Browsing by Subject "relative humidity"

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  • Kamlang-ek, Pimwalee (Helsingfors universitet, 2012)
    The literature survey reviewed principles of oxidation of edible oils, adverse effects of lipid oxidation and analysis of volatile oxidation products by SPME-GC-MS. The main aim of the experimental research was to study the influence of relative humidity (RH) on the release of volatile oxidation products from spray-dried emulsions with natural and cross-linked casein as emulsifier. The release of volatiles was determined by SPME-GC-MS. The sub aims were to study the effects of stabilization time at specific RHs, of temperature and agitation speed during the SPME extraction. The spray-dried emulsions were oxidised at 40oC in order to reach a certain level of oxidation. Next, the powders were stabilised under five RHs (0%, 11%, 33%, 54% and 75%) for one or two weeks in order to observe the effect of the RH and the stabilisation time on the release of volatiles. After adjusting the RHs, volatile compounds were analysed by SPME-GC-MS. The following SPME extraction conditions were tested: C1: temperature 40oC, agitation speed 250 rpm, C2: 50oC, 250 rpm, C3: 40oC, 500 rpm and C4: 50oC, 500 rpm. Identification of the compounds was carried out by matching their MS spectra with the NIST database. Altogether 45 volatiles released from the powders could be identified, and 18 of them were found in most samples. RH had an important effect on the release of volatiles from the encapsulated samples. The highest release was always observed at 11% and 33% RH, whereas the lowest release was found at 0% and/or 75% RH, depending on the SPME extraction conditions. The stabilisation time did not have a significant effect on the release of volatiles in most RHs. During the SPME extraction step, elevation of the temperature from 40oC to 50oC, as well as the agitation speed from 250 rpm to 500 rpm, facilitated higher release. However, the effect of temperature was greater than that of agitation speed. Although it was suspected that cross-linking of sodium-caseinate would enhance retention of volatiles, our experiment showed greater peak areas of most volatiles from the cross-linked samples than from the natural ones. By controlling the SPME parameters, it was possible to obtain repeatable volatile compound results. The SPME-GC-MS method applied in this study can be reliably used to analyse volatile oxidation products from spray-dried emulsions. Only at very low or high RH the release of volatiles may differ from samples stored at 11% -54% RH.
  • Mammola, Stefano; Piano, Elena; Cardoso, Pedro; Vernon, Philippe; Dominguez-Villar, David; Culver, David C.; Pipan, Tanja; Isaia, Marco (2019)
    Scientists of different disciplines have recognized the valuable role of terrestrial caves as ideal natural laboratories in which to study multiple eco-evolutionary processes, from genes to ecosystems. Because caves and other subterranean habitats are semi-closed systems characterized by a remarkable thermal stability, they should also represent insightful systems for understanding the effects of climate change on biodiversity in situ. Whilst a number of recent advances have demonstrated how promising this fast-moving field of research could be, a lack of synthesis is possibly holding back the adoption of caves as standard models for the study of the recent climatic alteration. By linking literature focusing on physics, geology, biology and ecology, we illustrate the rationale supporting the use of subterranean habitats as laboratories for studies of global change biology. We initially discuss the direct relationship between external and internal temperature, the stability of the subterranean climate and the dynamics of its alteration in an anthropogenic climate change perspective. Owing to their evolution in a stable environment, subterranean species are expected to exhibit low tolerance to climatic perturbations and could theoretically cope with such changes only by shifting their distributional range or by adapting to the new environmental conditions. However, they should have more obstacles to overcome than surface species in such shifts, and therefore could be more prone to local extinction. In the face of rapid climate change, subterranean habitats can be seen as refugia for some surface species, but at the same time they may turn into dead-end traps for some of their current obligate inhabitants. Together with other species living in confined habitats, we argue that subterranean species are particularly sensitive to climate change, and we stress the urgent need for future research, monitoring programs and conservation measures.
  • Gabucan, Ma.Heidi (Helsingin yliopisto, 2020)
    The literature review highlighted the principles of microencapsulation and spray drying, with emphasis on the properties of highly oxidizing oils, protein interface modification, and mechanism of lipid oxidation. The major aim of the research was to study the chemical and physical stability of microencapsulated flaxseed oil (MFSO) during storage under controlled relative humidity conditions (0%, 11%, 33%, 54%, and 75%RHs) and compare the results to bulk flaxseed oil (FSO). Microencapsulation was done by spray drying of non-cross linked (NCL) and transglutaminase cross-linked (CL) Na-caseinate FSO emulsions. Oxidative stability was examined through changes in physical and chemical properties of MFSOs and FSO as influenced by different RHs and storage periods. Chemical analyses were used to analyze the peroxide value (PV), fatty acid profile, γ-tocopherol, carotenoid and chlorophyll, phenolic compounds, and secondary oxidation products (hexanal and propanal) in MFSOs and FSO. Degree of secondary oxidation was determined by static headspace gas chromatography while the morphology of MFSOs was examined by scanning electron microscopy. Results showed that at dry condition (0%RH), surface lipids of CL and NCL MFSOs were unstable and more susceptible to oxidation after 17 weeks storage. Release of hexanal and propanal were higher for NCL than CL microencapsulated flaxseed oil which suggested that interfacial cross-linking of Na-caseinate was efficient. At high moisture condition (75%RH), MFSOs were oxidatively stable owing to their low PVs and structural transformation from porous structure to agglomerates or sticky form. High amounts of alpha-linolenic acid and γ-tocopherol were detected in FSO and MFSOs, and only minor losses occurred throughout storage period and under different RHs. FSO also contained considerable amounts of carotenoid and phenolic compounds but low in chlorophyll content. Oxidative stability of interface and matrix elucidated that humidity conditions considerably influenced the chemical and physical properties of CL and NCL MFSOs.
  • Sotunde, Sobowale Adedapo (Helsingfors universitet, 2016)
    In meeting the crop water needs in the arid and semi-arid regions, alternative source of water must be explored, like the harvesting of dew and fog. To estimate the quantity of potential harvestable water in semi-arid Nigeria, a 3-hourly meteorological data from 8 weathers stations across the semi-arid region of Nigeria were analysed. The data; from January to December 2009; was retrieved in June 2015 from the European Center for Medium range Weather Forecasting (ECMWF) database, by the Finnish Meteorological Institute (FMI). The available data includes the wind speed (WS) and direction, air temperature, and the relative humidity (RH). From the available data, the following needed parameters to calculate the potential water harvestable in each area were first calculated; the air saturated vapour pressure, air vapour pressure, absolute humidity, and finally the potential water harvestable through air humidity over 3hours (WH3). Only the RH ≥69% were used in calculating the WH3, at lower values water harvesting isn’t possible. Also, only the WS ≤2 was used, at higher values of WS, evaporation occurs. All the areas showed the possibility of harvesting water from dew and fog. The possibility was however higher during the wet season both in quantity and in frequency in all the areas considered than in the dry season.
  • Xiao, Mingzhong; Yu, Zhongbo; Kong, Dongdong; Gu, Xihui; Mammarella, Ivan; Montagnani, Leonardo; Arain, M. Altaf; Merbold, Lutz; Magliulo, Vincenzo; Lohila, Annalea; Buchmann, Nina; Wolf, Sebastian; Gharun, Mana; Hörtnagl, Lukas; Beringer, Jason; Gioli, Beniamino (2020)
    Terrestrial evapotranspiration (ET) is thermodynamically expected to increase with increasing atmospheric temperature; however, the actual constraints on the intensification of ET remain uncertain due to a lack of direct observations. Based on the FLUXNET2015 Dataset, we found that relative humidity (RH) is a more important driver of ET than temperature. While actual ET decrease at reduced RH, potential ET increases, consistently with the complementary relationship (CR) framework stating that the fraction of energy not used for actual ET is dissipated as increased sensible heat flux that in turn increases potential ET. In this study, we proposed an improved CR formulation requiring no parameter calibration and assessed its reliability in estimating ET both at site-level with the FLUXNET2015 Dataset and at basin-level. Using the ERA-Interim meteorological dataset for 1979-2017 to calculate ET, we found that the global terrestrial ET showed an increasing trend until 1998, while the trend started to decline afterwards. Such decline was largely associated with a reduced RH, inducing water stress conditions that triggered stomatal closure to conserve water. For the first time, this study quantified the global-scale implications of changes in RH on terrestrial ET, indicating that the temperature-driven acceleration of the terrestrial water cycle will be likely constrained by terrestrial vegetation feedbacks.
  • Pirinen, Pentti; Simola, Henriikka; Aalto, Juha; Kaukoranta, Juho-Pekka; Karlsson, Pirkko; Ruuhela, Reija (Ilmatieteen laitos, 2012)
    Raportteja - Rapporter - Reports 2012:1