Characterising poplar and New Zealand native plant resins and New Zealand propolis using volatile organic compounds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
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2022
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Massey University
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Abstract
Recent trends show a growing understanding and acceptance of natural remedies in health care. One such remedy is propolis, a substance produced by honeybees and sold commercially. The natural mixture of beeswax and resin sourced from nearby trees has a role in maintaining the health of the colony. Several health benefits, including antimicrobial, anticarcinogenic and antiviral properties have been demonstrated internationally. These properties are not limited to bees, and their role in human health has been, and continues to be, investigated. One of the challenges of dealing with a natural product involves natural variation. In the case of propolis, the most notable cause of variation is the botanical source of resin. Countries with differing flora produce different types of propolis. At a finer scale, propolis variation has also been identified within some countries, again often correlating with variation in available or preferred botanical sources. Diversity in the sources of resin collected during propolis production can lead to diversity in the chemical configuration of the final product. Such variation in the chemical make-up of propolis has also been demonstrated to correlate with variation in antimicrobial activity. Before propolis can be used as a health supplement for humans or bees, an understanding of the botanical sources used, and the chemical properties of the resulting propolis is required. The resin produced by plants is a tacky, water insoluble substance with a range of functions. The complex chemistry of plant resins can be species specific but can also vary greatly both within and between families. One way to identify the compounds present in the resin is to investigate its volatile organic compounds (VOCs). VOCs are emitted by all plants and plant-products and mediate biotic and abiotic interactions, having biological activity against pests and diseases. Propolis, a glue-like substance produced by honeybees, is composed of beeswax mixed with plant resins. Propolis has biological activity that benefits both bees and humans. This biological activity has been shown to vary depending on the geographical and therefore botanical origin of propolis. While research has been moving toward a geographical based approach, this is yet to be done comprehensively in New Zealand. This study aimed to investigate 1) the chemistry of the VOCs of poplar hybrids commonly planted in New Zealand, and that of species native to New Zealand, and 2) the VOCs of New Zealand propolis collected from nine different regions. The volatile profiles of the resin of six poplar hybrids and 17 native species collected in autumn and/or spring were analysed using gas chromatography-mass spectrometry (GC-MS). A total of 111 compounds were tentatively identified. Principal component analysis (PCA) showed divergence between the volatile profiles of the poplar resin and the native resin, and the season during which samples were collected. PCA also indicated some variance amongst the poplar hybrids, and between clones of the same hybrid. Cluster dendrograms were used to visualise the divergence between groups and showed that the resin of some poplar clones was more similar to native species than to other clones of the same hybrid. This analysis provides a better understanding of the chemical profiles of the resin of several common plant species in New Zealand, and how they relate to each other. 74 propolis samples were collected from nine different regions across New Zealand, and 91 compounds were tentatively identified. Principal component analysis revealed that the region from which samples were collected was not sufficient to explain the variation amongst the volatile profiles, although some regions were separated and clustered together. A cluster dendrogram highlighted the variation between the propolis samples, and the seemingly random relation between different samples. Additionally, initial suggestions were made regarding the potential contributions of resin from both poplar and native botanical sources. This analysis furthers our knowledge of the chemical profile of New Zealand propolis, its sources of variation, and the potentially contributing botanical sources.