Total Volatile Basic Nitrogen Research Articles

Tilapia gelatin films by incorporating metal-polyphenol network formed by procyanidin and zinc ion for pork preservation

There is a lack of information about the application of metal polyphenol networks (MPN) in the food industry nowadays. Herein, the MPN was prepared by procyanidin (PC) and zinc ion (Zn2+), and introduced into tilapia gelatin films. The MPN-modified films showed broader thickness, higher UV-Vis light barrier property, and lower water sensitivity and water vapor property than PC-modified films. When the molar ratio of Zn2+ to PC being 3:8, the incorporation of MPN induced the highest tensile strength of films reaching 82.47 MPa, good activity against oxidation, and improved inhibition activity to Staphylococcus aureus and Escherichia coli. The MPN-modified gelatin films could suppress the bacteria growth, and attenuate the generation of total volatile basic nitrogen and thiobarbituric acid reactive substances, causing the shelf life of pork extended by five and three days compared with the control and PC-modified films, respectively. The results suggested that MPN provided great potential in the application of food packaging.

EFFECT OF SUBZERO STORAGE ON THE QUALITY OF MUTTON FROM SHEEP AND GOATS IN D.I KHAN DISTRICT, KHYBER PAKHTUNKHWA

Mutton is widely recognized for its excellent nutritional value, containing essential components such as proteins, vitamins, and minerals. The objective of this research was to investigate the effects of subzero storage on the freshness and quality of mutton. To evaluate the attributes of frozen and stored mutton, we employed fresh control samples that underwent standard freezing procedures at -18°C. Determining the quality and freshness of the product required the evaluation of numerous parameters over a five-month storage period. Drip loss (comprising boiling and thawing loss), water-holding capacity (WHC), texture profile analysis (TPA), thiobarbituric acid reactive substances (TBARS), and total volatile basic nitrogen encompassed these parameters. Temperature influenced leak loss and water holding capacity (WHC), with severe freezing resulting in a reduction in moisture loss during frozen storage in comparison to standard freezing conditions. Extremely low-temperature freezing and subsequent storage of lamb resulted in a notable enhancement in tenderness when compared to standard freezing conditions. More precisely, sheep that underwent freezing at temperatures below -60℃ exhibited a tenderness akin to that of recently slaughtered mutton. Following a five-month period, frozen samples of mutton exhibited no indications of lipid oxidation, irrespective of temperature. The storage temperature of the samples, nevertheless, had an impact on the TVBN (total volatile basic nitrogen) concentration. In conclusion, our research indicates that mutton can maintain its freshness for a period of five months through the utilization subzero temperatures. A temperature of -60℃ is determined to be the most favorable condition for freezing and storing frozen mutton, taking into account both economic and qualitative considerations.

Enhanced pH-sensitive anthocyanin film based on chitosan quaternary ammonium salt: A promising colorimetric indicator for visual pork freshness monitoring

An intelligent pH response indicator film is an easy-to-use device for the real-time monitoring of meat freshness during transport and storage. Therefore, a novel pH-sensitive anthocyanin indicator film composed of polyvinyl alcohol–blueberry anthocyanin (BA)–2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) called PAH-2.0 with 1.2 mg/mL HACC to monitor meat freshness using HACC as the colorimetric enhancer has been developed. BA and HACC were mixed and immobilized in the polyvinyl alcohol matrix by hydrogen bonds, as confirmed via Fourier-transform infrared spectroscopy and X-ray diffraction. The inclusion of HACC improved the color stability and antioxidant and antibacterial properties of the PAH-2.0 film. When applied to pork for freshness monitoring at 4 °C, three freshness stages, including fresh, sub-fresh, and spoiled, could be clearly distinguished based on the color variations of the PAH-2.0 film. The distinct hierarchical color change from purple to blue-violet and finally to grayish-blue was highly correlated with the indicators of pork freshness: pH values, total volatile basic nitrogen, and total viable count. This study provides a simple and promising approach for fabricating meat freshness indicator films with high color recognition accuracy, thereby offering new possibilities for visual meat freshness monitoring.

Effects of slurry ice treatment on the physicochemical changes and proteome of large yellow croaker (Larimichthys crocea)

Large yellow croaker (Larimichthys crocea) is susceptible to oxidative denaturation during storage. This work is to investigate the quality alterations by analyzing its physicochemical changes and proteomics throughout preservation under refrigeration, frozen, and slurry ice (SI) conditions. Results revealed that the freshness of large yellow croaker, as evaluated by indicators such as total volatile basic nitrogen, total viable count, and thiobarbituric acid reactive substances, was well maintained while stored in the SI group. Meanwhile, the water distribution in the muscle tissue of group SI exhibited slower fluctuations, thereby preserving the integrity of fish muscle cells. Based on label-free proteomic analysis, a considerable downregulation was observed in the mitogen-activated protein kinase (MAPK) signaling pathway, indicating that SI decelerated this metabolic pathway and effectively delayed the deterioration of muscle. Therefore, the application of SI provides potential for maintaining the quality stability of large yellow croaker.

Towards Reducing Food Wastage: Analysis of Degradation Products Formed during Meat Spoilage under Different Conditions.

Foodstuffs, particularly perishable ones such as meat, are frequently discarded once the best-before date has been reached, despite the possibility of their continued suitability for human consumption. The implementation of intelligent packaging has the potential to contribute to a reduction in food wastage by enabling the monitoring of meat freshness during storage time independently of the best-before date. The process of meat spoilage is associated with the formation of specific degradation products, some of which can be potentially utilized as spoilage indicators in intelligent packaging. The aim of the review is to identify degradation products whose concentration correlates with meat shelf life and to evaluate their potential use as spoilage indicators in intelligent packaging. To this end, a comprehensive literature research was conducted to identify the factors influencing meat spoilage and the eight key degradation products (carboxylic acids, biogenic amines, total volatile basic nitrogen, aldehydes, alcohols, ketones, sulfur compounds, and esters) associated with this process. These degradation products were analyzed for their correlation with meat shelf life at different temperatures, atmospheres, and meat types and for their applicability in intelligent packaging. The review provides an overview of these degradation products, comparing their potential to indicate spoilage across different meat types and storage conditions. The findings suggest that while no single degradation product universally indicates spoilage across all meat types and conditions, compounds like carboxylic acids, biogenic amines, and volatile basic nitrogen warrant further investigation. The review elucidates the intricacies inherent in identifying a singular spoilage indicator but underscores the potential of combining specific degradation products to expand the scope of applications in intelligent packaging. Further research (e.g., storage tests in which the concentrations of these substances are specifically examined or research on which indicator substance responds to these degradation products) is recommended to explore these combinations with a view to broadening their applicability.

Simulation and Validation of a Novel Colorimetric Three‐Layer Intelligent Indicators With Different Binders to Monitor Freshness of Atlantic Bonito (Sarda sarda) Under Two Different Atmospheres

ABSTRACTReal‐time monitoring of spoilage/freshness of perishable food products using intelligent indicators under commercial packaging conditions is of interest. Thus, this study is aimed at fabricating intelligent indicators to determine the possibility of using developed indicators to monitor fish freshness packaged under real packaging conditions. Bromothymol blue (BTB) dye and two different binders (methyl cellulose [MC] and cellulose acetate [CA]) were used to fabricate four different indicators, with the addition of NaOH for carbon dioxide (CO2) or HCl for total volatile basic nitrogen (TVB‐N) sensitive indicators. The colour of produced indicators was observed during 10‐day simulations using CO2 and trimethyl amine (TMA) at different concentrations (0%–30% for both) at 4°C. BTB‐MC‐NaOH changed from blue to green at 15% CO2, while BTB‐CA‐NaOH changed from green to yellow at 25% CO2. Both BTB‐MC‐HCl and BTB‐CA‐HCl indicators changed colour completely at 15% TMA (BTB‐MC‐HCl from yellow to navy and BTB‐CA‐HCl from yellow to green). Indicators were used to monitor the spoilage of Atlantic bonito for 10 days at 4°C under two different modified atmosphere packaging (MAP) conditions (30% CO2, 70% nitrogen (N2) and 100% N2). Headspace gas analysis, pH, TVB‐N, TMA, microbiology, sensory and colour analyses were conducted. For 30% CO2 70% N2, CO2‐sensitive indicators showed a colour change responding to CO2 used, while TVB‐N sensitive indicators showed no visible colour change since the TMA level in packages did not reach the spoilage threshold. Colour transition was also not clear in any of indicators under 100% N2‐packaging, since neither colour‐changing range of CO2 or TMA was reached.

Farsi gum (zedo gum) coating incorporated with Lactobacillus sakei; a novel shelf-life extension for Turkey breast during refrigerated storage

Antioxidant and antibacterial coatings incorporated with biological agents are an emerging alternative for preserving meat products. In this study, Farsi gum-based coatings (FG) incorporated with Latilactobacillus sakei were used for the shelf-life extension of refrigerated turkey breast. The quality and safety properties of coated turkey breast were investigated during storage at refrigeration temperature. Results revealed that L. sakei loading into the FG coating could significantly (p < 0.05) improve the quality of turkey breast in a 16-day refrigerated storage. The increase in the values of pH (6.15–6.94), total volatile basic-nitrogen (TVB-N) (34.33–43.13 mg N/100 g), thiobarbituric acid reactive substances (TBARs) (2.27–3.67 mg MDA/kg), and protein carbonyl (PC) (1.62–2.14 nmol/mg protein) of samples during cold storage periods was as follows: FG 2% + L. Sakei < FG 1% + L. Sakei < FG 2% < FG 1% < uncoated (control). The microbial quality of turkey breast showed a significant (p < 0.05) improvement in the presence of the L. sakei coatings, ranging from 7.15 to 7.75 log10 CFU/g in different treatments. The texture, odor, color, and overall acceptability of the coated turkey breast samples were significantly (p < 0.05) more desirable than the uncoated turkey breast samples. The findings revealed that FG coating incorporated with L.sakei can improve turkey breast's shelf-life by reducing microbial growth and adverse chemical reactions.

Anthocyanin modified by chondroitin sulphate and tannic acid improved the quality-indicating properties of gelatin-based intelligent film

A highly pH-responsive gelatin film incorporating purple cabbage anthocyanin (PCA) and chondroitin sulphate (CS)/tannic acid (TA) was developed. Co-pigmentation of PCA via CS/TA improved its photothermal stability and visibility of color change in gelatin film. The morphological and structural properties of CS-PCA and TA-PCA films revealed that a more stable network was formed as new hydrogen bonds were generated by the co-pigmentation. Meanwhile, the co-pigmentation improved film's mechanical and hydrophobic properties, expressed as higher tensile strength (16.65 and 17.97 Mpa) and lower water vapor permeability (1.45 and 1.41) in CS-PCA and TA-PCA films, compared to PCA film. CS-PCA and TA-PCA films showed distinct color transitions for chilled fish fillets during storage. Total color difference (ΔE) of CS-PCA and TA-PCA films correlated well with the deterioration indexes of total volatile base nitrogen (TVB-N). All the results provided a novel pH-sensitive intelligent packaging strategy by co-pigmenting CS/TA with PCA for freshness monitoring.

Combination model for freshness prediction of pork using VIS/NIR hyperspectral imaging with chemometrics.

This study aimed to develop an enhanced model for predicting pork freshness by integrating hyperspectral imaging and chemometric analysis. A total of 30 Longissimus thoracis samples from three sows were stored under vacuum conditions at 4 ± 2℃ for 27 days to acquire data. The freshness prediction model for pork loin employed partial least squares regression (PLSR) with Monte Carlo data augmentation. Total bacterial count (TBC) and volatile basic nitrogen (VBN), which exhibited increases correlating with metabolite changes during storage, were designated as freshness indicators. Metabolic contents of the sample were quantified using NMR. A total of 64 metabolites were identified, with 34 and 35 showing high correlations with TBC and VBN, respectively. Lysine and malate for TBC (R2 = 0.886) and methionine and niacinamide for VBN (R2 = 0.909) were identified as the main metabolites in each indicator by Model 1. Model 2 predicted main metabolites using HSI spectral data. Model 3, which predicted freshness indicators with HSI spectral data, demonstrated high prediction coefficients; TBC R2p = 0.7220 and VBN R2p = 0.8392. Furthermore, the combination model (Model 4), utilizing HSI spectral data and predicted metabolites from Model 2 to predict freshness indicators, improved the prediction coefficients compared to Model 3; TBC R2p = 0.7583 and VBN R2p = 0.8441. Combining HSI spectral data with metabolites correlated to the meat freshness may elucidate why certain HSI spectra indicate meat freshness and prove to be more effective in predicting the freshness state of pork loin compared to using only HSI spectral data.

Development and antimicrobial activity of composite edible films of chitosan and nisin incorporated with perilla essential oil-glycerol monolaurate emulsions

Aquatic products are highly susceptible to spoilage, and preparing composite edible film with essential oil is an effective solution. In this study, composite edible films were prepared using perilla essential oil (PEO)-glycerol monolaurate emulsions incorporated with chitosan and nisin, and the film formulation was optimized by response surface methodology. These films were applied to ready-to-eat fish balls and evaluated over a period of 12 days. The films with the highest inhibition rate against Staphylococcus aureus were acquired using a polymer composition of 6 μL/mL PEO, 18.4 μg/mL glycerol monolaurate, 14.2 mg/mL chitosan, and 11.0 μg/mL nisin. The fish balls coated with the optimal edible film showed minimal changes in appearance during storage and significantly reduced total bacterial counts and total volatile basic nitrogen compared to the control groups. This work indicated that the composite edible films containing essential oils possess ideal properties as antimicrobial packaging materials for aquatic foods.

Combination of contact ultrasound and infrared radiation for improving the quality and flavor of air-dried beef during hot air drying

Air-dried beef, a traditional dry fermented meat product in China, whose quality is largely influenced by processing conditions. In this study, contact ultrasound (CU) and infrared radiation (IR) were employed to enhance hot air drying (HAD), with an investigation into the mechanisms underlying improvements in quality and flavor. Samples subjected to CU and IR treatments during HAD (CU-IRD) demonstrated superior color (L* = 42.68, a* = 5.05, b* = −3.86) and tenderness (140.59 N) than HAD group, primarily attributed to reduced drying times and alterations in ultrastructure. Analyses utilizing SDS-PAGE and total volatile basic nitrogen (TVB-N) revealed that HAD and CU-HAD resulted in significant protein oxidation (197.85 mg TVB-N/kg and 202.23 mg TVB-N/kg, respectively), while IR treatments were associated with increased thermal degradation of proteins, producing lower molecular weight peptides. Compared with HAD group, the activities of certain lipases and proteases were enhanced by ultrasound and infrared treatments, leading to the release of greater amounts of free fatty acids and flavor amino acids. Furthermore, the thermal effects of infrared and the cavitation effects of ultrasound contributed to increased fat oxidation, amino acid Strecker degradation, and esterification reactions, thereby augmenting the diversity and concentration of volatile flavor compounds, including alkanes, ketones, aldehydes, and esters. These findings indicate that the synergistic application of CU and IR represents a promising strategy for enhancing the quality of air-dried beef.

Lactobacillus plantarum derived nanoparticles deliver class IIa bacteriocin as a potential natural food preservatives

In recent years, the growing concern over human health risks associated with chemical preservatives in food has sparked increased interest in utilizing natural biopreservatives derived from probiotics. Bacteriocins, which are antibacterial peptides that have been deemed safe for human consumption and have been applied to food preservation. Several studies have emphasized that nanoparticles derived from edible plants can modulate microbes’ metabolic processes. In this study, we discovered that Lactobacillus plantarum LPL-1 can produce extracellular nanoparticles (LPL-NPs) containing a specific class IIa bacteriocin known as plantaricin LPL-1. LPL-NPs effectively suppressed the growth of Listeria monocytogenes 54002 by gradually disrupting their cell membranes. Intriguingly, we have also demonstrated that the ginger derived exosome-like NPs (GELNPs) enhance the antibacterial activity of LPL-NPs by enriching plantaricin LPL-1 within them through activation of a quorum sensing system component. Furthermore, GELNPs-treated LPL-NPs (GLPL-NPs) can effectively extend the storage period of sturgeon at 4 °C by mitigating pathogenic bacterial growth, preserving sensory quality, and reducing the levels of total volatile basic nitrogen (TVB-N), K value, trichloroacetic acid (TCA)-soluble peptides, and thiobarbituric acid reactive substances (TBARS). This study provides insight into a strategy for application of LPL-NPs as a natural biopreservative for food preservation.

Anti-biofilm and antioxidant activities of Sargassum muticum extracts and their preservation effect of Chinese shrimp (Penaeus chinensis)

Vibrio parahaemolyticus can enhance bacterial resistance to disinfectants and antimicrobials by forming biofilms. The development of new natural antimicrobials is essential for the control of biofilm-related contamination and infection. In this paper, we preliminarily explored the inhibitory activity of Sargassum muticum extracts (HA-PTs) against the biofilm of V. parahaemolyticus. HA-PTs exerted anti-biofilm activity by destroying the integrity of the cell membrane, curbing the motility of single and colonial bacteria, hindering the synthesis of polysaccharide intercellular adhesion, inhibiting the secretion of extracellular DNA, and reducing the metabolic activity of biofilms. Furthermore, experiments on four free radicals (DPPH•, •OH, ABTS+•, and O2−•) scavenging activity and total antioxidant capacity (FRAP method and phenanthroline method) demonstrated that HA-PTs have strong reducing properties and can capture a variety of free radicals, which in turn prevents them from participating in oxidative reactions. When HA-PTs were applied to Chinese shrimp infected with V. parahaemolyticus, it could prolong their shelf life by controlling the pH rise caused by protein degradation, inhibiting the bacterial proliferation, reducing the content of total volatile basic nitrogen produced by protein degradation, and reducing the accumulation of thiobarbiturates caused by oxidative deterioration of fats.

Double layer packaging based on active black chickpea protein isolate electrospun nanofibers and intelligent salep film containing black chickpea peel anthocyanins for seafood products

In this study, a double-layer active and intelligent packaging system was developed based on two main natural macromolecules i.e. protein and carbohydrate with green perspective. Firstly, the salep-based films containing different concentrations (0–8 % w/w) of the inclusion complex of β-cyclodextrin/black chickpea anthocyanins (βCD/BCPA) were produced. The salep film containing 8 % of βCD/BCPA complex was specified as the optimized film sample based on its performance as a color indicator. The electrospinning of black chickpea protein isolate nanofibers (BCPI NFs) containing citral nanoliposomes (NLPs) was done on the optimized salep film. The cross-sectional field emission scanning electron microscopy approved the creation of double-layer structure of the developed film. The study of chemical and crystalline structure, as well as the thermal properties of the film exhibited the physical attachment of BCPI electrospun NFs on salep film. The effectiveness of the developed system was studied in detection of spoilage and increasing the shelf life of seafood products, including shrimp and fish fillet. The performance of the intelligent layer in detection of freshness/spoilage was acceptable for both seafood products. In addition, the active layer of the film controlled the changes of pH, total volatile basic nitrogen, oxidation, and microbial load in samples during storage time.

Improving natto quality through Co-fermentation of functionally complementary Bacillus and Lactiplantibacillus species

Natto, a nutritious fermented soybean product, is known for its health benefits. Modern production methods use Bacillus subtilis as the starter culture to ensure consistent quality. However, this method overlooks the potential positive effects of other microbial species present in traditionally, naturally fermented natto. This study explored the effects of ARTP-induced mutants of B. subtilis var. natto and several strains of lactic acid bacteria (LAB) on natto quality. The results showed that these two types of bacteria have complementary roles in fermentation. B. subtilis var. natto, with enhanced extracellular protease activity, promotes the hydrolysis of soy protein and enhances the product's ACE inhibitory and fibrinolytic activities. Meanwhile, two strains of Lactiplantibacillus plantarum reduced the content of total volatile basic nitrogen (TVB-N) while increasing the content of folic acid in the final product. In addition, B. subtilis var. natto and LAB produce different profiles of volatile compounds (VOCs). Subsequently, B. subtilis var. natto and Lpb. plantarum were used to co-ferment natto in different ratios. The results showed that the two types of bacteria could co-colonize and enhance fermentation quality through their respective strengths. Specifically, Lpb. plantarum strains co-metabolized with B. subtilis var. natto to elevate the content of pyrazines, characteristic VOCs in natto. The optimal quality of natto was achieved when Lpb. plantarum HIS6, Lpb. plantarum LP3 and B. subtilis var. natto Y15-11 were combined in a 2:1:2 ratio. This study not only identified effective combinations of starter cultures with complementary benefits but also elucidated the metabolic pathways of key volatile compounds. Our findings also provide technical insights for improving natto quality, enhancing consumer acceptance, and supporting industrial production.

Microbial composition of spoiled irradiated ready-to-eat chicken feet and their spoilage characteristics

The spoilage of irradiated ready-to-eat chicken feet (RTECF) seriously affects the food's quality, resulting in package swelling and off-flavors, both of which are highly undesirable to stakeholders and consumers. To investigate the spoilage characteristics of irradiated RTECF and the microorganisms responsible for the spoilage and swelling, the changes in physicochemical properties, microbial community, and volatile organic compounds (VOCs) between normal and spoiled RTECF were evaluated. Compared with normal samples, the spoiled RTECF showed a higher pH value and total volatile basic nitrogen (TVB-N) value, lower color value, and texture features (P < 0.05). Acinetobacter, Pseudomonas, Lactobacillus, and Candida were the dominant genera responsible for RTECF spoilage as confirmed through both culture-dependent methods and high-throughput sequencing (HTS). The results of the verification for gas-producing strains showed that Lactobacillus brevis could cause RTECF packaging to swell. A total of 20 key VOCs were identified using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results of Pearson correlation analysis (|r|>0.8, P < 0.05) showed that 12 dominant core microbial genera had a significant effect on the flavor of RTECF before and after spoilage. This study provides a theoretical reference for solving the problem of RTECF spoilage and improving the overall quality of RTECF products.

Application of Lactiplantibacillus plantarum hydrogel coating in combination with ice temperature for the preservation of fresh yak meat

Fresh yak meat is highly nutritious and prone to spoilage, so developing suitable preservation methods is crucial. In this study, hydrogel coatings composed of konjac glucomannan, Lactiplantibacillus plantarum and gallic acid (KGX) were applied to preserve fresh yak meat under ice temperature (−1 °C). After 16 days, KGX group showed lowest total viable count (5.3 ± 0.1 log cfu/g) and total volatile basic nitrogen (13.02 ± 1.40 mg/100 g), which did not exceed the relevant standards of fresh meat. Combined assessments of color, texture, pH, drip loss rate, and thiobarbituric acid reactive substances indicated that KGX coating effectively prolonged yak meat preservation. High-throughput sequencing revealed that KGX coating effectively reduced the abundance of Pseudomonas and Candida. The application of L. plantarum hydrogel coatings in conjunction with ice temperature increased the shelf life of fresh yak meat to 16–20 days, suggesting its potential as a viable preservation method for fresh meat.

Sodium alginate-based indicator film with enhanced physicochemical properties induced by cellulose nanocrystals and monitor the freshness of chilled meat

Intelligent indicator films with colorimetric pH indicator properties were developed, incorporating black soybean seed coat anthocyanin (BA), cellulose nanocrystals (CNC), and sodium alginate (SA) to monitor meat freshness. The effect of different CNC additions on the microstructure, water barrier properties of the films, and BA release kinetics were comprehensively investigated. The results showed that with the increasement of CNC addition, the mechanical properties of SA/BA/CNC films were improved, the water contact angle significantly increased from 51.6° to 69°. Moreover, water solubility, vapor adsorption, and permeability significantly decreased, indicating enhanced water barrier properties. The release kinetic results showed that BA was released rapidly within 72 h and slowly thereafter, and its release process was described by Fick's model. Films with 7 % and 10 % CNC had lower BA diffusion coefficients. Their diffusions were formulated as linear regression equations (y = nx + a), where R2 was >0.80 and n was <0.50. Structural characterization showed that CNC immobilized BA mainly through hydrogen bonding, forming compact network microstructures with SA and BA. Meat freshness monitoring results showed that the film containing 7 % CNC showed visible color changes with increasing total volatile basic nitrogen and pH, along with low BA release, high water barrier and mechanical properties. Therefore, CNC has great potential for improving the physicochemical properties of indicator films, and the intelligent colorimetric indicator film could be applied to various food product.

Dynamic changes in volatile profiles and bacterial communities during natural fermentation of Mei yu, traditional Chinese fermented fish pieces

Microbial metabolism is important for the unique flavor formation of Mei yu, a kind of traditional Chinese fermented fish pieces. However, the interactive relationship between microorganisms and flavor components during fermentation is still unclear. In this study, electronic nose and headspace-solid-phase microextraction-gas chromatography-mass spectrometry analysis were performed to identify flavor components in Mei yu during the fermentation, and the absolute microbial quantification was conducted to identify the diversity and succession of microbial communities. During fermentation, there was an increase in the types of volatile compounds. Alcohols, aldehydes, aromatics and esters were the main flavor compounds and significantly increased in Mei yu, while hydrocarbon and aldehydes significantly decreased. The absolute abundances of Lactobacillus, Lactococcus and Weissella increased significantly after 3 days’ fermentation, which were closely associated with the productions of 1-nonanol, 2-methoxy-4-vinylphenol, guaiacol, ethyl palmitate and ethyl caprylate that might though pathways related to fatty acid biosynthesis and amino acid metabolism. However, these genera were negatively correlated with the production of indole. Additionally, the total volatile basic nitrogen (TVB-N) levels of Mei yu fermented during 3 days were within the limits of 25 mg TVB-N/100 g fish, with the contents of free amino acids and lipoxygenase activities were significant lower than that of 4 days’ fermentation. In view of food safety and flavor, it suggested that the natural fermented Mei yu at room temperature should be controlled within 3 days. This study highlights the application of absolute quantification to microbiome analysis in traditional fermented Mei yu and provides new insights into the roles of microorganisms in flavor formation during fermentation.

Effect of chitosan coating enriched with orange peel (Citrus sinensis) waste extract on prolonged preservation and chemical and functional properties of frozen beluga sturgeon (Huso huso) fillet

Fish is a crucial component of the diet in both developed and developing countries. It is highly digestible and contains a suitable combination of essential amino acids such as lysine and methionine, which are essential for good health and nutrition. The health benefits of essential polyunsaturated lipid acids, including omega-3 and omega-6 fats, have stimulated interest in increasing seafood intake. However, fresh fish is one of the most perishable foods due to the potent action of autolytic enzymes and microbial activity. In this study, chitosan biofilms containing different concentrations of the orange-peel extract (0.5, 1.0, and 1.5%) were prepared and their physical factors including water vapor permeability (WVP), color, and water solubility (WS) were characterized. Enriching the chitosan-based coatings with orange peel extracts improved physical characteristic factors and WVP, color and WS improved for extending preservation of refrigerated beluga sturgeon so that significant difference in these factors were observed between the enriched coatings and control ones (p&lt;0.05). The fish fillets were analyzed for total lipid (3.33 ± 0.41%), crude protein (14.90 ± 1.04%) and total volatile base nitrogen (10.12 ± 1.15 mg N/100 gr) and then subjected to the three treatments as well as blank coatings with 0.0-1.5% levels of orange peel waste extract for 14 days in 4 ⁰C. The results revealed that the biofilm enriched with 1.5% orange peel waste extract was effective on preserving phenolic compounds and maintaining antioxidant properties of fish fillets during preservation period (p&lt;0.05). The findings of this study revealed that chitosan coating enriched with orange peel extract improved physical factors in the coatings and preserved the antioxidant compounds in the fish fillets and maintained their shelf life through two week refrigerated time.