The main purpose of the present research was to investigate the changes in physical-chemical parameters of fresh Latvian cranberries during storage. Cranberry (′Steven′, ′Bergman′, ′Pilgrim′, ′Early Black′, and ′Ben Lear′) fruit were collected at a processing plant in Kurzeme region, Latvia, in the first part of October 2010. For the experiments, also wild cranberries were collected in the bogs of the same region and at the same time. The berries were rinsed with tap water for 3±1 min, then strained for 10±1 min (mainly for visual cleanness), and afterwards stored in closed non-perforated polypropylene (PP) boxes in air ambiance and in glass jars in a cold boiled-water ambiance at 3±1 °C. Quality parameters of the berries were tested each three months using standard methods: vitamin C content - by high-performance liquid chromatography (HPLC); organic acids - by HPLC; moisture - by oven-dry method; colour parameters - by device COLOR TEC PMC; pH - by potentiometric method; anthocyanin - by spectrophotometrical method; and phenolic compounds - by HPLC. The shelf life of cranberries packaged in closed PP boxes in air ambiance was six months, but of cranberries packaged in glass jars in water ambiance - 12 months. The research showed that differences in moisture content, pH value, colour intensity, and anthocyanin content among the cranberry cultivars under different ambient conditions during storage were not significant. During 12 months of cranberry storage in glass jars in water ambiance, the content of vitamin C decreased on average by 90%, organic acids - by 54%, and phenolic compounds - by 60%. During six-month storage in closed PP boxes in air ambiance, the content of vitamin C decreased on average by 99%, organic acids - by 30%, and phenolic compounds - by 34%.
The results of two years (2010-2011) of field studies using two types of nonwoven mulches (one biodegradable, polylactic acid PLA 54 g m-2, and traditional polypropylene PP 50 g m-2) on the yield and quality of tomato are presented. Seeds of tomato (‘Mundi’ F1) were sown in a greenhouse, in containers filled with perlite and sand, and then the plants at the cotyledon stage were replanted in multipot trays filled with substrate for vegetable plants. In the last week of May, seedlings were planted on mulches in the field at a spacing of 50 × 100 cm. The mulch was maintained throughout the growing season. A plot that remained unmulched served as the control. Tomatoes were harvested once a week. The fruits were evaluated for L-ascorbic acid, dry matter, soluble sugars and nitrate content. In 2011, the analysis of the plant material showed that the concentration of L-ascorbic acid was about 23% higher in the tomato fruits harvested from plants grown on biodegradable PLA 61 g m-2 mulch in comparison to the control. A similar effect was demonstrated for the soluble sugar concentration in 2011 for both types of nonwovens.
Field experiments using ‘melt-blown’ biodegradable nonwovens were carried out on the ‘Melodion’ butterhead lettuce (Lactuca sativa var. capitata L.) cultivar for early harvest. All biodegradable nonwovens were manufactured in the Institute of Biopolymers and Chemical Fibres and POLMATEX CENARO in Łódź, Poland. Lettuce seeds were sown into boxes in a greenhouse at the beginning of March, and transplants were planted into the field at the beginning of April. Biodegradable nonwovens - aromatic polyester IBWCH 75 g m-2, polybutylene succinate Bionolle 100 g m-2 and standard polypropylene PP Agro 20 g m-2 - were stretched over the lettuce in the field. The covers were kept on until 4-5 days before harvest. Plots without covers were defined as the control. Ascorbic acid, soluble sugar, dry matter, nitrates, chlorophyll a, chlorophyll b and carotenoid contents were recorded in the leaves. All biodegradable nonwovens showed a positive effect on yielding in comparison to the control in 2009. In the second year of the experiment, there were no significant differences between covers with regard to the yield. Dry matter and soluble sugar content in both years of the experiment was diversified. Nonwovens used as covers in 2009 significantly increased the content of nitrates in comparison to the control. In the second year, the highest level of nitrates was demonstrated in the control object. It is worth underlining that the maximum allowed limit of nitrate content in lettuce (4000 mg kg f.w.) was not exceed. The kind of cover had no significant effect on the level of chlorophyll a in 2009 or chlorophyll b and carotenoids in 2009 and 2010 in the lettuce