4. Discussion
weight loss
SEPARATION
This mastication study was conducted to test the hypotheses that mastication of commercially ground almonds would result in a PSD with smaller particles in comparison to whole almonds, and that this would influence subsequent predicted lipid bioaccessibility. Our results support the above hypotheses; there were differences in PSDs in which masticated ground almonds had significantly more particles <150 µm, and masticated whole almonds had significantly more particles >1000 µm. This resulted in a modest, but significantly greater predicted lipid release from masticated ground almonds, in comparison to masticated whole almonds.We confirm the results of previous studies demonstrating that following mastication whole almonds have a wide PSD, including many larger particles that prevent complete lipid release during digestion, with one study reporting masticated whole almonds containing 35–40% of particles >500 µm [There were significant differences in the number of mastication cycles required for whole and ground almonds. This variability is supported by previous suggestions that masticatory performance is determined by the requirement that a food bolus reaches a precisely determined texture before it can be swallowed [It is important to note the significant inter-individual variability in PSDs following mastication as indicated by large CVs (ranging from 0–100% for laser diffraction and 27–154% for mechanical sieving; Interestingly, the PSD profile of masticated ground almonds appeared to be bimodal when assessed using both measurement methods, with a peak in the proportion of particles recovered on the 45 µm sieve and the corresponding level of particle size for laser diffraction, and another larger peak in proportion of particles recovered on the 500 µm sieve or around the 1000 µm level for laser diffraction. This was not the case for whole almonds, which had a peak in proportion of particles recovered on the 1000 µm sieve only. This potentially indicates an uneven distribution of particle sizes following the grinding process, whereby certain particle sizes are over-represented following grinding and mastication has no further effect at these sizes. This theory is supported by research reporting that the granularity of a food during mastication must reach a predetermined state before swallowing is initiated, and that this is achieved by a highly individualised chewing strategy [This was the first study to analyse the lipid bioaccessibility from masticated commercially ground almonds. Predicted lipid bioaccessibility from masticated whole almonds was 9.3%, which agreed with previous analyses of lipid release from masticated whole almonds measured by Soxhlet extraction (7.8–11.1%) and predicted using the theoretical model (9.6%) [Bioaccessibility is only one factor that has an impact on the almond lipids available for absorption. Factors such as total fatty acid content of different almond harvests and method of storage will also influence the almond lipids available for absorption and their subsequent impact on human health [The results of the current study are not representative of the impact of later stages of digestion on lipid release from almond cells. The impact of enzymatic digestive processes in the stomach and duodenum on lipid release from almond cells would be technically difficult to measure in humans, and would require consumption of almonds in isolation over a prolonged period, a method that would have considerable practical and ethical implications [In the current study, PSD data from analysis of masticated almonds by mechanical sieving was used to predict lipid bioaccessibility using a theoretical model [We have demonstrated that both whole and ground almonds have PSDs that prevent complete lipid release during the first stage of digestion (mastication), and that this would likely result in lower metabolizable energy than predicted by Atwater factors when consuming these forms of almond. This has important implications for human health. In groups that could benefit from increased energy consumption, for example for recovery following injury, or in the elderly, it might be recommended that consuming almonds in a processed form (ground almonds, almond butter) is beneficial. Conversely, our findings support the evidence that despite their high lipid content and energy density, whole almonds can be added to the diets of those attempting weight loss without impacting this outcome [To our knowledge this is the first trial to investigate the impact of commercial grinding on the PSD and predicted lipid bioaccessibility of almonds. Limitations of the trial include storage of almonds prior to particle size analysis, which may result in further breakdown of almond particles due to the action of salivary enzymes, together with the mechanical forces of freezing. To limit these effects, masticated almond samples were snap frozen on dry ice prior to storage at −80 °C. At such temperatures, salivary enzymes are no longer active.It was not possible to calculate the total % recovery of the original weight of almonds that were masticated due to (1) separation of the masticated almond samples into aliquots for analysis; and (2) the contrasting outcome data of the methods (sieving—% weight; laser diffraction—% volume). Mastication sessions and sample collection were conducted based on previously published research, that reported 85.4% (SD 1.5%) recovery following mastication of whole natural almonds [