Identification of principal constituents in enzymatically hydrolyzed coix extract

The structural elucidation of the main constituents in enzymatically hydrolyzed coix extract, a natural food preservative, was carried out. After peracetylation, five compounds, namely peracetylated forms of glucose, maltose, maltotriose, maltotetraose, and maltopentaose were isolated. The structures were determined by PFG HMQC and HMBC experiments. In addition, by using HPLC with an RI detector, the main components of this coix extract were identified as a mixture of oligosaccharides having one to seven glucose units coupled through alpha-(1-->4) linkages. Since this extract showed no antimicrobial activity, its preservative effect may be caused by its covering of the food surface, thereby blocking contact with air.

Influence of various parameters on the browning of potassium sorbate in the presence of amines

Potassium sorbate can undergo oxidation to form carbonyl moieties and cause browning. This investigation studied the fate of the compounds produced by auto-oxidation of potassium sorbate and measured the browning in the presence of amines. Experimental plans in which four factors were combined (temperature, oxygen, amine and light) led to the observation that the interaction between oxygen and high temperature (75 degrees C) favoured browning, independently of the presence of amine. At 4 degrees C, the amine seemed to cause a decrease in the proportion of carbonyl-containing compounds which would appear to participate in carbonyl-amine reactions. At 75 degrees C, the amine forms adducts with the potassium sorbate. In parallel, high temperature favours auto-oxidation reactions that produce carbonyls. GC/MS and NMR analysis of the reaction products of potassium sorbate/amine mixtures led to the identification of cyclic products.

Effect of novel water-soluble polymeric forms of sorbic acid against Fusarium oxysporum f.sp. radicis-cucumerinum

New controlled release water-soluble formulations of sorbic (2,4-hexadienoic) acid were prepared and their inhibitory activity on mycelium growth of Fusarium oxysporum f.sp. radicis-cucumerinum was evaluated. The new products are epoxidized polymers of polyvinylpyrrolidone (PVP) containing covalently bonded sorbic acid (polymeric esters of sorbic acid) and complexes of PVP with hydrogen bonded sorbic acid, characterized by controlled release of sorbic acid. It was shown that the polymeric complexes of sorbic acid with PVP were more effective fungicidal agents than sorbic acid polymeric esters. In all cases the activity of polymeric derivatives (esters and complexes) was increased by lowering the molecular weight of the polymeric carriers. Controlled release formulations of these polymeric derivatives are new promising products due to their low toxicity, wide range of efficient concentrations for application and ability to regulate lyophilicity. Our data contribute to the understanding of the action mechanism of various polymeric sorbic acid formulations and can result in products which are particularly suitable for food and feed protection applications.

Mechanistic aspects of the induction of apoptosis by lauryl gallate in the murine B-cell lymphoma line Wehi 231

The effect of lauryl gallate (antioxidant E-312) has been studied on the mouse B-cell lymphoma line Wehi 231. This compound is able to inhibit protein tyrosine kinases (PTKs) in whole cells and in crude extracts with a better efficiency than other well-known PTK inhibitors such as herbimycin or genistein. Initial events triggered upon the incubation of cells with lauryl gallate in phosphate-buffered saline (up to 1 h) include the inhibition of tyrosine phosphorylation, discharge of the mitochondrial transmembrane potential, and induction of mRNA for Bcl-2. Long-term cultures in complete medium supplemented with fetal calf serum (up to 24 h) in the presence of this compound exhibit clear apoptotic features such as increase in phosphatidylserine in the cell surface, decrease in the functionality of mitochondria, cytochrome c release to the cytosol, activation of caspases, hypodiploidy, and oligonucleosomal breakdown of DNA. Comparison between Wehi cells overexpressing Bcl-2 (Wehi-bcl-2) with Wehi-neo cells shows a delay in the manifestations of the apoptotic signs, indicating that Bcl-2 has a partial protective effect on the apoptosis induced by lauryl gallate. The proapoptotic effect of lauryl gallate is not dependent on DNA or protein synthesis, is not blocked by the chelation of calcium, and is not reverted by N-acetylcysteine.

Mutagenicity and genotoxicity of sorbic acid-amine reaction products

Sorbic acid as well as potassium and calcium sorbate (E202 and E203) are legally used as preservatives in numerous processed foods. Owing to its system of conjugated double bonds, sorbic acid is likely to undergo a nucleophilic attack, which may turn it into mutagenic products. The cyclic derivatives resulting from a double addition reaction between sorbic acid and various amines at two different temperatures (50 degrees C and 80 degrees C) have been analysed. A genotoxicity study has been performed with HeLa cells and plasmid DNA. A mutagenesis study has been carried out by using the Ames test. A SOS spot test and a cytotoxicity study have been realised as well. The results showed that the products involved exhibited neither mutagenic nor genotoxic activities.

Preservation of alpha-tocopherol in sunflower oil by herbs and spices

The ability of some commercially available herb and spice extracts to preserve alpha-tocopherol in sunflower oil during heating at 85-105 degrees C was assessed using sunflower oil as a model system. The Rancimat was evaluated for the heating stage and was used throughout as it was shown to be viable: alpha-tocopherol did not evaporate under the test conditions. The delay in the onset of rancidity was found to be directly related to the initial alpha-tocopherol concentration (P < 0.01). Rosemary, thyme, turmeric, sage, oregano and cumin extracts (2000 mg.kg-1) delayed rancidity (P < 0.01) and preserved alpha-tocopherol (P < 0.01). Some preservation was observed with clove extract but coriander and cardamom extracts were pro-oxidants. With thyme extract, the log of the induction time (as an indicator of the delay in rancidity) was directly proportional to the temperature (85-100 degrees C). The ethyl acetate, hexane and methanol extracts of fresh sage were effective for preserving alpha-tocopherol (P < 0.01). With thyme, rosemary and sage extracts, the increase in the preservation of alpha-tocopherol was directly related to the concentration of the herb extract (P < 0.01) and was quite effective even at 100 mg.kg-1. The increased delay in the onset of rancidity was due directly to the improved preservation of alpha-tocopherol (P < 0.01). In further experiments, the preservative effect of turmeric was shown not to be due to its reported major antioxidant, curcumin, even though it delayed rancidity. When herb/spice extracts were examined mixed with thyme, bay and turmeric showed synergism (P < 0.01) whereas bay alone was slightly inhibitory. The mode of action appeared to be due to free radical activity rather than through singlet oxygen generation.

Antimicrobial films produced from chitosan

Antimicrobial films were prepared by dissolving chitosan into hydrochloric, formic, acetic, lactic and citric acid solutions. Below 40 degrees C, the counter ions could be classified into two groups based on their effect on zero-shear-rate viscosity in 2% solutions of organic acids. Chloride and citrate produced solutions with much lower viscosities than formate, acetate and lactate. At higher temperatures, these differences vanished, and the activation energies of viscous flow were all similar between 40 and 60 degrees C. Films prepared from these solutions were evaluated in tension for Young's modulus, stress and elongation at yield and break points. Films made from hydrochloric, formic and acetic acids were hard and brittle, whereas those from lactic and citric acids were soft and could be stretched. Good correlation was found between Young's modulus and volume of the counter ion. Film properties are essentially governed by the volume of the counter ion and not by the interactions between this counter ion and the macromolecule. Results suggest that acetate has the maximum molecular volume above which the film strength decreases very rapidly.

Computational study of nisin interaction with model membrane

Nisin is a 34-residue lantibiotic widely used as food preservative. Its mode of action on the bacterial cytoplasmic membrane is unclear. It should form ion channels but a molecular description of the interaction between nisin and phospholipids is lacking. The interactions between nisin and a membrane and the influence of phospholipids are here analysed by molecular modelling. The NMR structures of nisin in a micellar environment were previously determined (Van den Hooven et al., Eur. J. Biochem. 235 (1996) 382-393) Those structures were used to start with. They were refined by running a Monte Carlo procedure at a model lipid/water interface. It was shown that nisin is adsorbing onto the interface, with its N-terminal moiety more deeply inserted in lipids than the C-end, indicating distinct hydrophobic properties of the N- and C-domains. Therefore, we suggest that the N-terminal part is implied in the insertion of nisin in lipids, while the C-terminal moiety could be involved in the initial interaction with the membrane surface. Modelling the interaction of nisin with different neutral or anionic phospholipids shows that it disturbs the lipid organisation. The disturbance is maximal with phosphatidylglycerol. In this system, nisin curves the surface of phosphatidylglycerol layer round suggesting it could induce micelle formation. This could be a preliminary step to pore formation. It suggests that phosphatidylglycerol could have a direct action on nisin insertion and on ion channel formation. Appearance of a curvature also agrees with the 'wedge model' proposed in the literature for the nisin pore formation.

Characterization of permeability and morphological perturbations induced by nisin on phosphatidylcholine membranes

Nisin is an antimicrobial peptide used as food preservative. To gain some insights into the hypothesis that its bactericidal activity is due to the perturbation of the lipid fraction of the bacterial plasmic membrane, we have investigated the effect of nisin on model phosphatidylcholine (PC) membranes. We show that nisin affects the PC membrane permeability, and this perturbation is modulated by the lipid composition. Nisin-induced leakage from PC vesicles is inhibited by the presence of cholesterol. This inhibition is associated with the formation of a liquid ordered phase in the presence of cholesterol, which most likely reduces nisin affinity for the membrane. Conversely, phosphatidylglycerol (PG), an anionic lipid, promotes nisin-induced leakage, and this promotion is associated with an increased affinity of the peptide for the bilayer because nisin is a cationic peptide. When the electrostatic interactions are encouraged by the presence of 70 mol% PG in PC, the inhibitory effect of cholesterol is not observed anymore. Nisin drastically modifies the morphology of the dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) multilamellar dispersion without causing a significant change in the gel-to-liquid crystalline phase transition of the lipid. The morphological changes are observed from (31)P and (2)H NMR and cryo-electron microscopy. From the NMR point of view, the interactions giving rise to a broad signal (quadrupolar interactions and chemical shift anisotropy for (2)H NMR and (31)P NMR, respectively) are partly averaged out in the presence of nisin. This phenomenon is interpreted by the formation of curved lipid planes that lead to the lipid lateral diffusion occurring in the intermediate motional regime. By cryo-electron microscopy, large amorphous aggregates containing small dense globular particles are observed for samples quenched from 25 and 50 degrees C. Long thread-like structures are also observed in the fluid phase. A structural description of DPPC/nisin complex, consistent with the experimental observation, is proposed. The presence of 30 mol% cholesterol in DPPC completely inhibits the morphological changes induced by nisin. Therefore, it is concluded that nisin can significantly perturb PC bilayers from both the permeability and the structural points of view, and these perturbations are modulated by the lipidic species in the bilayer.

Digoxigenin-labeled probe for rapid identification of nisinogenic Lactococcus lactis strains

From the nisZ gene sequence, a non-radioactive digoxigenin-labeled DNA probe, was tested for detection of nisin-producing strains using polymerase chain reaction amplification. The digoxigenin-labeled DNA probe clearly discriminated between nisin-producing and non-producing strains with a high degree of sensitivity and specificity. By agarose gel electrophoresis, 1.4 ng of nisin DNA was detected using the digoxigenin-labeled DNA probe compared with 11 ng using direct polymerase chain reaction amplification. A colony hybridization method using digoxigenin-labeled DNA to selectively detect nisinogenic bacteria showed that the nis-probe was specific and did not react with any other non-bacteriocinogenic and non-nisinogenic strains.

Effect of nitrate and nitrite curing salts on microbial changes and sensory quality of non-fermented sausages

The effects of nitrate and nitrite curing salts on microbial changes and sensory quality of non-fermented sausages of small diameter were investigated. During pre-ripening (day 5), levels of lactic acid bacteria and yeasts were slightly higher in nitrite-made sausages than in those made with nitrate. In contrast, nitrite discouraged the growth of psychrotrophs as occurs in fermented sausages. By the end of ripening (day 26), levels of microorganisms were similar in both batches of sausages except for psychrotrophs being higher in those made with nitrite. Nitrate-made sausages showed higher aroma and taste intensity.

Maillard reaction and food processing. Application aspects

The Maillard reaction occurs widely in food and biological systems. This contribution reviews the relation between the Maillard reaction and food processing, particularly its contribution to flavor formation, antioxidative effects, desmutagenic activity and the improvement of protein functional properties. Proteins modified by glucose, and melanoidins are important components of foodstuffs while the reactions of amino acids or peptides with glucose or dicarbonyl compounds produce various kinds of flavor components. Melanoidins and Amadori rearrangement products play an important role in providing antioxidative effects, both in vitro and in vivo. Melanoidins also exhibit desmutagenic activity against carcinogenic compounds. Protein-polysaccharide conjugates, prepared by Maillard reaction at mild conditions, increase the emulsifying activity, as well as antioxidative and antimicrobial effects of the original proteins.

Sorbic acid-amine function interactions

Sorbic acid has a system of conjugated double bonds which makes it able to undergo nucleophilic addition reactions with certain functions. The interactions between sorbic acid and amine functions present in the endogenous constituents of food were quantified. The formation of new products was demonstrated and the underlying mechanisms studied using ethyl sorbate and various amines. HPLC, GC, GC-SM and NMR analyses of the reaction mixtures enabled the products to be isolated and identified. The addition reactions led, at 20 degrees C, to linear monoadducts and, at 50 degrees C and 80 degrees C, to cyclic derivatives resulting from double addition.

Multiresidue method for determination of organochlorine insecticides and polychlorinated biphenyl congeners in fatty processed foods

A previously published gel permeation chromatographic (GPC) procedure for determination of organophosphorus insecticides is used to determine 24 organochlorine (OC) pesticide and 9 polychlorinated biphenyl (PCB) residues in 8 fatty preserved foods of vegetable and animal origin. Samples are extracted with methylene chloride and cleaned up by automated GPC with a Biobeads SX3 column and a methylene chloride-cyclohexane (15 + 85) eluant. Compounds are quantitated by gas chromatography/ mass spectrometry (GC/MS) with selected ion monitoring using a DB-5 column. Average recoveries of OC pesticides from samples fortified at 0.010-0.080 mg/kg ranged from 73 to 98%. Average recoveries of 9 PCB congeners spiked at 2 levels (0.0025 and 0.020 mg/kg) were between 85 and 104%. Quantitation limits were between 0.002 and 0.025 mg/kg, depending on the compound. The purified extracts were analyzed further by GC with electron capture detection (ECD), and the results were compared with those obtained by MS. Determination of some OC pesticides and PCB congeners was not possible by ECD because of matrix interference.

Three-dimensional structure of the lantibiotic nisin in the presence of membrane-mimetic micelles of dodecylphosphocholine and of sodium dodecylsulphate

The lantibiotic nisin is a cationic, polycyclic bacteriocin of 34 residues, including several unusual dehydro residues and thioether-bridged lanthionines. The primary target of its antimicrobial action is the cytoplasmic membrane. Therefore the conformation of nisin when bound to membrane-mimicking micelles of zwitterionic dodecylphosphocholine and of anionic sodium dodecylsulphate was determined with high-resolution NMR spectroscopy. Structures were calculated on the basis of NMR-derived constraints with the distance-geometry program DIANA and were further refined by restrained energy minimization using X-PLOR. The conformation of nisin complexed to both types of micelles is the same, irrespective of the different polar head-groups of the detergents. The structure consists of two structured domains: an N-terminal domain (residues 3-19) containing three lanthionine rings, A, B and C; and a C-terminal domain (residues 22-28) containing two intertwined lanthionine rings numbered D and E. These domains are flanked by regions showing structural variability. Both domains are clearly amphipathic, a property characteristic for membrane-interacting polypeptides. The structures of the ring systems are better defined than those of the linear segments. The four-residue rings B, D and E of nisin all show a beta-turn structure, which is closed by the thioether linkage. The backbones of the rings B and D form type 11 beta-turns. Ring E resembles a type I beta-turn. Preceding the intertwined rings D (residues 23-26) and E (25-28) another type-II beta-turn is found formed by the residues 21-24, so that the C-terminal domain consists of three consecutive beta-turns. The structures of nisin in the micellar systems differ significantly from the previously determined (and now partially recalculated) structure in aqueous solution [van de Ven, F. J. M., van den Hooven, H. W., Konings, R. N. H. & Hilbers, C. W. (1991) Eur J. Biochem. 202, 1181-1188] in the first lanthionine ring around dehydroalanine 5.

Surface location and orientation of the lantibiotic nisin bound to membrane-mimicking micelles of dodecylphosphocholine and of sodium dodecylsulphate

The interaction of nisin, a membrane-interacting cationic polypeptide, with membrane-mimicking micelles of zwitterionic dodecylphosphocholine and of anionic sodium dodecylsulphate was studied. Direct contacts have been established through the observation of NOEs between nisin and micelle protons. Spin-labeled DOXYL-stearic acids were incorporated into the two micellar systems. From the paramagnetic broadening effects induced in the 1H-NMR spectrum of nisin it is concluded that the molecule is localized at the surface of the micelles. The interactions of nisin with zwitterionic and with anionic micelles resemble each other as do the nisin conformations [van den Hooven, H. W., Doeland, C. C. M., van de Kamp, M., Konings, R. N. H., Hilbers, C. W. & van de Ven, F. J. M. (1995) Eur J. Biochem. 235, 382-393]. The hydrophobic residues are immersed into the micelles and oriented towards the center, whereas the more polar or charged residues have an outward orientation. The micellar systems are considered to model the first step in the mechanism of antimicrobial action of nisin, this step is the binding of nisin to the cytoplasmic membrane of target bacteria. Detailed information on this initial binding step is obtained. Hydrophobic and electrostatic interactions appear to be involved in the nisin-micelle contacts. It is suggested that subtilin, a lantibiotic structurally related to nisin, has a comparable membrane interaction surface.

Effect of deep-fat frying on fat oxidation in soybean oil

The frying performance and stability of pure soybean oil (PSBO), soybean oil blended with palm kernel olein and PSBO with an antioxidant mixture of butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate and citric acid were compared. The oils were subjected to intermittent frying (up to 15 fryings, without any 'topping up') of potato slices, at 180 degrees C for a period of and 337 min. Analytical determinations on the oils included the peroxide value (PV), iodine value (IV), free fatty acid (FFA) value, saponification value (SV) and the refractive index (RI). Changes in the product at the sensory level were also assessed. Results showed that (1) fat oxidation hence, reduction of unsaturated fatty acids, as indicated by changes in the IV, was non-significant in the treated oils, (2) hydrolysis of fats, as shown by changes in the FFA value from the first to last frying, was lowest in the blended oil but highest in PSBO, (3) the same trend as above was observed for PV, an indicator of fat oxidation and rancidity, (4) changes in SV were non-significant in the treated soya oils while PSBO with the antioxidant showed the least change in RI, (5) treated oils exhibited no visual increase in viscosity or turbidity and (6) PSBO with the antioxidant had the lightest colour at the end of the frying period. Taste panellists were unable to discriminate between products fried in the treated oils and in PSBO. Sensory assessment showed an improved quality of the chips fried in the blend. Chips fried in PSBO scored the lowest ratings. Thus, the overall results showed an improved behaviour and quality of the treated oils in terms of themal stability during frying.

Enhancement of ethylenethiourea recoveries in food analyses by addition of cysteine hydrochloride

The effectiveness of cysteine hydrochloride (Cys-HCl) as a preservative of ethylenethiourea (ETU) in product matrixes and during analysis was studied. ETU recoveries were adversely affected by certain product matrixes when fortified directly into the product. Recoveries in 8 selected food items were 0-92% when analyzed 30 min after fortification and 0-51% when analyzed after 24 h. When Cys-HCl was added to product prior to fortification, recoveries increased to 71-95% even after frozen storage for 2-4 weeks. Cys-HCl was added during analysis of 53 untreated items. Recoveries improved an average of 15% with Cys-HCl. Without Cys-HCl, recoveries were erratic (20-98%), but with Cys-HCl, recoveries were 68-113%. Other antioxidants (sodium sulfite, butylated hydroxyanisole, butylated hydroxytoluene, and vitamins A and C) also were evaluated as ETU preservatives. When lettuce was treated first with sodium sulfite and then fortified with ETU, recoveries averaged 86%; without sodium sulfite, they averaged 1%. The other antioxidants were less effective for preserving ETU in lettuce, giving only 8-46% recoveries. The effect of oxidizers (potassium bromate, sodium hypochlorite, and hydrogen peroxide) on ETU recovery was also determined. Recovery of ETU from a baby food product (pears and pineapple) was 82%; with oxidizers, recoveries were 0-8%.

Kinetics of the reaction of sorbic acid with sulphite species

Under aerobic conditions, the reaction of sorbic acid with sulphite species, S(IV), involves a pH-dependent oxidative mechanism with the loss of S(IV). Sorbic acid is essential to the process. In the absence of air, a much slower nucleophilic addition of sulphite ion to undissociated sorbic acid takes place.