Insight into the Influence of Grinding on the Extraction Efficiency of Selected Bioactive Compounds from Various Plant Leaves

The impact of particle size on bioactive compounds recovery was investigated for two valuable plant matters. This project was to assess the effect of grinding on bioactives extraction of New Zealand Manuka leaves of the Leptospermum scoparium and Stevia rebaudiana plants. Non-grounded and grounded Manuka with particle sizes ranging from 68 μm to 1400 μm were processed using n-hexane extraction for 0–60 min. Moreover, the extraction of two sweeteners from Stevia powder (d ≤ 200 µm) was carried out using hot water extraction and Ultrasound as a non-conventional method. As particle size was reduced, the extraction of bioactives increased, which is expected. However, it was observed that for the small particle size, which was obtained by sever grinding, most of the extraction was achieved as soon as the powder was exposed to the solvent (at zero time) with no further extraction at an extended period. This indicates that short-time exposure appears to be sufficient to recover most of the bioactive compounds, since most of the release of these compounds happened during grinding to fine powder, an issue that has not been addressed in the literature.