Formation mechanism of aroma compounds in a glutathione-glucose reaction with fat or oxidized fat

Fatty Acid Composition of Meat Animals as Flavor Precursors

This article provides an overview of fatty acids in meat, their variation among animal species, and the roles of fatty acids as flavor precursors. Animal fat mostly consists of triglycerides and phospholipids. Fats from ruminant (cattle, sheep, and goats) and monogastric (pigs and horses) animals have similar fatty acids with more saturated fatty acids and monounsaturated fatty acids than polyunsaturated fatty acids. In monogastric animals, fatty acids in the muscle reflect the composition of diets, whereas ruminant fatty acids are more saturated because of biohydrogenation in the rumen. Lipid- derived flavor compounds are formed from the thermal oxidation of fatty acids during cooking, producing more desirable aromatic compounds than autoxidation. Monounsaturated fatty acids such as oleic acid and polyunsaturated fatty acids such as linoleic acid in meat produce various volatile compounds contributing to cooked meat aromas. Under most cooking conditions, lipid-derived flavor compounds are usually predominant. However, these compounds have greater thresholds than those derived from water-soluble compounds, such as the Maillard reaction products. The interactions between lipid oxidation products and Maillard compounds are more important for the development of meat flavor than originally thought. Moreover, fat-derived volatile compounds provide flavor notes indicative of species identification.

Development of meat flavors in peony seed-derived Maillard reaction products with the addition of chicken fat prepared under different conditions

To prepared Maillard reaction products (MRPs) enriched with chicken flavor, the effects of chicken fats on peony seed-derived MRPs were evaluated. The thermal treatments, lipase enzymatic hydrolysis and lipoxygenase with subsequent mild thermal treatments were applied to oxidized chicken fats before their use in the Maillard reaction. Different oxidized chicken fats led to diverse chemical properties and varied volatile compounds. The addition of oxidized chicken fat increased the meaty of MRPs. The chicken fat promoted the Maillard reaction, which produced more oxygenated compounds; however, it reduced the sulfur compounds. Correlation analysis of the chemical properties of chicken fat and the major volatile compounds showed that by controlling the chemical properties of chicken fat, it might be possible to control the content of some volatile compounds of chicken fat and MRPs. Our data elucidated that chicken fat contributes to the development of meat flavors after oxidation and thermal treatments.

New insight into the formation mechanism of 2-furfurylthiol in the glucose-cysteine reaction with ribose

The molecular formation mechanism of 2-furfurylthiol in the glucose-cysteine reaction is not reported. Knowledge of the molecular interaction of glucose and ribose on the generation of 2-furfurylthiol is still unclear. The carbon module labeling (CAMOLA) technical approach was applied to elucidate the formation mechanism of 2-furfurylthiol in the glucose-cysteine reaction. The effect of ribose on the glucose-cysteine reaction was also evaluated. The results showed that 2-furfural and 2-furanmethanol were important intermediates for the formation of 2-furfurylthiol. Irrespective of the heating time, 2-furfurylthiol was mainly generated from an intact C₅ glucose skeleton (88-89%), whereas the recombination of glucose fragments had minimal contribution. 2-Furfural could be generated from the Maillard reaction between glucose and cysteine or glucose alone, which further formed 2-furanmethanol. Immediately, 2-furfurylthiol could arise from the reaction of 2-furanmethanol and H₂S from cysteine. Moreover, the reaction of glucose, ribose, and cysteine could generate 2-furfural, 2-furanmethanol, and 2-furfurylthiol by an addition effect confirmed by the model reaction and food system.

Formation of naphthoquinones and anthraquinones by carbonyl-hydroquinone/benzoquinone reactions: A potential route for the origin of 9,10-anthraquinone in tea

The reaction of 2-alkenals (crotonaldehyde and 2-pentenal) with hydroquinones (hydroquinone and tert-butylhydroquinone) and benzoquinones (benzoquinone, methylbenzoquinone, and methoxybenzoquinone) was studied as a potential route for the endogenous formation of naphthoquinones and anthraquinones in foods. Polycyclic quinones were produced at a low water activity, within a wide pH range, and in the presence of air. 9,10-Anthraquinone formation had an activation energy of 46.1 ± 0.1 kJ·mol^-1, and a reaction pathway for the formation of the different naphthoquinones and anthraquinones is proposed. These reactions also took place in tea, therefore suggesting that the common tea pollutant 9,10-anthraquinone is also a process-induced contaminant. In fact, when four commercial teas (from a total of eight studied teas) were heated at 60 °C for 72 h, they significantly (p < 0.05) increased the amount of this toxicant. Reduction of 9,10-anthraquinone formation in teas is suggested to be carried out by reducing/scavenging its precursors.

Impact of aluminosilicates on productivity, carcass traits, meat quality, and jejunum morphology of broiler chickens

The aim of the study was to compare production results and quality of meat, as well as histological features of the jejunum in broiler chickens administered feed with 1% addition of zeolite or halloysite, with the addition of aluminosilicates to litter (4.50 kg/m2) throughout the rearing. In the experiment, 300 male broilers were used for 6 wk. They were divided into 3 groups, each of 10 repetitions (10 birds each). Group 1 was a control, halloysite was added to feed and litter in group 2, while zeolite was applied instead of halloysite in group 3. After rearing, 10 selected birds from each group were slaughtered. Selected production properties and degree of footpad dermatitis were examined, and histomorphometric examination of the jejunum was performed. The lowest yield and the highest proportion of neck with skin in the carcass were demonstrated in group 2 (P < 0.05). The lowest percentage of skin with subcutaneous fat was found in group 3 (P < 0.05). A decrease in lightness (L∗) and yellowness (b∗) was demonstrated in group 2, while redness (a∗) was the lowest in group 3 (P < 0.05). Group 2 was characterized by the lowest water-holding capacity in breast muscles, and in group 3, in leg muscles (P < 0.05). In group 3, the highest fat content and the lowest water content in the breast muscles (P < 0.05) were found. The leg muscles in groups 2 and 3 were characterized by the highest a∗, and in group 2, by b∗. The control group had the lowest protein and the highest fat content in leg muscles. In the intestine from group 2, a higher height (P < 0.05) and surface area (P < 0.01) of intestinal villi were found, in comparison to group 3. The width of intestinal villi was higher in groups 2 and 1 than in group 3 (P < 0.05), similarly the depth of intestinal crypts. The addition of zeolite could be proposed because of the obtained production results, while the halloysite had a positive effect on the histomorphometric features of the jejunum.

Effect of Breed on the Volatile Compound Precursors and Odor Profile Attributes of Lamb Meat

The objective was to characterize the effect of breed on the volatile compound precursors and odor profile attributes and to provide an insight into improving the lamb production and meat flavor. Three-month-old Tan (n = 10), Hu (n = 10) and Dorper lambs (n = 10) were raised for 90 days in single barns. Longissimus thoracis et lumborum muscle of all lambs were collected for analysis of intramuscular fat, fatty acids, amino acids, and volatile compounds. The results showed Tan and Hu accumulated more intramuscular fat and saturated fatty acid than Dorper. However, Tan had lower linoleic acid, alpha linolenic acid and total polyunsaturated fatty acid proportion than Dorper. Amino acid in Dorper was significantly higher than Tan and Hu. Furthermore, (E)-2-hexenal was only found in Tan lambs, while (E)-2-nonenal and (E,E)-2,4-nonadienal were only found in Dorper lambs. Hu had the fewest volatile compounds. The results of this study demonstrated that Dorper had larger proportion of polyunsaturated fatty acids (PUFA), amino acid and volatile compounds than Tan and Hu. However, the specific PUFA derivates of Dorper had a negative impact on the odor profile. Hence, we suggest that further works should be focused on crossbreed lambs by Dorper and Tan, to enhance the lamb production and improve meat flavor.

Generation of key aroma compounds in Beijing roasted duck induced via Maillard reaction and lipid pyrolysis reaction

This study explores the evolution of key aroma compounds and the chemical changes of their precursors, including reducing sugars, free amino acids, free fatty acids, thiamine and proximate compositions in Beijing roasted duck during roasting for 0-80 min. The results showed that the amounts and contents of 9 key aroma compounds in roasted ducks first quickly increased (p < 0.05) and subsequently remained constant (p > 0.05) after 50 min, except for a slight decrease between 70 and 80 min. Cysteine, cystine and methionine were the main free amino acids and could react with glucose and ribose to generate 2-furfurylthiol, dimethyl trisulfide and methional. Linoleic acid, α-linolenic acid and arachidonic acid had important effects on the increase of hexanal, octanal and nonanal together with the emergence and formation of heptanal, (E, E)-2,4-decadienal and 1-octene-3-ol. However, thiamine might not be the main precursor of the key aroma compounds in Beijing roasted duck.

Characterization of Volatile Profiles and Marker Substances by HS-SPME/GC-MS during the Concentration of Coconut Jam

Characteristic aromas are usually key labels for food products. In this study, the volatile profiles and marker substances of coconut jam during concentration were characterized via sensory evaluation combined with headspace solid phase microextraction-gas chromatography-tandem mass spectrometry (HSPME/GC-MS). A total of 33 aroma compounds were detected by HSPME/GC-MS. Principal component analysis revealed the concentration process of coconut jam can be divided into three stages. In the first stage, esters and alcohols were the two main contributors to the aroma of the coconut jam. Next, a caramel smell was gradually formed during the second stage, which was mainly derived from aldehydes, ketones and alcohols. The concentration of aldehydes increased gradually at this stage, which may be the result of a combination of the Maillard reaction and the caramelization reaction. In the final sterilization stage, the 'odor intensity' of caramel reached the maximum level and a variety of aroma compounds were produced, thereby forming a unique flavor for the coconut jam. Finally, furfural fit a logistic model with a regression coefficient (r2) of 0.97034. Therefore, furfural can be used as a marker substance for monitoring the concentration of coconut jam.

Aromatic effects of immobilized enzymatic oxidation of chicken fat on flaxseed (Linum usitatissimum L.) derived Maillard reaction products

To control the oxidation in chicken fat by immobilized lipoxygenase (LOX), Maillard reaction products (MRPs) with chicken flavor were prepared and analyzed for flavor mechanism. >50% activity of immobilized LOX was retained after repeated use for five times or five weeks. The oxidized chicken fats were prepared by thermal, free LOX, and immobilized LOX treatments. After addition of chicken fats, Maillard reaction produced more aliphatic aldehydes and alcohols (126.0-839.5 ng/g and 493.5-2332.4 ng/g, respectively) which resulted in noticeable enhanced reaction, but the content of sulfur compounds such as thiols and thiophenes decreased significantly (870.8-1233.9 ng/g and 1125.0-2880.3 ng/g, respectively), and the structure of sulfur compounds could easily form alkyl side chains. However, there was no significant difference in sensory and flavors between oxidized chicken after treatments, which may be related to oxidized degree. The mechanism was proposed or aromatic effects of oxidized chicken fat on flaxseed derived MRPs.

Studies on the Origin of Carbons in Aroma Compounds from [13C₆]Glucose -Cysteine-(E)-2-Nonenal Model Reaction Systems

The thermal degradation of lipid oxidation products with amino acids and reducing sugars is known to be important for the characteristic aroma generation in both meat and meat-like process flavorings. SPME(solid phase microextraction)/GC-MS was used to analyze the volatiles produced from a solution of [¹³C₆]glucose, cysteine, and lipid degradation product- (E)-2-nonenal, heated at 130 °C for 90 min. Analysis of the mass spectra showed that the resulting 2-butyl-thiophene and 5-butyldihydro-2(3H)-furanone were ¹³C₆-labeled and hence stemmed from glucose. Glucose and (E)-2-nonenal were equally important for the formation of 2-pentylfuran, whether cysteine was present in the reaction or not. 2-Furanmethanol, (E)-2-(1-pentenyl)-furan, 2-hexanoylfuran, ethanethiol, 5-methyl-2(5H)-thiophenone, 1-methyl-5-mercaptotetrazole, 4-pentyl-pyridine, 2-pentyl-thiophene, and 2-mercaptopropanoic acid were virtually ¹³C₁-¹³C₄ labeled, suggesting an origin from both glucose and cysteine and/or (E)-2-nonenal carbons. Thus, the relative contribution of aldehyde to the C-skeleton of a particular aroma compound changed substantially when both glucose and cysteine were involved in its formation.

Simultaneous Detection of Eight Prohibited Flavor Compounds in Foodstuffs Using Gas Chromatography-Tandem Mass Spectrometry

A multiflavor detection method, using gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS), has been developed for the simultaneous identification and quantification of eight prohibited flavor compounds in daily foods. Under the optimized extraction conditions, samples were purified directly through membrane filtration. Variables affecting the GC-MS/MS were optimized to obtain better separation. The excellent selectivity and sensitivity achieved in multiple reactions monitoring mode allowed satisfactory confirmation and quantitation. In this study, the linear ranges of the target compounds were 0.05 to 500 ng/L with good correlation coefficients ( R² > 0.999). The limits of detection of target compounds ranged from 0.005 to 0.2 μg/kg. The average recoveries were in the range of 80.2 to 110.6% (beef jerky), 82.3 to 94.1% (cod liver oil), and 83.6 to 104.1% (candy).

Aroma Compounds in Chicken Broths of Beijing Youji and Commercial Broilers

The unique flavor of Beijing Youji (BJY) chicken broth compared with that of commercial broilers (CB) was investigated by solvent-assisted flavor evaporation combined with AEDA/GC-O (aroma extract dilution analysis of gas chromatography-olfactometry), quantitation, and aroma recombination. A total of 71 odorants with almost the same major odorants (≥10 ng/g broth) were found by GC-O in both BJY and CB broths. However, BJY broth had thirty-two more extra odorants than CB broth, indicating the rich fragrance of the former. Aroma recombination and omission experiments demonstrated that 21 versus 17 odorants (with OAV ≥ 1) contributed significantly to BJY and CB broth aromas, respectively. Those key odorants mainly included sulfur-containing compounds and aliphatic aldehydes, such as 2-methyl-3-furanthiol, 3-(methylthio)propanal, ( E, E)-2,4-decadienal, etc. Furthermore, composition analysis of the meat suggested that the better flavor, with rather more odorants, of BJY broth is probably due to higher contents of polyunsaturated fatty acids and water-soluble flavor precursor, including ribose, cysteine, thiamine, etc., present in the BJY meat.