Free Amino Acids Research Articles

Flowering in aged white tea: Recovering umami taste and amplifying of stale aroma

Throughout the natural aging process from new to aged white tea, the flavor evolves into a ‘stale flavor’, despite the initial umami diminishes. The flowering process, inoculation of Eurotium cristatum to white tea, improves the flavor. The impact on sensory qualities and underlying chemical basis of flowering in aged white tea warrant investigation. Sensory analysis, non-targeted metabolomics and volatilomics together deciphered flavor modifications of flowering in aged white tea from different aging years (FAWTs). Findings indicate the flowering process can recover the umami of aged white tea, enhancing the ‘stale flavor’. These changes primarily stem from oxidations of catechins and free amino acids, enrichments of flavonols and soluble sugars, and 16 pivotal aroma compounds from degradations of lipids and glycosides. Additionally, 15 volatile and 39 non-volatile compounds were identified as potential biomarkers for FAWTs. These findings offer a viable strategy to improving the quality of aged white tea.

Effects of acetic acid fermentation on the phytochemicals content, taste and aroma of pineapple vinegar

Acetic acid fermentation of pineapple vinegar was processed by self-priming fermenter, and this study aimed to show the relationship between flavor and metabolic substances in industrial production. E-nose and E-tongue respectively characterized the changes in aroma and taste. Meanwhile, the organic acids, free amino acids, volatile components were monitored in real time by HPLC and HS-SPME-GC-MS. The results show that the most significant flavor changes took place in the initial stage (0–4 days). The floral aromas initially provided by ethanol diminished, was replaced by the emergence of rich fatty and fruity aromas attributed to acetic acid and Ethyl-2-methylbutanoate, respectively. The bitter of pineapple vinegar was reduced, acidity and astringency were significantly increased, which may be due to changes in amino acids and organic acids. In addition, the DPPH radical and FRAP scavenging activity remain stable, while HFRC radical scavenging activity increased significantly in pineapple vinegar, reached 55.78%. Our study findings provided valuable information on the functional characteristics and quality of pineapple vinegar.

Analyses of the physicochemical and sensory characteristics of black goat triceps brachii muscle based on slaughter age

In this study, we aimed to analyze the effects of slaughter age on black goat meat's physicochemical and nutritional characteristics. Goats (age: 3, 6, 9, 12, 24, and 36 months) reared under identical conditions were used in this study. The key parameters were analyzed, including color, cooking yield, shear force, free amino acid (FAA) levels, free fatty acid levels, and sensory attributes. Hue values decreased, whereas redness increased with age. Umami and sweet FAA levels increased with age, and bitter FAA levels increased from 9 months. The flavor scores increased with age up to 9 months. Off-flavors were significantly higher in goats aged 24 and 36 months than in those aged 3 and 6 months. Goats aged 9 and 12 months had significantly higher texture scores than those aged 3, 6, and 36 months. Overall, our findings suggest that goats aged 9 and 12 months exhibit the best sensory qualities.

Amino Acid Bitterness: Characterization and Suppression.

Amino acids are necessary for life, and many must be consumed because they cannot be endogenously synthesized. Typically, we eat them as proteins and peptides, which have little taste. However, we also directly ingest free amino acids, several of which are aversive because they elicit bitterness. This bitterness often prevents many patient populations from taking formulas and supplements containing free amino acids. Here, we characterize which amino acids are the most bitter, their concentration-intensity functions, and individual differences in bitterness perception, and we explore how sodium salts suppress the bitterness of amino acids. We found that the essential amino acids comprise the most bitter stimuli, with six of them conveying the most bitterness. Clustering and correlating amino acids by individual differences in bitterness perception show that there are approximately four groupings of amino acids and suggest that within these clusters, amino acids may be activating the same or overlapping TAS2Rs. We also show that bitterness can be largely suppressed by sodium salts for 5 of the 6 most bitter amino acids. These results hold promise for managing the bitter taste of nutritional supplements that contain amino acids and improving compliance.

Synergistic effect of cyclodextrins and electrolytes at high concentrations on protein aggregation inhibition

The stabilization of protein therapeutics against aggregation is crucial for maintaining their efficacy and safety. This study investigated the synergistic effects of cyclodextrins (CDs) and electrolytes at high concentrations on the stabilization of immunoglobulin G (IgG), insulin, and adeno-associated virus (AAV) vectors. The effects of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) combined with various electrolytes were evaluated using human plasma-derived IgG as a model protein. The HP-β-CD and L(+)-arginine hydrochloride combination synergistically increased the onset temperature of protein aggregation and inhibited the formation of soluble and insoluble aggregates during long-term storage. Notably, this synergistic effect was not observed when sucrose was used instead of HP-β-CD. Similar synergistic effects were observed with insulin and AAV vectors. The findings suggest that the stabilization mechanism could potentially involve enhanced interactions between HP-β-CD and IgG, preventing protein–protein interactions. However, the combination did not synergistically improve the solubility of free aromatic amino acids, including tyrosine and tryptophan. This study highlights the potential of using the combination of CDs and electrolytes as a promising formulation strategy for stabilizing complex protein therapeutics. However, further studies are needed to elucidate the underlying mechanisms and generalize the approach to other proteins with varying physicochemical properties.

Physio-biochemical mechanism of melatonin seed priming in stimulating growth and drought tolerance in bread wheat

Drought stress (DS) adversely affects a plant’s development and growth by negatively altering the plant’s physio-biochemical functions. Previous investigations have illustrated that seed priming with growth regulators is an accessible, affordable, and effective practice to elevate a plant’s tolerance to drought stress. Melatonin (MT) is derived from the precursor tryptophan and can improve germination, biomass, and photosynthesis under stress conditions. The current study examined the effect of melatonin seed priming on two wheat cultivars (Fakhar-e-Bhakkar and Akber-19) cultivated under severe drought conditions (35% FC). There were 6 levels of melatonin (i.e., M0 = control, M1 = 1 mg L− 1, M2 = 2 mg L− 1, M3 = 3 mg L− 1, M4 = 4 mg L− 1 and M5 = mg L− 1) which were used for seed priming. Our results confirmed that seed priming with M2 = 2 mgL− 1 concentration of MT alleviates the negative effects of DS by boosting the germination rate by 54.84% in Akber-19 and 33.33% in Fakhar-e-Bhakkar. Similarly, leaf-relative water contents were enhanced by 22.38% and 13.28% in Akber-19 and Fakhar-e-Bhakkar, respectively. Melatonin pre-treatment with 2 mgL− 1 significantly enhanced fresh and dry biomass of shoot and root, leaf area, photosynthetic pigments, osmoprotectants accumulation [total soluble proteins (TSP), total free amino acids (TFAA), proline, soluble sugars, glycine betaine (GB)] and lowered the amount of malondialdehyde (MDA) and hydrogen peroxide (H2O2) production by elevating antioxidants [Ascorbic acid, catalase (CAT), Phenolics, peroxidase (POD) and superoxide dismutase (SOD)] activity under drought stress (DS). Meanwhile, under control conditions (NoDS), the melatonin treatment M1 = 1 mgL− 1 effectively enhanced all the growth-related physio-biochemical attributes in both wheat cultivars. In the future, more investigations are suggested on different crops under variable agroclimatic conditions to declare 2 mgL− 1 melatonin as an efficacious amendment to alleviate drought stress.

Muscle Proteins, Technological Properties, and Free Amino Acids of Epaxial Muscle Collected from Asian Seabass (Lates calcarifer) at Different Postmortem Durations

The aim of this study was to compare the changes in the epaxial muscle proteins of Asian seabass at two different postmortem durations. The epaxial muscles of Asian seabass were collected 1 h or 24 h postmortem (PM). Whole, ungutted fish were stored in an ice box, with the ice refilled every two hours. The results show significant increases in the MFI values and the contents of solubilized sarcoplasmic proteins, with a molecular weight of proteins of 47 kDa in the 24 h PM samples (p < 0.05). Myofibrillar and alkaline-soluble proteins in the epaxial muscle remained intact 24 h postmortem. Compared with the 1 h PM samples, the 24 h PM meat exhibited lower degrees of expressible water and hardness (p < 0.05), indicating superior water-holding capacity and meat tenderness. However, no differences in springiness or cohesiveness of the cooked meat were observed. Free L-glutamic acid, known as an umami-tasting amino acid, was significantly increased upon the extension of postmortem duration, and its level was above the taste threshold concentration. Overall, the findings indicated that the 24 h PM epaxial muscle of Asian seabass exhibited superior technological properties, along with higher contents of taste-related amino acids.

Effect of ultrasound and enzymatic pre-treatments on the profile of bioactive peptides of beef liver hydrolysates

The use of meat by-products as a potential source of protein hydrolysates rich in bioactive peptides is of growing interest to valorise these products and improve their sustainable use. This study aimed to evaluate the effect of different pre-treatments (hydrolysis with pepsin, ultrasounds, and ultrasounds-assisted pepsin hydrolysis) on the peptide profile and bioactivity of beef liver hydrolysed with flavourzyme. The pre-treatments with pepsin increased the degree of hydrolysis and generation of free amino acids in the liver hydrolysates, whereas the subsequent hydrolysis with flavourzyme influenced the molecular weight distribution of the peptides. Samples pre-treated with pepsin and ultrasounds-assisted pepsin hydrolysates showed the highest values of antioxidant and inhibitory activity of ACE-I, ECE-I, DPP-IV, and neprilysin enzymes, and therefore these hydrolysates were characterised to obtain the bioactive peptide profiles. A total of 995 peptides were identified by tandem mass spectrometry in the most active fractions separated by reversed-phase liquid chromatography, and 20 of them were predicted as potentially responsible for the observed bioactivities and subsequently characterised by in silico tools. These results evidenced the potential of hydrolysis pre-treatments with pepsin and ultrasounds-assisted pepsin to obtain beef liver hydrolysates rich in bioactive peptides that could exert multifunctional bioactivities such as antioxidant, antihypertensive, and antidiabetic, while giving added value to this meat by-product.

Biological conversion of red garlic (Allium sativum L) protein to bioactive peptides: ACE- DPP-IV inhibitory, and Techno-functional features

This study explores the impact of enzymolysis on the free amino acid content, techno-functional properties, free-radical scavenging, ACE, DPP-IV inhibition, iron-ion chelation and TBARS production in O/W emulsion stabilized with red garlic protein (RGP) and hydrolysates (RGPHs). The research reveals that enzymolysis time and pH significantly influence the amino acid content (antioxidant, hydrophobic, and essential ones), functional and biological quality of RGP/RGPHs. The study demonstrates that enzymolysis positively correlates with solubility (up to 90 %), health-promoting and antioxidant characteristics like DPPH (74.2 %), ABTS (81.3 %), OH (63.4 %), Reducing power (1.1 Abs700), NO (59.5 %), TAA (1.4 Abs695), ACE (71.9 %), DPP-IV (51.5 %) inhibitory, Fe2+ chelating (46.8 %) activity, and leading to reduced water/oil holding capacities, TBARS (from 0.61 to 0.38) value and lipid oxidation. However, extensive enzymatic hydrolysis (over 90 min) reduced emulsion and foaming abilities. On the other hand, the techno-functional properties of RGP and RGPHs exhibited a significant decline near the isoelectric point. This enhancement suggests that RGP could be used as a natural antioxidant with potential health benefits (antihypertensive and antidiabetic) in food and pharmaceutical formulations.

Drying-induced metabolic changes in daylily: A comprehensive analysis of VOC profiles and antidepressant compounds

Daylilies are mellow-colored edible items with significant medicinal value. This study systematically evaluates the changes in the morphology and texture of daylily buds (DLB) dried by three different techniques (vacuum freeze-drying (FD), vacuum drying (VD), and hot-air drying (HD)). FD-DLB retain a more complete microstructure appearance with brighter colors and a better rehydration ability than VD-DLB or HD-DLB. According to the results of electronic-tongue and free amino acid content analyses of nutritional components, FD-DLB retain the freshness, taste, and nutritional value of DLB more than HD-DLB and VD-DLB. GC–IMS detected 28 differential metabolites; among them, the VD-DLB samples contain a relatively high content of 24 volatile components such as methyl hexanoate-D. LC–MS indicates that FD enables the retention of a high level of certain flavonoid components with strong antidepressant activity such as hyperoside, rutin, quercetin. The results of this study confirm that the FD method, which enables a better retention of nutritional and antidepressant active ingredients in DLB samples, exhibits promising potential for industrial application as a drying technology for the manufacture of DLB samples with dual-use value as medicine and food. Therefore, this study contributes significantly to guide future research on optimal methods for the treatment of functional foods.

Effect of inoculation with different Eurotium cristatum strains on the microbial communities and volatile organic compounds of Fu brick tea

Eurotium cristatum is the primary fungus in Fu brick tea (FBT) and plays a crucial role in its special flavor. This study investigated the effect of inoculation with different E. cristatum strains (i.e., ZJ, GX, GZ, HN, and SX) on the microbial communities and volatile organic compounds (VOCs) of FBT. A total of 113 VOCs were identified in all samples, with the concentration of VOCs (alcohols, aldehydes, and ketones) significantly higher in GXE FBT than in other samples. The core VOCs of GXE (19), GZE (16), HNE (19), SXE (15), and ZJE (13) FBT were identified using orthogonal partial least squares discriminant analysis and relative odor activity value (ROAV) analysis. Methional (a27), butanal (a41), 1-octen-3-one (a69), and ethyl acetate (a77) were key markers for inoculated FBTs, and 1-octen-3-ol, dimethyl disulfide, and acetoin-M were the specific markers of HNE. Linalool and (E)-2-octenal were particularly prominent in GXE, and isoamyl acetate-D was an important aroma component of GZE. Differences in microbial diversity were observed among the different inoculated fermented FBTs, and E. cristatum inoculation remarkably influenced the richness and diversity of bacterial communities. The VOCs were closely associated with fungi and bacteria, and 19 potentially dominant microorganisms (10 fungal and 9 bacterial genera) correlated with VOCs were identified. Among them, Aspergillus (fungi) and Pseudomonas (bacteria) exerted the greatest role. The FBT inoculated with E. cristatum from ZJ had the highest content of theaflavins and theabrownins, which intensified the red and yellow colors of the tea. E. cristatum greatly decreased the free amino acids and fatty acids, contributing to the aroma formation of FBT. Therefore, inoculating FBT with E. cristatum remarkably influenced the microbial communities and improved its flavor profile. This work provides a theoretical foundation on the role of E. cristatum in the formation and regulation of FBT flavor.

A new approach to assess post-mortem interval: A machine learning-assisted label-free ATR-FTIR analysis of human vitreous humor

A crucial issue in forensics is determining the post-mortem interval (PMI), the time between death and the finding of a body. Despite various methods already employed for its estimation, only approximate values are currently achievable. Vitreous humor (VH) is an avascular tissue between the lens and the retina, mainly composed by a collagen fibers network, hyaluronic acid, and hyalocytes. Recently, it has received interest in forensic medicine, being easy to collect and susceptible to low microbiological contamination and putrefaction. Based on this evidence and thanks to the ability of Attenuated Total Reflectance – Fourier Transform InfraRed (ATR–FTIR) spectroscopy to perform fast analyses on a minimal sample amount, in this study, a new analytical approach to reliably estimate PMI is proposed combining ATR-FTIR analysis of VH human samples with multivariate statistical procedures, such as Principal Component Analysis (PCA) and Partial Least Squares-Discriminant Analysis (PLS-DA), for discriminant classification. Regression procedures, including Partial Least Squares Regression (PLSR), were performed: extremely positive results were obtained, and the most discriminant spectral features were highlighted (peaks at 1665, 1630, 1585, 1400, 1220, 1200, 1120, 854, 835, and 740 cm−1) and associated to PMI classes (average accuracy over 80 %). Specific and reliable markers able to correlate the macromolecular composition of VH with the PMI were identified, revealing a post-mortem protein degradation and amino acids deamination (decrease of proteins and increase of free amino acids and NH3), an increase of lactate, which diffuses from the retina to the VH, and changes in the hyaluronic acid component.

The effect of packaging material and adjunct culture on the biogenic amine content, microbiological and textural properties of Dutch-type cheese

The aim of the study was to assess the effects of the packaging materials applied (shrink foil, copolymer coating and food wax) in combination with Lacticaseibacillus casei CCDM 198 microbial strain on biochemical, microbiological and textural properties of Dutch-type cheese during ripening (at 12 ± 1 °C for 168 days). A multivariate principal component analysis method based on a correlation matrix was employed to evaluate the relationships between basic chemical properties, textural and microbiological parameters, biogenic amine and free amino acid contents in relation to the packaging material used and the length of the ripening time. The use of different packaging materials did not have a significant effect on the salt content, fat content, and pH values, whereas significant differences were observed for dry matter content and textural properties development. The presence of Lacticaseibacillus casei CCDM 198 strain accelerated proteolysis in all samples. Shrink foil and food wax had similar effects on the development of biogenic amine content during ripening, while considerable differences were observed for the samples wrapped in copolymer coating. Copolymer coating in combination with Lacticaseibacillus casei CCDM 198 strain was able to reduce biogenic amine content by up to 28% after 168 days.

The effect of adding Gracilaria on flavor and quality of low-salt fermented soy sauce

With the increasing awareness of health, there are higher expectations of customers for the unique flavor, umami, and nutritional value of soy sauce. To explore the potential application of edible seaweed in soy sauce, this study utilized high nutritional value seaweeds to ferment soy sauce and investigated the effects of the addition of Gracilaria on the physicochemical properties and flavor substances of soy sauce. The contents of amino acid nitrogen and total nitrogen in Gracilaria soy sauce were 0.8 g/100g and 1.4 g/100g, respectively, which were higher than those in traditional soy sauce. The free amino acid content of Gracilaria soy sauce (17.82 mg/g) was 1.35 times higher than that of traditional soy sauce, the organic acids content of Gracilaria soy sauce (15.78 mg/mL) was 1.12 times higher than that of traditional soy sauce. Compared with traditional soy sauce, the addition of Gracilaria promoted the accumulation of pyrazines and acids in soy sauce, which contributed to the seafood-like flavor. In general, the addition of Gracilaria to ferment soy sauce can improve the quality and give it a unique flavor. This study can provide a reference for improving the quality and flavor diversity of soy sauce by using seaweed as a fermentation substrate.

Effect of commercial Saccharomyces cerevisiae and non-Saccharomyces yeasts on the chemical composition and bioaccessibility of pineapple wine

Alcoholic fermentation is one of man’s most efficient food preservation processes, and innovations in this area are a trend in food science and nutrition. In addition to the classic Saccharomyces yeasts, various other species may have desirable characteristics for obtaining fruit wines. This study investigated the profile of non-Saccharomyces commercial yeasts compared with S. cerevisiae regarding pineapple wine’s chemical composition and bioaccessibility. The fermentation profile of the yeasts Lachancea thermotolerans, Brettanomyces bruxellensis, Brettanomyces lambicus, and S. cerevisiae was evaluated for sugar and alcohol content, and the pineapple wines obtained were analyzed for amino acids, phenolics, and organic acids by HPLC and volatile profile by GC/MS. All yeast strains were able to produce ethanol and glycerol at acceptable levels. L. thermotolerans produced higher levels of lactic acid (0.95 g/L) and higher consumption of free amino acids. B. bruxellensis produced higher levels of individual phenolics and ethanol 109 g/L. The alcoholic fermentation process improved the bioaccessibility of phenolics such as catechin (237 %), epigallocatechin gallate (81 %), procyanidin B1 (61 %) and procyanidin B2 (61 %). The yeasts differed in their volatile profiles, with Brettanomyces and Lachancea producing higher levels of compounds associated with pineapple aroma, such as ester ethyl butyrate (260–270 µg/L). These results demonstrate the importance of choosing the yeast strain for the conduction of alcoholic fermentation and that the yeasts Brettanomyces and Lachancea showed technological potential in obtaining pineapple wines. This study contributes to developing processes for obtaining fruit wines by highlighting two non-Saccharomyces yeast species with technological potential for alcoholic fermentations.

Fermentation dynamics of bile salt hydrolase production in Heyndrickxia coagulans ATCC 7050 and Lactiplantibacillus plantarum ATCC 10012: Addressing ninhydrin assay limitations with a novel HPTLC–MS method

Bile salt hydrolase (BSH), a pivotal enzyme in cholesterol management, holds significant promise in both human and animal subjects. This study investigated the effect of fermentation dynamics in Heyndrickxia coagulans ATCC 7050 and Lactiplantibacillus plantarum ATCC 10012 to enhance BSH production. Cultivation of cultures in MRS and M17 media revealed that MRS medium enhanced BSH production by 235.98 % in H. coagulans ATCC 7050 and 147.37 % in L. plantarum ATCC 10012, compared to M 17 medium. Additionally, varying oxygen concentration levels indicated that H. coagulans ATCC 7050 exhibited its minimum doubling time of 79.8 ± 0.64 min in anaerobic conditions, whereas L.plantarum ATCC 10012 demonstrated its minimum doubling time of 85.5 ± 1.2 min under microaerophilic conditions. However, their highest BSH activity was observed during the stationary phase under anaerobic conditions, yielding 17.14 ± 0.78 U/mL by H. coagulans ATCC 7050 and 19.04 ± 0.81 U/mL by L.plantarum ATCC 10012. Furthermore, it was observed that both organisms did not retain BSH within their cells. BSH activity was assessed using ninhydrin assay that detected free taurine liberated from sodium taurocholate. However, ninhydrin can yield false–positive results owing to its interaction with other free amino acids. To subjugate this limitation, the study introduced a novel and sensitive HPTLC–MS method capable of accurately detecting taurine. By comprehending fermentation dynamics and selecting appropriate conditions, BSH production increased 2.1–fold in both organisms. These findings illuminate critical insights, offering a pathway for novel strategies to enhance the BSH–producing capabilities of these LAB strains.

Green Seaweeds as a Potential Source of Biomolecules and Bioactive Peptides: Recent Progress and Applications - A Review.

Over the past few decades, seaweed has been explored as a sustainable source in biotechnological and biomedical industries because of its multiple biopotential actions. However, the composition of biomolecules such as carbohydrates, lipids, fatty acids, free amino acids, ash, minerals, vitamins, and especially protein in green seaweeds varies from species to species based on their growth stage and the environmental conditions. Specifically, seaweed-derived bioactive proteins and peptides have the potential for several health benefits. They serve as a balanced diet. Protein which is an extensive macronutrient in human nutrition, should be explored to avoid using animal-sourced protein, which is expensive to consume. Bioactive peptides that are isolated from marine algae consist of various kinds of functional properties. In the food industry, seaweeds are novel molecules for being used in both nutritional foods and nutraceuticals. In both in vitro and In vivo conditions, various seaweed-derived bioactive compounds have shown a broad range of biological activities including anti-cancer and immunomodulatory, anti-hypertensive, and anti-coagulant activities. Hence, this review paper discusses the screening of seaweed-derived biochemicals with a special focus on their proteins, peptide contents, and nutra-pharmaceutical values.

Multi-omics profiling the dynamic variations of flavor and nutritional components during pearl gentian grouper soup processing

Flavor and nutritional value are essential components of fish soup, as highlighted by both producers and consumers. This study systematically examined the color, aroma, taste, and nutritional composition of pearl gentian grouper soup (PGGS) samples processed over varying durations, employing multi-omics technologies, including sensomics, volatilomics, lipidomics, and metabolomics. A comprehensive identification of 58 volatile aroma compounds, 407 lipids, 203 metabolites, and 47 taste components was achieved. The findings indicated that as processing time increased, the brightness of PGGS diminished, resulting in a thicker consistency. The aroma profile of PGGS was predominantly characterized by meaty and fatty notes, which were closely associated with carbonyl compounds (nonanal, dodecanal, (E)-2-octenal, and 2-undecanone) that developed due to glyceride oxidation during prolonged thermal processing. The predominant taste profile of PGGS was identified as umami, likely resulting from the synergistic effects of umami-enhancing amino acids (glutamic acid, aspartic acid) and 5ʹ-nucleotides (adenosine monophosphate, inosine monophosphate, guanosine monophosphate). Furthermore, PGGS may represent a significant source of taurine, with its taurine content accounting for over 60% of the total free amino acids (FAAs). Considering the variations in color, flavor, and nutritional content throughout the processing of PGGS, as well as the associated time costs, a processing duration of 2 h was optimal.

Effects of Variable-Temperature Roasting on the Flavor Compounds of Xinjiang Tannur-Roasted Mutton.

This study investigates the effect of variable-temperature roasting on the flavor compounds of Xinjiang tannur-roasted mutton. Gas chromatography coupled with ion mobility spectroscopy (GC-IMS) was used to compare and analyze the volatile components and flavor fingerprints of Xinjiang tannur-roasted mutton using variable-temperature electrically heated air roasting (VTR), constant-temperature electrically heated air roasting (EHAR), and constant-burning charcoal roasting (BCR) techniques. The changes in fatty acids and free amino acids in Xinjiang tannur-roasted mutton under different roasting conditions were compared. By using GC-IMS analysis, 11 flavor compounds, including 4-methyl-3-penten-2-one, isoamyl propionate, trans-2-heptenal, trans-2-heptenal, 2-hexanone, n-hexanol, 2-hexenal, 2-ethylfuran, and ethyl 2-methylbutanoate, were identified as characteristic volatile compounds in the temperature-controlled electrothermal roasting of Xinjiang tannur-roasted mutton using the following conditions: 0-4 min, 300 °C; 5-10 min, 220 °C; and 11-17 min, 130 °C (VTR3). Through principal component analysis, it was found that the substances with the highest positive correlation with PC1 and PC2 were n-hexanol and 3-methylbutanol. The sensory evaluation showed that VTR3 had high acceptability (p < 0.05) and a fat flavor (p < 0.05). There was no significant difference in the total fatty acid (TFA) content between the VTR3 and burning charcoal roast for 1-17 min at 300 °C (BCR3) (p > 0.05), but it was lower than that in the other experimental groups (p < 0.05). The lowest proportion of glutamic acid content in VTR3 was 22.44%, and the total free amino acid content in the electric thermostatic roasting for the 1-17 min, 300 °C (EHAR3) group (347.05 mg/100 g) was significantly higher than that in the other experimental groups (p < 0.05). By using Spearman correlation analysis, the roasting loss rate showed a highly significant negative correlation with essential amino acids (EAAs), non-essential amino acids (NEAAs), and total free amino acids (TAAs) (the correlation coefficients (r) were 0.82, 0.87, and 0.87, respectively) with p < 0.01. There was no correlation between changes in the free amino acid content and fatty acid content (p > 0.05). By using Differential scanning calorimetry (DSC) analysis, we also found that there was no significant difference in peak temperature (Tp) between the VTR3 and EHAR experimental groups (p > 0.05). Variable temperature electric heating can affect the flavor of lamb, and there are significant differences in the content of flavor precursors such as fatty acids and amino acids in Xinjiang tannur-roasted mutton.

Changes of physicochemical and volatile flavor compounds of dry-cured Diqing Tibetan pig hams during fermentation

This study aimed to explore the flavor formation mechanism of Diqing Tibetan pig hams by investigating changes of their physicochemical and volatile flavor compounds during fermentation (0, 30, 90, 180, 360, and 540d) using amino acid analyzer , texture profile analysis, and gas chromatography-ion mobility spectroscopy (GC-IMS). During fermentation, the hams significantly decreased in moisture and centrifugal loss, while increased in chewiness, hardness, and proteolysis index, with their free amino acids content reaching the maximum at 360d and significantly decreasing at 540d. GC-IMS identified 78 volatile organic compounds, with the highest total content of alcohols and aldehydes at 180d, ketones and heterocycles at 360d, and esters at 540d. PLS-DA screened 24 volatile flavor markers, with aldehyde (2-methyl-2-propenal), ketone (2-heptanone-D), alcohol (3-methylbutanol-D), ester (ethyl3-methylbutanoate-M), and heterocyclic substances (2,3-dimethylpyrazine-M) as the main VFMs at 360d. The unique flavor of 540d Diqing Tibetan pig hams was attributed to their higher content of 3-methyl-2-butenal, 3-(methylthio) propanal, ethyl caproate and 2-butanone. These findings provide a scientific basis for the flavor formation mechanism of hams which favoring the further development processing strategies for Diqing Tibetan pig.