Development and characterization of edible and biodegradable nano-laminate coatings as vehicle of incorporation of functional and antimicrobial agents from Aloe vera, for extending shelf life of Lycopersicum esculentum Mill. (tomato)

Doctoral Dissertation for PhD degree in Chemical and Biological Engineering.During the last decades, there has been an increasing demand for fresh fruits and vegetables forcing the food industry to develop new and better methods for maintaining food quality and extending shelf life. Great losses (from 20% to 80%) in the quality of fresh fruits have been reported; such losses occur from harvesting to final consumption. In this context, edible coatings offer a beneficial impact on the produce quality (e.g. acting as a selective gas barrier and presenting an antimicrobial effect) and also to the environment, by means of reducing food waste. Currently, the utilization of nanotechnology represents a good tool to overcome problems regarding the application of edible coatings, such as high water vapour permeability and poor mechanical properties in comparison with synthetic materials. Some advantages when these coatings are at nanoscale are: higher stability at the substrate surface, facility of preparation and lower concentration of materials are required. Also, these systems can provide additional protection for the produce, and can incorporate antimicrobial, antifungal and antioxidant substances into their structure. Based in these ideas, the main purpose of this thesis was the development and characterization of nano-laminate coatings using bioactive components of Aloe vera for extending the shelf life of tomato fruit (Lycopersicum esculentum Mill.). Tomato was utilized here as model, being of course possible to apply these systems to other fruits. Aloe vera fractions (gel and liquid) evidenced both antifungal and antioxidant activities, representing a good alternative to extend the shelf life of tomato fruit. Therefore, polyelectrolyte solutions based on alginate and chitosan and their optimal concentrations were selected to build nano-laminate coatings; also, the effect of surfactant and plasticizer concentrations was determined. The best formulations were selected based on their wettability on tomato fruit surface. On the other hand, nano-laminate coatings with carvacrol (directly applied or encapsulated into zein) also showed (in vitro) their potential to be a good candidate to improve the shelf-life of foodstuffs due to the improved barrier properties and antifungal activity. Nano-laminate films functionalized with bioactive fractions of A. vera (gel and liquid fraction) have shown good barrier properties and evidenced in vitro antifungal activity. The system based on alginate/chitosan functionalized with A. vera liquid fraction was selected in order to evaluate its effectiveness in vivo. Tomatoes coated with this system exhibited a lower weight loss and microbial contamination was delayed (mainly in terms of yeasts and molds), together with a reduction in the gas transfer rate and ethylene production during cold (11 °C and 90% relative humidity, RH) and room temperature (20 °C and 85% RH) storage of tomato fruits. It should be noted that nano-laminate coating technology is transferable to other fruit models (both climacteric and non-climacteric), being an attractive postharvest tool for extending the quality and shelf life of fruits and vegetables.Durante as últimas décadas, verificou-se uma crescente procura de frutas e vegetais frescos, o que obrigou a indústria alimentar a desenvolver novos e melhores métodos para manter a qualidade dos alimentos e prolongar a sua de vida de prateleira. Elevadas perdas (de 20% a 80%) na qualidade de frutos frescos foram reportadas; tais perdas ocorrem desde a colheita até o seu consumo final. Neste contexto, os revestimentos comestíveis oferecem um impacto benéfico sobre a qualidade do produto (por exemplo, atuando como uma barreira seletiva a gases e apresentando efeito antimicrobiano) e também para o meio ambiente, através da redução do desperdício de alimentos. Atualmente, o uso da nanotecnologia representa uma boa ferramenta para superar os problemas relacionados com a aplicação de revestimentos comestíveis, tais como a elevada permeabilidade ao vapor de água e fracas propriedades mecânicas em comparação com materiais sintéticos. Algumas vantagens quando estes revestimentos são à escala manométrica são: maior estabilidade na superfície do substrato, facilidade de preparação e menor concentração de materiais necessários. Adicionalmente, estes sistemas podem oferecer uma proteção adicional para o produto, e podem incorporar substâncias antimicrobianas, antifúngicas e antioxidantes na sua estrutura. Com base nestas ideias, o principal propósito desta tese foi o desenvolvimento e caracterização de revestimentos nano-laminados utilizando componentes bioativos de Aloe vera para prolongar a vida de prateleira do fruto de tomate (Lycopersicum esculentum Mill.). O tomate foi utilizado como modelo, sendo, naturalmente, possível aplicar estes sistemas a outros frutos. Ambas as frações de Aloe vera (gel e líquido) evidenciaram atividades antifúngicas e antioxidantes, o que representa uma boa alternativa para prolongar a vida de prateleira do fruto de tomate. Deste modo, soluções de polieletrólitos baseadas em alginato e quitosano e as suas concentrações ótimas foram selecionadas para construir revestimentos nano-laminados; além disso, determinou-se o efeito das concentrações de surfactante e plasticizante. As melhores formulações foram selecionadas com base na sua capacidade molhante da superfície do fruto de tomate. Por outro lado, os revestimentos nano-laminados com carvacrol (aplicado diretamente ou encapsulado em zeína) também demonstraram (in vitro) o seu potencial para serem bons candidatos para melhorar a vida de prateleira dos produtos alimentares devido às propriedades de barreira melhoradas e à atividade antifúngica. Os filmes nano-laminados funcionalizados com frações bioativas de A. vera (frações gel e líquida) demonstraram boas propriedades de barreira e evidenciaram atividade antifúngica in vitro. Selecionou-se o sistema baseado em alginato/quitosano funcionalizado com fração líquida de A. vera com a finalidade de avaliar a sua eficácia in vivo. Tomates revestidos com este sistema registaram a menor perda de peso e a contaminação microbiana foi retardada (principalmente em termos de leveduras e bolores), juntamente com uma redução da taxa de transferência de gás e produção de etileno durante armazenamento sob refrigeração (11 °C e 90% de humidade relativa, HR) e a temperatura ambiente (20 °C e 85% HR) de frutos de tomate. Finalmente, é importante referir que a tecnologia de revestimentos nano-laminados é transferível para outros frutos (climatéricos e não climatéricos), sendo uma ferramenta de pós-colheira atrativa para prolongar a qualidade e vida de prateleira de frutos e vegetais

Validation of the 3-under-2 principle of cell wall growth in Gram-positive bacteria by simulation of a simple coarse-grained model

The aim of this work is to propose a first coarse-grained model of Bacillus subtilis cell wall, handling explicitly the existence of multiple layers of peptidoglycans. In this first work, we aim at the validation of the recently proposed "three under two" principle.Comment: Revised introduction, results unchange

Final-state, Open-loop Control of the Heat equation in Tensorial Domains (full version)

In this paper, a quadratic optimal control problem will be considered for the heat equation in tensorial domains with homogeneous Dirichlet boundary conditions, in which the control function (depending only on time) constitutes a source term. These problems involve choosing a control function (with or without "peak-value" constraints) to approximately steer the solution of the heat equation to a desired function at the end of a prescribed (finite) time-interval. To compute approximations to the desired optimal control functions, semi-discrete, spectral (with eigenfunctions) Galerkin approximations to the corresponding heat equation and the corresponding (approximating) control problems are tackled. Two simple, illustrative examples are presented in the final section.Comment: 32 pages, 11 figures, submitte

Dynamic equivalence between atomic and colloidal liquids

We show that the kinetic-theoretical self-diffusion coefficient of an atomic fluid plays the same role as the short-time self-diffusion coefficient D_S in a colloidal liquid, in the sense that the dynamic properties of the former, at times much longer than the mean free time, and properly scaled with D_S, will indistinguishable from those of a colloidal liquid with the same interaction potential. One important consequence of such dynamic equivalence is that the ratio D_L/ D_S of the long-time to the short-time self-diffusion coefficients must then be the same for both, an atomic and a colloidal system characterized by the same inter-particle interactions. This naturally extends to atomic fluids a well-known dynamic criterion for freezing of colloidal liquids[Phys. Rev. Lett. 70, 1557 (1993)]. We corroborate these predictions by comparing molecular and Brownian dynamics simulations on (soft- and hard-sphere) model systems, representative of what we may refer to as the "hard-sphere" dynamic universality class

FORTY YEARS OF BEHAVIOR ANALYSIS IN MEXICO: A REVIEW OF THE MEXICAN JOURNAL OF BEHAVIOR ANALYSIS

The present paper shows a current review of the Mexican Journal of Behavior Analysis (MJBA). The review includes a brief historical summary of the Mexican Society of Behavior Analysis, along with some aspects about the academic and social context of behavior analysis in Mexico which are mentioned in order to understand the origin of MJBA. The paper presents the number of articles published in English and Spanish, an analysis of the articles related to human and non-human behavior, basic and applied research. The paper also reports the first authors’ university affiliation with higher percentage of articles published.Keywords: behavior analysis in Mexico, Mexican Journal of Behavior Analysis, Mexican Society of Behavior Analysi

Characterization and evaluation of antifungal activity in vitro of Aloe vera fractions against postharvest fungi

Aloe vera leaves can be separated in a liquid fraction (exudate) and a mucilaginous pulp (gel). Recently, the antifungal activity of their components has been reported. The common technique for gel extraction from A. vera leaves are the traditional manual (in this case the liquid fraction is not separated) and a mechanical methods. Moreover, as a result of its processing the bagasse is obtained. The aim of this work was to recover and characterize the fractions of A. vera and to identify the fraction with highest antifungal activity against phytopathogen postharvest fungi (Botrytis cinerea and Penicillium spp.). A simple and inexpensive extraction method was used to obtain A. vera fractions from 50 kg leaves by means of a designed laboratory roll processor. The yields of extraction were as follows: 15.76% ± 4.0, 51.20% ± 5.20, and 33.02% ± 5.0 for gel, liquid fraction and bagasse, respectively. The three fractions were physico-chemically characterized (protein, monosaccharide composition, ashes, lipids) and resulted to be mainly composed by glucose and mannose in all the cases. Results showed the effectiveness of A. vera fractions in the growth control of phytopathogen postharvest fungi, with visible reduction of fungal growth

Evaluation of the Self-healing Capability of Ultra-High-Performance Fiber-Reinforced Concrete with Nano-Particles and Crystalline Admixtures by Means of Permeability

[EN] Self-healing is the capability of a material to repair its damage autonomously. Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) has potentially higher self-healing properties than conventional concrete because of its lower water/binder content and controlled microcracking due to the high fiber content. This work uses a novel methodology based on the permeability to evaluate autogenous self-healing of UHPFRC and enhanced self-healing, incorporating several additions. To this purpose, one UHPFRC was selected and modified to include alumina nanofibers in 0.25% by the cement weight, nanocellulose (nanocrystals and nanofibers), in a dosage of 0.15% by the cement weight, and 0.8-1.6% of a crystalline admixture. The results obtained show that the methodology proposed allows the evaluation of the self-healing capability of different families of concrete mixes that suffered a similar level of damage using permeability tests adapted to the specific properties of UHPFRC.The authors would like to acknowledge the European Union¿s Horizon 2020 ReSHEALience project (Grant Agreement No. 760824).Doostkami, H.; Roig-Flores, M.; Negrini, A.; Mezquida-Alcaraz, EJ.; Serna Ros, P. (2020). Evaluation of the Self-healing Capability of Ultra-High-Performance Fiber-Reinforced Concrete with Nano-Particles and Crystalline Admixtures by Means of Permeability. Springer. 489-499. https://doi.org/10.1007/978-3-030-58482-5_45489499Homma, D., Mihashi, H., Nishiwaki, T.: Self-healing capability of fibre reinforced cementitious composites. J. Adv. Concr. Technol. 7(2), 217–228 (2009)Maes, M., Snoeck, D., De Belie, N.: Chloride penetration in cracked mortar and the influence of autogenous crack healing. Constr. Build. Mater. 115, 114–124 (2016)Edvardsen, C.: Water Permeability and Autogenous Healing of Cracks in Concrete, vol. 96 (1999)De Belie, N., et al.: A review of self-healing concrete for damage management of structures. Adv. Mater. Interfaces 5(17) (2018)Wang, H.L., Dai, J.G., Sun, X.Y., Zhang, X.L.: Characteristics of concrete cracks and their influence on chloride penetration. Constr. Build. Mater. 107, 216–225 (2016)Wang, K., Jansen, D.C., Shah, S.P., Karr, A.F.: Permeability study of cracked concrete. Cem. Concr. Res. (1997)Šavija, B., Schlangen, E.: Autogeneous healing and chloride ingress in cracked concrete. Heron 61(1), 15–32 (2016)Ismail, M., Toumi, A., François, R., Gagné, R.: Effect of crack opening on the local diffusion of chloride in cracked mortar samples. Cem. Concr. Res. 38(8–9), 1106–1111 (2008)Habel, K., Gauvreau, P.: Response of ultra-high performance fiber reinforced concrete (UHPFRC) to impact and static loading. Cem. Concr. Compos. 30(10), 938–946 (2008)Denarié, E., Brühwiler, E.: Strain-hardening ultra-high performance fibre reinforced concrete: deformability versus strength optimization. Restor. Build. Monum. 17(6), 397–410 (2014)Granger, S., Pijaudier-Cabot, G., Loukili, A.: Mechanical behavior of self-healed ultra high performance concrete: from experimental evidence to modeling. In: Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, vol. 3, pp. 1827–1834 (2007)Escoffres, P., Desmettre, C., Charron, J.P.: Effect of a crystalline admixture on the self-healing capability of high-performance fiber reinforced concretes in service conditions. Constr. Build. Mater. 173, 763–774 (2018)Sisomphon, K., Copuroglu, O., Koenders, E.A.B.: Self-healing of surface cracks in mortars with expansive additive and crystalline additive. Cem. Concr. Compos. 34(4), 566–574 (2012)Roig-Flores, M., Moscato, S., Serna, P., Ferrara, L.: Self-healing capability of concrete with crystalline admixtures in different environments. Constr. Build. Mater. 86, 1–11 (2015)Roig-Flores, M., Pirritano, F., Serna, P., Ferrara, L.: Effect of crystalline admixtures on the self-healing capability of early-age concrete studied by means of permeability and crack closing tests. Constr. Build. Mater. 114, 447–457 (2016)Ferrara, L., Krelani, V., Carsana, M.: A ‘fracture testing’ based approach to assess crack healing of concrete with and without crystalline admixtures. Constr. Build. Mater. 68, 535–551 (2014)Ferrara, L., Krelani, V., Moretti, F.: On the use of crystalline admixtures in cement based construction materials: from porosity reducers to promoters of self healing. Smart Mater. Struct. 25(8), 1–17 (2016)Cuenca, E., Cislaghi, G., Puricelli, M., Ferrara, L.: Influence of self-healing stimulated via crystalline admixtures on chloride penetration. In: America Concrete Institute, vol. 2018(SP 326), pp. 1–10. ACI Spec. Publ. (2018)Borg, R.P., Cuenca, E., Gastaldo Brac, E.M., Ferrara, L.: Crack sealing capacity in chloride-rich environments of mortars containing different cement substitutes and crystalline admixtures. J. Sustain. Cem. Mater. 7(3), 141–159 (2018)López, J.Á., Serna, P., Navarro-Gregori, J., Camacho, E.: An inverse analysis method based on deflection to curvature transformation to determine the tensile properties of UHPFRC. Mater. Struct. 48(11), 3703–3718 (2014). https://doi.org/10.1617/s11527-014-0434-0López, J.Á.: Characterisation of the Tensile Behaviour of UHPFRC By Means of Four-Point Bending Tests, March 2017Negrini, A., Roig-Flores, M., Mezquida-Alcaraz, E.J., Ferrara, L., Serna, P.: Effect of crack pattern on the self-healing capability in traditional, HPC and UHPFRC concretes measured by water and chloride permeability. In: MATEC Web Conference, vol. 289, p. 01006 (2019

Postharvest shelf life extension of blueberries using a chitosan-based edible coating containing aloe vera juice

PosterBlueberries are currently one of the most valuable fruits worldwide, due to their organoleptic and nutritional properties. However these fruits are highly perishable due to their susceptibility to fungal infections (e.g. Botrytis cinerea) and water loss during storage. Edible coatings can improve fruits quality and extend their shelf life by providing a barrier to moisture and gases. The incorporation of natural antifungal compounds, e.g. Aloe vera, into edible coatings provides a novel way to enhance edible coatings properties without using synthetic compounds. In this study, chitosan-based coating (0.5% (w/v)) incorporating Aloe vera juice (0.5% (w/v)) was applied to blueberries to evaluate: (1) their antifungal efficiency and (2) postharvest quality of cold-stored blueberries. Uncoated (B) and coated blueberry (BC) samples were monitored over 25 days at 5.5±0.6 °C and 90±3 % relative humidity. During storage time, samples were analyzed in terms of weight loss, microbiological growth, titratable acidity, pH, soluble solids content, and color properties. Results showed that BC treatment delayed blueberries dehydration after 25 days, since B and BC samples weight losses were 6.2% and 3.7%, respectively. B samples presented contamination after 2 days of storage (2.0 log CFU/g), whilst BC samples presented mold contamination only after 9 days of storage (1.3 log CFU/g). The pH of BC samples remained lower (3.15) than that of B samples (3.54) after 12 days of storage. During storage, B samples had significantly lower titratable acidity values than BC samples (p<0.05), demonstrating that the coating helped retaining acidity of blueberries. Chitosan-based coatings with Aloe vera demonstrated great potential in extending blueberries shelf-life (about 5 days). Moreover, two main factors of blueberry postharvest deterioration (microbiological growth and water loss levels) were reduced, which may represent a significant commercial value to blueberries producers

Comparación de la percepción social en playas recreativas arenosas de dos bahías localizadas en el Pacífico Mexicano

En el presente trabajo se desarrollaron dos formatos de encuesta, para incorporar la percepción de los usuarios a la evaluación de la calidad de las playas (Cervantes, 2006 y Silva-Iñiguez, 2006); ambos basados en un modelo cuantitativo para revelar la percepción social de las playas localizadas en la bahía de Santiago, Manzanillo, Col (MZO) y en Acapulco, Gro (ACA). Se aplicaron un total de 790 encuestas (ACA: 390 y MZO: 400), que permitieron conocer el perfil de los usuarios, sus hábitos de recreación y sus opiniones sobre las condiciones biofísicas y de infraestructura de cada playa. En ambas playas la mayoría prefirieron asistir acompañados por sus familias; las principales actividades recreativas fueron nadar, descansar, comer y beber. En general las demandas en ambos sitios coincidieron con incrementar el número de botes de basura, la frecuencia en el servicio de recolección y limpieza, baños y regaderas. Las razones por la que los usuarios seleccionaron la playa a visitar fueron la seguridad y vigilancia, así como las características biofísicas de la misma. La incorporación de esta información a modelos y/o esquemas de evaluación y gestión de playa (a través de índices ambientales) permitió realizar la valoración integral de la playa.In this paper it was developed two survey formats, to include the perception of users on the assessment of the quality of the beaches (Cervantes, 2006 and Silva-Iñiguez, 2006), both based on a quantitative model to reveal the social perception of the beaches on Santiago Bay, Manzanillo, Col (MZO) and Acapulco, Guerrero (ACA). We did a total of 790 surveys (ACA: 390 and MZO: 400), which allowed the user profile, recreation habits and their views on the biophysical and infrastructure of each beach. In both beaches, most people, attended with their families, the main recreational activities were swimming, resting, eating and drinking. In general the demands on both sites agreed to increase the number of waste baskets, the frequency of collection service and cleaning bathrooms and showers. The reasons why the users selected to visit the beach were the safety and security, as well as the biophysical characteristics of the same. Incorporating this information to models and / or evaluation schemes and beach management (through environmental ratings) allowed the comprehensive assessment of the beach

Effect of chitosan-Aloe vera coating on postharvest quality of blueberry (Vaccinium corymbosum) fruit

The present study was carried out to evaluate the effect of chitosan-based edible coatings with Aloe vera extract on the postharvest blueberry fruit quality during storage at 5 °C. Firstly, A. vera fractions (pulp and liquid) were extracted from leaves and evaluated in terms of antifungal and antioxidant capacities. The choice of the most adequate chitosan and A. vera fraction concentrations to be incorporated in coating formulation was made based on the wettability of the corresponding coating solutions. Coatings with 0.5% (w/v) chitosan + 0.5% (w/v) glycerol + 0.1% (w/v) Tween 80 + 0.5% (v/v) A. vera liquid fraction presented the best characteristics to uniformly coat blueberry surface. Physico-chemical (i.e., titratable acidity, pH, weight loss) and microbiological analyses of coated blueberries (non-inoculated or artificially inoculated with Botrytis cinerea) were performed during 25 d. Microbiological growth and water loss levels were approximately reduced by 50% and 42%, respectively, in coated blueberries after 25 d compared to uncoated blueberries. After 15 d, weight loss values were 6.2% and 3.7% for uncoated and chitosanA. vera coated blueberries, respectively. Uncoated fruits presented mold contamination after 2 d of storage (2.0 ± 0.32 log CFU g1), whilst fruits with chitosan-based coatings with A. vera presented mold contamination only after 9 d of storage (1.3 ± 0.35 log CFU g1). Overall, coatings developed in this study extend blueberries shelf-life for about 5 d, demonstrating for the first time that the combination of chitosan and A. vera liquid fraction as edible coating materials has great potential in expanding the shelf-life of fruits.Joana T. Martins (SFRH/BPD/89992/2012) is the recipient of a fellowship from the Fundação para a Ciência e Tecnologia (FCT, Portugal). María L. Flores-López thanks Mexican Science and Technology Council(CONACYT, Mexico) for PhD fellowship support (CONACYT Grant number: 215499/310847). The authors thank the FCT the strategic funding of UID/BIO/04469/2013 unit and the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER- 027462)