Elucidation of the formation of CO2 in culinary dry products

 The formation of CO₂ in tomato powder, chosen as an example of a dry culinary product, was investigated at room temperature and at low values of water activity (a _w). CO₂ formation correlated well with parameters that represent the beginning and progression of the Maillard reaction. In the absence of O₂, CO₂ formation decreased. Pectin and depolymerized pectin did not influence CO₂ formation while galacturonic acid (GalA) had a large effect. Determination of ¹³CO₂ in low-moisture model systems revealed that CO₂ was not formed by decarboxylation of GalA alone. Only a small proportion of [1-¹³C]glycine and GalA was degraded by the Strecker pathway; however, glucose reacted with the labelled amino acid forming ¹³CO₂ which amounted to over 90% of the total CO₂ formed. Therefore, CO₂ could be used as an early indicator for the beginning of the Maillard reaction in dry culinary products. Received: 28 October 1996     

Effects of supercritical carbon dioxide on volatile formation from Maillard reaction between ribose and cysteine

BACKGROUND: Supercritical carbon dioxide (SC‐CO₂) technology is being used in an increasing number of food‐manufacturing applications; however, its effect on the Maillard reaction is not well studied. The objective of this study was to investigate the effect of SC‐CO₂ treatment (140 °C, 40 MPa) on the Maillard reaction of an aqueous ribose–cysteine model system under varying pH conditions (5.6, 7.0 and 8.0), with emphasis on the formation of volatile compounds. RESULTS: SC‐CO₂ had a suppressing effect on the browning stages of the reaction under acidic and neutral pH conditions, while it appeared to have an accelerating effect at pH 8.0. Over 70 volatile compounds were positively identified from the headspace of the model system by gas chromatography–mass spectrometry. The volatiles were dominated by sulfur‐containing compounds including thiophenes and fused bicyclic sulfur‐containing compounds under all experimental conditions. Several compounds, including 2‐methyl‐3‐furanthiol, 2‐furanmethanethiol, 3‐thiophenethiol, and 2‐methyl‐3‐thiophenethiol, and one of the intermediates, furfural, were generated in much higher amounts in the SC‐CO₂‐treated samples, especially at alkaline and neutral pH values. CONCLUSION: SC‐CO₂ treatment was inhibitory to the formation of most volatiles in the Maillard reaction, but enhanced the formation of some intermediates and well‐known meaty flavoured compounds. Copyright © 2007 Society of Chemical Industry     

Quantitative analysis of the isoflavone content and biological growth of soybean (Glycine max L.) at elevated temperature,CO2 level and N application

Effects of ambient and elevated CO₂ levels (360 and 650 µmol mol^?1 respectively), ambient and high (5 °C above ambient) temperatures and their interactions with N application on soybean (Glycine max L.) were studied in 2001. Overall, total isoflavones in whole soybean seeds were highest (1383.0 µg g^?1) in the elevated CO₂ (AE) treatment without N application and lowest (414.1 µg g^?1) in the elevated temperature (EA) treatment with N application. Malonylgenistin (449.2 µg g^?1) and malonyldaidzin (435.9 µg g^?1) concentrations in the AE treatment without N application were highest among the 12 individual isoflavones, while aglycon and acetyl conjugates showed lower concentrations (below 10 µg g^?1) than glucoside and malonyl conjugates in all treatments. Overall, N application had no effect on total isoflavone concentration, while both temperature and CO₂ level had a higher effect on increasing isoflavones, including aglycon and acetyl conjugates (P = 0.001). In the biological growth analysis, total dry weight was highest (100.9 g) in the elevated temperature and CO₂ (EE) treatment with N application, while leaf area was more affected by CO₂ than by temperature and increased with N application. There were larger numbers of pods (99) and seeds (176) per plant in the EE treatment with N application, and generally the AE treatment showed a greater increase in 100‐seed weight (g per 100 seeds) and in pods and seeds per plant than other treatments. Overall, total dry weight was highly affected (P = 0.001) by three main factors, temperature, CO₂ and N application, but the interactions temperature × N and temperature × CO₂× N did not affect total dry weight. Also, total dry weight tended to increase with increasing numbers of pods (r² = 0.93***) and seeds (r² = 0.93***) and larger leaf area (r² = 0.85***). In addition, numbers of pods and seeds were significantly affected (P = 0.01–0.001) by temperature, CO₂ and temperature × CO₂. Generally, elevated CO₂ and temperature did not affect N, P and K concentrations in the seeds but did decrease the concentrations of Ca and Mg, which were increased in the AE treatment. Among the nutrients, Ca and Mg were highly correlated with temperature and CO₂ level. N concentration in the seeds increased with applied N and in particular showed a high increase with elevated temperature and ambient CO₂ (EA treatment). The variation in isoflavones was correlated with temperature (r² = ?0.70**) and CO₂ (r² = 0.67**), while N application was not correlated with isoflavone concentration. Also, Ca (r² = ?0.85***) and Mg (r² = ?0.57*) in the seeds were correlated with variation in isoflavones. This indicated that isoflavones were in higher concentrations under conditions of low temperature and increasing CO₂, which also resulted in low Ca and Mg concentrations in the seeds. The results of this study suggest that the long‐term adaptation of the soybean to growth at elevated CO₂ level and high temperature might potentially increase its isoflavone content, growth and yield. Copyright © 2005 Society of Chemical Industry     

Key meat flavour compounds formation mechanism in a glutathione-xylose Maillard reaction

The formation mechanism of meat flavours formed from a glutathione-xylose Maillard reaction was studied using a group of model reactions with [¹³C₅] xylose/xylose (1:1), heated at 132 °C for 90 min. Volatiles, especially the aroma-active compounds, and non-volatiles were analysed respectively with GC-O-MS and LC-TOF-MS. Analysis of the mass spectra showed that furfural, 2-furfurylthiol and thiophene were ¹³C₅-labelled and hence stem from xylose, whereas 2-methyl-3-furanthiol, 2-methyl-thiophene and 2-pentyl-thiophene, which showed similar formation patterns with only unlabelled compounds, may be from thiamine and/or cysteine carbons. In the process of Maillard reactions, GSH can be capable of cleaving in the position of glutamyl and cysteinyl, and then form 5-oxoproline or pyroglutamic acid (PCA), cysteine, and Cys-Gly dipeptide, which can form cyclic (Cys-Gly).     

Amino acid-dependent formation pathways of 2-acetylfuran and 2,5-dimethyl-4-hydroxy-3[2H]-furanone in the Maillard reaction

The formation pathways of two furanoids, 2-acetylfuran and 2,5-dimethyl-4-hydroxy-3[2H]-furanone (DMHF) were studied by GC–MS in the Maillard-type model system based on glucose and selected amino acids. The reaction was performed in 0.01 M phosphate buffer by heating a 1:1 mixture of [¹³C6] glucose and [¹²C6] glucose with amino acid. There is only one major formation pathway for DMHF in which the glucose carbon skeleton stayed intact. Formation pathways for 2-acetylfuran were more complicated. They formed either from glucose or from glucose and glycine. In the presence of glycine, the [C-5] unit of glucose combined with formaldehyde from glycine leads to 2-acetylfuran. For other amino acids, either cyclisation of intact glucose or recombination of glucose fragments can lead to 2-acetylfuran formation. These results indicate a competitive trend in controlling Maillard reaction. Therefore, besides changing Miallard reaction impact factors (temperature, time, pH etc.), inhibiting or preventing the competitive reaction cascade may direct desired pathways of Maillard reaction.     

Elevated carbon dioxide affects fruit flavor in field‐grown strawberries (Fragaria × ananassa Duch)

The effect of elevated carbon dioxide on fruit quality and aroma volatile composition in field‐grown strawberries (Fragaria × ananassa Duch) was studied. Elevating the ambient CO₂ concentration (ambient + 300, and ambient +600 µmol mol^?1 CO₂) resulted in high fruit dry matter, fructose, glucose and total sugar contents and low citric and malic acid contents. High CO₂ growing conditions significantly enhanced the fruit content of ethyl hexanoate, ethyl butanoate, methyl hexanoate, methyl butanonate, hexyl acetate, hexyl hexanoate, furaneol, linalool and methyl octanoate. Thus, the total amounts of these compounds were higher in berries grown in CO₂‐enriched conditions than those grown in ambient conditions. The highest CO₂ enrichment (600 µmol mol^?1) condition yielded fruit with the highest levels of these aroma compounds. Copyright © 2004 Society of Chemical Industry     

Monitoring Technology for Gamma‐Aminobutyric acid Production in Polished Mochi Barley Grains using a Carbon Dioxide Sensor

Gamma‐aminobutyric acid (GABA) has many biological functions, including the inhibition of blood pressure increases and acceleration of growth hormone secretion. In this study, we discovered the utility of measuring the concentration of carbon dioxide (CO₂) dissolved in the reaction solution, for development of a real‐time and convenient technique to estimate GABA production. In addition to mochi barley bran, we examined the polished grains of three species: mochi barley (a variant of hulless barley), barley, and Japanese millet, all soaked in l ‐glutamic acid (l ‐Glu) solution at pH 4.5. We found a positive correlation between GABA and CO₂ concentrations, and the production of CO₂ was suppressed in the absence of l ‐Glu at pH 4.5. These results suggest that GABA content can be easily predicted by measuring the aqueous CO₂ content using a CO₂ sensor, during the process of GABA production in polished mochi barley grains and bran.     

Antimicrobial Effects of Pressured Carbon Dioxide in a Continuous Flow System

The application of microbubbles of pressured CO₂ greatly increased CO₂ concentration in the solution treated. By treatment at 6 MPa, 35°C and average residence time 15 min, L. brevis was completely inactivated at the level of dissolved CO₂,γ≧ 11 (γ, Kuenen's gas absorption coefficient). E. coli and S. cerevisiae required γ≧ 17, and T. versatilis required γ≧ 21 for complete inactivation. Z. rouxii could be sterilized at 20 MPa and 26. A comparison of the continuous and batch method showed that L. brevis was inactivated completely under pressured CO₂ > 0.16 g/cm³ with the continuous method and >0.9 g/cm³ with the batch method.     

Continuous dense‐phase CO2 processing of a coconut water beverage

Effects of dense‐phase CO₂ (DPCD) on microbial, physical, chemical and sensorial quality of coconut water (CW) beverage were evaluated. Pressure during DPCD treatment was not significant in microbial reduction whereas temperature and % CO₂ levels were significant. DPCD‐treated (34.5 MPa, 25 °C, 13% CO₂, 6 min), heat‐pasteurised (74 °C, 15 s) and untreated CW beverages were evaluated during 9 weeks of refrigerated storage (4 °C). Total aerobic bacteria of DPCD and heat‐treated samples decreased whereas that of untreated samples increased to >10⁵ CFU mL^?1 after 9 weeks. DPCD increased titratable acidity but did not change pH (4.20) and °Brix (6.0). Likeability of DPCD‐treated CW was similar to untreated. Heat‐treated samples were less liked (α = 0.05) at the beginning of storage. Off flavour and taste‐difference‐from‐control scores of heated samples were higher than DPCD during the first two weeks. DPCD extended shelf life of acidified, sweetened and carbonated CW over 9 weeks at 4 °C.     

Physicochemical properties and emulsion stabilization of rice dreg glutelin conjugated with κ‐carrageenan through Maillard reaction

BACKGROUND: Rice dreg is an underutilized source of cereal protein with good potential for application in the food industry. Glutelin represents about 850 g kg^?1 of total storage protein in rice dreg. The objective of this study was to characterize the physicochemical properties and emulsion stabilization of the Maillard type conjugate formed with rice dreg glutelin (RDG) and κ‐carrageenan (1:2 weight ratio) dry‐heated at 60 °C and 79% relative humidity for 24 h. RESULTS: Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and Fourier transform‐infrared analysis provided evidence on the formation of the Maillard type conjugation. Amino acid analysis suggested that the major locus during the Maillard reaction were lysine and arginine. Circular dichroism spectra showed decreasing amounts of α‐helix and β‐strand in the products with increment in the amount of turns and random coil. Conjugation with κ‐carrageenan could significantly improve solubility of RDG (P < 0.05). Measurements of mean droplet size and creaming stability in oil‐in‐water emulsions showed that the conjugate was more effective at stabilizing emulsions at low pH or in the presence of high ionic strength. CONCLUSION: The Maillard reaction can be successfully used as a coupling method for RDG and κ‐carrageenan to form the conjugate with improved solubility and emulsion stabilization. Copyright © 2012 Society of Chemical Industry     

Physicochemical properties of extruded germinated wheat and barley as modified by CO2 injection and difference extrusion conditions

Germinated wheat and barley were extruded with a pilot‐scale corotating twin‐screw extruder under different barrel temperatures (100 and 120 °C), feed moisture content (30 and 35%) and CO₂ injection. The effect of germination, barrel temperature, feed moisture content and CO₂ injection on physical properties, proximate composition, γ‐aminobutyric acid, β‐glucan, phytic acid and protease activity was investigated. Results indicated that the barrel temperature, moisture content and CO₂ injection significantly affected water absorption index (WAI), water‐soluble solid index (WSI), specific length, expansion ratio, bulk density, mechanical properties and colour of all extruded products (P < 0.05). Extrusion process significantly decreased γ‐aminobutyric acid and protease activity in extruded germinated wheat (EGW) and barley (EGB) products (with and without CO₂ injection). However, extrusion process (with and without CO₂ injection) increased β‐glucan in EGB and decreased phytic acid in EGW. The content of proximate composition, γ‐aminobutyric acid, β‐glucan, phytic acid and protease activity was slightly affected by CO₂ injection.     

Reactive intermediates and carbohydrate fragmentation in Maillard chemistry

Much research is devoted to the elucidation of mechanisms in the Maillard reaction. Model studies with reactive intermediates and ¹³C-labelled precursors have contributed significantly to our understanding of flavour formation in the Maillard reaction. Several examples are discussed here: The formation of methyl pyrazines and 2-acetyl-1-pyrroline, the role of ARP's and deoxyglycosones and the formation of carbohydrate fragments from reducing sugars, 3-deoxy-glucosone and ARP's. It is concluded that carbohydrate fragments, and also flavour substances derived therof, are formed from the starting reducing sugars (or the corresponding imines), deoxyglycosones, and possibly ARP's. A general scheme for flavour formation in the Maillard reaction is proposed.     

Inactivation Kinetics of Lactobacillus plantarum by High Pressure Carbon Dioxide

Inactivation kinetics of Lactobacillus plantarum by high pressure CO₂ was investigated to understand the mechanism of microbial inactivation. The inactivation rates increased with pressure, temperature and exposure time, and with decreasing pH of media. Microbial inactivation was governed essentially by penetration of CO₂ into cells and its effectiveness could be improved by the enhanced transfer rate. Microbial reduction of 8 log cycles was observed within 120 min under CO₂ pressure of 70 kg/cm² at 30°C. We hypothesized that the cell death resulted from the lowered intracellular pH and damage to the cell membrane due to penetration of CO₂. Pressurized CO₂ treatment is a potential nonthermal technology for food preservation.     

Method of Measurement of CO2 Adsorbed into α-Cyclodextrin by Infra-Red CO2 Probe

A simple CO₂ probe system for quantifying CO₂ gas adsorbed in solid matrix of α-cyclodextrin powder (α-CD) by measuring the gas concentration in the headspace was developed and validated. The essential components of this system are an infrared CO₂ probe and an air tight chamber equipped with a two-fan system to uniformly mix the relatively high density CO₂ gas. First, a known weight of dry ice (considered as pure CO₂) was used to create different amounts of CO₂ in the headspace of the chamber, and the resultant gas concentrations were measured by the probe and gas chromatography. The gas concentrations measured by both methods were quite similar (R² = 0.9950), and the calculated amount of dry-ice in the headspace using the probe was highly comparable to the amount of dry ice initially added in the chamber (R² = 0.9970). This system was then tested to measure adsorbed CO₂ content in CO₂-α-CD complexed powder by using water injection to release CO₂ from the complexed powder into the headspace. The measured results using this system were quite similar (R² = 0.9972) to those determined by a conventional acid-base titration method.     

Pecan Oil Recovery and Composition as Affected by Temperature, Pressure, and Supercritical CO2 Flow Rate

Effects of supercritical CO₂ flow rate, extraction temperature, and pressure were studied on oil recovery, fatty acid composition, and factors that control solute extraction from intact pecan halves. After an initial solubility dominant period, extraction was influenced by diffusion of oil from within the pecan. The effective diffusion coefficient was 9.76 × 10^-12 m²/s. In the first 105 min, more oil was extracted as CO₂ flow increased from 1.0 to 7.5 standard L/min (slpm). Beyond 120 min, increasing CO₂ flow from 4 to 7.5 slpm produced negligible differences in amounts of extracted oil. At 2.5 slpm CO₂ flow and 45–75°C, the oil extracted increased by 60% when pressure increased from 41.3 to 55.1 MPa and yielded slightly more at 66.8 MPa. Temperature, pressure, micrometering valve temperature, cultivar (but not extraction time) affected fatty acid (palmitic, stearic, oleic, linoleic, and linolenic) composition of pecan oil.     

Ultrasound‐assisted extraction of ginsenosides in supercritical CO2 reverse microemulsions

Ultrasound‐assisted extraction of ginsenosides from ginseng in supercritical CO₂ reverse microemulsions formed by bis(2‐ethylhexyl) sodium sulfosuccinate (AOT) was studied. Prior to extraction the ginseng was soaked in water for 12 h. It was found that ultrasound significantly enhanced supercritical CO₂ reverse microemulsion extraction. The ginsenoside extraction yield from supercritical CO₂ reverse microemulsion with ultrasound of 20 kHz, 15.2 W cm^?2 and 3/6 s was 2.63 times that without ultrasound at 24 MPa extraction pressure, 45 °C extraction temperature, 4 h extraction time, 5 MPa separation pressure, 55 °C separation temperature and 2 L h^?1 CO₂ flow rate with 140 mL of 0.07 mol L^?1 AOT/ethanol. The maximum extraction yields of ginsenosides from different concentrations of reverse microemulsions were obtained at different ultrasonic intensities. The extraction yield with 20 kHz ultrasound was higher than that with 38 kHz ultrasound at suitably low intensity; however, it was lower at high intensity. The yield improvement may be basically attributed to the mechanical and thermal effects of ultrasound. Copyright © 2006 Society of Chemical Industry     

Supercritical CO2 Extraction of β-Carotene from Sweet Potatoes

Using supercritical CO₂ to extract β-carotene there was approximately a five-fold or a three-fold increase in amount of carotenoids extracted from freeze-dried tissue relative to the amount extracted from oven-dried or fresh tissue, respectively. The most efficient conditions were at 48°C and 41.4 MPa. Of the total carotenoid content ～20% was inaccessible to supercritical CO₂. The HPLC carotenoid profile of sweet potatoes showed that the unextracted tissue contained 90%β-carotene, primarily as all-trans (ca. 99%). Supercritical CO₂ extracts contained up to 94%β-carotene. The isomer composition of β-carotene of supercritical extracts showed ～ 14% 13-cis and 11% 9-cis.     

Formation of the peptide-specific imidazolidin-4-one moiety in alanine containing Maillard reaction mixtures

Due to the facile formation of amide linkages during Maillard reaction and their possible conversion into imidazolidin-4-one moiety through interaction with aldehydes, such structures were sought and identified in simple Maillard model systems such as alanine, glucose/alanine, and glyoxal/alanine to minimise the complexity of the possible imidazolidin-4-one structures and to facilitate the interpretation of label incorporation data. To confirm the formation of imidazolidin-4-ones in these model systems a useful strategy based on Py-GC/MS analysis was developed using isotope labelling technique to identify products incorporating two nitrogen atoms, three C-3′, three C-2′ and one C-1′ atom from alanine. Products simultaneously possessing these atom configurations and having a molecular weight of 142 amu were targeted using specifically labelled precursors such as [¹⁵N]alanine, [¹³C-1]alanine, [¹³C-2]alanine, [¹³C-3]alanine and [U-¹³C₆]glucose. Based on isotope labelling studies, spiking with known precursors and comparison with established mass spectral fragmentation patterns, the formation of isomeric 3-ethyl-2,5-dimethylimidazolidin-4-ones was proposed.     

Supercritical CO2 and N2O pasteurisation of peach and kiwi juice

The microbial inactivation and qualitative parameters (pH, sugar content, titratable acidity, absorbance at 420 nm and turbidity) of peach and kiwi juices treated at 35 °C with supercritical carbon dioxide (SC‐CO₂) and nitrous oxide (SC‐N₂O) were determined as a function of pressure and treatment time. Total inactivation of both naturally occurring microorganisms and Saccharomyces cerevisiae strain (10⁵ cfu mL^?1) was obtained after 15 min of SC‐CO₂/N₂O treatment, 10 MPa and 35 °C, for both juices. No significant changes in chemical‐physical or in sensorial characteristics between untreated and treated juice were detected. The results obtained demonstrate the feasibility and the potential of SC‐CO₂/N₂O treatment as an alternative low temperature pasteurisation process for peach and kiwi juices.     

Kinetics of colour development in aqueous fructose systems at high temperatures

Non‐enzymatic browning was studied in aqueous model systems containing fructose and aspartic acid, glutamic acid or asparagine at three different soluble solid concentrations (150, 300 and 450 g kg⁻¹), which were heat treated for different times at four temperatures (85, 90, 95 and 100 °C). Various indicators were used to evaluate the extent of the Maillard reaction: spectrophotometric measurements at 280 and 420 nm (A₂₈₀ and A₄₂₀) and CIE (Commission Internationale de l'Eclairage) parameters L* (lightness), a* (redness), b* (yellowness) and ΔE* (colour difference, which is expressed as [(Δa*)² + (Δb*)² + (ΔL*)²]^1/2). The pH and the formol index were also determined. The indicator for colourless intermediate formation, A₂₈₀, showed that the kinetic constant values increased with increasing heat treatment temperature, while the influence of soluble solid concentration was not clear. After a short induction period the data were well described by assuming zero‐order kinetics. Glutamic acid turned out to be the most reactive amino acid, while asparagine was the least reactive. With reference to brown pigment formation, A₄₂₀ and ΔE*, glutamic acid was the least reactive amino acid. In all the experiments assayed, except for glutamic solutions with fructose concentrations of 150 and 300 g kg⁻¹, the data were best correlated with combined kinetics. © 2000 Society of Chemical Industry