Properties and volatile profile of process flavorings prepared from d-xylose with glycine, alanine or valine by direct extrusion method

Role of exogenous xylose during its co-heating with alanine-xylose Amadori compound: Competitively promoting 2-furfural formation and limiting pyrazines generation

Exogenous xylose (Xyl) could promote 2-furfural formation but inhibit pyrazines generation during its co-heating with alanine (Ala)-Xyl Amadori rearrangement product (AX-ARP). The activation energy of AX-ARP formation from Ala and Xyl was considerably lower than that of pyrazine formation from Ala and glyoxal (GO). Accordingly, the preferential interaction of exogenous Xyl with regenerated Ala triggered a continuous cycle of consumption and regeneration of Ala in AX-ARP-Xyl model. In this way, functioning as a catalyst, regenerated Ala facilitated the continuous conversion of AX-ARP into deoxyxylosones (DXs). However, exogenous Xyl accelerated the pH drop during the thermal treatment of AX-ARP, which favored the conversion of DXs into 2-furfural while limiting the transformation of their α-dicarbonyl fragments into pyrazines. Model reactions of AX-ARP-[13C5-Xyl] further confirmed that exogenous Xyl was progressively converted into 2-furfural, while its downstream products, such as GO and methylglyoxal (MGO), did not exhibit an enhanced tendency to form pyrazines.

Disclosing the Nitrogen Sources via Isotope Labeling Technique and the Formation Mechanism of Pyrazine and Alkylpyrazines during the Heat Treatment of N-(1-Deoxy-d-xylulos-1-yl)-alanine and Exogenous Alanine

The formation pathway and mechanism of various pyrazines were investigated during the thermal treatment of the alanine-xylose Amadori compound (Ala-ARP) and exogenous alanine (Ala). 15N-labeled Ala was used to coheated with Ala-ARP to clarify the nitrogen sources and the respective contributions of exogenous Ala and the regenerated Ala released from Ala-ARP to different pyrazine formation. It was found that exogenous Ala exhibited a priority in capturing glyoxal (GO) to form pyrazine during the thermal degradation of ARP. Compared to the Ala-methylglyoxal (MGO) model, a lower activation energy was required for the Ala-GO reaction, where the reaction dynamics of Ala-GO followed a zero-order model. In addition to forming pyrazine, the interaction between existing exogenous Ala and GO would accelerate the thermal degradation of Ala-ARP and retro-aldolization reaction of deoxyxylosones (DXs) to α-dicarbonyls. During this process, the release of regenerated Ala and MGO was promoted. Accordingly, as GO was expended by exogenous Ala during the initial stage of ARP-Ala degradation, the condensation between regenerated Ala and MGO became intensified, leading to the generation of methylpyrazine and 2,5-dimethylpyrazine. As a result, in the thermally treated mixture of Ala-ARP and exogenous Ala, 55% of the formed pyrazine originated from exogenous Ala, while 63% of the formed methylpyrazine and 57% of the formed 2,5-dimethylpyrazine were derived from regenerated Ala (120 °C, 30 min).

Establishment of compound database of emerging antioxidants and high-resolution mass spectrometry screening in lake sediment from Taihu Lake Basin, China

Antioxidants are ubiquitous in various environmental samples, leading to increasing concern regarding their potential risk to environments or humans. However, there is dearth of information regarding the environmental fate of antioxidants and unknown/unexpected antioxidants in the environment. Here, we established a compound database (CDB) containing 320 current-used antioxidants by collecting the chemicals from EPA's functional use database and published documents. Physical-chemical characteristics of these antioxidants were estimated, and 19 ones were considered as persistent and bioaccumulative (P&B) substances. This CDB was further coupled with high resolution mass spectrometry (HRMS) technique, which was employed for suspect screening of antioxidants in extracts of sediments (n = 88) collected from Taihu Lake basin. We screened 119 HRMS features that can match 135 chemical formulas in the CDB, and 20 out of them exhibited the detection frequencies ≥ 90%. The total concentrations of suspect antioxidants in sediments ranged from 6.41 to 830 ng/g dw. Statistical analysis demonstrated that concentrations of suspect antioxidants in Taihu Lake were statistically significantly lower than those in Shihu and Jiulihu Lake, but greater than those from other small lakes. Collectively, this study provided a CDB that could be helpful for further monitoring studies of antioxidant in the environments, and also provided the first evidence regarding the ubiquity of antioxidants in aquatic environment of Taihu Lake basin.

Extrusion of process flavorings from methionine and dextrose using modified starch as a carrier

This study aimed to produce process flavorings from methionine and glucose via Maillard reaction by extrusion method. Modified starch was used as a carrier to reduce the torque and facilitate the production process. Five formulations of process flavorings with different ratios of methionine: dextrose: modified starch: water as MS5 (72:18:5:5), MS15 (64:16:15:5), MS25 (56:14:25:5), MS35 (42:12:35:5), and MS45 (40:10:45:5) were prepared and feded into the extruder. The temperatures of the extruder barrel in zones 1 and 2 were controlled at 100, and 120°C, with a screw speed of 30 rpm. The appearance of the obtained products, torque, pH before and after extrusion, color, volatile compounds, and sensory evaluation were determined. The extrudate from the formulation containing the highest amount of modified starch (MS45) gave the highest L* (lightness) of 88.00, which increased to 93.00 (very light) after grinding into a powder. The process flavorings from all formulations exhibited similar sensory scores in terms of aroma, taste, and water solubility, with a very slight difference in color. However, MS25, MS35 and MS45 indicated the torque at 10 Nm/cm3, while MS5 and MS 15 exhibited higher torque at 18, and 25 Nm/cm3, respectively. Extruded process flavorings from MS25 were analyzed for their flavor profiles by gas chromatography-mass spectrometry. Twelve volatile compounds including the key volatile compounds for sulfurous and vegetable odor type, dimethyl disulfide, methional, and methanethiol, were found. Four pyrazine compounds presented nutty, musty and caramelly odor; and 3-hydroxybutan-2-one and heptane-2,3-dione, which gave buttery odor type, were also detected. The results demonstrated a successful production of process flavorings using modified starch as carrier to facilitate and reduce the torque during the extrusion process.

Competitive Formation of 2,3-Butanedione and Pyrazines through Intervention of Added Cysteine during Thermal Processing of Alanine-Xylose Amadori Compounds

The intervention of cysteine (Cys) on the formation of 2,3-butanedione and pyrazines was evaluated during the thermal processing of the alanine-xylose Amadori compound (AX-ARP). With the involvement of Cys, the competitive formation of 2,3-butanedione and pyrazines was induced. The formation of 2,3-butanedione in the AX-ARP/Cys model was suppressed due to the inhibitory effect of the precursors of 2,3-butanedione like deoxypentosones, while the added Cys in the AX-ARP/Cys model competed with the recovered alanine (Ala) to capture glyoxal and methylglyoxal to make up for the absence of pyrazines in the AX-ARP model at an initial pH value of 7. The content of pyrazines increased from 0 up to 16.48 μg/L (120 °C, 120 min). Exogenous Cys itself showed lower reactivity with 2,3-butanedione through the Strecker degradation reaction; while the pH was increased to 8, the degradative products of Cys were facilitated to consume the residual 2,3-butanedione giving rise to the formation of 2,4,5-trimethylthiazole at 120 °C. It was the degradative products of Cys that accelerated the reaction for consumption of 2,3-butanedione rather than Cys itself. Additionally, the inhibitory effect of Cys on 2,3-butanedione formation was weakened under a basic condition, while the promotional effect on the formation of pyrazines was further boosted. With more Cys participating in the process of AX-ARP thermal degradation, the formation of 2,3-butanedione was further inhibited, while the yields of pyrazines were increased.

Biosynthesis of value-added bioproducts from hemicellulose of biomass through microbial metabolic engineering

Hemicellulose is the second most abundant carbohydrate in lignocellulosic biomass and has extensive applications. In conventional biomass refinery, hemicellulose is easily converted to unwanted by-products in pretreatment and therefore can't be fully utilized. The present study aims to summarize the most recent development of lignocellulosic polysaccharide degradation and fully convert it to value-added bioproducts through microbial and enzymatic catalysis. Firstly, bioprocess and microbial metabolic engineering for enhanced utilization of lignocellulosic carbohydrates were discussed. The bioprocess for degradation and conversion of natural lignocellulose to monosaccharides and organic acids using anaerobic thermophilic bacteria and thermostable glycoside hydrolases were summarized. Xylose transmembrane transporting systems in natural microorganisms and the latest strategies for promoting the transporting capacity by metabolic engineering were summarized. The carbon catabolite repression effect restricting xylose utilization in microorganisms, and metabolic engineering strategies developed for co-utilization of glucose and xylose were discussed. Secondly, the metabolic pathways of xylose catabolism in microorganisms were comparatively analyzed. Microbial metabolic engineering for converting xylose to value-added bioproducts based on redox pathways, non-redox pathways, pentose phosphate pathway, and improving inhibitors resistance were summarized. Thirdly, strategies for degrading lignocellulosic polysaccharides and fully converting hemicellulose to value-added bioproducts through microbial metabolic engineering were proposed.

Kinetic Study of the Maillard Reaction in Thin Film Generated by Microdroplets Deposition

The Maillard reaction kinetics in the confined volume of the thin film produced by ESI microdroplet deposition was studied by mass spectrometry. The almost exclusive formation of the Amadori product from the reaction of D-xylose and D-glucose toward L-glycine and L-lysine was demonstrated. The thin film Maillard reaction occurred at a mild synthetic condition under which the same process in solution was not observed. The comparison of the thin film kinetics with that of the reaction performed in solution showed strong thin film rate acceleration factors.

Production of process flavorings from methionine, thiamine with d-xylose or dextrose by direct extrusion: Physical properties and volatile profiles

The conventional method to produce process flavoring is non-continuous, time consuming, and generates a high volume of effluent. This research aimed to evaluate the use of methionine, thiamine, and reducing sugars to develop process flavorings by direct extrusion, as a potential alternative to the conventional method. The mixed substrates consisted of methionine: d-xylose (MX), methionine: dextrose (MD), thiamine: d-xylose (TX), and thiamine: dextrose (TD) at 80:20 w/w. Three barrel temperatures of the extruder were controlled at 65, 80, and 50°C, respectively, a screw speed of 30 rpm and feed rate at 3 kg/hr. Appearance, pH, odor, and taste description of the product from each mixture were determined. Volatile compounds, possibly occurred from the Maillard reaction during the extrusion were analyzed by gas chromatography-mass spectrometry. The products exhibited different levels of meaty odor and bitter taste. Those obtained from MD showed the highest L* (lightness, 85.37) and frequency for just-about-right in terms of taste (33.33%) and odor (60.00%). Products from MX and MD presented the highest frequency for intense taste, and higher frequency for color compared to TX and TD. More volatile compounds were detected from the use of methionine than from thiamine. The key meaty odor compounds such as dimethyl disulfide, dimethyl trisulfide, methional, and methanethiol were found in the samples from MX and MD, while only dimethyl disulfide was detected in the mixture of TX and TD. Finally, the results demonstrated that direct extrusion reaction from methionine and d-xylose or dextrose is a highly efficient method to produce meaty process flavorings. PRACTICAL APPLICATION: The manuscript describes the production of process flavorings that exhibited meaty flavors by extrusion process. Physical properties, volatile profiles, and sensory evaluation of the products from methionine, thiamine, d-xylose, and glucose were evaluated. The extruded products from methionine and dextrose exhibited acceptable color, taste, and odor and presented many volatiles compounds contributing to meaty flavors. The results revealed the high potential to use a direct extrusion process with very low effluent, compared to the conventional method, to produce meaty flavors for industrial application.