Investigations on the formation of α-dicarbonyl compounds and 5-hydroxymethylfurfural in fruit products during storage: New insights into the role of Maillard reaction

Constant temperature and humidity combined with vacuum-steam pulsed steaming of Polygonatum cyrtonema rhizome: Quality attribute and browning mechanism

The quality of Polygonatum cyrtonema rhizome is considerably influenced by steaming, a post-harvest procedure; however, the mechanisms behind this quality formation are not well understood. This study explored two innovative streaming methods for Polygonatum cyrtonema rhizome: constant temperature and humidity steaming and drying (CTHSD) and constant temperature and humidity combined with vacuum-steam pulsed steaming and drying (CTH + VSPSD). Traditional atmospheric steaming, simmering, and drying (ASD) were also used. We evaluated the microstructure, colour and polysaccharide, reducing sugar, 5-hydroxymethylfurfural, amino acid, phenolics and diosgenin contents as well as its antioxidant capacity. Results indicated that all methods enhanced antioxidant activity, released phenolic compounds and disrupted the microscopic pore wall structure. The processed samples exhibited increased browning values owing to non-enzymatic browning reactions between amino acids and reducing sugars. Notably, the CTH + VSPSD method yielded the highest antioxidant capacity, better preservation of polysaccharides and lower levels of 5-hydroxymethylfurfural compared to other methods. Additionally, CTH + VSPSD reduced production time by 66.7 % while achieving a comparable colour profile to that of conventional ASD technology. Therefore, the CTH + VSPSD method shows great promise for producing high-quality Polygonatum cyrtonema rhizome products.

Effect of chemical components on color variation during processing of Crataegi Fructus

The color and chemical composition of Crataegi Fructus (CF) vary greatly during processing, but few studies have explored the relationship between them. To address this issue, the effect of chemical composition on the color change of CF during processing was evaluated by mass spectrometry and color detection. A total of 107 compounds, including organic acids, flavonoids, furans, terpenoids, lignans and alkaloids, were identified from 26 representative samples by UHPLC-Q-TOF-MS, among them, the first three compounds changed most significantly during CF processing. Based on Spearman's rho correlation and multiple linear regression analysis, 85 variables from 107 compounds were identified to be associated with color value (P < 0.01). There are 12 compounds that are considered to be the key substances that cause color changes. This study not only realized the objectification of color evaluation, but also verified the relationship between color and chemical composition in food processing.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01576-2.

Role of galacturonic acid in acrylamide formation: Insights from structural analysis

Acrylamide (AA) is a neoformed compound in heated foods, mainly produced between asparagine (Asn) and glucose (Glc) during the Maillard reaction. Galacturonic acid (GalA), the major component of pectin, exhibits high activity in AA formation. This study investigated the pathway for AA formation between GalA and Asn. Three possible pathways were proposed: 1) The carbonyl group of GalA directly interacts with Asn to produce AA; 2) GalA undergoes an oxidative cleavage reaction to release α-dicarbonyl compounds, which subsequently leads to AA production; 3) 5-formyl-2-furancarboxylic acid, the thermal degradation product of GalA, reacts with Asn to generate AA. Structural analysis revealed that the COOH group in GalA accelerated intramolecular protonation and electron transfer processes, thereby increasing the formation of AA precursors such as decarboxylated Schiff base and α-dicarbonyl compounds, promoting AA formation. This study provides a theoretical basis and new insights into the formation and control of AA.

Mechanisms underlying the formation of main volatile odor sulfur compounds in foods during thermal processing

Volatile sulfur compounds (VSCs) significantly influence food flavor and garner considerable attention in flavor research due to their low sensory thresholds, diverse odor attributes, and high reactivity. Extensive research studies have explored VSC formation through thermal processes such as the Maillard reaction, thermal pyrolysis, oxidation, and enzymatic reactions. However, understanding of the specific reaction mechanisms and processes remains limited. This is due to the dispersed nature of existing studies, the undefined intermediates involved, and the complexity of the matrices and processing conditions. Given these limitations, the authors have shifted their focus from foods to sulfides. The structure, source, and chemical characteristics of common precursors (sulfur-containing amino acids and derivatives, thiamine, thioglucoside, and lentinic acid) and their corresponding reactive intermediates (hydrogen sulfide, thiol, alkyl sulfide, alkyl sulfenic acid, and thial) are provided, and the degradation mechanisms, reaction rules, and matrix conditions are summarized based on their chemical characteristics. Additionally, the VSC formation processes in several typical foods during processing are elucidated, adhering to these identified rules. This article provides a comprehensive overview of VSCs, from precursors and intermediates to end products, and is crucial for understanding the mechanisms behind VSC formation and managing the flavor qualities of processed foods.

Determination of α-Dicarbonyl compounds in traditional Chinese herbal medicines

α-DCs (α-dicarbonyls) have been proven to be closely related to aging and the onset and development of many chronic diseases. The wide presence of this kind of components in various foods and beverages has been unambiguously determined, but their occurrence in various phytomedicines remains in obscurity. In this study, we established and evaluated an HPLC-UV method and used it to measure the contents of four α-DCs including 3-deoxyglucosone (3-DG), glyoxal (GO), methylglyoxal (MGO), and diacetyl (DA) in 35 Chinese herbs after they have been derivatized with 4-nitro-1,2-phenylenediamine. The results uncover that 3-DG is the major component among the α-DCs, being detectable in all the selected herbs in concentrations ranging from 22.80 μg/g in the seeds of Alpinia katsumadai to 7032.75 μg/g in the fruit of Siraitia grosuenorii. The contents of the other three compounds are much lower than those of 3-DG, with GO being up to 22.65 μg/g, MGO being up to 55.50 μg/g, and DA to 18.75 μg/g, respectively. The data show as well the contents of the total four α-DCs in the herbs are generally in a comparable level to those in various foods, implying that herb medicines may have potential risks on human heath in view of the α-DCs.

Changes in α-Dicarbonyl Compound Contents during Storage of Various Fruits and Juices

α-Dicarbonyl compounds (α-DCs) are commonly present in various foods. We conducted the investigation into concentration changes of α-DCs including 3-deoxyglucosone (3-DG), glyoxal (GO), and methylglyoxal (MGO) in fresh fruits and decapped commercial juices during storage at room temperature and 4 °C, as well as in homemade juices during storage at 4 °C. The studies indicate the presence of α-DCs in all samples. The initial contents of 3-DG in the commercial juices (6.74 to 65.61 μg/mL) are higher than those in the homemade ones (1.97 to 4.65 μg/mL) as well as fruits (1.58 to 3.33 μg/g). The initial concentrations of GO and MGO are normally less than 1 μg/mL in all samples. During storage, the α-DC levels in the fruits exhibit an initial increase followed by a subsequent decrease, whereas, in all juices, they tend to accumulate continuously over time. As expected, 4 °C storage reduces the increase rates of the α-DC concentrations in most samples. From the viewpoint of the α-DC contents, fruits and homemade juices should always be the first choice for daily intake of nutrients and commercial juices ought to be mostly avoided.

Effects of Different Varieties on Physicochemical Properties, Browning Characteristics, and Quality Attributes of Mume fructus (Wumei)

The dried Mume fructus (MF) is a special food and herbal medicine with a long history of processing and application. The browning index (BI) of Prunus mume (PM) is pivotal in determining the medicinal value and edible quality of MF. Exploring the BI of PM holds significant importance for both the selection of PM varieties and understanding the formation mechanism of high-quality MF. This study systematically analyzed the physicochemical properties, BI, and quality indicators of four PM varieties (Qingzhu Mei, Yesheng Mei, Nangao Mei, and Zhaoshui Mei) after processing into MF. The results showed significant differences in eight physicochemical indicators among the four PM varieties (p < 0.05). Notably, Qingzhu Mei exhibited the highest titratable acid content, Nangao Mei had the most prominent soluble solid and soluble sugar content, and Zhaoshui Mei showed outstanding performance in reducing sugar, soluble protein, and free amino acids. Regarding drying characteristics, Yesheng Mei and Nangao Mei required a shorter drying time. In terms of BI, Nangao Mei exhibited the greatest degree of browning and its color appearance was darker. When considering quality evaluation, Nangao Mei excelled in rehydration ability and extract content, while Zhaoshui Mei demonstrated outstanding levels of total phenols, total flavonoids, and total antioxidant capacity. Overall, the evaluation suggested that the Nangao Mei variety was more suitable for MF processing. These research results provide a valuable theoretical foundation for understanding the BI of PM varieties and serve as a reference for the selection of PM varieties as raw materials for processing MF.

Microwave infrared vibrating bed drying of ginger: Drying qualities, microstructure and browning mechanism

In this study, microwave infrared vibrating bed drying (MIVBD) method was used to dry ginger and the key characteristics of the product were determined, in terms of drying characteristics, microstructure, phenolic and flavonoid contents, ascorbic acid (AA), sugar content, and antioxidant properties. The mechanism of sample browning during drying was investigated. The results showed that increased infrared temperature and microwave power increased the drying rate and caused microstructure damage to the samples. At the same time, which caused the degradation of the active ingredients, promoted Maillard reaction between reducing sugar and amino acid, and caused the increase of 5-hydroxymethylfurfural, then the degree of browning increased. The AA reacted with amino acid to also caused browning. Antioxidant activity was significantly affected by AA and phenolics (r > 0.95). The quality and efficiency of drying can be effectively improved by MIVBD, and the browning can be reduced by controlling infrared temperature and microwave power.

Effect of high hydrostatic pressure treatment on the inactivation and sublethal injury of foodborne pathogens and quality of apple puree at different pH

The objectives of this study were to evaluate the survival of high hydrostatic pressure (HHP)-treated Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes in apple puree, as well as to determine the levels of HHP-induced cell injury according to the pressure level, holding time, and pH of apple puree. Apple puree was inoculated with three foodborne pathogens and treated at pressures of 300-600 MPa for up to 7 min at 22 °C using HHP equipment. Increasing the pressure level and lowering the pH of apple puree led to larger microbial reductions, and E. coli O157:H7 showed higher resistance compared to S. Typhimurium and L. monocytogenes. Besides, approximately 5-log injured cells of E. coli O157:H7 were induced in apple puree at pH 3.5 and 3.8. HHP treatment at 500 MPa for 2 min effectively achieved complete inactivation of the three pathogens in apple puree at pH 3.5. For apple puree at pH 3.8, more than 2 min treatment of HHP at 600 MPa is seemingly needed to achieve complete inactivation of the three pathogens. Transmission electron microscopy analysis was conducted to identify ultrastructural changes in the injured or dead cells after HHP treatment. Plasmolysis and uneven cavities in the cytoplasm were observed in injured cells, and additional deformations, such as distorted and rough cell envelopes, and cell disruption occurred in dead cells. No changes in solid soluble content (SSC) and color of apple puree were observed after HHP treatment, and no differences were detected between control and HHP-treated samples during 10 d of storage at 5 °C. The results of this study could be useful in determining the acidity of apple purees or the treatment time at specific acidity levels when applying the HHP processing.

Formation of aroma characteristics driven by volatile components during long-term storage of An tea

The aim of this study was to reveal the molecular basis of aroma changes during storage of An tea (AT). The key volatile compounds in AT were screened using SPME-GC-MS and SPE-GC-MS analytical techniques in combination with odor activity value (OAV) and flavor dilution factor (FD). The results showed that with the increase of storage time the stale and woody aromas were revealed. Esters, acids and hydrocarbons are the main types of volatile compounds in AT, and their content accounts for 52.69 %-61.29 % of the total volatile compounds. The key volatile compounds with stale and woody aromas during AT storage were obtained by OAV value and FD value, namely ketoisophorone (flavor dilution factor, FD = 64), linalool oxide C (FD = 64), 1-octen-3-ol (OAV > 1, FD = 32), 1,2-dimethoxybenzene (FD = 16), naphthalene (OAV > 1, FD = 32), 3,4-dimethoxytoluene (FD = 16), and 1,2,3-trimethoxybenzene (FD = 8). Our research provides a scientific basis and insights for the improvement of quality during the storage of dark tea.

Chaste honey in long term-storage: Occurrence and accumulation of Maillard reaction products, and safety assessment

Honey, a natural sweetener that can be stored long-term, is prone to Maillard reactions. Maillard reaction products (MRPs), such as 5-hydroxymethylfurfural (5-HMF), α-dicarbonyl compounds (α-DCs), and advanced glycation end products (AGEs), negatively affect human health. We analyzed MRP accumulation in chaste honey over four years. In the first year, α-DCs were dominant with total contents of 509.7 mg/kg. In the second year, Amadori compounds increased, accounting for the largest percentage. Their formation at the initial stage showed inhibition of the Maillard reaction over time. AGE contents were approximately 1.00 mg/kg over four years, which is negligible compared to other foods. Increased 5-HMF was significantly correlated with storage time (p < 0.01), making it a suitable indicator of honey quality. Due to the lack of MRP risk assessments, we compared our findings with daily intake of MRPs from other foods, and the levels of MRPs in honey over four years are acceptable.

Magnetically driven nanorobots based on peptides nanodots with tunable photoluminescence for rapid scavenging reactive α-dicarbonyl species and effective blocking of advanced glycation end products

The present work constructed magnetically driven nanorobots by conjugating the photoluminescent β-alanine-histidine (β-AH) nanodots to superparamagnetic nanoparticles (SPNPs) for simultaneously sensitive determination and fast trapping RDS in food processing, achieving efficient regulation of advanced glycation end products (AGEs) risk. Bio-derivative β-AH nanodots with orderly self-assembly nanostructure and tunable photoluminescent properties served as both biorecognition elements to effectively bind and scavenge the reactive α-dicarbonyl species (RDS), as well as the indicator with sensitive fluorescence response in the food matrix. The magnetically driven nanorobots with excellent biosafety of endogenous dipeptides displayed a high binding capacity of 80.12 mg g^-1 with ultrafast equilibrium time. Furthermore, the magnetically driven nanorobots achieved rapid removal of the RDS with the manipulation of the external magnetic field, which enabled intercepting AGEs generation without byproducts residual as well as ease-of-operation. This work provided a promising strategy with biosafety and versatility for both accurate determination and efficient removal of hazards.

Inhibition of Browning in Apples Using Betacyclodextrin-Assisted Extracts of Green Rooibos (Aspalathus linearis)

Green rooibos' bioactive compounds contribute greatly towards its antioxidant activity. The anti-browning activity of aqueous (GRE) and beta-cyclodextrin (β-GRE)-assisted extracts of green rooibos was investigated in canned apples. Freeze-dried extracts (GRE and β-GRE) obtained at 40 °C for 60 min were added in canned apples at 0.25 and 0.5% prior to heat processing and stored at 23 and 37 °C for 24 weeks. Lightness (L*), colour difference (DE*), furfural and hydroxymethyl furfural (HMF) were determined to establish the effect of extracts against non-enzymatic browning (NEB) development. The L* value decreased, whereas DE*, HMF and furfural increased with increased storage time and temperature. A higher inhibition was observed for samples stored at 23 °C, and storage at 37 °C reduced (p < 0.05) the inhibitory capacity of extracts. Greater inhibition against NEB development was reported for β-GRE 0.25 and 0.5 via the L* value (40.93-46.67%), β-GRE 0.25 for DE* (46.67%) and β-GRE 0.25 and 0.5 for HMF (59.55-67.33%). No differences (p > 0.05) were observed in furfural inhibition between all extracts, although inhibition was reported at 62.69-72.29%. Browning inhibition correlated with the reaction rate constant (k₀) and activation energy (Ea), exhibiting a correlation coefficient of 0.925, 0.964, 0.932 and 0.754 for L*, DE*, HMF and furfural, respectively.

Investigation on the contents of heat-induced hazards in commercial nuts

The purpose was to investigate the contents of heat-induced hazards by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in 44 commercial nuts. Results showed that content ranges of Acrylamide (AA), 5-hydroxymethylfurfural (5-HMF), N^ε-carboxymethyl-lysine (CML), N^ε-carboxyethyl-lysine (CEL), 3-Deoxyglucosone (3-DG), Glyoxal (GO), and Methylglyoxal (MGO) were ND-123.57 µg/kg, 0.57-213.42 mg/kg, 3.18-18.67 mg/kg, 3.98-57.85 mg/kg, 1.5-133.86 mg/kg, 0.45-1.59 mg/kg and 0.29-13.84 mg/kg, respectively. Sunflower seeds contained more heat-induced hazards followed by pistachios, cashews, almonds, walnuts and hazelnuts. The content of 5-HMF was positively correlated with the content of 3-DG. CML exhibited positive correlation with content of GO while no correlation between CEL and MGO. Higher levels of 3-DG and 5-HMF were observed in nuts produced with sugar and honey. Deep processing had a stronger promoting effect on CML and CEL formation. These data could provide a crucial guide for consumers to select nut products which might reduce heat-induced hazards intake.