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In the last decades, the production of value-added products from lignocellulosic biomass (LCB) has gained relevance. Xylans, which are the main hemicellulose compounds in LCB, may be extracted by alkaline pretreatment and employed for xylooligosaccharide (XOS) production. However, xylan extraction currently works as a black box due to the lack of characterization of the involved streams. Therefore, the appropriate operational conditions often remain unclear, especially in hardwoods. In this study, alkaline/thermal pretreatments at different operational conditions were evaluated for xylan extractions from Chilean Nothofagus species sawdust, determining the chemical compositions of the fractions at each step of the process. Results indicated that increasing alkali concentration (NaOH) leads to a higher xylan extraction, but also to high salt production during the acid neutralization step, decreasing xylan's purity and therefore XOS production. In this context, decreasing NaOH concentration and neutralizing it by membrane filtration, allow extracting xylans (62.5 %) of higher-purity (77 %).

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Xylooligosaccharides (XOS), produced from lignocellulosic biomass (LCB), are short-chain polymers with prebiotic activity which, in the last few decades, have gained commercial interest due to their potential application as ingredients for the nutraceutical industry. This article reviews relevant topics to consider when researching XOS productive processes, such as the selection of raw materials and strategies for XOS production, purification, characterisation, quantification and evaluation of the prebiotic effects. With regard to the production approach, this article focuses on LCB pre-treatments and the enzymatic hydrolysis of xylan, exploring the reported alternatives and enzymes. A critical view on the current process reveals that comparative analysis between different studies is difficult due to the lack of consensus on the criteria and parameters used in the evaluation of XOS production processes. However, the most generally recommended XOS production strategy is the two-stage approach through alkaline pre-treatment and enzymatic hydrolysis with further purification through membrane filtration.

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Resumen El objetivo fue identificar las asociaciones entre apoyo social percibido, riesgo suicida y presencia de enfermedad crónica no transmisible en estudiantes universitarios. Utilizando un diseño de casos y controles, con 41 estudiantes universitarios por grupo. La mediana de edad fue de 22 años (R = 9), un 81,8% eran mujeres, el 26,8% de los sujetos tenía Asma y el 26,8% Hipotiroidismo, y el 63,6% pertenecía a la Facultad de Educación. No se comprobó la asociación entre enfermedad crónica, apoyo social, ni tampoco con riesgo suicida. Hay asociación indirecta entre riesgo suicida y apoyo social, no así cuando se evalúa el intento de suicidio previo. El nivel de riesgo suicida y apoyo social se asocian independiente de la presencia de enfermedad crónica. Esperamos que nuestros resultados permitan fomentar el apoyo social como una herramienta fundamental para la prevención de la suicidabilidad, especialmente en sujetos con enfermedad crónica.

Abstract The objective was to identify associations between perceived social support, suicidal risk and the presence of chronic or communicable disease in university students. Using a case-control design, consisting of 41 subjects in each group. The median age was 22 years (R = 9), 81,8% were women, 26,8% of the subjects had asthma and 26,8% had hypothyroidism, 63,6% were students of the faculties of Education. The association between chronic disease and social support was not proven, nor was there a suicidal risk. There is an indirect association between suicide risk and social support, not so when assessing the previous suicide attempt. The levels of suicide risk and social support are associated, independent of an existing chronic disease. We are hopeful that our results will be effective in promoting social support as a basic tool for suicide prevention, especially in subjects with chronic disease.

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