Aroma Deterioration Research Articles

Unraveling the core microorganisms and metabolic pathways related to off-flavor compounds formation during Jiang-flavor Baijiu fermentation

Off-flavor is one of the most frequent and serious causes for the aroma deterioration in Jiang-flavor Baijiu. However, the key compounds and their formation mechanism responsible for off-flavor are still unclear. This study identified 271 volatile compounds from 1 normal and 5 types of off-flavor fermented grains (putrid, rancidity, mud, musty, and burnt) by headspace solid-phase microextraction combined with gas chromatography–mass spectrometry. Using VIP and OAV analysis, 47 key flavor compounds including indole, phenol, isoamyl alcohol, diacetyl, acetic acid, isobutyric acid, and isovaleric acid were found to distinguish normal and off-flavor fermented grains. Furthermore, 40 microbial genera (mainly Monascus, Enterococcus, Dyadobacter, Ottowia, Pseudoxanthomonas, Stenotrophomonas, Pseudomonas, and Xanthomonas) were significantly (p < 0.05, Pearson correlation) related to these 47 compounds. Finally, metabolic pathways for off-flavor compounds formation were constructed. This study provides comprehensive information on the off-flavor compounds and their potential formation mechanism during Jiang-flavor Baijiu fermentation.

The potential of glucosidase and glucose oxidase for aroma improvement in concentrated peach puree based on volatilomics and metabolomics

Cooked off-flavor was produced during the processing of concentrated peach puree (CPP), which led to aroma deterioration. Enzymatic treatment was beneficial in eliminating off-flavors and improving the aroma quality. Herein, the efficacy of glycosidase (AR2000), glucose oxidation (GOD), and their combination on the inhibition of off-flavors and aroma enhancement were evaluated. Compared with CPP, contents of benzaldehyde, benzyl alcohol, nonanal, and linalool increased by 198%, 1222%, 781%, and 71% after AR2000 treatment via the metabolisms of shikimate, glucose, linoleic acid, and linolenic acid, leading to the strengthening of floral and grassy. Due to the removal of 1-octen-3-one via linolenic acid metabolism, cooked off-flavor could be significantly weakened by GOD. Furthermore, Furthermore, the combination of AR2000 and GOD could not only inhibit the production of 1-octen-3-one to weaken the cooked note but also enhance grassy and floral attributes via the increase of aldehydes and alcohols.

Combination of pure oxygen pretreatment and near‐freezing temperature storage inhibits browning, maintains antioxidant and physicochemical quality of fresh‐cut nectarines

AbstractFresh‐cut fruits were convenient for consumers but vulnerable to quality deterioration, including browning, softening, and volatile aroma loss. In this study, the whole nectarines were pretreated with 100% O2 (pure oxygen, PO) for 2 h and stored at near‐freezing temperature (NFT, −1.5 ± 0.1°C) for 9 days after cutting. We investigated the changes of samples in browning degree, enzyme activity, cell membrane permeability, antioxidant activity, and aroma components. Specifically, PO pretreatment increased the peroxidase (POD) and phenylalanine ammonia‐lyase (PAL) activities, which endows the whole nectarines with resistance to environmental stresses before fresh‐cut. NFT storage effectively inhibited the activity of the polyphenol oxidase (PPO) and the increase of the total phenolic content (TPC). Higher antioxidant levels and anti‐browning effects were observed in fresh‐cut nectarines treated with PO + NFT, which demonstrated by higher levels of 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free radical scavenging capacity, ferricion reducing antioxidant power (FRAP), and enzyme activity ratios (ratio 1 and ratio 2). During the storage of 9 days, the firmness and membrane permeability were preserved, malondialdehyde (MDA) content was suppressed, which delayed the softening of nectarine tissue. Furthermore, soluble solids content (SSC) and titratable acid (TA) were also well preserved by PO + NFT, which maintained the physiological and metabolic qualities. Electronic nose tests revealed that PO + NFT postponed the volatile aroma deterioration. In conclusion, PO + NFT effectively maintains the storage quality of fresh‐cut nectarines.

Widely targeted metabolomics reveals the effect of different raw materials and drying methods on the quality of instant tea.

Instant teas are particularly rich in tea polyphenols and caffeine and have great potential as food ingredients or additives to improve the quality of food and enhance their nutritional and commercial value. To determine the relationships between raw material, drying method, and sensory and other quality attributes, instant teas were prepared from three tea varieties, namely black, green and jasmine tea, using two drying methods, namely spray-drying (SD) and freeze-drying (FD). Both the raw tea material and drying method influenced the quality of the finished instant teas. Black tea was quality stable under two drying, while green tea taste deteriorated much after SD. Jasmine tea must be produced from FD due to huge aroma deterioration after SD. FD produced instant tea with higher sensory quality, which was attributed to the lower processing temperature. Chemical compositional analysis and widely targeted metabolomics revealed that SD caused greater degradation of tea biochemical components. The flavonoids content changed markedly after drying, and metabolomics, combined with OPLS-DA, was able to differentiate the three varieties of tea. Instant tea preparations via SD often lost a large proportion of the original tea aroma compounds, but FD minimized the loss of floral and fruity aroma compounds. Changes in the tea flavonoids composition, especially during drying, contributed to the flavor development of instant tea. These results will provide an practicle method for high-quality instant tea production through choosing proper raw tea material and lowering down drying temperature with non-thermal technologies like FD.

Identification of volatile organic compounds as markers to detect Monilinia fructicola infection in fresh peaches

Monilinia spp. are among the main fungal pathogen affecting peaches, and they can cause severe pre- and postharvest losses. Development of smart packaging technologies (e.g., volatile indicators), facilitating infection detection and preventing other fruit from being contaminated, is still limited. In this study, we compared for the first time the aroma profile of whole healthy fresh peaches to Monilinia fructicola-artificially inoculated peaches, identifying discriminant volatile organic compounds (VOCs). More than one hundred VOCs were detected by applying head space solid-phase microextraction followed by GC-MS analysis. The level of methyl esters, hydrocarbons, lactones, and acids decreased in infected peaches indicating fruit aroma deterioration, while the concentration of ethyl esters and alcohols increased. In particular, the amount of ethanol and derived ethyl acetate reached a maximum of 24- and 20-fold increase in the infected peaches, respectively. Isobutanol, propyl acetate, and ethyl isovalerate were specifically emitted by M. fructicola-infected peaches. These compounds might serve as markers for the development of smart sensors allowing the detection of fungal infection.

Effects of konjac glucan-nan/low-acyl gellan edible coatings loaded thymol-β-cyclodextrin microcapsules on postharvest blueberry

This study developed an edible antimicrobial coating using a blend of konjac glucomannan (KGM) and low acyl gellan gum (LAG) hydrogel to incorporate thymol nanoparticles (TKL). The optimized TKL formulation (TKL60) comprised 0.22% thymol microcapsules (TMs), 0.075% total polysaccharide content (KGM:LAG = 1:2), and 99.63% distilled water. When applied to blueberries, TKL60 significantly extended their shelf life to 42 d at 2 ± 0.5 °C, tripling that of control fruit. TKL60 reduced decay rate, weight loss, and respiration rate, delayed softening and senescence during cold storage. It preserved the outer epidermis by retaining cuticular waxes, curbing lipid oxidation, and sustaining defense-related enzyme activities. Flavor analysis revealed altered volatile compound concentrations in TKL60-treated berries, including decreased terpenes and benzaldehyde, and increased esters and aldehydes like 2-methylbutanol, 3-methylbutanol, and linalool. Discriminant Analysis highlighted TKL60′s efficacy in delaying aroma deterioration by over 21 d. TKL60 exhibits potential as a substitute for synthetic coatings and chemical insecticides.

Roles of sulfur-containing compounds in fermented beverages with 2-furfurylthiol as a case example.

Aroma is a critical component of the flavor and quality of beverages. Among the volatile chemicals responsible for fragrance perception, sulfur compounds are unique odorants due to their extremely low odor threshold. Although trace amounts of sulfur compounds can enhance the flavor profile of beverages, they can lead to off-odors. Sulfur compounds can be formed via Maillard reaction and microbial metabolism, imparting coffee aroma and altering the flavor of beverages. In order to increase the understanding of sulfur compounds in the field of food flavor, 2-furfurylthiol (FFT) was chosen as a representative to discuss the current status of their generation, sensory impact, enrichment, analytical methods, formation mechanisms, aroma deterioration, and aroma regulation. FFT is comprehensively reviewed, and the main beverages of interest are typically baijiu, beer, wine, and coffee. Challenges and recommendations for FFT are also discussed, including analytical methods and mechanisms of formation, interactions between FFT and other compounds, and the development of specific materials to extend the duration of aroma after release.

Effects of Hydrogen Peroxide Produced by Catechins on the Aroma of Tea Beverages.

Hydrogen peroxide has a significant effect on the flavor of tea beverages. In this study, the yield of hydrogen peroxide in (–)-epigallocatechin gallate (EGCG) solution was first investigated and found to be significantly enhanced under specific conditions, and the above phenomenon was amplified by the addition of linalool. Then, an aqueous hydrogen peroxide solution was added to a linalool solution and it was found that the concentration of linalool was significantly reduced in the above-reconstituted system. These findings were verified by extending the study system to the whole green tea infusions. The results suggested that the production of hydrogen peroxide in tea beverages may be dominated by catechins, with multiple factors acting synergistically, thereby leading to aroma deterioration and affecting the quality of tea beverages. The above results provided a feasible explanation for the deterioration of flavor quality of green tea beverages with shelf life.

Functional Ingredients and Food Preservative in Immature Persimmon “Tekka-Kaki”

Immature persimmons are unripe fruits that are cut off during the persimmon cultivation process and immediately discarded, amounting to an annual fruit loss of approximately 100 to 400 kg per 1000 m2. The purpose of this study was to make effective use of unused resources, namely, immature persimmons, and attempt to use them as food additives. In this study, we studied the Tone Wase (fully astringent persimmon) and Fuyu (fully sweet persimmon) cultivars. As a result, we performed a component analysis of the immature persimmons, isolating 12 compounds, of which two were newly identified. Differences in the components and their contents were found between cultivars and between the peel and flesh. To effectively use immature persimmons as food for the elderly, we searched for active substances that inhibit AGE formation and found that extracts of immature persimmons and isolated compounds showed high activity. In particular, high activity was observed for catechin and its polymeric form, procyanidin. Regarding the inhibition of aroma deterioration, 5 mg/L of gallic acid in octadecane was found to be the optimal condition for the inhibition of citral deterioration. As for antimicrobial activity, we found that extracts at a concentration of 500 mg/L had no antimicrobial effect. Based on these findings, we made a microencapsulation process, and plan to advance to the clinical trial study in future. These findings confirmed the effectiveness of immature persimmons, which are an unused resource, and reveal their potential as a food for the elderly and as a food additive in other food products, which we hope will lead to new industrial innovations.

Effect of Ferrous Ion on Heat-Induced Aroma Deterioration of Green Tea Infusion.

Aroma deterioration is one of the biggest problems in processing tea beverages. The aroma of tea infusion deteriorates fast during heat sterilization and the presence of ferrous ion (Fe2+) aggravates it. The underlying mechanism remains unveiled. In this study, Fe2+ was verified to deteriorate the aroma quality of green tea infusion with heat treatment. Catechins were necessary for Fe2+-mediated aroma deterioration. By enhancing the degradation of catechins, Fe2+ dramatically increased the production of hydrogen peroxide (H2O2). Fe2+ and H2O2 together exacerbated the aroma of green tea infusion with heat treatment. GC-MS analysis revealed that the presence of Fe2+ enhanced the loss of green/grassy volatiles and promoted the formation of new volatiles with diversified aroma characteristics, resulting in a dull scent of green tea infusion. Our results revealed how Fe2+ induced aroma deterioration of green tea infusion with heat treatment and could help guide tea producers in attenuating the aroma deterioration of tea infusion during processing.

Characterization of Artisanal Spontaneous Sourdough Wheat Bread from Central Greece: Evaluation of Physico-Chemical, Microbiological, and Sensory Properties in Relation to Conventional Yeast Leavened Wheat Bread.

In the present study, both yeast leavened bread (YLB) and artisanal sourdough wheat bread (SDB) were prepared. The physico-chemical, microbiological, and sensory properties of breads were monitored as a function of storage time (T = 25 °C). As expected, the titratable acidity (TA) values of SDB were higher than those of YLB. The aroma profile of SDB was similar to that of YLB, including classes of compounds such as alcohols, aldehydes, ketones, esters, organic acids, terpenes, and sulfur compounds; however, the concentrations between the two were different. Aroma deterioration of bread during storage was partly related to the loss of several volatiles. Texture and sensory analysis showed that SDB was harder, less elastic, but richer in aroma and light sour taste than YLB. Mold growth was apparent when the population of yeasts/molds reached approximately 4 log cfu/g. This yeast/mold count was reached on days 4–5 for YLB and day 18 + for SDB. A 16S amplicon meta-barcoding analysis showed that the bacterial profile of SDB was dominated by a single genus, (Lactobacillus). Analysis of the eukaryotic load showed that at the genus level, Saccharomyces and Alternaria were the most abundant genera, independently of the gene sequenced (18S or ITS). Based primarily on mold growth and texture data, which proved to be the most sensitive quality parameters, the shelf life was ca. 4–5 days for YLB and 10 days for SDB.

Red Light Exposure Delays Appearance and Aroma Deterioration of Fresh-Cut Watermelon during Retail Display

Appearance and aroma deterioration are the main concerns during the retail display of fresh-cut watermelons. Here, fresh-cut watermelons were exposed to the red, green, blue, and conventional white light at 4°C for 4 days, respectively, and their resulting qualities were compared with the conventional white light as the control. Specifically, the red light presented its maximum emissions in 620–650 nm with a purity of 100% and an intensity of 1104.7 lux. The red light exposure reduced the weight loss to 1.81%, which was reduced by 51.1% of the control. The red light exposure reduced the color difference of the fruit surface significantly as well as maintaining its redness. The water-soaking ratio of the red light exposure was also reduced by 62.8% of the control. Moreover, the red light exposure delayed the aroma deterioration, which resulted from both microbial metabolism and the self-metabolism of volatiles of the fresh-cut watermelon. In summary, the red light exposure was better to delay the appearance and aroma deterioration of fresh-cut watermelons than the conventional white light during their retail display.

Inhibition of Lipid and Aroma Deterioration in Rice Bran by Infrared Heating

This study was aimed to investigate the inhibition of the deteriorations of rice bran by infrared radiation (IR) heating and its effects on the chemical and biological profiles during short-term storage. Freshly milled paddy rice bran was exposed to the IR until the surface temperature reached 85 °C. The results indicated that after 20 days of storage, the activities of relevant enzymes, including lipase, lipoxygenase, and peroxidase all decreased after IR-treated. The rising trend of the free fatty acid content decreased significantly during storage. IR treatment can reduce the oxidation and hydroperoxides of rice bran, which can control the rise of peroxide value till the 15 days of storage (9.7 meq/kg). The contents of palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2) were well maintained by IR heating during the whole storage period. The aroma of fresh rice bran was acceptably preserved with abundant amount of aldehydes and alkanes. After quantification of the volatile chemical compounds in rice bran, potential biomarkers specific for rice bran storage should be highlighted, being 3-octen-2-one, acetophenone, 2,4-dimethylcumene, 5,6-dimethylindane, and phytane. This study illustrates that the IR processing can effectively guarantee the stabilization of rice bran in terms of desirable FAs profiles, relevant enzymes activities, and aroma features.

Are bacteria responsible for aroma deterioration upon storage of the black truffle Tuber aestivum: A microbiome and volatilome study

Truffle fungi, luxurious food items with captivating aromas, are highly valued in the culinary world. However, truffles are perishable and their aroma undergoes deep changes upon storage. Additionally, truffle aroma might be partially derived from microbes. Hence, we investigated here the influence of storage on two factors, namely the volatile profile and bacterial community composition in the black truffle Tuber aestivum. The possible linkage among those factors was further explored.Our results demonstrate important changes in the volatile profiles of truffles over nine days of storage at room temperature. In the same time frame, dominant bacterial classes characteristic of fresh truffles (α-Proteobacteria, β-Proteobacteria, and Sphingobacteria classes) were gradually replaced by food spoilage bacteria (γ-Proteobacteria and Bacilli classes). Freshness and spoilage volatile markers (i.e. dimethyl sulfide (DMS), butan-2-one, 2- and, 2- and 3-methylbutan-1-ol, and 2-phenylethan-1-ol) were identified. Lastly, network analysis showed correlations between those markers and specific bacterial classes typical of fresh and spoiled truffles.Overall, our results demonstrate the profound effect of storage on the aroma and bacterial community composition of truffles and highlight how the gradual replacement of the commensal microbiome by spoilage microbes mirrors shifts in aroma profile and the possible loss of fresh truffle flavor.

Ultrasound-assisted thawing of mango pulp: Effect on thawing rate, sensory, and nutritional properties

Sensory and nutritional properties of mango pulp thawed by different ultrasound intensities and temperatures were studied. Compared to water immersion thawing, a thawing time reduction of 16–64% (p < 0.05) and more phenolic acids contents (gallic, hydroxybenzoic, and caffeic acid) were observed after ultrasonic thawing. The sensory evaluation revealed texture and aroma deterioration at higher ultrasonic intensities (4 °C:0.074 W/mL; 25 °C:0.123 W/mL) due to increase in viscosity and some volatile compounds in the mango pulp. Ultrasonic thawing treatment at 25 °C reduced thawing time by 51–73% compared to that at 4 °C. Mango pulp processed at 25 °C exhibited better sensory quality and retained 26.5–58.5% more total phenol and 8.7–11.0% more total carotenoid contents. In short, higher ultrasonic intensities (0.074–0.123 W/mL) at a temperature of 25 °C contributed to better thawing efficiency and nutritional quality. The results demonstrated that ultrasound processing at optimized conditions could serve as a potential alternative to conventional thawing processing of mango pulp.

Investigation of sunlight-induced deterioration of aroma of pummelo (Citrus maxima) essential oil.

Deterioration of aromas of pummelo essential oil (EO) induced by sunlight was compared to those induced by heat and oxygen exposure using the techniques of sensory evaluation and GC-MS analysis. The sunlight-exposed EO was found to possess an oily off-flavor odor, which was significantly different from its counterparts induced by oxygen and heat. The strong oily note of the sunlight-exposed EO was attributed to the existence of linalool oxides and limonene oxides, as well as the lack of neral and geranial, for which UV sunlight was revealed to be the critical contributor causing the chemical reactions for the aroma changes. The results demonstrated that UV sunlight could significantly affect the aroma of the pummelo EO, providing valuable information that will benefit the production and storage of EO-based aromatic products.

Characterization of Geosmin as Source of Earthy Odor in Different Aroma Type Chinese Liquors

Earthy odor is one of the most frequent and serious causes for the aroma deterioration in Chinese liquor, which causes a dirty and dusty impression. The odor in Chinese liquor is similar to that of rice husk, one kind of auxiliary material widely used as a filler in the distillation process. So it is experientially hypothesized that such odor may derive from rice husk. In this paper, the gas chromatography-olfactometry (GC-O) technique and gas chromatography-mass spectrometry (GC-MS) were used to discover and identify the characteristic odoriferous zone of Chinese liquor marked by earthy odor. Geosmin was found to be responsible for this odor. The levels of the compound in ten bottled liquors and thirty liquors aging for different years belonging to four different aroma types were determined by the optimized headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method. Quantitative analysis of bottled liquor revealed the presence of geosmin in all aroma type liquors with concentrations ranging from 1.10 μg/L to 9.90 μg/L, except for strong-aroma type liquor. Meanwhile in the aged liquors belonging to the same aroma type, geosmin was detected with significant concentrations and high odor activity values (OAVs) during different years of aging. However, geosmin was not detected in steamed rice husk nor in nonsteamed rice husk, which suggests that rice husk is not the origin of earthy odor in Chinese liquor, and there may be another origin of it during the brewing process.

Meat Shelf-life and Extension using Collagen/Gelatin Coatings: A Review

Different factors lead to the end of shelf-life for fresh meat products. The factors depend upon the animal including breed difference and muscle fiber type, external influences such as diet and stress, and post-harvest storage conditions including time, temperature, and packaging atmosphere. The characteristics that indicate the end of shelf-life for fresh meat products include water loss/purge accumulation, color deterioration due to myoglobin oxidation, rancidity due to lipid oxidation, and microbial spoilage. The characteristics can be measured and studied in the laboratory. Meat shelf-life is extended with the application of a surface coating because it provides a water and oxygen barrier. Collagen and gelatin coatings are used as a barrier on meat products to reduce purge, color deterioration, aroma deterioration, and spoilage, improve sensory scores, and act as an antioxidant.

Further Insights into the Role of Methional and Phenylacetaldehyde in Lager Beer Flavor Stability

This work attempts to measure the importance of methional and phenylacetaldehyde on the flavor stability of beer, as direct participants or as indicators of aroma deterioration. A trained sensory panel identified the most important descriptors related to the typical aroma of aged beer: "malty", "honey-like", "cooked potato", and "metallic". By GC-olfactometry analysis, six aromatic zones related to the selected descriptors were highlighted, and by using GC-MS techniques it was possible to identify methional and phenylacetaldehyde as being responsible for two odor zones. The quantification of these molecules in samples submitted to forced aging treatments showed that the levels of methional and phenylacetaldehyde are dependent on the temperature of storage. Normal aged beers were also analyzed, and it was observed that these compounds accumulate with time of storage. Furthermore, these molecules were negatively correlated with the aroma quality of beer as evaluated by a sensorial panel. To validate the sensory impact of these substances, a fresh beer was spiked with these molecules and also with trans-2-nonenal, singly and in combination, and the similarity value between samples and the aged beer was then determined. The highest value from the similarity tests was 72% when the three compounds were added simultaneously. The combination of the two Strecker aldehydes increases by 54% the degree of similarity, indicating the key role played by these molecules in the aroma deterioration of beer. Finally, the kinetic parameters, Ea and k, were calculated, and it was observed that the Arrhenius equation described well the temperature dependence of the reaction rate constant. Measuring the concentration of methional and phenylacetaldehyde may provide information about the key steps along the process that most affect the flavor stability of beer, which may be useful in establishing the best storage conditions.