Changes of physicochemical properties and predominant microbiota during storage of birch sap
2018
Nikolajeva, V. | Zommere, Z.
Birch sap derived from silver birch Betula pendula is the most common spring sap. It is usually used as a fresh drink during the first days or as beverage during summer. It is important for it to be safe. The aim of this study was to identify predominant culturable microorganisms and changes in the composition of microbiota as well as some physicochemical parameters during storage. Fresh frozen sap gathered in Latvia was investigated. Defrosted sap underwent physicochemical and microbiological changes during two months’ storage at temperatures of 4o C and 20° C. The pH value decreased from 5.52 to 3.41. Electrical conductivity was 0.453 mS cm-1 and protein content was 12.19 mg l-1 in the beginning and increased during storage. Total counts of colony-forming units (CFU) of aerobic bacteria ranged from log 3.5 in the fresh defrosted sap to log 11.3 after 38 days of storage at 4° C. The number of CFU of microorganisms showed a rapid increase during the first week of storage without a significant difference regardless of the temperature. Afterwards, the number of microorganisms tended to decrease at 20°C. The highest counts were detected after storage of the sap at 4°C. Predominant culturable bacteria belonged to the Alpha-, Beta-, and Gamma-Proteobacteria, to the Actinobacteria, Flavobacteria and Sphingobacteria. Indicators of faecal pollution were not found. Three species of yeasts and 14 species of bacteria were identified. Attention must be paid to the presence and growth of pathogenic bacteria and facultative pathogens.
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