Adriana-Inés Rodríguez-Hernández

Effect of equilibrium moisture content on barrier, mechanical and thermal properties of chitosan films

Water molecules modify the properties of biodegradable films obtained from hydrophilic materials. Most studies dealing with thermal, mechanical and barrier properties of hydrophilic films are carried out under one relative humidity (RH) condition. The objective of this work was to evaluate the effect of the moisture content on the thermal, mechanical and barrier properties of chitosan films under several RH conditions. Microclimates, obtained with saturated salt solutions were used for conditioning samples and the properties of the films were evaluated under each RH condition. Chitosan films absorbed up to 40% of moisture at the higher RH studied. The percentage of elongation and the water vapour permeability increased while tensile strength, Youngs modulus and glass transition temperature decreased, when the moisture content increased. The results suggest that the water molecules plasticized the polymer matrix, changing the properties when the films were in contact with high RH environments.

Monoxenic production of the entomopathogenic nematode Steinernema carpocapsae using culture media containing agave juice (aguamiel) from Mexican maguey-pulquero (Agave spp). Effects of the contents of nitrogen, carbohydrates and fat on infective juvenile production

The production of infective juvenile stages (IJ) of the entomopathogenic nematode Steinernema carpocapsae in the presence of its symbiotic bacterium Xenorhabdus nematophilus was carried out in orbitally agitated bottles. Four complex culture media (M1–M4) were used, containing from 8% to 28% (by vol.) agave juice (aguamiel) from Mexican maguey-pulquero (Agave spp) as the main carbohydrate source. After 20 days of fermentation, a maximum viable IJ concentration of 249,000 IJ/ml and an initial nematode population multiplication factor of ×620 were achieved when medium M4 was used (aguamiel concentration in this medium was 28% by vol.). M4 medium contained (w/v): 0.3% total nitrogen, 3.2% total carbohydrates and 3.0% total fat. According to the results obtained, total carbohydrates concentration appeared to be of great importance in obtaining high IJ concentrations.

LAB bacteriocin applications in the last decade

ABSTRACT In the early 2000s, the expectations about bacteriocins produced by lactic acid bacteria (LABs) were aimed at food applications. However, the effectiveness of bacteriocins against undesirable micro-organisms opened endless possibilities for innovative research. In the present review, we collected a database including 429 published papers and 245 granted patents (from 2004 to 2015). Based on bibliometric analysis, the progress of bacteriocin research in the last 11 years was discussed in detail. It was found that 164 patents were granted in 2010–2015, which is equivalent to 60% in comparison with previous years (i.e. only 81 patents were granted in 2004–2009). Currently, the research on bacteriocins is still gaining importance. In the realm of therapeutic strategies, about a 37% of the published research was focused on biomedical applications in the last decade. This vein of research is currently seeking for alternative solutions to problems such as cancer, systemic infections, oral-care, vaginal infections, contraception and skincare. On the other hand, food preservation, bio-nanomaterial and veterinary applications represent 29%, 25% and 9%, respectively. All this technology is being applied and will surely grow in the future, since about 31% of the patents granted since 2004 are focused on the biomedical area, 29% on food preservation, 5% on veterinary use; whereas 13% and 16% correspond to patents granted on production–purification systems and recombinant proteins or molecular modifications in the producer strains. This review contributes to the analysis of recent LAB bacteriocin applications and their role in safety, quality and improvement of human health.

Physical properties of emulsified films based on chitosan and oleic acid

Film-forming emulsions were formulated with chitosan (CH (g L−1): 7, 10, 15), oleic acid (OA (g L−1): 0, 3, 6) and glycerol as plasticizer (10 g L−1). The films were characterized on their physical properties (colour, water solubility, water vapour permeability and oxygen permeability (PO2)), in order to gain a better understanding of the functional properties of chitosan-lipid films. The incorporation of OA limited water vapour transfer in films obtained with 15 g L−1 CH, likely because the viscosity of the film-forming dispersion was high enough (η0 = 2.07 Pa s) to ensure the emulsion stabilization during the drying film process. The incorporation of OA did not generate significant (p > 0.05) differences of the PO2 values in the CH films; besides, they showed a slight yellow-green colour. The results of this study provide further evidence to promote the chitosan-lipid films to be used as biodegradable food packaging.

Antilisterial activity and physical-mechanical properties of bioactive caseinate films

Antimicrobial films were formulated with sodium caseinate (C), glycerol and antimicrobial substances (AM) produced by Streptococcus infantarius. The antilisterial activity of the films was evaluated using Listeria monocytogenes as test microorganism and two incubation conditions: T = 35°C, 32 ± 10% RH and T = 4°C, 98 ± 10% RH. A comparison of the antimicrobial action was made with caseinate films carrying equivalent activity units of commercial nisin (Nis). At 35°C and 32% RH, AM increased the lag-phase and inhibited 80% of the growth of L. monocytogenes. At 4°C and 98% RH, C-Nis and C-AM films extended the lag-phase of the bacterial growth up to 11 and 38 days, respectively. AM showed a higher antilisterial effect than nisin at both incubation conditions. The incorporation of AM or Nis did not produce significant differences in the barrier properties of the films, but AM acted as an additional plasticizer into the films.

Evolution of culture broth rheological properties during propagation of the entomopathogenic nematode Steinernema carpocapsae, in submerged monoxenic culture.

This article presents the evolution of culture broth rheological properties during monoxenic cultures of Steinernema carpocapsaein cylindrical bottles agitated orbitally. Rheological properties were evaluated in simple‐shear flow conditions and were well‐modeled by the Ostwald‐de Waele model. Rheological properties varied from slightly dilatant, n= 1.2 (–), to moderately pseudoplastic flow behavior, n= 0.6 (–). Nematode concentrations increased from 750 ± 190 to 130 900 ± 6900 nematodes/mL, and the apparent viscosity (ηa) evolved from 4.5 ± 0.7 to 46.6 ± 3.2 mPa·s during the fermentations. Rheological behavior did not appear to be strongly influenced by nematode number and/or its stage of development; however, the release of substances from the decomposition of nematode cadavers appeared to be of great importance. Among the different developmental stages of the nematodes, only juveniles of the first stage (J1) were highly susceptible to the shearing conditions tested (shear stress, θrθ, from 0.9 to 3.5 Pa during periods of 80–100 min), resulting in the viability loss of 85% of J1 nematodes.

Effect of the storage conditions on mechanical properties and microstructure of biodegradable baked starch foams

ABSTRACT Starch-based foams (SBFs) were prepared with corn, potato, tapioca, and chayotextle starches. A compression baking process was used to develop the SBFs. Biodegradation studies showed that different sources of starch have a particular behavior. The starches showed values of degradation of ~85%, while the degradation of SBFs was ~70%. The SBFs were conditioned at relative humidities (RHs) of 0 and 75% and temperatures of 4 and 65°C. The starch source used to prepare the SBFs did not have an effect on the mechanical properties, but the storage conditions showed a significant effect on those properties; an increase of RH causes an increase in the mechanical properties. A similar behavior was observed in the conditioned SBFs at different temperatures. The increase of the storage temperature showed a slight reduction in the values of elongation at break. Microscopy revealed that the conditions of RH and storage temperature affect the internal structure of the SBFs.

Specific oxygen uptake of the entomopathogenic nematode, Steinernema carpocapsae CABA01, in submerged culture

The specific oxygen uptake rate (qO2) of stages of the entomopathogenic nematode (EPN) Steinernema carpocapsae CABA01 in liquid culture was measured. Nematodes were grown into previously pasteurised culture broths of their symbiotic bacterium, Xenorhabdus nematophila, in orbitally agitated flask cultures (VL = 125 mL) at N = 150 rpm and T = 25°C. The basal medium contained 3% (w/v) soy trypticase broth and 0.5% (w/v) yeast extract. The EPNs developed from the egg stage to the adult stage exhibiting qO2 values of 1.92, 5.48, 0.48, 0.28 and 0.0014 [10−1 mmolO2/(gnematode-wet base h)] for the egg-Juvenile 1 (J1), J2, J3, J4 and the adult stages, respectively.

Antimicrobial pectin-gellan films: effects on three foodborne pathogens in a meat medium, and selected physical-mechanical properties

ABSTRACT It is first reported the elaboration and characterization of films (F2) containing 1% (w/v) citrus pectin, 0.2% (w/v) gellan gum, 0.5% (w/v) glycerol, CaCl2 5 mM, ethylenediaminetetraacetic acid (EDTA) 0.05 M and 90 (Arbitrary Units)/mL of an antimicrobial concentrated supernatant (ACS) from fermentation culture broths of the lactic acid bacterium, Streptococcus infantarius. The functional films inhibited the growth of Listeria monocytogenes, Escherichia coli and Staphylococcus aureus in “Barbacoa” medium in 7-day cultures at 35°C. “Barbacoa” is a highly appreciated Mexican meat product. In contrast, the control cultures exhibited bacterial-growths up to 107–109 (Colony-Forming Units)/g. An antimicrobial-activity synergy between ACS and EDTA was demonstrated. Some film-physical properties were modified by the EDTA-ACS incorporation [F2/control-film]: Young’s modulus (MPa), 1,394/707; elongation at break (%), 1.9/9.3; stress at break (MPa), 5.7/12.6; water vapor permeability (10–11 g m Pa−1 s−1 m−2), 3/20 and oxygen permeability (10–12 g m Pa−1 s−1 m−2), 1.9/1.2.

In-vitro liquid culture of the entomopathogenic nematode, Steinernema colombiense, in orbitally shaken flasks

ABSTRACT Steinernema colombiense, an entomopathogenic nematode species (EPN) was grown in two types of orbitally shaken flasks at 130 rpm and 28°C, containing 10 or 20 mL, respectively of a complex culture medium with an initial EPN-concentration of 1,000 Infective Juveniles (IJ)/mL. At the 10th day, the EPN-concentration was 58,771 individuals/mL with 87% of them in the IJ stage. No significant differences were found between the EPN growth kinetics in both types of flasks. The nematode-population growth was modelled by a re-parameterized Gompertz equation of three-parameters with best-fit values of 3.8 days for the lag time, 33.8 day-1 for the maximum growth rate, and 57.3 (dimensionless) for the maximum asymptotic growth.