Worldwide it is of great interest to find new and safe antioxidants from natural sources. Green leafy vegetables and wild plant leaves are healthy nutrients, containing vitamins, minerals and biological active compounds, therefore these plants provide beneficial health effects due to the presence of antioxidant compounds. It is useful and popular to supplement human diets with fresh or frozen edible plants. It is known that freezing may help to preserve the quality of plants, and is superior to other preservation methods. The aim of research was to compare the phenolic compounds content of fresh and frozen edible wild plants leaves grown in Latvia. The samples were processed using freezing -20 °C and for a comparison fresh samples were analysed. The leaves of stinging nettle (Urtica dioica), common goutweed (Aegopodium podagraria), dandelion (Taraxacum officinale) and chickweed (Stellaria media) were collected in May 2016 in Latvia. In the current research the content of total phenolics was determined in four types of fresh and frozen plant leaves and they can be arranged as follows (starting from plant with less phenolics content as gallic acid equivalent): dandelion

Phenolic compounds are of a considerable interest and have received more and more attention in recent years due to their bioactive functions. These components are known as secondary plant metabolites and also possess antimicrobial, antiviral and anti-inflammatory properties. The popular Latvian herbals – Calendula (Calendula officinalis L.), Lady’s-mantle (Alchemilla vulgaris L.), Yarrow (Achillea millefolium L.), Peppermint (Mentha × piperita L.) and Bellis (Bellis perennis L.) – are widely used for herbal teas. The objective of this study was to determine individual phenolic compounds in herbal infusions using high-performance liquid chromatography. The obtained results showed significant differences (p ˂ 0.05) of the phenolics content in the analysed herbal teas. The total content of the identified 14 phenolic compounds in Yarrow tea was on the average 136.76 ± 0.8 mg 100 g–1, in Peppermint tea 304.38 ± 10.7 mg 100 g–1, in Lady’s-mantle tea 319.53 ± 12.5 mg 100 g–1, in Calendula tea 586.36 ± 17.6 mg 100 g–1, but in Bellis tea it was 802.96 ± 21.3 mg 100 g–1. The dominant phenolic compound in Peppermint, Lady’s-mantle and Yarrow teas was rutin, but chlorogenic acid in Bellis tea. Calendula tea has an abundant quantity of sinapic acid.

-The objective of the current research is to evaluate the quality changes of shredded carrots treated with 2 ppm ozonated tap water for 60 s ± 1 s. Treated carrots have been packed in several materials (hermetically sealed by breathing polymer film BOPP Propafilm TM P2GAF, cellulose based biodegradable NatureFlex NVS and Polilactid BIO-PLA Containers) and stored at the temperature of + 4 C ± 1 C for 10 days. Main quality parameters using standard methods have been analysed: total carotenoids and β-carotene, total phenolic, antioxidant capacity, soluble solids, mass loses, moisture, pH, firmness, colour, CO2 and O2 and microbiological parameters. Testing of the samples has been carried out before packaging and during storage. In the present research it has been proved that is possible to maintain the chemical composition of shredded carrots during storage by treatment of carrots with ozonated tap water; as a result, the shelflife of shredded carrots can prolong till 10 days.

The profile of amino acids and mono- and disaccharides in conventional polyfloral honey originated from Latvia and Tajikistan and less found in nature bumblebee honey from Russia was investigated. The analysis of free amino acids (FAAs) accomplished by multiple reaction monitoring (MRM) using triple quadrupole mass selective detection (HPLC-ESI-TQ-MS/MS) revealed the presence of 17 FAAs. The concentration of FAAs varied in the range of 0.02–44.41 mg 100 g−1 FW. Proline was the main representative of FAAs, contributing to the total amount of FAAs from 41.7% to 80.52%. The highest concentration of proline was found in bumblebee and buckwheat honey, corresponding to 44.41 and 41.02 mg 100 g−1, respectively. The concentration of essential amino acids (AAs), i.e., leucine, and isoleucine was found to be the highest in buckwheat honey contributing up to 12.5% to the total amount of FAAs. While, the concentration of branched-chain AAs fluctuated within the range of 1.08–31.13 mg 100 g−1 FW, with buckwheat honey having the highest content and polyfloral honey the lowest, respectively. The results of this study confirmed the abundance of FAAs both in honeybee and bumblebee honey. However, the concentration of individual FAAs, such as proline, aspartic acid, leucine, and isoleucine in bumblebee honey was many folds higher than observed in honeybee polyfloral honey.

The main purpose of the study was to determine changes of polyphenol concentrations in hybrids of Nante type carrots during storage. Fresh Nante type ‘Forto’ variety carrots and carrot hybrids ‘Bolero’ F1, ‘Champion’ F1, and ‘Maestro’ F1 were cultivated in the Zemgale region of Latvia. Carrots were stored for six months in air (+3 ± 1 °C, RH = 89 ± 1%) and polyphenol compound concentrations were determined at two month intervals. High-performance liquid chromatography was used to determine concentrations of eight polyphenols in carrots: gallic acid, catechin, epicatechin, caffeic acid, chlorogenic acid, ferulic acid, vanillin, and rutin. Significant differences occurred in polyphenol concentrations of fresh Nante type variety ‘Forto’ carrots and several hybrids (‘Bolero’ F1, ‘Champion’ F1, and ‘Maestro’ F1) during storage. After six months of storage, the concentration of polyphenol compounds of Nante type carrots decreased — caffeic acid by 64.6%, chlorogenic acid — by 37.9% and vanillin — by 81.5%. However, during storage, concentration of some polyphenol compounds increased, as catechin by 30.5%, epicatechin by 85.2%, gallic acid by 48.5% and ferulic acid by 87.9%.