associated with intake ratios using partial least-squares regression (PLSR) found nine significantly positive and three significantly negative compounds that made a significant contribution to the palatability of DFs. Validation tests undertaken by adding three significantly positive compounds, one significantly negative compound, and one nonsignificant compound into the odorless matrix successfully verified the accuracy prediction of the PLSR model. The nine significantly positive compounds were heptanal, nonanal, octanal, (E)-2-hexenal, (E,E)-2,4-decadienal, 2-pentylfuran, 4-methyl-5-thiazoleethanol, 2-furfurylthiol, and (E)-2-decenal. The contributions of nine key aroma compounds were further analyzed by the preference test. (E)-2-decenal, 2-furfurylthiol, and 4-methyl-5-thiazoleethanol showed higher first choice, consumption ratio, and unit contribution rate and were vital to the overall preferred aroma of DFs.

Flavor scalping by polyethylene sealants

• The degree of scalping of a flavorant is inversely related with its water solubility. • Higher scalping was observed for LLDPE sealants with the lowest density. • Sensorial differentiation between LLDPE sealants based on flavor scalping will not occur. Flavor scalping, i.e. the sorption of food aroma compounds by packaging materials, can lead to a loss of product quality and potential damage to the package. In this study, the flavor scalping performance of 14 different Linear Low Density Polyethylene sealant resins was comparatively evaluated in stand-up pouch applications. In sunflower oil as the matrix, no significant flavor scalping was observed. In aqueous model systems clear indications of flavor scalping were observed for limonene, decanal and 2(E)-nonenal. The degree of scalping of a specific flavorant was found to be inversely related with the water solubility. Comparing the flavor scalping data obtained for the different sealant resins in aqueous model systems showed significantly higher scalping for the sealants with the lowest density. Differences between the tested sealant resins are limited, and are not expected to generate sensorial differentiation between the sealant resins, in the density range (0.902 – 0.919 g/ml) evaluated.

Recent Progress in Rapid Analyses of Vitamins, Phenolic, and Volatile Compounds in Foods Using Vibrational Spectroscopy Combined with Chemometrics: a Review

Nowadays, progresses in data processing software have promoted the application of infrared (e.g., FT-IR, NIR, MIR), Raman, and hyperspectral imaging (HSI) techniques for quantitative analysis of biological material and/or aroma compounds in foods. In this review, applications of vibrational spectroscopy combined with chemometrics are summarized including analysis of total polyphenol, individual polyphenols, vitamins, and aromatic compounds in raw and some processed products. Laboratory-based and online application of vibrational spectroscopies monitoring for analysis of phenolic compounds have been described. In addition, technical challenges and future trends have been covered. Based on the literature, the near-infrared technique often has an advantage over other spectroscopy approaches and the expensive and time-consuming chemical methods such as high-performance liquid chromatography and gas chromatography. Overall, the current review suggests that vibrational spectroscopies are promising and powerful techniques that can be used for rapid and accurate determinations of food nutraceuticals and volatile compounds in both academic and industrial contexts.

Scalping of aroma compounds from food simulants into polyethylene terephthalate laminated steel.

Aroma scalping is a very common problem and can affect the sensory quality of packaged food. To study the aroma scalping characteristics of polyethylene terephthalate laminated steel (PET-LS), the sorption kinetics of six common aroma compounds (2-pentanone, 2-heptanone, hexanal, citral, butyl acetate, isopentyl acetate) in foods were assessed for drawn-redrawn cans made with PET-LS. Storage temperature and initial concentration were proved as important factors to affect compound sorption and diffusion for flavors. The correlation between logarithm of equilibrium absorption lnM∞ and reciprocal of absolute temperature 1/T showed good linear relationship (R2 = 0.9380-0.9998) at 4°C, 20 °C and 50 °C, and the M∞ obtained by the experiment was very close to the predicted value at 37 °C. At low initial concentration (below 500 µL L-1 ), the absorption capacity and initial concentration showed a slow linear growth trend, whereas there was a rapid change at high initial concentration. The values of diffusion coefficient D were on the order of 10-11 -10-12 m2 day-1 , which were lower than reported for other polymer materials (linear low-density polyethylene, polybutylene succinate, polylactic acid). The equilibrium absorption amount of each flavor component was dependent on the temperature under the same concentration (500 µL L-1 ). The Fickian diffusion model was used for fitting the experimental kinetics values satisfactorily (R2 = 0.9158-0.9885). © 2019 Society of Chemical Industry.

Aroma scalping characteristics of polybutylene succinate based films

The removal of aroma compounds from packaged food items - aroma scalping – can be primarily controlled by the choice of packaging materials. Although the utilization of biodegradable polymers as packaging materials can greatly contribute to the sustainability of the packaging industry, only limited data on their aroma scalping properties are available. In this work, the aroma scalping characteristics of a series of films made from biodegradable polybutylene succinate (PBS) and polybutylene succinate-co-addipate (PBSA) for common aroma compounds in foods (ethyl acetate, ethyl butyrate, ethyl hexanoate, hexan-1-ol, heptanal and (R)-(+)-limonene) are reported. The aroma scalping characteristics of a film made from poorly biodegradable low density polyethylene (LDPE) are reported for comparison.The aroma scalping characteristics, namely sorption and diffusion coefficients, of the tested aroma compounds were determined at 23 °C by means of sorption microgravimetry, and the permeability coefficients were estimated using the solution-diffusion model. The permeability coefficients for the films made from PBS, PBSA and LDPE were comparable for the more polar compounds: hexan-1-ol, ethyl acetate and ethyl butyrate. Conversely, the permeability coefficients of the less polar aroma compounds (ethyl hexanoate, heptanal and (R)-(+)-limonene) in PBS and PBSA-based films were by one to two orders of magnitude lower than those of the LDPE. In addition, a new mathematical model was proposed for the kinetics of the transient sorption of aroma compounds of low volatility (psat < 1 kPa).

Behaviour and hormonal status in healthy rats on a diet rich in Maillard reaction products with or without solvent extractable aroma compounds

Maillard reaction products (MRPs) are generated upon thermal processing of foods, modifying their colour and flavour. We asked whether aroma compounds generated via Maillard-type reactions modulate the in vivo effects of MRP-rich diets (MRPD). Male Wistar rats were fed for 3weeks either with a standard rat chow, an aroma compounds containing MRPD comprising 25% bread crust, or an aroma-extracted MRPD. In contrast to standard rat chow, consumption of MRPDs affected glucose control, induced hyper-leptinemia and hyper-adiponectinemia. Plasma adipokines were significantly higher in rats on aroma containing MRPD in comparison with those consuming aroma-extracted MRPD. Consumption of both MRPDs significantly increased the expression of the insulin receptor in the olfactory bulb, and mildly in the hypothalamus. Administration of the aroma containing MRPD significantly increased the leptin receptor expression in the olfactory bulb, and in the hypothalamus. Under both MRPDs, strong expression of c-fos indicated an increased neuronal activity in the olfactory bulb. Neuronal activity in brain areas involved in the central regulation of food intake and energy homeostasis was more pronounced in rats fed by the aroma containing MRPD. In conclusion, short-term consumption of a MRPD fortified with bread crust, particularly if containing solvent extractable volatile aroma compounds, affected the leptin-induced central signalling of anorexigenic/orexigenic hormones, and the neuronal activity in the central nervous system. Behavioural changes and altered glucose control were more evident in rats on the aroma containing MRPD. Our data suggest that volatile aroma compounds in foods might affect endocrine signalling and neuronal regulation of metabolism.

Ionization effects on the partitioning behavior of food and beverage aroma compounds between aqueous phases and air and organic matrices

Ionization effects on the partitioning behavior of food and beverage aroma compounds between aqueous phases and air and organic matrices

Re-investigation on odour thresholds of key food aroma compounds and development of an aroma language based on odour qualities of defined aqueous odorant solutions

Literature data on odour thresholds of volatile food constituents, and, in particular on their odour quality, may differ significantly. In order to obtain more reliable sensory data, the odour thresholds of eighty-four compounds previously characterised as key food odorants were re-evaluated and compared to literature results. In addition, the odour thresholds of ten odorants are reported here for the first time. On the basis of a distinct protocol, also the aroma attributes of the odorants were evaluated in order to define an aroma language, which can be used for specific purposes, e.g., training of panellists for GC-Olfactometry.

Food aroma compounds and their positive effect referring to human health

Food aroma compounds and their positive effect referring to human health

Solid-phase microextraction method for the determination of hexanal in hazelnuts as an indicator of the interaction of active packaging materials with food aroma compounds

Fatty foods are susceptible to lipid oxidation resulting in deterioration of product quality due to the generation of off-flavours. Hexanal is a good indicator of rancidity. Therefore, a method based on solid-phase microextraction (SPME) coupled to gas chromatograph with flame ionization detection was developed to determine hexanal formation in hazelnuts during storage. Optimum conditions were as follows: carboxen–polydimethylsiloxane 75 µm fibre, extraction time 10 min, equilibrium time 10 min and equilibrium temperature 60°C. The effect of oxygen scavengers on the oxidation process was also evaluated by measuring hexanal formation in hazelnuts stored with/without oxygen absorber sachets. Oxygen scavengers were shown to reduce oxidation; however, analysis of the sachet revealed that other volatile compounds from the headspace were also absorbed.

Mechanisms of Extraction of Aroma Compounds from Foods, Using Adsorbents. Effect of Various Parameters

Due to their high adsorbing capacity, different solids (carbonaceous adsorbents, zeolites, and polymers) are used to extract and concentrate aroma compounds from foods. Adsorption mechanisms are described in two phases, a kinetic stage that involves the diffusion of the analytes within the adsorbent pores and a thermodynamic stage that can be described by adsorption isotherms. These two phases determine the extraction time and the capacity of the adsorbent for a given aroma compound. Several applications involving adsorbents or sorbents have been developed, including purge and trap, solid-phase microextraction (SPME), and stir bar sorptive extractions (SBSE), headspace sorptive extraction (HSSE), which now are widely used for aroma extractions. Different extraction modes (in the headspace or by immersion in the sample) can be used to recover aroma compounds in foods. The same adsorption mechanisms take place in both cases. Various parameters affecting the extraction kinetics and the capacity of the adsorbent have to be optimized when developing an extraction method. They can be divided into three groups: physicochemical characteristics of the adsorbent, including its porosity and hydrophobia; physicochemical characteristics of the aroma compounds (among them, two parameters play an important role, the sample/adsorbent partition coefficient, which determines the affinity for the adsorbent and the volumetric mass, which influences the diffusion in the adsorbent pores); and the extrinsic parameters that depend on the sampling conditions such as pH, temperature, gas or solvent flows, time, and composition of the sample. Several models used to determine the diffusivity and partition coefficient of aroma between the food sample and the adsorbents have been developed. They are useful to understand the behavior of aroma compounds in regards to various adsorbents and in selecting the adsorbent material with the greatest affinity for the target aroma compounds. Quantitative studies based on adsorbent extraction of volatiles have been carried out. Nevertheless, competition between analytes and the saturation of these materials are limiting parameters. Thus, new strategies (SBSE, HSSE) are being developed to avoid these limiting aspects of adsorbents in order to use them in a quantitative way.

An Expeditious, High-Yielding Construction of the Food Aroma Compounds 6-Acetyl-1,2,3,4-tetrahydropyridine and 2-Acetyl-1-pyrroline

[reaction: see text] The key compound responsible for the aroma of bread, 6-acetyl-1,2,3,4-tetrahydropyridine (1), has been constructed in an efficient three-step procedure from 2-piperidone in an overall yield of 56%. Compound 1 was liberated in the final step under basic conditions. A related synthetic route produced 2-acetyl-1-pyrroline (2), the principal component of cooked rice, in 10% overall yield.

Stabilization of aroma compounds through sorption-release by packaging polymers.

Plastic packaging materials are often associated to aroma losses and to a decrease of the organoleptic quality of foods. This work defines situations where, on the contrary, plastics play a regulating role on the concentration of reactive aroma compounds in foods. These systems can be described by a two step mechanism; first, aroma is sorbed in the polymer, while the fraction in solution degrades quickly; in a second step, as the concentration is close to zero in the solution, the polymer liberates progressively the sorbed aroma back to the food. A simple numerical model is proposed, describing competitive processes of aroma degradation in solution and sorption by a polymer in contact with a homogeneous aqueous food. The classical limonene/low density polyethylene (LDPE) system is studied experimentally for the validation of the model: in an acidic medium, limonene both degrades quickly and is sorbed quickly, with a large solubility in LDPE. To define which aroma packaging systems could also display this interesting behavior, all types of possible interactions, using thermodynamic and kinetic parameters describing most practical situations, are simulated. For that purpose, 35 values of reference diffusion coefficients and 35 partition coefficients of usual aroma compounds between polymers and water have been measured and combined with the few available data from literature. The situations where polymers regulate the aroma concentration in food correspond to large partition coefficients (above 10), large diffusion coefficients (>10(-9) cm2 x s(-1)), and large degradation constants.

Investigation of the interaction of active packaging material with food aroma compounds

The aim of the reported investigation was the determination of beneficial or adverse effects of active packaging material on aroma compounds in food. The effects of storage on the aroma of packaged food was characterized by a multi-sensor system or electronic nose (e-nose) in comparison to measurements with gas chromatography coupled to mass spectrometry (GC–MS) using different sample uptake techniques. For the measurements of aroma compounds static headspace extraction (HSS) and solid phase micro extraction (SPME) were used for sampling. For the monitoring of food ageing and the determination of shelf-life, the study focussed on off-flavours generated by lipid oxidation in fat containing foods during storage. Of special interest was the monitoring of hexanal, which can be used as a shelf-life indicator for many fatty foods. The effect of active packaging was assessed by the comparison of food and food simulants in contact with active packaging material in inert media or conventional packaging materials during storage under various conditions. Active packaging proved to reduce oxidation and prolong shelf-life but also absorbed components from the headspace enclosed with the investigated model food. Within the study, the applicability of chemical sensor arrays for the screening of food and the assessment of shelf-life was evaluated. Hereby, measurement results obtained with the electronic nose could be correlated to the GC–MS data and therefore to the sample constituents. The evaluated electronic nose confirmed the possibility of use as a screening tool for the monitoring of ageing and quality of certain foods after careful calibration.