1. Introduction
gastrointestinal tract, upper gastrointestinal tract
Almonds are rich in unsaturated lipids, which play a role in some of the reported benefits of almond consumption for human health. Almond lipids are poorly bioaccessible due to almonds’ unique physicochemical properties that influence particle size distribution (PSD) following mastication, allowing much intracellular lipid to escape digestion in the upper gastrointestinal tract. To investigate the impact of commercial processing (grinding almonds into flour), on PSD and predicted lipid bioaccessibility following mastication, a randomised cross-over design mastication study was conducted in healthy adults. The PSDs of masticated whole and ground almonds was assessed using two laboratory methods (mechanical sieving and laser diffraction). PSD from mechanical sieving was used to calculate lipid bioaccessibility using a theoretical mathematical model. Thirty-one healthy adults (18–45 years) completed both mastication sessions. Following mastication, ground almonds had a PSD with significantly fewer larger particles and more smaller particles, compared with whole almonds. Predicted lipid bioaccessibility of masticated ground almonds (10.4%, SD 1.8) was marginally but significantly greater than the predicted lipid bioaccessibility of masticated whole almonds (9.3%, SD 2.0; Nuts are rich in fibre, polyphenols and unsaturated lipids [The term “bioaccessibility” refers to the proportion of a nutrient released from a complex food matrix that is therefore potentially available for absorption in the gastrointestinal tract [The impact of mastication and processing on particle size distribution (PSD) and lipid bioaccessibility has been demonstrated in experiments in which almonds were subjected to simulated mastication whereby almonds were first minced, to simulate the mechanical breakdown of food, and then mixed with salivary enzymes [The impact of commercial processing on almond lipid bioaccessibility has important implications for human health. A systematic review and meta-analysis including trials investigating the impact of nuts on gut microbiota and gut health related outcomes revealed almond specific effects on gut microbiota composition at the genus level, and α-diversity [A recent randomised controlled trial (RCT) [The PSD and nutrient bioaccessibility of almonds have not been extensively explored and the impact of commercial grinding of almonds on PSD and lipid bioaccessibility is unknown. The majority of studies reporting health benefits of almonds have tested the effects of whole almonds, and attributed benefits to nutrient content of almonds. Thus, the investigation of nutrient bioaccessibility following processing may have important implications for human health. We therefore performed a randomised mastication study with the aim to: (a) measure and compare the PSDs of masticated whole and ground almonds, using two different techniques; and (b) compare the predicted lipid bioaccessibility of masticated whole and ground almonds.