Aroma improvement by repeated freeze-thaw treatment during Tuber melanosporum fermentation

Application and Effect of Pediococcus pentosaceus and Lactiplantibacillus plantarum as Starter Cultures on Bacterial Communities and Volatile Flavor Compounds of Zhayu, a Chinese Traditional Fermented Fish Product

Zhayu is a type of traditional fermented fish product in China that is made through the fermentation of salted fish with a mixture of cereals and spices. Inoculation fermentation was performed using Pediococcus pentosaceus P1, Lactiplantibacillus plantarum L1, and a mixture of two strains, which were isolated from cured fish in Hunan Province. Compared with the natural fermentation, inoculation with lactic acid bacteria (LAB) accelerated the degradation of myosin and actin in Zhayu, increased the trichloroacetic acid (TCA)-soluble peptide content by about 1.3-fold, reduced the colony counts of Enterobacteriaceae and Staphylococcus aureus by about 40%, and inhibited their lipid oxidation. In the texture profile analysis performed, higher levels of hardness and chewiness were observed in the inoculation groups. In this study, the bacterial community and volatile flavor compounds were detected through 16S high-throughput sequencing and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Inoculation with L. plantarum L1 reduced around 75% abundance of Klebsiella compared with the natural fermentation group, which was positively correlated with 2,3-Butanediol, resulting in a less pungent alcohol odor in Zhayu products. The abundances of 2-pentylfuran and 2-butyl-3-methylpyrazine were increased over threefold in the L1 group, which may give Zhayu its unique flavor and aroma.

Comparative proteome and volatile metabolome analysis of Aspergillus oryzae 3.042 and Aspergillus sojae 3.495 during koji fermentation

Aspergillus oryzae 3.042 and Aspergillus sojae 3.495 are crucial starters for fermented soybean foods since their abundant secreted enzymes. This study aimed to compare the differences in protein secretion between A. oryzae 3.042 and A. sojae 3.495 during the soy sauce koji fermentation and the effect on volatile metabolites to understand the fermentation characteristics of the strains better. Label-free proteomics detected 210 differentially expressed proteins (DEPs) enriched in amino acid metabolism and protein folding, sorting and degradation pathways. Subsequently, extracellular enzyme analysis showed that three peptidases, including peptide hydrolase, dipeptidyl aminopeptidase, and peptidase S41, were up-regulated in A. sojae 3.495. Seven carbohydrases, including α-galactosidase, endo-arabinase, β-glucosidase, α-galactosidase, α-glucuronidase, arabinan-endo 1,5-α-l-arabinase, and endo-1,4-β-xylanase were up-regulated in A. oryzae 3.042, contributing to the difference in enzyme activity. Significantly different extracellular enzymes influenced the content of volatile alcohols, aldehydes and esters such as (R, R)-2,3-butanediol, 1-hexanol, hexanal, decanal, ethyl l-lactate and methyl myristate in both strains, which affected the type of aroma of koji. Overall, this study revealed the differences in molecular mechanisms between A. oryzae 3.042 and A. sojae 3.495 under solid-state fermentation, providing a reference for targeted enhancement strains.

Methods used for extraction of plant volatiles have potential to preserve truffle aroma: A review

Truffles are considered one of the world's most highly prized foods mainly due to their desirable organoleptic properties and rarity. However, truffles are seasonal (harvested mostly in winter from June to August in the Southern Hemisphere and from December to February in the Northern Hemisphere) and extremely perishable. Truffles deteriorate rapidly showing undesirable changes within 10 days from harvest in aroma and visual appearance after harvest. The very short postharvest shelf life (about 7-10 days) limits the potential for export and domestic consumption all year round. Several preservation methods have been studied to prolong their shelf life without the loss of aroma. However, all traditional preservation techniques have their own shortcomings and remain challenging. The extraction of natural truffle aroma volatiles for food applications could be a potential alternative to replace the existing synthetic flavoring used for processed truffle products. Four commonly used extraction methods for recovering volatile compounds from plants, namely, supercritical carbon dioxide extraction, Soxhlet extraction, distillation, and cold pressing, are critically analyzed. Up to date, existing research about the extraction of aroma volatiles from truffles is limited in the literature but based on the volatility of the key truffle volatile compounds, supercritical carbon dioxide extraction may offer the best possibility so that a natural truffle-based product that can be used in food applications throughout the year can be made available.

Tour of Truffles: Aromas, Aphrodisiacs, Adaptogens, and More

Truffles are the fruiting bodies of ascomycete fungi that form underground. Truffles are globally valued, culturally celebrated as aphrodisiacs, and highly sought-after delicacies in the culinary world. For centuries, naturalists have speculated about their mode of formation, and in cultures surrounding the Mediterranean Sea, many species have been prized as a delectable food source. Truffle fruiting bodies form underground and emit a variety of volatile organic compounds (VOCs). Truffle volatiles are believed to have evolved to attract animals that disperse their spores. The main VOCs identified from truffles include sulfur compounds, such as dimethyl sulfide (DMS) and dimethyl disulfide (DMDS); in addition, 1-octen-3-ol and 2-methyl-1-propanol have been found in most truffle species. Humans use pigs and dogs trained to detect truffle VOCs in order to find these prized subterranean macrofungi. Truffles have pharmacological potential, but until more reliable cultivation methods become available their high price means they are unlikely to see widespread use as medicinals.

Free Amino Acid and Volatile Compound Profiles of Jeotgal Alternatives and Its Application to Kimchi

Jeotgal containing abundant free amino acids plays an important role in the unique savory taste (umami) and flavor in kimchi. However, it is also responsible for the unpleasant fishy smell and high salt content of kimchi. Therefore, the present study aimed to identify alternative jeotgal sources and investigate the fermentation properties of jeotgal alternatives added to kimchi. The tomato hot-water extract (TH2) and dry-aged beef hot-water extract (DBH) were selected as jeotgal alternatives for kimchi preparation based on their glutamic acid contents. Characteristics of kimchi with TH2 alone (JA1) and TH2 and DBH in combination (1:1, JA2) were compared with kimchi prepared using commercially available anchovy fish sauce (CON). The pH of JA1 and JA2 was slightly decreased during fermentation, whereas the salinity was significantly lower than CON (p < 0.05). Notably, the most effective factor of the savory taste of kimchi, glutamic acid contents of JA1 and JA2 were significantly higher than that of CON (p < 0.05). In conclusion, JA1 showed slower fermentation with lower salinity and higher glutamic acid content than CON. Overall, this study showed that JA1 derived from TH2 could improve the taste and quality of kimchi by increasing glutamic acid content and decreasing the unpleasant flavor.

Comparative analysis of volatile profiles in two grafted pine nuts by headspace-SPME/GC-MS and electronic nose as responses to different roasting conditions

As an attempt to fulfill the massive demand for pine nuts, two grafted trees were cultivated: grafted Pinus koraiensis on the same scions (PK) and grafted Pinus koraiensis on Pinus sylvestris rootstocks (PKS) trees. Both PK and PKS are acknowledged as important economic trees in the northeastern area of China. This study aimed to compare the volatile compounds and aroma profiles in PK and PKS by Headspace Solid Phase Microextraction (HS-SPME) coupled with Gas Chromatography-Mass Spectrometry (GC-MS) and Electronic nose (E-nose) as responses to different roasting conditions. The results showed that a total of 286 volatile compounds were identified in the PK and PKS samples, which some of them were considered to contribute to the desirable aroma of samples. Abundance of terpenes and aromatic hydrocarbons, such as D-limonene and toluene, were respectively present in both raw PK and PKS. The increasing temperature and duration of roasting significantly decreased terpenes and aromatic hydrocarbons content, while more alkanes/alkenes, acids, and ketones were generated in the medium temperature condition. The late phase of roasting was dominated by aldehydes, furans, furfurals, pyrazines, and pyrroles, for which PKS showed a higher content than PK. The aroma profiles detected by E-nose showed that the influence of roasting time was less at high temperatures than those at low and medium temperatures. This study also highlighted the feasibility of principal component analysis (PCA) combined with HS-SPME/GC-MS and E-nose to discriminate the samples.

An Overview on Truffle Aroma and Main Volatile Compounds

Truffles are underground edible fungi that grow symbiotically with plant roots. They have been globally considered as one of the most expensive foods because of their rarity, unique aroma, and high nutritional value as antioxidant, anti-inflammatory, antiviral, hepatoprotective, anti-mutagenic, antituberculoid immunomodulatory, antitumor, antimicrobial, and aphrodisiac. The unique flavor and fragrance of truffles is one of the main reasons to get worldwide attraction as a food product. So, the aim of this review was to summarize the relevant literature with particular attention to the active aroma components as well as the various sample preparation and analytical techniques used to identify them. The major analytical methods used for the determination of volatile organic compounds (VOC) in truffles are gas chromatography (GC), proton-transfer-reaction mass spectrometry (PTR-MS), and electronic nose sensing (EN). In addition, factors influencing truffle aroma are also highlighted. For this reason, this review can be considered a good reference for research concerning aroma profiles of different species of truffles to deepen the knowledge about a complex odor of various truffles.

Potentials of truffles in nutritional and medicinal applications: a review

Truffles, the symbiotic hypogeous edible fungi, have been worldwide regarded as a great delicacy because of their unique flavor and high nutritional value. By identifying their bioactive components such as phenolics, terpenoids, polysaccharides, anandamide, fatty acids, and ergosterols, researchers have paid attention to their biological activities including antitumor, antioxidant, antibacterial, anti-inflammatory, and hepatoprotective activities. In addition, numerous factors have been investigating that can affect the quality and productivity of truffles to overcome their difficulty in culturing and preserving. To provide the information for their potential applications in medicine as well as in functional food, this review summarizes the relevant literature about the biochemical composition, aromatic and nutritional benefits, and biological properties of truffles. Besides, various factors affecting their productivity and quality as well as the preservation methods are also highlighted.

Multi-platform metabolomic approach to discriminate ripening markers of black truffles (Tuber melanosporum)

Black truffle is characterized by a black ascocarp and white veins. This hypogeous fruit body is known for its aroma. Understanding metabolic variation during ripening can shed light on truffle biology. In this work, the comprehensive polar metabolome and the volatile organic compounds of T. melanosporum were studied at different ripening stages by means of a metabolomic approach using GC-MS. Multivariate statistical data analysis indicated that the metabolic profile changed during ripening and that the metabolites that mostly discriminated truffles in the early ripening stages belonged to the classes of carbohydrates, while free fatty acids and amino acids, among which precursors of VOCs, characterized the late stages of ripening. Principal component analysis of the volatilome indicated that dimethylsulfide and dimethyldisulfide characterized most of the samples collected in December-January, while 1-octen-3-ol samples collected in February-March.

Exploring the flavor formation mechanism under osmotic conditions during soy sauce fermentation in Aspergillus oryzae by proteomic analysis

Aspergillus oryzae is a common starter in the soy sauce industry and struggles to grow under complex fermentation conditions. However, little is known about the flavor formation mechanism under osmotic conditions (low-temperature and high-salt) in A. oryzae. This work investigated the flavors and the relative protein expression patterns by gas chromatography-mass spectrometry (GC-MS) and proteomic analysis. Low-temperature and a high-salt content are unfavorable to the secretion of hydrolases and the formation of fragrant aldehydes. The aldehyde contents under osmotic conditions were reduced to 1.4-3.7 times lower than that of the control. Besides, copper amine oxidases which decreased under low-temperature stress and salt stress were shown to be important in catalyzing the oxidative deamination of several amine substrates to fragrant aldehydes. Furthermore, alcohol dehydrogenase and polyketide synthase are beneficial to the formation of alcohols and aromatic flavors under low-temperature stress and salt stress. Particularly, the ethanol content under 16 °C stress was 3.5 times higher than that under 28 °C.

Extracellular Proteome Analysis and Flavor Formation During Soy Sauce Fermentation

Aspergillus oryzae is an excellent strain for soy sauce fermentation because of its complicated enzyme system, especially protease. The aim of this study was to investigate the key enzymes and flavors during soy sauce fermentation, and a comparative assessment of extracellular enzymes during various fermentation stages at the proteomic level via iTRAQ analysis is presented. Many important enzymes related to the amino acid and glucose metabolisms participated in the material decomposition under high-salt stress. Dipeptidase, dipeptidyl aminopeptidase, leucine aminopeptidase, aspartic protease pep1, and extracellular metalloproteinase played positive roles during the early stage of soybean mash fermentation, whilst leucine aminopeptidase A and extracellular metalloproteinase NpI were the dominant proteolytic enzymes during the later period of fermentation. At the same time, β-glucosidase and β-xylanase exerted great effects upon glucose metabolism throughout the fermentation process. The results show that protease and amylolytic enzymes are complementary in the formation of flavors such as alcohols, acids, esters, aldehydes, furans, and pyrazines during soy sauce fermentation.

Effects of physicochemical parameters on volatile sulphur compound formation from L-methionine catabolism by non-growing cells of Kluyveromyces lactis

The present study investigated for the first time the effects of various physicochemical parameters on the production of volatile sulphur compounds (VSCs) by non-growing cells of Kluyveromyces lactis supplemented with l-methionine. The results showed that the production of VSCs positively correlated with the cell biomass, but it seemed that no clear relationship with l-methionine concentration existed. Temperature and pH significantly affected the formation of VSCs with more production at 30 °C and pH 5, respectively. Nitrogen supplementation (in the form of diammonium phosphate, DAP) repressed the production of VSCs. It is interesting to note that DAP and yeast extract supplementation induced the production of methional, but not Mn²⁺ supplementation. The presence of Mn²⁺ improved the production of methionol and dimethyl disulphide, but inhibited the formation of S-methyl thioacetate. The study indicated that optimization of physicochemical conditions and media composition would be crucial for producing l-methionine-derived VSC bioflavor.

Improving truffle mycelium flavour through strain selection targeting volatiles of the Ehrlich pathway

Truffles (Tuber spp.) are the fruiting bodies of symbiotic fungi, which are prized food delicacies. The marked aroma variability observed among truffles of the same species has been attributed to a series of factors that are still debated. This is because factors (i.e. genetics, maturation, geographical location and the microbial community colonizing truffles) often co-vary in truffle orchards. Here, we removed the co-variance effect by investigating truffle flavour in axenic cultures of nine strains of the white truffle Tuber borchii. This allowed us to investigate the influence of genetics on truffle aroma. Specifically, we quantified aroma variability and explored whether strain selection could be used to improve human-sensed truffle flavour. Our results illustrate that aroma variability among strains is predominantly linked to amino acid catabolism through the Ehrlich pathway, as confirmed by 13C labelling experiments. We furthermore exemplified through sensory analysis that the human nose is able to distinguish among strains and that sulfur volatiles derived from the catabolism of methionine have the strongest influence on aroma characteristics. Overall, our results demonstrate that genetics influences truffle aroma much more deeply than previously thought and illustrate the usefulness of strain selection for improving truffle flavour.