Formation of heterocyclic amine–amino acid adducts by heating in a model system

Although mutagenic and carcinogenic heterocyclic amines (HCAs) are known to be formed in cooked meat and fish, human HCA exposure and carcinogenic risk have not been elucidated in sufficient detail. In this work, we investigated the formations of HCA–amino acid adducts in a model system by using a liquid chromatography–mass spectrometry to elucidate another source of human HCA exposure. The 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) adduct with glycine was formed easily by heating at 200 °C within 5 min, which is probably based on the dehydration condensation of the amino group of PhIP and carboxyl group of glycine. PhIP and other HCAs such as 2-amino-3-methyl-3H-imidazo[4,5-f]quinolone, 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline and 3-amino-1,4-dimethyl-5H-pyrido[3,4-b]indole, also bound with various amino acids by heating. Among these amino acids, proline tends to form adducts with HCAs, but serine, cysteine and lysine hardly bound with HCAs. These results provided a basic understanding of the formation of HCA adducts with amino acids during cooking.     

Stability of antioxidants in an apple polyphenol–milk model system

The stability of antioxidants in an apple polyphenol–milk model system was examined. The model system consisted of skim milk fortified with pH-neutralised apple polyphenols (AP, 0–200 mg per 100 ml milk), with or without ascorbic acid (100 mg per 100 ml milk). Physical and chemical changes were evaluated after thermal treatment (120 °C, 5 min) and oxidative storage (20 °C and 38 °C, up to 12 weeks). Antioxidant capacity was determined using both oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay. Significant antioxidant capacity was detected in the presence of milk. Antioxidant capacity was retained during thermal treatment but decreased slowly during storage.     

Biological activities of Maillard reaction products (MRPs) in a sugar–amino acid model system

The various biological activities of Maillard reaction products (MRPs) from sugar (fructose and glucose) and 20 amino acid model systems were evaluated. Colour development, in vitro antioxidant, α-glucosidase inhibitory, antihypertensive, and antiproliferative activities of aqueous solutions of MRPs produced by heating at 130 °C for 2 h were measured. The fructose–amino acid mixture showed higher UV-absorbance and browning intensity than the glucose–amino acid mixture. The fructose–amino acid model MRPs showed higher DPPH and ABTS radical scavenging and ACE inhibitory activities than the glucose–amino acid model MRPs. The α-glucosidase inhibitory effect of MRPs derived from fructose– and glucose–tyrosine showed higher α-glucosidase inhibitory activity than that of other MRPs. Sugar–amino acid model MRPs inhibited the growth of HCT116 colon cancer cell in a dose-dependent manner (from 0.5 to 1.5 mg/ml). Glucose MRPs showed slightly higher antiproliferative activity than fructose MRPs. In particular, sugar–tryptophan and –tyrosine MRPs exerted higher biological activities than the other MRPs.     

Determination of volatile compounds formed in a glucose–selenomethionine model system by gas chromatography–atomic emission detector and gas chromatography–mass spectrometry

In order to gain a better understanding of the formation of organoselenium compounds in food system, the Maillard reaction of selenomethionine and glucose was studied in a model system. The effects of heating time and pH on the volatile compounds formed in a glucose–selenomethionine reaction were also investigated. Nine organoselenium compounds were identified. Pyrazines and dimethyldiselenide are major volatile compounds generated from the glucose–selenomethionine model system. A high pH level favours the formation of pyrazine and dimethyldiselenide. In unbuffered systems, a pH change of three or more pH units may occur, and this may significantly affect the formation of Maillard reaction products.     

Characteristics and antioxidant activity of ultrafiltrated Maillard reaction products from a casein–glucose model system

Maillard reaction products (MRPs) were prepared from casein–glucose by refluxing for 130 min at 102 °C and initial pH 12.0 without pH control to investigate the characteristics of casein–glucose Maillard reaction and the antioxidant activity difference among different fractions of MRPs. Browning and intermediate products increased, however, the pH of the system decreased with increase in the heating time. Free amino group content decreased 78% during first 10 min and did not change nearly thereafter. Amino acid analysis indicated that lysine and arginine decreased significantly, and casein was partially hydrolysed to peptides or free amino acid. High molecular weight compounds were dominant in the MRPs, determined by high performance gel-filtration chromatography. After ultrafiltration, antioxidant activity of each MRPs fraction was investigated by DPPH radical-scavenging activity, reducing power, Fe²⁺ chelating activity and lecithin oxidation assay. MRPs of different molecular weight exhibited distinctly different antioxidant activities.     

Emulsifying properties of soy whey protein isolate–fenugreek gum conjugates in oil-in-water emulsion model system

Soy whey protein isolate (SWPI)–fenugreek gum conjugates were prepared by Maillard type reactions in a controlled dry state condition (60 °C, 75% relative humidity for 3 days) to improve emulsification properties. SDS-PAGE electropherogram showed that conjugation formed high molecular weight products with the disappearance of 7S fraction, acidic subunits of the 11S fractions and protein band at molecular weight 21 and 24 kDa. However, the amount of protein at molecular weight 30 kDa remained unchanged. The protein solubility of SWPI–fenugreek gum conjugates improved as compared to SWPI and SWPI–fenugreek gum non-conjugated mixture especially at isoelectric point of protein when assessed in the pH range 3–8 at 22 °C. In comparison to SWPI, fenugreek gum and non-conjugated SWPI–fenugreek gum, SWPI–fenugreek gum conjugates had better emulsifying properties near the isoelectric pH of protein. Emulsification at near the isoelectric pH of protein was chosen as at this pH the proteins are prone to aggregate, which could destabilize the emulsion. Heating solutions of the conjugates prior to emulsification further improved their emulsification properties. The conjugates also showed a better emulsifying property at high salt concentration as compared to SWPI alone.     

Relationship between chlorophyll a and β-carotene in a lipid-containing model system during illumination

The relationship between chlorophyll a (Chl a) and β-carotene during illumination in the presence of fatty acid esters, methyl stearate methyl oleate and methyl linoleate was studied. Mixtures of Chl a, β-carotene and fatty acid esters were exposed to a 40 w light for 3 h. Isomerization and degradation reations of Chl a and β-carotene were monitored using HPLC with diode array detection Three isomers of Chl a and four cis isomers of β-carotene were separated and detected. Both the degradations of total amount of Chl a and β-carotene fit the first-order model. The degradation rate of total amount of β-carotene was highest in methyl stearate, followed by in methyl oleate and in methyl linoleate, while a reverse order was observed for the degradation rate of total amount of Chl a. In the presence of three fatty acid esters, Chl a is more susceptible to isomerization and degradation than β-carotene, and the degradation rates for both Chl a and β-carotene are significantly different (p < 0.05).     

Effects of pulsed electric field treatment on a bovine serum albumin–dextran model system,a means of promoting the Maillard reaction

Effects of pulsed electric field treatment on browning intensity, antioxidant activity, protein patterns and chemical structure of the bovine serum albumin–dextran copolymer were investigated. Results showed Maillard reaction between bovine serum albumin and dextran was significantly accelerated when the electric field intensity was higher than 10 kV/cm, which was proved by changes in A₂₉₄, browning, antioxidant activity and electrophoresis tests. At the same time, pronounced changes of chemical structure were found by circular dichroism test. The α-helix, β-sheet, β-turns and random coil were changed from approximately 42.6%, 1.9%, 17.5% and 33.9% to 14.5%, 33.0%, 21.2% and 30.2%, respectively, after treatment at 20 kV/cm for 7.35 ms. All data indicated that pulsed electric field was a means to promote Maillard-based copolymerisation.     

Effects of α-tocopherol on the oxidative stability and incorporation of deuterium in volatiles from a linoleic acid-deuterium model system

The effects of α-tocopherol on the oxidative stability and incorporation of deuterium in volatiles were evaluated in linoleic acid-water model systems treated at 60°C by analyzing headspace oxygen depletion, formation of lipid hydroperoxides, and profiles of headspace volatiles. Deuterium oxide accelerated the rates of linoleic acid oxidation compared to samples in deuterium-free water. As the concentration of α-tocopherol increased from 0 to 1500 ppm, the consumption of headspace oxygen and the formation of volatiles decreased, whereas the contents of lipid hydroperoxides did not decrease in the linoleic acid-water system. The mass to charge ratios (m/z) of volatiles in linoleic aciddeuterium oxide were significantly higher than those with deuterium oxide-free water. Generally, the presence of α-tocopherol decreased the mass to charge ratios (m/z) of volatiles including pentanal, hexanal, t-2-heptenal, and 2-octenal, implying that α-tocopherol may be involved in the aldehyde formation from lipid oxidation.     

Study on the interaction between gliadins and a coumarin as molecular model system of the gliadins–anthocyanidins complexes

To clarify the conformational changes of gliadins (Glia) upon complexation with anthocyanidins (in particular cyanidin, Cya), the interaction of Glia with a coumarin derivative (3-ethoxycarbonylcoumarin, 3-EcC), having a benzocondensed structure similar to that of Cya, has been investigated by NMR, IR, and Raman spectroscopy under acidic and neutral conditions. Raman spectra showed that both molecules produce a similar effect on the Glia structure, i.e. an increase in the α-helix conformation and a decrease in β-sheet and β-turns content. In the presence of both molecules, this effect is more marked; the spectroscopic results showed that both Cya and 3-EcC interact with Glia and 3-EcC favors the complex formation with Glia. The results obtained in this study provide new insights into anthocyanidins–Glia interactions and may have relevance to human health, in the field of the attempts to modify gluten proteins to decrease allergen immunoreactivity.     

Chitosan–tripolyphosphate submicron particles as the carrier of entrapped rutin

Chitosan (CH)–tripolyphosphate (TPP) submicron particles were formed as carriers of entrapped rutin, and the release properties characterized using simulated gastric juices and fluids of the small intestine. Particle size, charge and entrapment efficiencies were investigated as a function of the CH:TPP molar ratio (2.0:1.0–5.0:1.0). Size was found to decrease from ∼814 nm for the 2.0:1:0 mass ratio to ∼528 nm for the ratios between 2.5:1.0 and 4.0:1.0, and then again to ∼322 nm for the 5:0:1.0 mass ratio, whereas all particles carried a positive surface charge, increasing from +21 to +59 mV as the ratio increased from 2.0:1.0 to 5.0:1.0. The percent entrapment was found to rise from 3.68% to 57.6% as the ratios increased from 2.0:1:0 to 4.0:1:0, before reaching a plateau. Submicron particles (4.0:1.0 mass ratio only) were found to retain rutin in simulated gastric fluids, whereas in conditions which simulated fluids from the small intestine, only 20% of the entrapped rutin was released and 80% remained absorbed to the CH:TPP carriers. Such particles have applications for the delivery of phenolics in food and natural health products.     

Ultrasound monitoring of a deformable tongue-food gel system during uniaxial compression–an in vitro study

This study presents a novel ultrasound method for exploring the mechanical deformability of artificial tongue models (ATMs) topped with agar and/or gelatin food gels during uniaxial compression. The ATMs were made from polyvinyl alcohol and displayed different levels of rigidity and surface roughness. We quantified deformation of the ATM-food system as it underwent compression induced by a texture analyzer. We collected real-time measurements via an ultrasound transducer (1 MHz) placed beneath the ATM, enabling to monitor non-invasively the ultrasound time of flight (ToF) and the apparent reflection coefficient (R*) of the ATM-food interface. The results on ToF reflected the tie between the level of force and ATM deformation; they were also precise enough to identify gel fracture. R* was a crucial parameter influenced by both ATM properties (rigidity, surface roughness) and food gel properties (syneresis, ability to mold to surface asperities).     

Microbial inactivation of E. coli cells by a combined PEF–HPCD treatment in a continuous flow system

A laboratory scale continuous flow unit was set up and used to study the effect of pulsed electric fields (PEF) pre-treatments on microbial inactivation by high pressure carbon dioxide (HPCD) processing with the aim of investigating the synergistic effect of the combined treatment. McIlvaine buffer solution inoculated with Escherichia coli cells ATCC26 was pre-treated with PEF (25 °C) at different field strength (E = 6–12 kV/cm) and energy input (W_T = 10–40 J/mL) and then processed with HPCD (25 °C) at pressures of 8.0, 14.0 and 20.0 MPa and holding times of 4, 7 and 11 min.Results showed that treating the microbial suspension only with PEF, the inactivation level slightly increased with increasing the field strength and energy input with no significant effect of the pressure applied. The maximum inactivation level obtained was 2.25 Log-cycles at 12 kV/cm and 40 J/mL. When the bacterial cells were treated only with HPCD, the inactivation level was almost independent on the pressure of CO₂, and gradually increased with increasing the holding time up to a maximum value of 2.41 Log-cycles. The combination of PEF and HPCD treatment resulted in a marked increase of the microbial inactivation with increasing the field strength, energy input, holding time and operative pressure. A clear synergistic effect was evident when holding time was longer than 4 min, regardless the intensity of the PEF treatment applied.Industrial relevanceConsumers demand for fresh and natural products forces food manufacturers to investigate milder preservation processes and stimulate the current trend to use hurdle technologies. Pulsed electric field (PEF) and high pressure carbon dioxide (HPCD) are emerging non-thermal technologies which have antimicrobial capabilities when applied alone or in combination with other physicochemical hurdles. The present work demonstrated, for the first time, the feasibility of combined PEF-HCPD process based on the coupling of a PEF pretreatment stage to HPCD treatment in a continuous flow unit. The results support the view that the combined process is able to induce substantial microbial inactivation at mild treatment conditions and at room temperature suggesting the idea that this process could be applied to foods with thermosensitive components.     

Identification of active compounds from Aurantii Immatri Pericarpium attenuating brain injury in a rat model of ischemia–reperfusion

Ischemic stroke is caused by brain injury due to prolonged ischemia by occlusion of cerebral arteries. In this study, we isolated active compounds from an ethanol extract of Aurantii Immatri Pericarpium (HY5356). We first showed by DNA fragmentation assay that HY5356 improved human hepatocellular carcinoma cells (HepG2) under hypoxic conditions by inhibiting apoptosis. When HY5356 was fractionated with dichloromethane (MC), ethyl acetate (EA) and n-butanol (BU), the MC fraction improved cell viability at the lowest concentration (100 μg/ml). Intraperitoneal injection of HY5356 (200 mg/kg) or the MC fraction (200 mg/kg) to rats prior to occlusion attenuated brain injury significantly in a rat model of ischemia–reperfusion. Adopting cell viability under hypoxic conditions as an activity screening system, we isolated nobiletin and tangeretin as active compounds. The results suggest that intake of Aurantii Immatri Pericarpium containing nobiletin and tangeretin as active compounds might be beneficial for preventing ischemic stroke.     

Antioxidative potential of melanoidins isolated from a roasted glucose–glycine model

The antioxidative activity of the total water soluble fraction (sol A), high molecular weight (HMW; MW>12,400 Dalton), low molecular weight (LMW) and the insoluble fraction (IS) of a glucose–glycine model system roasted at 120°C was studied in hydrophilic solutions (PBS buffer, fruit juices; addition: 0.01–0.1%) at ambient temperature and lipophilic (coconut fat, triolein and corn oil; addition: 0.01–0.5%) matrices at 60°C and frying conditions at 200°C. The hydrophilic reducing power in the water-soluble fractions was evaluated with the ABTS [2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid)] method. Fat stability was determined by observing the development of the peroxide value and conjugated dienes. All fractions increased the hydrophilic reducing power in the water-soluble fractions as a matter of concentration with highest effects for the 0.1% enrichment. In PBS buffer the HMW was most effective, in fruit juices the IS. A slight antioxidative effect in fats was observed only for 0.5% IS and 0.5% sol A in corn oil. Neither in coconut fat at 200°C nor in triolein at 60°C Maillard reaction products (MRPs) were able to extend shelf life. The results performed describe MRPs as highly antioxidative in water-soluble but less effective in water-insoluble fractions.     

Use of food-grade proteases to recover umami protein–peptide mixtures from rice middlings

The effects of enzymatic hydrolysis induced by food-grade exo- plus endo-proteases (i.e. Umamizyme and Flavourzyme) on the sensory characteristics and functional properties of rice middlings were investigated. Enzymatic hydrolysis was confirmed by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), by monitoring the rate of hydrolysis with the Coefficient of Protein Degradation (CPD). The presence of medium-low size polypeptides at the end point of 24 h was detected, resulting from 24.84 ± 1.28 % and 67.04 ± 0.55 % hydrolysis for Flavourzyme and Umamyzyme, respectively. Sensory and functional properties, including emulsifying and foaming properties, were evaluated on hydrolysates obtained after 24 h incubation. The sensory analysis described the umami taste as the most intense attribute for all the products and good emulsifying and foaming properties were observed, mainly in Umamizyme hydrolysates. Then the hydrolysis procedure here described could be convenient to provide ingredients characterized by a good taste profile and by functional properties useful for industrial food processing, storage and consumption.     

Effect of Maillard reaction conditions on browning and antiradical activity of sugar–tuna stomach hydrolysate model system

The antiradical activity of Maillard reaction products (MRPs) made from sugar–tuna stomach hydrolysate model system was tested. The antiradical activity of the MRPs derived from ribose was 11-fold higher than that of MRPs derived from glucose due to the acyclic form of the ribose. The activity reached the plateau at a 30 mg/mL ribose concentration. The ribose caramelization contributed to the antiradical activity and browning reactions at 95 °C and 115 °C. The increase in DPPH radical scavenging of MRPs is attributed not only to the temperature but also to the buffer type and buffer concentration. Phosphate buffer showed the most efficient compared to citrate or Tris–HCl buffers. A positive correlation (R² = 0.98) was observed between the antiradical activity, the browning and the phosphate concentration. The MRPs obtained under these mild experimental conditions exhibited no toxicity towards Vero cells and 3T3 cells, despite their high antiradical activity.     

Effect of 3 lactobacilli on immunoregulation and intestinal microbiota in a β-lactoglobulin–induced allergic mouse model

Milk is one of the earliest and most common allergen sources in the world, with β-lactoglobulin representing a major allergen protein. Numerous studies have reported that probiotics exert antiallergic and anti-inflammatory effects. Here, we examined the effects of 3 strains of Lactobacillus on immunomodulatory functions, intestinal barrier functions, and intestinal microbiota through a β-lactoglobulin–induced allergic mouse model. We found that the oral administration of Lactobacillus plantarum ZDY2013 and Lactobacillus rhamnosus GG suppressed allergic response, attenuating serum IgE and relieving anaphylaxis symptoms. The 3 strains of Lactobacillus could induce T helper (Th) 1 or T regulatory cells to differentiate to inhibit the Th2-biased response for regulating Th1/Th2 immune balance. Furthermore, L. plantarum ZDY2013 and L. rhamnosus GG enhanced intestinal barrier function through the regulation of tight junction. We also found that L. plantarum ZDY2013 and L. plantarum WLPL04 could regulate alterations in intestinal microbiota caused by allergies. In particular, Rikenella, Ruminiclostridium, and Lachnospiraceae UCG-006 were considerably reduced after treatment with L. plantarum ZDY2013 and L. plantarum WLPL04. These results suggested that 3 Lactobacillus strains may serve as an effective tool for the treatment of food allergies by regulating immune and gut microbiota.