Influence of heating temperatures and storage on the odor of duck meat and identification of characteristic odorous smell compounds.

To clarify the characteristic odor of compounds present in duck meat, especially reheating after storage, the effect of duck breast cooked at three temperatures (90 °C, 100 °C, 105 °C) and reheating after 7 days of storage was studied. Electronic nose analysis and sensory evaluation revealed a significant increase (p < 0.05) in reheated duck meat odor after 7 days of storage. The 90 °C treatment group had the heaviest odor, which increased by 12.19 % after seven days of storage. Using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS), 60 volatile flavor compounds were identified across various groups. Although the volatile compounds were consistent among different groups, their relative contents varied. By combining the sensory evaluation results with the Relative Odor Activity Value (ROAV) of these flavor compounds, chemometric orthogonal partial least squares discriminant analysis (OPLS-DA) was used to identify the following 9 characteristic volatile compounds: 2-methylbutanal, pentanal, octanal, heptanal, hexanal, (E)-2-octenal, (E)-2-nonenal, and 2-pentyl furan.

Selection of yeast strains in naturally fermented cured meat as promising starter cultures for fermented cured beef, a traditional fermented meat product of northern China.

BACKGROUND: Fermented meat products are meat products with a unique flavor, color, and texture as well as an extended shelf life under natural or artificially controlled conditions. Microorganisms or enzymes are used to ferment the raw meat so that it undergoes a series of biochemical and physical changes. Common fermentation strains are lactic acid bacteria, yeasts, staphylococci, molds, and so forth. Studies on the inhibitory effect of yeast fermentation strain on N-nitrosamines in fermented meat products have not been reported. Two excellent yeast starters were identified to solve the problem of nitrosamines in fermented meat products. RESULTS: Meyerozyma guilliermondii and Debaryomyces hansenii led to weak acid production, strong resistance to NaCl and NaNO2 , and high tolerance to low acidic conditions. The inoculated fermented beef exhibited decreased lightness, moisture content, water activity, pH, protein content, nitrite content, and N-nitrosamine content in comparison with the control group fermented bacon. M. guilliermondii had a better effect, reducing pH from 5.69 to 5.41, protein content from 254.24 to 221.92 g·kg-1 , nitrite content from 28.61 to 25.33 mg·kg-1 and N-nitrosamine by 18.97%, and giving the fermented beef the desired meat color, mouthfeel, odor, taste, and tissue quality. CONCLUSION: In this study, two strains of yeast fermenters that can degrade N-nitrosamine precursors were identified, which to some extent solves the problem of the high risk of generating nitrosamines such as N-nitrosodiethylamine (NDEA) by processing fermented meat products with nitrites as precursors. These two strains are likely to be used as starter cultures for fermented meat products. © 2023 Society of Chemical Industry.

Myosin heavy chain isoform expression and meat quality characteristics of different muscles in yak (Bos grunniens).

Myosin heavy chain (MHC) isoforms and meat quality characteristics of different muscles were investigated to explore their potential relationships in yaks. Results showed that semitendinosus (ST), longissimus thoracis (LT), and infraspinatus (IS) have a greater ratio of MHC IIb (47.84%), MHC IIa (73.27%), and MHC I (24.26%), respectively, than the other two muscles. Compared with LT or ST, IS exhibited more intense color, greater water-holding capacity, and initial tenderness with higher intermuscular fat (IMF) and collagen (of lower cross-linking level), presenting overall better quality. Variations in MHC isoforms accounted for the muscle-specific meat quality. Specifically, MHC I was positively associated with redness, myoglobin, IMF, collagen, pH, and thermal stability and negatively associated with myofibril fragmentation index, fiber thickness, collagen cross-linking, and drip loss. These results provide insights into the relationships between MHC isoforms and meat quality in yaks and the MHC I isoform has an extensive influence on meat quality.

Effect of slaughter age and postmortem aging time on tenderness and water-holding capacity of yak (Bos grunniens) longissimus thoracis muscle.

The present study investigated the effect of slaughter age (2.43 ± 0.20, 4.15 ± 0.19, 6.62 ± 0.18, 10.59 ± 0.74 years) and postmortem aging time (1, 24, and 72 h) on the tenderness and water-holding capacity (WHC) of yak longissimus thoracis muscles to determine the most suitable age for slaughter to ensure product consistency. Under conventional postmortem aging conditions (4 °C), muscles of each age group exhibited the effect of cold shortening. Once the cold shortening occurred, the age effect on thickening muscle fiber and developing cross-links of collagen, considered to intensify the meat toughness, became less important. Owing to greater carcass weight and intramuscular fat, muscles of the older carcass (over 6-year-old) were less influenced by the cold shortening effect during the chilling process and showed lessened sarcomere contraction, delayed formation of drip loss channels, and increased level of myofibril fragmentation index (MFI) and myofiber structural disintegration, resulting in greater tenderness and WHC, especially 6-7 years group. Aging of 72 h structurally disintegrated the collagen cross-linking and integrity of muscle fibers and elevated the MFI, improving the meat tenderness. Therefore, the suitable slaughter age for yak is 6-7 years old and after 72 h aging, improved quality of yak meat can be obtained.

Exploring in vitro gastrointestinal digestion of myofibrillar proteins at different heating temperatures.

The effects of different heating temperatures (40-115 °C) on the structure, oxidation, and digestibility of beef myofibrillar protein were investigated. Reductions in the number of sulfhydryl groups were observed, together with gradual increases in the number of carbonyl groups, indicating oxidation of the protein by the increased temperatures. At temperatures between 40 °C and 85 °C, ß-sheets were converted to α-helices, and increased surface hydrophobicity showed that the protein expanded as the temperature approached 85 °C. These changes were reversed at temperatures over 85 °C, indicative of aggregation induced by thermal oxidation. Between 40 °C and 85 °C, the digestibility of the myofibrillar protein was increased, reaching a maximum of 59.5 % at 85 °C, after which it began to decrease. These results indicated that moderate heating and oxidation-induced protein expansion were beneficial to digestion while protein aggregation resulting from excessive heating is not conducive to digestion.

Effects of NaCl-assisted regulation on the emulsifying properties of heat-induced type I collagen.

Although collagen is widely used as an emulsifier in the food industry, its emulsifying properties are strongly influenced by processing conditions. This research investigated the effects of NaCl on the emulsifying properties of type I collagen after heating. Before heating, the solubility, emulsifying activity index (EAI), emulsifying stability index (ESI), and viscosity of type I collagen initially increased after adding NaCl (0.2 M), after which decreased with increasing NaCl concentration (0.4 M and 0.6 M) due to salt-in effect and the salt-out effects of the protein. While after heating (90℃, 30 min), the collagen became more soluble, with improved EAI and ESI, viscosity, and reduced particle size in response to increasing NaCl concentrations. It was found that NaCl increased the EAI of type I collagen twice after heating, and the EAI reached its maximum at 0.6 M NaCl concentration. We concluded that the improved emulsifying properties may due to thermal denaturation of the protein, resulting in an unfolded and disordered structure with increase of hydrogen bonds with water, rupture of disulfide bonds, and exposure of hydrophobic groups, leading to the increase of adsorption at the oil/water interface. Meanwhile, the Raman spectra analysis and Atomic Force Microscope (AFM) images showed that unfolding of the collagen triple helix was gradually destroyed after NaCl addition and heating, with emulsifying properties improved. The specific outcomes of present study can be adapted towards the requirements to improve the quality of emulsified meat products in the food industry.

Muscle fiber composition affects the postmortem redox characteristics of yak beef.

Yak infraspinatus (IS), longissimus thoracis (LT), and semitendinosus (ST) muscles were used to explore relationships between myofiber types and postmortem redox characteristics. IS mainly consisted of myofiber type Ⅰ (49.2%), LT has a vast majority of type IIa (72.7%), while ST possessed a similar percentage of type IIa (44.7%) and IIb (51.5%). Compared with LT and ST, IS exhibited higher initial H2O2, myoglobin (T-Mb), and metmyoglobin (MetMb) contents that provoked severe protein oxidation despite higher endogenous antioxidative capacity (e.g., glutathione antioxidative system). Three muscles showed specificities in myofiber type composition and redox characteristics, which were strongly correlated. Specifically, type Ⅰ myofiber positively correlated with H2O2, T-Mb, and multiple antioxidase activity/content while negatively correlated with lipid peroxidation, MetMb, and lactic dehydrogenase activity; also, they tended to employ more SFAs in more intermuscular fat assembly. Overall, muscle-specific myofiber type/redox attributes required differentiated processing to prevent meat oxidation and produce standardized products.

Multiple Technologies Combined to Analyze the Changes of Odor and Taste in Daokou Braised Chicken during Processing.

This study analyzed the changes of odor and taste in Daokou braised chicken during processing by GC-MS, GC-IMS, e-nose and e-tongue. The 75 and 55 volatile compounds identified in Daokou braised chicken by GC-MS and GC-IMS, respectively, included hydrocarbons, aldehydes, alcohols, terpenes, ketones, heterocyclics, esters, acids and phenols; among them, aldehydes, alcohols and ketones were the most abundant. The number and proportion of volatile compounds in Daokou braised chicken changed significantly (p < 0.05) in the process. The proportion of volatile compounds with animal fatty odor, such as aldehydes and alcohols, decreased, while that of esters, ketones and terpenes from spices with fruity fragrance increased, especially in the braising stage. An e-nose showed that the odor intensities of sulfur-containing and nitrogen oxide compounds were higher (p < 0.05) after the braising stage, but weakened after 2 h braising. An e-tongue showed that saltiness and richness increased significantly (p < 0.05) after braising. The results of these four techniques showed that braising promoted the release of flavor compounds, and was beneficial to salt penetration and umami release. However, long braising could lead to weakened flavor intensity and the introduction of bitterness and astringency. This study also found that GC-IMS and e-nose were more sensitive to trace compounds such as sulfur-containing and nitrogen oxide compounds, esters, acids and phenolics in Daokou braised chicken than GC-MS. The use of multiple technologies could provide more comprehensive flavor profiles for Daokou braised chicken during processing. This study provides insights into the control of flavor of Daokou braised chicken, and may be of practical relevance for the poultry industry.

The effect of shower time, electrolyte treatment, and electrical stimulation on meat quality of cattle longissimus thoracis muscle in cold weather.

The effects of three treatments (two levels each), namely shower time (ST), electrolyte treatment (ET), and electrical stimulation (ES), on meat quality were investigated using 112 cattle which were randomly allocated to different combinations of each treatment level. ST2, compared with ST1, increased ultimate pH from 6.05 to 6.23 and blood adrenaline levels while deteriorating beef color. ST2 also improved the water-holding capacity (WHC), exhibiting more immobilized water and less free water. Finally, it promoted protein unfolding and the conversion of α-helix to random coil, thus producing tenderer beef. In contrast, results indicated that ET either decreased pHu in ST1 groups or relieved pre-slaughter stress in ST2 groups. ES accelerated pH1 drop with maximum efficiency in an ST1-ET combination, but it did not alter pHu. In addition, ES decreased WHC with an enlarged relaxation time for bound water while causing beef tenderization through protein unfolding. ST1-ET(-ES/NES) maximized pHu reduction and provided an alternative for dark-cutting prevention in cold weather.

Age-specific effect on endogenous oxidative and antioxidative characteristics of longissimus thoracis muscle of yak during early postmortem period.

Effects of age on postmortem redox states were investigated in yak muscles. Extended postmortem time reduced the muscle antioxidant capacity and induced oxidation in lipids, myoglobin, and proteins. Compared with older yaks, muscles of younger ones could delay this oxidation process due to lower initial myoglobin content of 30.7%, lipid peroxidation of 42.4%, H2O2 of 41.2%, and intramuscular fat of 65.6% (of 3.66 times higher PUFAs). They also possessed greater antioxidase content/activity, such as phospholipase A2 content of 30.7% and glutathione reductase activity of 50.6%. Muscles exhibited age-specific overall antioxidative characteristics during 72 h postmortem and gradually formed overall oxidative ones after 72 h postmortem with an initial similarity between 2- and 4-year (or 6- and 12-year) on canonical discriminant analyses. The formation of age-specific overall oxidative characteristics can be attributable to the antioxidative specificity of age on canonical correlation analyses. Age-specific redox characteristics required differentiated preference in meat processing and preservation.

Near-infrared spectroscopy coupled with chemometrics algorithms for the quantitative determination of the germinability of Clostridium perfringens in four different matrices.

Clostridium perfringens (C. perfringens) has the ability to form metabolically-dormant spores that can survive food preservation processes and cause food spoilage and foodborne safety risks upon germination outgrowth. This study was conducted to investigate the effects of different AGFK concentrations (0, 50, 100, 200 mM/mL) on the spore germination of C. perfringens in four matrices, including Tris-HCl, FTG, milk, and chicken soup. C. perfringens spore germinability was investigated using near infrared spectroscopy (NIRS) combined with chemometrics. The spore germination rate (S), the OD600%, and the Ca2+-DPA% were measured using traditional spore germination methods. The results of spore germination assays showed that the optimum germination rate was obtained using 100 mM/L concentrations of AGFK in the FTG medium, and the S, OD600% and Ca2+-DPA% were 98.6%, 59.3% and 95%, respectively. The best prediction models for the S, OD600% and Ca2+-DPA% were obtained using SNV as the preprocessing method for the original spectra, with the competitive adaptive weighted resampling method (CARS) as the characteristic variables related to the selected spore germination methods from NIRS data. The results of the S showed that the optimum model was built by CARS-PLSR (RMSEV = 0.745, Rc = 0.897, RMSEP = 0.769, Rp = 0.883). For the OD600%, interval partial least squares regression (CARS-siPLS) was performed to optimize the models. The calibration yielded acceptable results (RMSEV = 0.218, Rc = 0.879, RMSEP = 0.257, Rp = 0.845). For the Ca2+-DPA%, the optimum model with CARS-siPLS yielded acceptable results (RMSEV = 44.7, Rc = 0.883, RMSEP = 50.2, Rp = 0.872). This indicated that quantitative determinations of the germinability of C. perfringens spores using NIR technology is feasible. A new method based on NIR was provided for rapid, automatic, and non-destructive determination of the germinability of C. perfringens spores.

Contribution of Histidine and Lysine to the Generation of Volatile Compounds in Jinhua Ham Exposed to Ripening Conditions Via Maillard Reaction.

To evaluate the role of Maillard reactions in the generation of flavor compounds in Jinhua ham, the reactions of glucose and ethanal with histidine and lysine, respectively, were studied by simulating the ripening conditions of Jinhua ham. The volatile products produced were analyzed using solid phase microextraction-gas chromatography/mass spectrometry. The results showed that 8 volatile compounds were generated by the reaction of glucose and histidine and 10 volatile compounds were generated by the reaction of glucose and lysine. Reactions of ethanal with lysine and with histidine both generated 31 volatile compounds that contributed to the flavor of Jinhua ham. This indicates that histidine and lysine related to Maillard reactions possibly play important roles in the generation of the unique flavor compounds in Jinhua ham. This research demonstrates that free amino acids participate in the generation of volatile compounds from Jinhua ham via the Maillard reaction and provides a basic mechanism to explain flavor formation in Jinhua ham. PRACTICAL APPLICATION: Jinhua ham is a well-known traditional Chinese dry-cured meat product. However, the formation of the compounds comprising its special flavor is not well understood. Our results indicate that Maillard reactions occur in Jinhua ham under ripening conditions. This work illustrates the contribution of Maillard reactions to the flavor of Jinhua ham.

Identification of antioxidant peptides of Jinhua ham generated in the products and through the simulated gastrointestinal digestion system.

BACKGROUND: The objective of this study was to purify and identify antioxidant peptides present in the extract of Chinese dry-cured Jinhua ham. Jinhua ham extracts were separated into five fractions (A-E) by size-exclusion chromatography. Each fraction was subjected to a simulated gastrointestinal (GI) digestion system and fractions showing strong antioxidant activities were collected and subjected to liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) for further purification and identification. RESULTS: Using MS/MS analysis, 33 peptides were identified in these fractions. Several key peptides were selected for synthesis and their antioxidant activity determined. The peptide showing strongest DPPH radical scavenging activity was GKFNV, which showed 92.7% antioxidant activity at a concentration of 1 mg mL(-1); the peptide LPGGGHGDL showed the highest hydroxyl radical scavenging activity; and LPGGGT and HA showed strong inhibition activity against erythrocyte hemolysis (about 45%) before digestion. On the other hand, KEER may contribute to Fe(2+) chelating ability in fraction C after GI digestion. CONCLUSION: Jinhua dry-cured ham seems to be a potential source of antioxidant peptides generated in the products and in GI digestion.

Effect of beating processing, as a means of reducing salt content in frankfurters: a physico-chemical and Raman spectroscopic study.

Structural changes, L(⁎)-value, cooking yield changes and textural properties of pork frankfurters containing 1% or 2% salt, produced by the two methods were studied by Raman spectroscopy and texture profile analysis. Increasing salt content from 1% to 2% increased the L(⁎)-value, cooking yield and hardness, and decreased (p<0.05) the C-H stretching and CH2 and CH3 bending vibrations, but did not affect the changes of secondary structures, tryptophan or tyrosine residues. Compared with the chopping, the beating increased L(⁎)-value, cooking yield and hardness of the frankfurters in both salt concentrations. It also resulted in an increase in ß-sheets, accompanied by a significant (p<0.05) decrease in α-helix content, a greater exposure of tyrosine residues to the polar environment and a decrease in the CH stretching and CH2 and CH3 bending vibrations. The results showed that the beating process enabled lowering of the salt content while improving the L(⁎)-value, cooking yield and hardness of the frankfurters.

Effect of a beating process, as a means of reducing salt content in Chinese-style meatballs (kung-wan): a dynamic rheological and Raman spectroscopy study.

Chopping and beating processes were used as meat-cutting methods in preparing kung-wan to produce low-salt products while retaining or improving the emulsion stability, sensory evaluation, and physico-chemical properties of the standard high-salt formulation. Increased salt content improved emulsion stability and dynamic rheology. However, 3% salt content decreased the overall acceptance of kung-wan. Compared with the chopping process, beating resulted in higher emulsion stability, overall acceptance, and ß-sheet content (P<0.05). Additionally, the beating process formed more compact and continuous structures at the same salt content. Kung-wan produced by beating with 1% and 2% salt had similar emulsion stabilities, sensory evaluation, and secondary structures (P>0.05). Therefore, this process allows reduction of salt content, suggesting that the kung-wan produced in this manner is healthier and has better texture.

Stability of an antioxidant peptide extracted from Jinhua ham.

The effects of NaCl, temperature, pH, light intensity and a simulated gastro-intestinal digestion were assessed to determine the stability of antioxidant peptides extracted from Chinese Jinhua ham. Antioxidant peptides showed good stabilities when NaCl content was less than 6%, temperature was lower than 60 °C and they were not exposed to light directly. However, the antioxidant peptides lost antioxidant activities rapidly under alkaline condition. The results of a simulated two-stage digestion system showed that antioxidant activity increased with pepsin treatment but declined with further hydrolysis with trypsin. Pepsin was effective to hydrolyze peptides into smaller fractions leading to the increased exposure of internal hydrophobic amino acids, but trypsin could hydrolyze peptides into more free amino acids resulting in the decline in surface hydrophobicity which affected antioxidant activity of peptides. These suggest that antioxidant peptides extracted from Jinhua ham could maintain their antioxidant activity under the proper conditions.

Effect of a beating process, as a means of reducing salt content in Chinese-style meatballs (kung-wan): a physico-chemical and textural study.

Two different meat-cutting methods were used to prepare kung-wans in an attempt to produce low-salt products while retaining the same, or improved, textural and physicochemical properties of the standard high-salt formulation. The level of salt and the processing method significantly affected color, cooking yield, texture and changes in the secondary structures of proteins. Improved salt levels resulted in firmer texture. At the same salt levels, compared with chopping, the beating method resulted in higher L(*)-values, improved cooking yields and changes in the ß-sheet content of the proteins, which resulted in an improved product with better texture. Using the beating process, the kung-wans prepared with 1% and 2% salt had similar L(*)-values, cooking yield and texture, and were better than those prepared by chopping with 2% salt. Overall, the beating process enabled lowering of the salt content, making the kung-wans more hard, brittle and elastic.

Isolation and identification of antioxidant peptides from jinhua ham.

The antioxidant activities of the peptides extracted from Jinhua ham were evaluated on the basis of hydroxyl radical scavenging activity, DPPH radical scavenging activity, and Fe(2+) chelating ability. The peptide extracts exhibited great hydroxyl radical scavenging activity and DPPH radical scavenging activity as well as Fe(2+) chelating ability at the concentration of 1 mg/mL, which suggested the presence of peptides with antioxidant activity. The peptides were separated using size exclusion chromatography and reversed-phase HPLC. The fraction with highest DPPH radical scavenging activity was further purified and identified using liquid chromatography tandem matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (HPLC-MALDI-TOF/TOF-MS). The sequence of the antioxidant peptide was identified as Gly-Lys-Phe-Asn-Val. The assessment of fractions indicated that the hydrophobic fractions contributed more to free radical scavenging activities than the hydrophilic peptides. It was concluded that natural peptides extracted and isolated from the Jinhua ham by several chromatographic techniques have antioxidant activities.

[Effects of different years of planting Pennisetum sp. on the plant- and insect diversity in Pennisetum sp. communities].

This paper studied the effects of 1-, 2- and 3 years of planting Pennisetum sp. on the plant- and insect diversity in the Pennisetum sp. communities, taking the barren mountain land without planting Pennisetum sp. as the control (CK). Compared with CK, the plant species richness in Pennisetum sp. communities with different years of planting was lower, but the coverage was higher. The coverage in the Pennisetum sp. community having been planted for 3 years was the highest, up to 91.6%, and 75.8% higher than the CK. The insect species richness in the Pennisetum sp. communities having been planted for 1, 2 and 3 years was 3.6, 5.3 and 5.6 times of the CK, respectively. The plant- and insect diversity indices, including Simpson index, Shannon index, evenness, Brillouin index, and McIntosh index for the Pennisetum sp. communities with different years of planting were significantly higher than the CK, which indicated that the growth of Pennisetum sp. could affect the plant- and insect diversity. With the increasing year of planting, the plant- and insect diversity in Pennisetum sp. communities tended to be stable.

[Spatiotemporal distribution of air temperature and precipitation in rice growth period in Fujian Province of East China and the effects of this distribution on rice planting pattern].

In order to investigate the effects of climate change on the rice production and rice planting pattern in Fujian Province, an analysis was made on the spatiotemporal distribution of air temperature and precipitation in rice growth period in the Province, and the possible changes of the local rice planting pattern in the future, based on the A2, B2, and A1 B scenarios of IPCC Special Report on Emission Scenario (SRES). In the future, the rice growth period's air temperature in the Province tended to be increased, and the increment would be increased with time, with the maximum for single cropping rice and being 0.3-2.4 degrees C and 1.5-3.4 degrees C in 2011-2030 and 2031 -2050, respectively. For early rice and late rice, the increment of their growth period's air temperature would be 0.2-0.9 degrees C and 0.7-1.7 degrees C in 2011-2030 and 0.3-2.1 degrees C and 0.5-3.6 degrees C in 2031-2050, respectively, but the annual fluctuation of the mean daily temperature would be most obvious for late rice. The rice growth period's precipitation in most parts of the Province also tended to be increased, and the increment for early rice, single cropping rice, and late rice would be 10%-40%, 10%-30%, and 10%-20%, respectively. The annual fluctuation of the precipitation would be most obvious for the early rice in southeastern Fujian. The elevated air temperature in the future could induce the increase of > or = 10 degrees C accumulated temperature, and lengthen the rice growth season, making it possible to replace early and medium-maturity varieties with late-maturity varieties, and to adopt double-rice planting pattern instead of single-rice planting pattern.