Analisys of the microbiological and antioxidant properties of dried fruit and leaf extracts of blueberry (Vaccinium corymbosum)

Abstract

Vaccinium corymbosum is a rapidly growing production in Portugal, so the study of its potential applications may support its valorization and, possibly, provide alternatives to diversify the markets to commercialize this plant. Additionally, teas and other types of infusions are one of the most common beverages in the world, thus the use of V. corymbosum to produce these products is should be systematically explored. As such, this work is aimed at the study of the properties of infused and boiled extracts from V. corymbosum dry fruits and leaves, specifically characterizing antioxidant capacities, phenolic compounds (content and profile) and overall effect upon several lactic acid bacteria and potentially contaminant/pathogenic microorganisms, namely through the determination of the antimicrobial and antibiofilm activities and its impact upon some extracellular enzymes. During our work we found that leaf extracts had a considerably higher content of both phenolic compounds (ranging from 2.5 to 6.0 and 3.5 to 6.8 times higher for infused and boiled extracts) and antioxidant activity (ranging from 1.9 to 15.1 and 11.3 to 16.0 times higher for infused and boiled extracts) than fruit extracts. However, when considering the specific case of total anthocyanins, we found that fruit extracts were, clearly, richer than leaf extracts. The identification of the specific compounds present in the leaf extracts showed that the main compound found was chlorogenic acid (122.17 ± 0.12 and 122.19 ± 0.30 μg/mL for infused and boiled extracts) representing ca. 62% of the total peak area, although quercetin-3-D-galactoside (51.41 ± 0.43 and 28.38 ± 1.07 μg/mL for infused and boiled extracts), cynidin-3-D-galactoside (2.06 ± 0.07 and 1.01 ± 0.02 μg/mL for infused and boiled extracts), p-coumaric (7.01 ± 0.10 and 10.28 ± 0.00 μg/mL for infused and boiled extracts) and caffeic acids were also found. Compound identification in fruits was limited with chlorogenic acid being the most common compound identified (43.26 ± 0.50 and 52.38 ± 4.18 μg/mL for infused and boiled extracts), though some anthocyanins namely, delphinidin-3-O-galactoside (1.73 ± 0.03 e 1.39 ± 0.01 μg/mL for infused and boiled extracts), mavidin-3-O-galactoside (1.61 ± 0.04 e 1.31 ± 0.01 μg/mL for infused and boiled extracts) and, in infusions, peonidin-3-O-glicoside (0.61 ± 0.02 μg/mL), were also identified. Additionally, we found that blueberry fruit extracts had no relevant activity upon the prevention or promotion of the oxidation of the DNA molecule. The leaf extracts showed slight pro-oxidant activity but the results require further analysis to be conclusive. Concerning the antimicrobial activity we found that, the tested extracts were only capable of inhibiting the growth of P. aeruginosa (only fruit extracts), B. cereus, L. innocua, S. enteritidis, E. faecium, MRSA and MSSA, with leaf extracts exhibiting a stronger activity than fruit, except for P. aeruginosa. From the analysis of the minimum inhibitory and bactericidal concentration (MIC and MBC) values we found that MRSA, MSSA and L. innocua were more sensitive to leaf extracts (MIC of 12.5 mg/mL and MBC of 25 mg/mL) than the other microorganisms tested (MIC of 25 mg/mL and no detected MBC). Among all the bacteria tested only MRSA, MSSA and P. aeruginosa were biofilm producers and only MRSA and MSSA biofilm production was inhibited by the extracts. When considering the enzyme activity assays we observed that extracts interfered with the activity of all enzymes tested, except lipase.

Date of Award	Sept 2012
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Maria Manuela Pintado (Supervisor)