The effects of nitric oxide (NO) and nitrite treatment on alcohol dehydrogenase activity and the shelf life of apple tissue were investigated. Fresh-cut apple slices were stored for 2 days at 6 degrees C in 0.25-1% NO (v/v, balance N-2) or 100% N-2 atmospheres. Slices were also treated with 1% NO or 2 mM sodium nitrite (NaNO2) for 20 min, stored for 6 weeks in 100% N-2 at 6 degrees C, and analyzed for acetaldehyde, ethanol, and ethyl acetate accumulation, firmness, and color. Compared with N-2 or deionized water controls, treatment with 1% NO or 2 mM NaNO2 inhibited ethanol accumulation, whereas that of acetaldehyde increased. Ethyl acetate accumulation was inhibited only by NO. Slice firmness was not affected by NO or NaNO2 treatment, but slices were darker than the untreated controls. NO and nitrite may extend the shelf life of fresh-cut produce with low concentrations of phenolic compounds.

In this study, multiple approaches have been developed to provide nanoscale modifications on the surface of packaging materials to enable surface functionalization. Most packaging film surfaces are inert and do not offer surface functional groups for coupling reaction. For instance, polyethylene does not contain chemically functional groups along the hydrocarbon backbone to which the active species can be covalently coupled. Therefore, the surface must first be chemically modified to introduce reactive groups (i.e. -OH, -COOH, -NH2, etc) which are capable of acting as a starting point for the immobilization stage. Low density polyethylene (LDPE), polyethylene terephthalate (PET), and poly(L-lactic acid)(PLA) film surfaces were functionalized by chromic acid oxidation, UV/ozone treatment, or alkali hydrolysis to provide carboxylic acid groups. Then, the surface carboxylic acid groups were activated by using carbodiimide, allowing conjugation to metal chelating agents. Carbodiimide is a "zero-length" crosslinker which reacts with surface carboxylic acids to form amide linkages with primary amine-bearing chelating agent ligands. In order to minimize the possible steric hindrances between polymer surface and chelating agent, long-chain spacers were attached to the surface of the films which were then bound covalently to metal chelating agents. Polyamino carboxylates were used as metal chelating agents. Iron was chosen to demonstrate chelation. The formation of carboxylic acid groups on the surface of the films and further immobilization of chelating agent was characterized and confirmed by water contact angle measurements, dye-adsorption assays, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Chelating abilities of the immobilized chelating agents were examined using atomic absorption spectroscopy (AAS) and UV-Vis Spectroscopy. Thermal behaviour and stability were also investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Surface interactions between an enzyme and support influence the retention of activity after immobilization. Chemical modification of enzymes prior to immobilization may be used to alter these interactions and enhance activity retention. Lactase (A. oryzae) was covalently conjugated to P(S/V-COOH) microspheres, with surface carboxylic acid densities of 9 mu eq/g and 137 mu eq/g, using carbodiimide chemistry. Under optimum pH and temperature conditions, activity retention was greater when the enzyme was conjugated to microspheres containing a lower density of surface carboxylic acid groups (32% activity retention) than when the enzyme was conjugated to microspheres having a greater density of surface carboxylic acid groups (11% activity retention). Chemical modification of lactase carboxylic acid groups with glucosamine prior to immobilization was evaluated as a means to increase activity retention. Under optimal conditions, modification resulted in a 17% decrease in soluble enzyme activity compared to the native enzyme. However, immobilization of the modified enzyme yielded 85% and 64% activity retention after conjugation to microspheres with a lower and higher density of surface carboxylic acid groups, respectively. The results suggest that increases in surface carboxylic acid density on the carrier promote the loss of lactase activity after immobilization, and chemical modification of the enzyme with glucosamine provides a means to retain catalytic activity after attachment to these supports.

Surface interactions between an enzyme and carrier can reduce activity retention after immobilization. Using compatible polymers to tether the enzyme provides a means of maintaining bulk properties of the carrier while limiting disadvantageous associations that reduce activity retention of the enzyme. In this work, chitosan was attached to P(S/V-COOH) microspheres by carbodiimide chemistry. Lactase (Aspergillus oryzae) was then covalently conjugated to the microspheres having the chitosan tether as well as directly to microspheres without the chitosan tether. Relative to the soluble enzyme, activity retention of lactase attached directly to the microspheres without the chitosan tether resulted in 11% activity retention after immobilization. Comparatively, attachment of lactase to microspheres having the chitosan tether yielded a retained activity that was not significantly different from that of the soluble enzyme, under optimum conditions for the immobilized conjugate. Chitosan-tethered microspheres also enabled an increase in protein loading—achieving 18mg/g of support compared to 5mg/g of support on microspheres without the chitosan-tether. However, beyond a protein loading of 12mg/g of support, the immobilization efficiency on chitosan-tethered microspheres decreased. Lactase conjugation to chitosan-tethered microspheres resulted in shift in optimum pH from pH 4.5 to pH 4.0, but no significant change in temperature stability relative to the soluble enzyme. The results suggest that altering the material surface interface can lead to greater enzyme activity retention after immobilization.

Shelf life determinations under non-refrigerated conditions, especially high temperature regimes characteristic of tropical/subtropical regions, deserve more attention. In this study, we investigated effects of modified atmosphere packaging (MAP) on longevity of conidia of Beauveria bassiana (Bb) strain GHA. Similar rates of conidial survival were observed after storage for 60days at 50°C in atmospheres of pure CO2, N2, H2, or He (49–51% viability), but few conidia (⩽2%) survived storage in O2-rich atmospheres. Viability of conidia stored in an atmosphere of 20% CO2/80% N2 decreased to <80% within 180days at 40°C and within 30days at 50°C but remained high (87%) after a 16-month storage period at 25°C. O2 concentrations in the storage containers ranged from 0.3% at the start to as high as 12.4% at the end of experiments (due to container leakage). When active packaging (hermetically sealed packages with O2/moisture scavengers) was employed, shelf lives were substantially improved. Viabilities ⩾80% were consistently recorded after 6months at 40°C or 2months at 50°C when a dual O2/moisture absorber or a combination of sachets (dual O2 absorber/CO2 generator+desiccant) were used. Water activities (aw) supporting greatest survival were ⩽0.030, suggesting that optimal aw for long-term storage under anaerobic conditions is lower than determined in previous studies of storage in the presence of O2. Additionally, we have shown that actively packaged conidia with higher than desirable initial aw should be allowed an equilibration period at a moderate temperature before exposure to high storage temperatures. Active packaging of dried conidia (aw⩽0.032) preserved 71% viability for 16months at 40°C and 63–65% for 3months at 50°C. To our knowledge, these are the longest survival times yet reported for Bb conidia under high-temperature conditions.

Germination of Beauveria bassiana (Bb) and Metarhizium anisopliae (Ma) conidia determined from a fast-rehydration (FR) protocol were compared to those obtained when dry conidia were subjected to slow rehydration (SR) by holding under high humidity conditions prior to aqueous suspension. Differences in viability estimates obtained using the FR vs. SR protocols increased markedly after conidia were exposed to various stress factors in storage (high aw, temperature, and O2 concentrations), with the SR protocol producing higher estimates of viability in all cases. After Bb conidia were stored under moist conditions for 21days at 25°C, the SR estimate of viability was >21% greater than the FR estimate. In jars flushed with different O2 concentrations and stored at 50°C for 34days, proportional differences between protocols varied, depending on water activity, from 18–44% in jars flushed with 0% O2 (100% N2) to as high as 63–93% when treated with 21–22% O2. For conidia stored over a broad range of moderate to high temperatures in the absence of O2, SR–FR differences were ⩽9% at 25–40°C but 30% at 50°C. Germination of stressed Bb and Ma conidia increased substantially when incubation time on the germination substrate was increased from 24 to 72h, whereas germination of non-stressed conidia showed little change. Conidia debilitated by stress were characterized by hypersensitivity to lethal imbibitional damage (damage that is mitigated by slow rehydration) and slow germination. Viability protocols that may provide more reliable assessments of overall mycopesticide quality are discussed.

In order to functionalize the surface of blown low-density polyethylene (LDPE) and cast polypropylene (CPP) films, and ultimately to maximize the attachment of active molecules onto them, the optimum treatment parameters of capacitively-coupled radio-frequency (13.56 MHz) oxygen plasma were investigated by using contact angle, toluidine blue dye assay, X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). Contact angle values of LDPE and CPP samples decreased significantly after oxygen plasma treatment. They further decreased as the plasma power level increased. The treatment time had no substantial effect on contact angle value. The optimum treatment conditions for LDPE and CPP films for maximizing carboxyl functionality without causing observable surface changes were found to be 200 W/200 mTorr and 250 W/50 mTorr, respectively, when treated for 3 min. The maximum carboxyl group concentration obtained with LDPE and CPP films were 0.46 and 0.56 nmol/cm(2) respectively. The percent of oxygen atoms on the surface of plasma-treated LDPE and CPP films was determined by XPS analysis to be 22.6 and 28.7%, respectively. The ATR-FTIR absorption bands at 1725-1700 cm(-1) confirmed the presence of carboxylic acids on LDPE and CPP films. By exposing the plasma-treated sample to air rather than water and treating films repeatedly with oxygen plasma, a higher carboxyl group concentration could be obtained. Copyright (C) 2008 John Wiley & Sons, Ltd.

L'invention concerne un systeme et un procede capables d'hydrolyser le lactose, ou le systeme comprend un support forme d'un polymere hydrophobe fonctionnalise qui est lie de maniere covalente a une molecule hydrophile qui elle-meme a son tour est liee de maniere covalente a une enzyme telle que le lactose. Le procede comprend les etapes de fonctionnalisation d'un support de polymere hydrophobe, de liaison covalente d'une molecule hydrophile audit support de polymere fonctionnalise, et une liaison covalente d'une enzyme telle que la lactase a ladite molecule hydrophile. Le systeme et le procede concernent generalement le domaine de la science et de l'ingenierie alimentaire, et, plus particulierement, les produits alimentaires a base de lait et leur production y compris les solutions aux problemes associes a l'intolerance au lactose tels que des procedes de traitement de produits et des produits fabriques par ces procedes.

An antimicrobial film was produced by covalently attaching synthetic peptide E14LKK to poly(ethylene) film. E14LKK is a 14 residue, magainin-class peptide with broad-spectrum antimicrobial activity. The poly(ethylene) surface was first oxidized with chromic/sulphuric acid, then PEGylated by using carbodiimide chemistry to attach omega-amino-alpha-carboxyl-poly(ethylene glycol) (PEG). The peptide was covalently coupled to the free terminus of the PEG, again using carbodiimide coupling. Surface contact angles for distilled water decreased from 101 degrees initially to 61 degrees following oxidation and 45 degrees following PEGylation. Film surface chemistry showed the expected changes during the modifications: dye adsorption assays indicated changes in the number of acidic and basic groups and X-ray photoemission spectroscopy showed increasing oxygen and nitrogen levels. Antimicrobial activity was demonstrated in broth cultures against E.coli: growth was reduced by atleast 3 log cycles compared to controls. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2665-2670, 2008

This study evaluated the effects of the deposition of a thin hydrophobic silicon coating onto a polysaccharide film's surface. The goal was to improve the water vapour barrier of the hydrophilic film in order to increase the film's usefulness in packaging applications. A cold-plasma technique was used to create a thin hexamethyldisilazane deposition on a chitosan film surface. The modification was investigated using Fourier transform infrared. The effect on the surface was characterized through contact angle measurements and degree of swelling. A significant reduction in hydrophilicity and water vapour permeability was observed. Gas barrier measurements indicated that there were no substantial differences in O-2 and CO2 permeabilities under the conditions used in this investigation. Copyright (c) 2007 John Wiley & Sons, Ltd.

Changes in distribution patterns and demand for increased food quality have resulted in a desire to improve the shelf life of nonsterile dairy products. Refrigerated shelf life extension typically requires, at a minimum, reductions in the growth rate of spoilage microorganisms and subsequent product deterioration. Reducing initial bacterial loads, increasing pasteurization regimes, and reducing postprocessing contamination have all been employed with measured success. The use of antimicrobial additives has been discouraged primarily due to labeling requirements and perceived toxicity risks. Carbon dioxide (CO2) is a naturally occurring milk component and inhibitory toward select dairy spoilage microorganisms; however, the precise mechanism is not fully understood. CO2 addition through modified atmosphere packaging or direct injection as a cost-effective shelf life extension strategy is used commercially worldwide for some dairy products and is being considered for others as well. New CO2 technologies are being developed for improvements in the shelf life, quality, and yield of a diversity of dairy products, including raw and pasteurized milk, cheeses, cottage cheese, yogurt, and fermented dairy beverages. Here we present a comprehensive review of past and present research related to quality improvement of such dairy products using CO2.

The effects of dense phase CO2 processing parameters, including temperature (25 and 35 degrees C), CO2 concentration (0, 85 and 170g kg(-1)) and pressure (6.9, 27.6 and 48.3MPa), on yeast survival and sensory properties of grape juice were investigated. The dense phase CO2 process resulted in more than a 6 log reduction in yeast population. As the CO2 to juice concentration, temperature and pressure increased, the inactivation rate increased. CO2 in the supercritical state was more effective in inactivating yeast than in the subcritical state. The process did not cause detectable flavor degradation. Dense phase CO2 processing can be an effective non-thermal alternative process for pasteurization of grape juice. (c) 2005 Society of Chemical Industry.