Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia

Abstract

Background: The particle size and structure of masticated almonds have a significant impact on nutrient release (bioaccessibility) and digestion kinetics.Objectives: The goals of this study were to quantify the effects of mastication on the bioaccessibility of intracellular lipid of almond tissue and examine microstructural characteristics of masticated almonds.Design: In a randomized, subject-blind, crossover trial, 17 healthy subjects chewed natural almonds (NAs) or roasted almonds (RAs) in 4 separate mastication sessions. Particle size distributions (PSDs) of the expectorated boluses were measured by using mechanical sieving and laser diffraction (primary outcome). The microstructure of masticated almonds, including the structural integrity of the cell walls (i.e., dietary fiber), was examined with microscopy. Lipid bioaccessibility was predicted by using a theoretical model, based on almond particle size and cell dimensions, and then compared with empirically derived release data.Results: Intersubject variations (n = 15; 2 subjects withdrew) in PSDs of both NA and RA samples were small (e.g., laser diffraction; CV: 12% and 9%, respectively). Significant differences in PSDs were found between these 2 almond forms (P < 0.05). A small proportion of lipid was released from ruptured cells on fractured surfaces of masticated particles, as predicted by using the mathematical model (8.5% and 11.3% for NAs and RAs, respectively). This low percentage of lipid bioaccessibility is attributable to the high proportion (35–40%) of large particles (>500 μm) in masticated almonds. Microstructural examination of the almonds indicated that most intracellular lipid remained undisturbed in intact cells after mastication. No adverse events were recorded.Conclusions: Following mastication, most of the almond cells remained intact with lipid encapsulated by cell walls. Thus, most of the lipid in masticated almonds is not immediately bioaccessible and remains unavailable for early stages of digestion. The lipid encapsulation mechanism provides a convincing explanation for why almonds have a low metabolizable energy content and an attenuated impact on postprandial lipemia. This trial was registered at isrctn.org as ISRCTN58438021.

Perceptions and Knowledge of Nuts amongst Health Professionals in New Zealand

“…In addition, a meta-analysis of clinical trials reported that nut consumption was associated with non-significant decreases in body weight (0.47 kg), BMI (0.40 kg/m 2 ), and waist circumference (1.25 cm) [34]. The lack of weight change with regular nut consumption may be explained by dietary compensation, inefficient energy absorption, and an increase in metabolic rate [27,28,34,59,60]. While collectively these data indicate that adding nuts to the diet does not result in weight gain, it should be noted that this research emphasises the inclusion of whole nuts into the diet, and this information should not be extrapolated to nuts in the form of snack bars and confectionery products.…”

A review of the impact of processing on nutrient bioaccessibility and digestion of almonds

“…However, the oil bodies and the endoplasmic network were largely destroyed, and the volume of extracellular pores enlarged. Roasting can therefore greatly affect the structure of almond cells, the cell walls as well as the intra‐cellular oil bodies (Pascual‐Albero et al ., ; Varela et al ., ; Mandalari et al ., ; Grundy et al ., ,b). In these studies, roasted almond oil bodies appeared to coalesce to form larger oil droplets than the ones observed in raw almond cells.…”

“…The roasted almonds used in our recent studies (Grassby et al ., ; Mandalari et al ., ; Grundy et al ., ,b, ) were provided by the Almond Board of California and were roasted using a two‐step standard procedure of hot air roasting with typical temperatures ranging from ~130 to 154 °C (Almond Board of California, ). The first step employed an intermediate temperature to stabilise the nut microstructure, and the second step was performed at a higher temperature in order to generate the distinctive roasted flavour and brown colour of the cotyledon.…”

“…Obtaining information about the changes occurring to the structure of the almond tissue as the digestion process progresses and the mechanisms of lipid release is of crucial importance (Ellis et al ., ; Mandalari et al ., ; Grundy et al ., ,b). For instance, the size and microstructure of the particles following oral processing have a significant effect on nutrient bioaccessibility (release), digestion kinetics and other physiological processes in the GI tract (Grundy et al ., ). The purpose of this review is to present the most common processing techniques applied to almond kernels, and how they affect almond structure and their subsequent impact on the digestion of lipid and other nutrients.…”

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“…There have been several reported reasons for this less-than-predicted weight gain observed with the inclusion of nuts into the regular diet. These include an increase in satiety due to the protein and fibre content of nuts; an increase in energy expenditure due to the high unsaturated fat content; and loss of energy in the faeces as a result of the indigestibility of the cell wall and/or incomplete mastication [47][48][49][50].…”