Bitechnology&Food Engineering

There is a lack of efficient and safe preservatives in the food industry. Massive use of some common food preservation methods has led, over the years, to development of a resistance to different treatments by various food pathogens. Enteric bacteria are especially tolerant to adverse environmental conditions-such as low pH and high salt concentrations-which limits efficiency of some preservation methods. Consumers demand for natural, preservative-free, and minimally processed foods and worldwide concern regarding disease outbreaks caused by food-related pathogens have created a need for development of new classes of antimicrobial (AM) agents. The twentieth century revealed a massive array of new peptide-based antimicrobials. Small ribosomally made compounds are found in practically all living species where they act as important component of host defense. Certain indubitable advantages of peptides-pertaining to simplicity, activity spectra, and bacterial resistance-over known preservative agents advocate their potential for food preservation. Nisin, an AM compound originating from bacteria, is so far the only FDA-approved peptide. However, a growing number of reports describe the potential of animal-derived antimicrobial peptides as food preservatives. These studies have yielded various native compounds and/or derivatives that possess markedly improved antimicrobial properties under a broad range of incubation conditions. The present work reviews the most investigated peptides and accounts for their potential use as alternatives to the preservatives used today. The focus is on research aspects aiming at understanding the mechanism of action of these peptides at extreme environments of various food systems. Collectively, the data accumulated are convincingly indicative of potential applications of these peptides in food safety, namely, with respect to fighting multidrug-resistant pathogens.

The feasibility of low-density polyethylene (LDPE)-based films containing linalool or methylchavicol as antimicrobial (AM) packages to retard microbial growth on food surfaces was investigated. The AM LDPE-based films were tested for inhibition against selected microorganisms. Both compounds retained their AM activity, after an extrusion film-blowing process, against Escherichia coli in solid medium. Cheddar cheese was wrapped with the AM films and the packaged cheese samples were stored at 4 1C. The changes in the mesophilic aerobic bacteria and coliform, as well as yeast and mould counts were monitored. In addition, cheese samples inoculated with E. coli or Listeria innocua were wrapped with the AM films, stored at refrigerated (4 1C) or at abuse (12 1C) temperatures and the count of these microorganisms was monitored as a function of time. The results showed an inhibitory effect of these AM films against microbial growth in naturally contaminated cheese and in inoculated samples. The effect on suppression of E. coli and L. innocua growth was more pronounced at the abuse temperature. Methylchavicol-LDPE-based film exhibited a higher efficacy of inhibition than that of linalool-LDPE-based film. In addition, a sensory evaluation was performed with regards to possible taint in the flavour of the cheese. Taint in flavour as affected by linalool or methylchavicol was not significantly detectable by the panelists at the end of the storage period of 6 weeks. This study shows the potential use of polymeric films containing the principal constituents of basil as the AM components for enhancing quality and safety of cheeses.

A careful characterization and rheological study of low density polyethylene (LDPE) reveals that long-chain branching (LCB) plays a decisive role. At constant molecular weight (gW) higher LCB reduces the Newtonian viscosity 7, and the shear sensitivity, increases the activation energy E,, and finally delays transition to pseudoplastic flow to higher shear rates and the onset of melt fracture to higher shear stresses (~d ) . The flow parameters qo, ycr, Td, and the derived flow relaxation times are uniquely correlatable by means of a modified molecular weight (g%fw) incorporating the LCB effect. High density polyethylene are less shear sensitive than their low-density counterparts, have a lower activation energy, fracture at higher shear stress levels and cannot be regarded as branchless LDPE's.

A i?wdd based on energy considerations for predicting temperature profiles in a microwaved dough placed in contact with a susceptor was developed. Using a commerciul finite element software ("Ansys 5.01 "), for an axisymmetric and transient heat transfer problem, the temperatures at the dough/susceptor interface and in the whole dough were calculated. The calculated temperatures at the susceptor/dough interface were superimposed on previously published curves (based on la correlation relating temperatures at the interface with heating time, dough and susceptor parameters) and compared to experimentally determined values. A very good agreement between the experimentally determined temperatures and the values predicted from this model and from the previously described correlation was obtained. In the dough, an uneven temperature distributio,n in the radial direction, caused mainly by evaporative cooling at the surface, was predicted. The calculated temperatures for different susceptors, heating times and various locations in the dough correlated well with experimenlally determined values.

The diffusion coefficients of styrene in polystyrene were studied using inverse gas chromatography (i.g.c.). Values between 4.3 x 10-lo and 5.5 × 10 -9 cm 2 S-1 were found in the temperature range from 110°C to 140°C respectively. An Arrhenius type dependence of the diffusion coefficient on temperature was found in this narrow temperature range with an activation energy of 13.5 kcal mol-~. The i.g.c, method was found to be fast and accurate for diffusion coefficient determination of vapours in molten polymers.

The state of cure of low density crosslinked polyethylene, measured by solvent extraction as a [unction of the peroxide level, was found to be dependent on the melt flow index. A simple and rapid [low test was found to be sensitive to the degree of crosslinking and applicable for quality-control purposes.

Thiobarbituric acid (TBA) determinations of malondialdehyde (MDA) in thermally preserved red turkey meat packed in high barrier plastic trays and in cans, were carried out as a function of product layer and storage temperature (15, 25 and 35C). Several types of plastic trays, with different oxygen permeabilities, were evaluated. In the most permeable plastic trays the product in the surface layer reached m i m u m TBA values at all storage temperatures afrer a certain storage period, followed by their decrease. In the higher barrier trays and in the cans, the TBA values decreased continuously with time. The peak TBA values, observed in the least barrier plastic trays declined with storage temperature. In the inner product layers, the TBA values decreased during storage in all types of packages and ar all temperatures. The reduction in TBA values can be explained by the disappearance of TBA reacting substances (TBARS). The extent of TBARS disappearance was greater in the absence of oxygen than in its presence. The results of this study indicate that TBA determinations are not a reliable indicator for quality deterioration during storage of thermally treated meat products in plastic packages.

The migration of the natural antimicrobial (AM) agents: linalool, carvacrol and thymol, from lowdensity polyethylene (LDPE) films containing ethylene vinyl acetate (EVA) into the food simulants: isooctane and various ethanol/water mixtures, was studied with a view towards examining the applicability of a first-order kinetic approach as well as a diffusion model approach for describing these systems. The results suggest the proposed models adequately describe the release of AM agents. The combination of kinetic and diffusion analyses can provide additional information about the release process using the same data set. The analyses suggest that the release of linalool from LDPE/EVA depends on the EVA content in the formulation and that an optimum level of EVA is required to minimize the rate of release. An extension to the existing "idealized diffusion" model is proposed that enables the model to be applied to systems that demonstrate a departure from linearity when subjected to conventional analysis. The applicability of the idealized diffusion model was compared with the "simulant-limited" model and the results suggest that the former model is appropriate for describing most real systems when the simulant (or foodstuff) is favored in the partitioning of the AM agent between the film and the simulant.

The present study was aimed at carrying out a survey on the knowledge and acceptance level of food irradiation. The work was carried out in Santiago, Chile. As an above-average level country in South and Central America, the results may give an indication about the situation in other countries. The survey could also provide an indication about the impression of the public regarding the international ''Radura'' symbol, indicating on a food product that has been irradiated. A total of 497 persons were interviewed. Among the interviewed people, 76.5% did not know that irradiation could be used as a method for food preservation; 46% expressed their belief that irradiated food means the same as radioactive food. Nevertheless, 91% claimed that they would become consumers of irradiated food if they knew that ''irradiated'' is not ''radioactive'' and that proper irradiation enhances food safety; 95.8% of the interviewed persons were not familiar with the ''Radura'' symbol. However, 55.8% expressed their opinion that they would buy irradiated food because of the symbol, affirming that the ''Radura'' symbol transmits the sensation of confidence and safety.

The diffusion of linalool and methylchavicol from thin (45e50 mm) antimicrobial low-density polyethylene-based films was evaluated after immersion in isooctane and the effect of temperature (4, 10, or 25 C) on the diffusion rate was evaluated. The kinetics of linalool and methylchavicol release showed a non-Fickian behavior at the lowest temperature. An increase in temperature from 4 C to 25 C resulted in an increase in the diffusion coefficient from 4.2 Â 10 À13 m 2 s À1 to 2.5 Â 10 À12 m 2 s À1 for linalool and from 3.5 Â 10 À13 m 2 s À1 to 1.1 Â 10 À12 m 2 s À1 for methylchavicol. The effect of temperature on the diffusion coefficient followed an Arrhenius-type model (r 2 ¼ 0.972) in relation to a time-response function with a Hill coefficient. Activation energies of 57.8 kJ mol À1 (linalool) and 42.8 kJ mol À1 (methylchavicol) were observed.

A Brazilian ham-flavored cream cheese was developed using gamma-irradiated beetroot extract as the colorant. An irradiation dose of 5.0 kGy was used based on previous studies that indicated no growth of moulds, yeasts and aerobic psychotropic microorganisms during 12 days at 5 1C, and with no changes in the structure of the pigment. One part of the cheese was colored with the irradiated beetroot extract and the other part with carmine cochineal, which is a natural stable colorant but expensive and difficult to extract. Both portions were submitted to sensory evaluation with 67 panelists. No significant differences were found in flavor and overall appearance. The cream cheese containing carmine cochineal was slightly preferred in regards to color. However, being a new product, these results were encouraging and point towards the potential use of irradiated beetroot extract as a natural food colorant.