Browsing by Subject "relative humidity"

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.

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.