Browsing by Subject "potato"

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.

This Master's thesis compares the commercial cooking tests of potatoes in Finland and Europe. The cooking type comprises the structural properties of potato, which are described e.g. in terms of floury and waxy or types A-D. Other measures of cooking quality, such as color, taste and odor, were excluded from the work. The main focus of the thesis was on the survey of European cooking type tests and on the comparative study of descriptors for different varieties. As the use of descriptors and terminology differ slightly from one country to another, the significance of the differences in the resulting cooking type result was also considered. In the study, seven varieties with seven different meters and a total of 12 different measuring methods were compared. The key method of the thesis was sensory evaluation by descriptive method. The descriptors were used as unambiguously as possible, such as evaluating flouriness by appearance and by palpation in the mouth. In addition to sensory evaluations, experiments with structure analysis, hyperspectral imaging, and color measurement were included in the study. The purpose of the analysis was to look at the descriptor ensembles, and to observe their dimension on the axis waxy - floury and possible other independent dimensions that would diversify the description of the cooking quality. The results were examined statistically by means of generalized linear models, correlations and principal component analysis. The thesis concluded that there are some differences between European ways of determining the cooking type, and in borderline cases, different results are possible. In general, European descriptor ensembles are strongly built to support the waxy-floury axis. In addition to the descriptor ensembles, the cooking type determination include procedures and calculation methods and cannot be separated from the whole. The results of the study support the fact that hardness/softness is an independent dimension, and hardness determined by the texture analyzer clearly distinguished the varieties. In sensory comparison, external observation and mouthfeel evaluation produced similar results, except for hardness assessment. The instrumental methods distinguished the varieties more clearly than sensory evaluation. Disintegration analyzed by color measurement and starch content is a viable combination for cooking type determination.

Potato virus Y (PVY) is currently the most yield and quality limiting pathogen of the cultivated potato (Solanum tuberosum L.) globally. While yield losses specific to PVY are hard to measure in presence of other pathogens they are estimated as 20 to 80 %. The most important way by which the virus spreads are virus-infected seed potatoes. High quality seed potato is very important for food, food industry and starch potato production. Visual inspection of the potato plants underestimates usually the real percentage of PVY infection. Laboratory tests provide more accurate results about the incidence of infections. The problem with testing PVY is that the virus cannot be detected reliably from samples taken from dormant tubers. Different treatments have been used to break dormancy of tubers e.g. chemicals (Rindite, bromoethane), plant hormones (gibberellic acid) and adjusted storage temperatures (cold and heat treatment). The results have varied a lot. In this thesis an experiment with oxygen-carbon dioxide (O2 40 %-CO2 20 %) treatment with different periods of time was used to end dormancy of potato tubers. The aim was to test whether the treatment could end dormancy of tubers earlier than normally and to see if the treatment has an effect on detection of PVY. One aim was also to test how reliably PVY could be detected from tuber and sprout samples compared with potato leaf samples which are normally used for virus testing. Results from the sprouting treatment were variable and could not be readily generalized. The treatment had no effect on the detection of PVY incidence. When the different plant materials were compared with each other, tuber material showed the lowest PVY percentage when compared to sprouts and leaves. Testing sprouts also underestimated the incidence PVY. The best material for testing PVY in potatoes were the leaf samples.

Potato (Solanum tuberosum L.) is a plant that belongs to the group of nightshades (Solanaeceae). Enzymatic browning occurs in potato tuber when it is peeled or bruised. Polyphenols in tuber (e.g. chlorogenic acid and tyrosine) are oxidised into o-kinones by polyphenol oxidase. When kinones polymerise, melanins are formed. These compounds cause the brown colour in potato tubers. Sulfites are used as food additives in potatoes preventing enzymatic browning reactions. The maximum permitted usage levels in European Union are 50 mg SO2/kg in peeled potatoes, 100 mg SO2/kg in cooled and frozen potatoes and 400 mg SO2/kg in dried potato products (No 1333/2008). The allergy threshold limit for sulfites in food products is 10 mg SO2/kg (No 1169/2011). The objectives of this study were 1) to determine the sulfite content in various potato products on the market, 2) to examine the binding of sulfite on potato in the relation with temperature, time and concentration, 3) to examine sulfite content in different potato varieties and 4) to compare the HPLC results with the rapid determination methods. The objectives in the literature review were to study the use of a potato as a food component, industrial peeling of potatoes, enzymatic browning reactions, sulfites and their analytical methods. In this study, a modified RP-IP-HPLC-PC (Reversed Phase Ion-Pair High Performance Liquid Chromatography Post-Column) method was used. For rapid determination methods, two kits were used: Merck MQuantTM Sulfite Test and Neogen ALERT® for Sulphites in Seafood. 18 food products were selected to this study (6 mashed potato flours, 3 fresh products and 9 frozen). Box-Behnken Experimental Design was carried out prior to the examination of sulfite binding in different potato varieties (Belana, Nicola, Siikli, Gala, Jelly, Melody, Bellarosa, Afra and Puikula). Sulfite was found in four mashed potato flours and three fresh potato products. In flours, the content of sulfites were below the maximum limit, but over the allergy threshold limit (10 mg SO2/kg). However, sulfite was labelled. In fresh products, the content of sulfite in the first product was below the allergy threshold limit, the second product fell under the maximum limit but the third product exceeded it. In the first product sulfite was not labelled but in the other two ones it was. In Box-Behnken Experimental Design, results were analysed with one-way ANOVA. Concentration (%) had the biggest influence on sulfite binding on potato (p = 0,000) and then time (s) (p = 0,0079). Temperature (°C) didn’t have any statistical significance (p = 0,3513). According to the results, the best measurement point was 1 %, 60 s, +5 °C. The peeled potato varieties were sulfite treated in these conditions. Statistical analysis was carried out with one-way ANOVA and then Tukey HSD. According to the results, there was a statistical significance (p = 0,000) in sulfite binding in different potato varieties. Sulfite was bound most in Puikula (67,0 ± 8,8 mg SO2/kg) and least in Gala (19,7 ± 5,3 mg SO2/kg). The most difference within the varieties in sulfite binding were with Belana, Gala and Puikula. Jelly had a difference only with Gala. In rapid determination methods, ALERT® was more accurate than MQuantTM. ALERT® could be applied on the surface of the sample contrary to MQuantTM that needed 3 or 5 times dilution before measurement. ALERT® is a good choice for semiquantitative rapid method. MQuantTM, however, is not suitable for rapid measurement of sulfites in potato products.

A field experiment was conducted at Potato Reseach Institute during 1997-2002 in Lammi, Finland. The first aim of the work was to find out the suitability of three- and four-year crop rotation on potato production. The second aim was to investigate the effect of three different tilling methods and four different preceding crops on yield and quality of potato. The tilling methods were autumn and spring ploughing and light cultivation. The preceding crops were barley with straw left in the plots, barley with straw harvested, oat with straw harvested and two-year-grass. There were no differences on yield or quality of tubers between the studied crop rotations. The tuber yield did not differ between the tilling methods or the preciding crops. There was an interaction between all studied rotation and tilling methods. Three-year rotation resulted in approximately 5 % higher tuber yield and 14 % higher marketable yield following spring ploughing and light cultivation in comparison to autumn ploughing. However, four-year rotation resulted in an opposite result, since the tuber yield was 7 % and marketable yield 17 % higher following autumn ploughing in comparison to both spring ploughing and light cultivation. The most effecting factor on tuber quality was the two-year-grass as a preceding crop. Starch content was a little less than one percentage point higher following grass in comparison to all other preceding crops studied. Plant stand was also slightly sparser and tubers were slightly larger following grass in comparison to other preceding crops studied. This was due to grass lumps which caused problems in planting and resulted in uneven plant stand density. There were more green tubers following grass in comparison to other preceding crops studied. The starch content was a little less than one percentage point lower following spring ploughing in comparison to other tilling methods. Common scab was observed somewhat more following spring ploughing. The light cultivation resulted in the highest number of green tubers. Three- and four-year crop rotations seem to fit for potato cultivation, and oat and barley are suitable as preceding crops for potato. Yield is not affected when spring ploughing- and light cultivation is applied with cereals as preceding crops. The two-year-grass is also suitable preceding crop for potato. It increases the tuber starch content, even tough it can decrease the quality. Thus, autumn ploughing is the best option as a tilling method to be used for grass as a preceding crop in potato cultivation.