Browsing by Subject "valo"
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(2019)Ruukkusalaattien tuotanto on kasvanut Suomessa jo vuosikymmeniä. Kasvihuoneet mahdollistavat tuoreiden lehtivihannesten kasvatuksen ympärivuotisesti, mutta pimeä vuodenaika tai valonsaannin heikentyminen yhdessä korkean nitraattilannoituksen kanssa aiheuttavat nitraatin kertymistä salaattiin. Nitraatti ei itsessään ole kovin myrkyllistä ihmiselle, mutta sen aineenvaihduntatuotteet elimistössä voivat olla haitallisia. Siksi ravinnon nitraattipitoisuuksia rajoitetaan EU asetuksella ja kasvisten nitraattipitoisuuksia valvoo Ruokavirasto. Tutkimuksen tavoitteena oli selvittää jääsalaatin (Lactuca sativa L.) nitraattipitoisuuteen vaikuttavia tekijöitä yksityisellä kasvihuonepuutarhalla, ja ehdottaa helposti sovellettavia keinoja nitraattipitoisuuden alentamiseksi. Tutkimuksessa mitattiin vuorokaudenajan, iän ja olosuhteiden vaikutusta jääsalaatin nitraattipitoisuuteen. Mittaukset tehtiin eri kellonaikoina korjatuilta salaateilta, neljän, viiden ja kuuden viikon ikäisiltä salaateilta, sekä viikoittaisilla seurantamittauksilla kolmen kuukauden ajan syksyllä 2017. Salaattien nitraattipitoisuus määriteltiin pikamittausmenetelmällä. Kasveille tulevaa PAR-valoa ja kiertoliuoksen nitraattityppipitoisuutta mitattiin jatkuvatoimisella mittalaitteella. Lisäksi kasvihuoneen automaattisesta ohjausjärjestelmästä saatiin tietoa muista kasvuolosuhteista. Sadonkorjuun kellonaika ei vaikuttanut jääsalaatin nitraattipitoisuuteen. Ikä vaikutti neljän ja viiden viikon ikäisten salaattien nitraattipitoisuuteen, mutta paremmissa valo-olosuhteissa iän vaikutus heikkeni kuuden viikon ikäisillä salaateilla. Nitraattityppilannoituksella ei ollut suoraa vaikutusta salaatin nitraattipitoisuuteen, mutta enemmän valoa saaneissa salaateissa oli vähemmän nitraattia. Kasvuston tasolta tehdystä jatkuvatoimisesta valon mittauksesta on hyötyä salaatin nitraattipitoisuuden hallinnassa. Riski nitraatin enimmäispitoisuusrajan ylitykseen on suuri syyskuussa luonnonvalon määrän vähentyessä. Tekovalojen käytön lisäämisellä voidaan alentaa salaatin nitraattipitoisuutta.
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(2009)The literature review of this thesis deals with light, different light sources and their properties. LED (Light Emitting Diode) light was specially taken into consideration, because the use of LED lights will increase in general illumination. The literature review also deals with the quality changes of dairy products and potatoes caused by exposure to light. The aim of this study was to search for such a spectral distribution of light which would cause only minor changes in the sensory quality of milk and the surface colour of potatoes. Objective was to also find out if there is a difference between the effects of fluorescent light and LED light on the quality of milk and greening of potatoes. Reduced (1,5 %) fat milk and new potatoes were used as testing materials. The milk in commercial carton board packages was exposed to six different light sources: white fluorescent lamp, white LED and LED of four different colours. The potatoes packed in transparent LDPE (Low Density Poly Ethylene) bags were stored under five different light sources: white fluorescent lamp, white LED and LED of three different colours. The light intensity at the surface of the packages was about 1000 lx in both studies. In the milk study, the effects of light were evaluated with a sensory method using descriptive analysis. In the potato study, the light effects were analysed with colour measurements (avalue) using a spectrophotometer and with surface temperature measurements using a laser thermometer. Sensory evaluation of milk there resulted in few statistically significant differences in the intensity of the attributes between the milks stored under different light sources. Light exposure caused a rapid greening of potatoes in every illumination. According to colour change percentage, the greening order under different lights was: white LED < yellow LED < green LED < turquoise LED < fluorescent light. The potatoes which were stored in dark had no change in their surface colour. The surface temperature of potatoes increased most under white LED and turquoise LED lights. A spectral distribution of light which would have caused less changes in sensory quality of milk than commonly used fluorescent light was not found in this study. The results showed, however, that in addition to blue light which has always been considered the most harmful for milk the red light also caused remarkable quality changes. Based on the results of this study, it could be suggested that under the LED lights the quality of packed milk retained its quality characteristics at least as well as under the fluorescent light. There were differences between the effects of different lights on the greening of potatoes. White and yellow LED light caused less greening of potatoes than the other lights. The strongest greening of potatoes was observed under the fluorescent light.
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(2009)The literature review of this thesis deals with light, conventional light sources and the effects of light on the quality of foods. Impacts of light on the quality of frozen foods were also discussed. Effects of fluorescent light on frozen food have been previously reported in the literature, but effects of LED light have not. The literature review also deals with the quality changes of foods caused by freezing and frozen storage. The significance of package during frozen storage was reviewed. The aim of the experimental study was to investigate whether there are differences between the effects on frozen food when exposed to fluorescent or LED light. Frozen strawberries, shrimps, lamb loins and ice cream were exposed to fluorescent and LED light for 4 weeks. The samples were packed in transparent LDPE pouches except the lamb loins, which were vacuum-packed in transparent PA/PE film. References were packed in aluminium foil. Temperature of the samples was monitored by the sensors attached to the surfaces of the packages. The colour of the samples was measured every week using a spectrophotometer. Thiobarbituric acid (TBA) values of the shrimps and lamb loins were analysed after 0, 2 and 4 weeks of exposure. The odour of shrimps was evaluated with sensory evaluation using a multiple comparison test. Sensory evaluations of ice cream was conducted by trained panelists using a multiple comparison test. All the sensory evaluations were conducted after 2 and 4 weeks of exposure. In addition, ice cream was exposed to light under a yellow plastic film to find out the effects of riboflavin, which is known to operate as a sensitiser. After 4 weeks of exposure to the fluorescent light the total colour difference of the samples was higher than that of the products exposed to the LED light. Differences were pronounced especially in ice cream exposed to light under transparent film. The smell and taste of ice cream were affected when exposed to light under transparent or yellow plastic films. There were no statistically significant differences in the taste of ice cream when exposed to fluorescent or LED light for 4 weeks, but the smell of ice cream appeared to be more divergent from the reference when exposed to LED light under transparent film for 4 weeks than the smell of ice cream exposed to fluorescent light for 4 weeks. On the basis of this study, fluorescent light affected the colour of the frozen food more than LED light. Light sources did not differ from each other, when the results of the sensory evaluation of shrimps were considered. Because TBA values of lamb loins and shrimps also increased in reference samples, the effects of light could not be separated. Sensory properties of ice cream were affected by light exposures, but on the basis of sensory evaluation it is not possible to state which light source was more detrimental to the quality of ice cream.
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