Oxidation of fats and oils reduces the nutritional value of food and causes various health problems. The addition of antioxidants prevents the oxidation of fats in the food. The antioxidant activity of antioxidants represents the ability to inhibit the process of oxidation. The antioxidant activity of herbal extracts has usually been assessed in a linoleic acid emulsion system. The aim of the present study was to evaluate inhibition of conjugated diene formation in Latvian linseed oil. Ethanol extract of the calyx of Hibiscus sabdariffa L., vanillin, α-tocopherol and 2,6-di-tert-butyl-4-methylphenol as additives were compared for their antioxidative activity. The samples of linseed oil with additives were incubated for 24 h at 60 °C and then analysed using UV spectrophotometry (λ = 234 nm). The antioxidant activity of additives was characterised by the percentage of formation of conjugated dienes. The ability of additives to inhibit oxidation in linseed oil decreases as follows: vanillin, 2,6-di-tert-butyl-4-methylphenol and α-tocopherol. Our results indicate that linseed oil can be used to test antioxidative activity of substances.

The objective of this study was to evaluate the effect of blanching temperature on structure, colour, chemical composition, and rehydration capacity of microwave-vacuum dried chanterelle ( Cantharellus cibarius ). Fruiting bodies of chanterelle were collected from the forests in Jelgava region of Latvia. Prior to drying, fresh mushrooms were blanched in water at various temperatures of 70, 80, 90 and 100oC for 3 min, then cooled in water (20oC). After blanching mushrooms were dried in a microwave-vacuum drier according to the specially designed program. The content of dry matter of chanterelle was 9.5 ± 0.5%. The results revealed that weight loss at 70 -90oC was significantly smaller compared to blanching at 100oC temperature. The results indicated the tendency of smaller changes in microstructure, weight loss and colour for samples blanched at 70 -80°C temperature comparing to the samples unblanched or blanched at higher temperatures. Electrical conductivity in water extract of microwave-vacuum dried chanterelle decreased with increased blanching temperature. Titratable acidity of chanterelle significantly reduced after blanching due to leakage of soluble acids into blanching water.

The aim of this study was to investigate the chemical composition of widely used wild edible mushroom Cantharellus cibarius. Mushrooms Cantharellus cibarius were collected in Jelgava region (Latvia) in late summer 2011. Mushrooms were freeze-dried and used to determine chemical composition. Ash amount was determined by incineration at 550 C; protein content was determined by Lowry method; total content of phenolic compounds was determined by Folin-Ciocalteu assay. The concentrations of -carotene and lycopene were determined spectrophotometrically in methanol extract. Protein content in dry matter of Cantharellus cibarius was 190 mg g. Electrical conductivity (2550 s cm), titratable acidity (0.238 mmol of NaOH per g of dry matter) and formol number (0.163 mmol NaOH per g of mushrooms dry matter) were measured in water extract. The total content of phenolic compounds was 5.09 mg of gallic acid equivalents per 1 g of mushrooms dry matter. The content of -carotene was 4 times higher than the content of lycopene for Cantharellus cibarius, but 4.6 times less than for Boletus edulis f. beticola. Using gas chromatography-mass spectrometry (GC-MS) volatile compounds for the first time were determined in both fresh and freeze-dried samples of mushroom Cantharellus cibarius and the dominant compound was found to be oct-1-en-3-ol. Results of the chemical composition of Latvian mushroom Cantharellus cibarius were compared to previously published chemical composition of Cantharellus cibarius collected in other European regions and to our previous results of the chemical composition of Latvian mushroom Boletus edulis. Although the amount of substances tested is slightly higher in mushroom Boletus edulis, Latvian mushroom Cantharellus cibarius is a rich source of biocompounds and mineral substances.

Birch and maple saps contain carbohydrates and organic acids, B complex vitamins and vitamin C, tannins, flavonoids, glycosides and mineral substances. The aim of the study was to quantitatively determine the concentrations of bioactive compounds and mineral substances in Latvian birch (Betula pendula Roth.) and maple (Acer platanoides L.) saps. Electrical conductivity was determined (629 and 967 S/cm in birch and maple saps, respectively) to characterise the total amount of mineral substances. In birch and maple saps the titratable acidity (0.50 and 0.70 mmol of NaOH per litre of sap, respectively) and formol number (0.25 and 0.20 mmol NaOH per litre of sap, respectively) were determined. The protein concentration was found to be higher in maple sap (171 and 127 mg/l, respectively). The antioxidant concentration, determined using quercetin as a standard, was 0.35 mg of quercetin equivalents (QE)/l in birch sap and 0.77 mg QE/l in maple sap. In conclusion, Latvian maple sap contains more bioactive and mineral compounds than birch sap. Latvian birch sap contains up to 20% more glucose and fructose than birch sap produced in Finland, but Latvian maple sap contains 10 to 40% less sucrose than sap produced in North America.

The main carbohydrates of honey are fructose, glucose, sucrose and maltose. Invertase hydrolyzes sucrose about fructose and glucose. Therefore low content of sucrose and high content of glucose and fructose in honey are parameters for characterization of honey quality. Several sorts of honey contain heightened content of maltose. Therefore it is possible to use this criteria for identification several honey sorts. Each carbohydrate has a specific angle of rotation of polarized light (specific rotation). It depends on relations and content of carbohydrates in honey. The aim of the present research was to establish the relationship between honey sorts and content of carbohydrates as well as specific rotation and possibilities of using these criteria (content of carbohydrates, specific rotation, and activity of invertase) for characterization of honey quality. Following parameters were determined with different physico – chemical methods: specific rotation – by method of polarimetry, content of sugars with high pressure liquid chromatography and activity of invertase – spectrophotometrically. The following results of honey analysis were obtained: the activity of invertase 4–30 (invertase number); content of carbohydrates (sucrose 0.5–3.0%, glucose 30–38%, fructose 35–42%, and maltose 1–6%); specific rotation 20 ] [ D α at -16° to -5°. The obtained results indicated that content of carbohydrates partially dependent on honey sorts. Content of sucrose depends from invertase activity in honey. Invertase is good parameter for honey characterization. Specific angle of rotation of polarized light is not available for identification of honey sorts.