Quantification of fracture properties and microstructural features of roasted Marcona almonds by image analysis

Valorization of Local Legumes and Nuts as Key Components of the Mediterranean Diet

Legumes and nuts are components of high importance in the diet of many countries, mainly those in the Mediterranean region. They are also very versatile and culturally diverse foods found all over the world, acting as a basic protein source in certain countries. Their genetic diversity is needed to sustain the food supply and security for humans and livestock, especially because of the current loss of habitats, species, and genetic diversity worldwide, but also because of the ever present need to feed the increasing human population. Even though both legumes and nuts are considered as high-protein food and environmentally friendly crops, developed countries have lower consumption rates when compared to Asia or Africa. With a view to increasing the consumption of legumes and nuts, the objective of this review is to present the advantages on the use of autochthonous varieties from different countries around the world, thus providing a boost to the local market in the area. The consumption of these varieties could be helped by their use in ready-to-eat foods (RTE), which are now on the rise thanks to today's fast-paced lifestyles and the search for more nutritious and sustainable foods. The versatility of legumes and nuts covers a wide range of possibilities through their use in plant-based dairy analogues, providing alternative-protein and maximal amounts of nutrients and bioactive compounds, potential plant-based flours for bakery and pasta, and added-value traditional RTE meals. For this reason, information about legume and nut nutrition could possibly increase its acceptance with consumers.

Energy extraction from nuts: walnuts, almonds and pistachios

The bioaccessibility of fat has implications for satiety and postprandial lipidaemia. The prevailing view holds that the integrity of plant cell wall structure is the primary determinant of energy and nutrient extraction from plant cells as they pass through the gastrointestinal (GI) tract. However, comparisons across nuts (walnuts, almonds and pistachios) with varying physical properties do not support this view. In the present study, masticated samples of three nuts from healthy adults were exposed to a static model of gastric digestion followed by simulated intestinal digestion. Primary outcomes were particle size and lipid release at each phase of digestion. Walnuts produced a significantly larger particle size post-mastication compared with almonds. Under gastric and intestinal conditions, the particle size was larger for walnuts compared with pistachios and almonds (P < 0·05). However, the masticated and digesta particle sizes were not related to the integrity of cell walls or lipid release. The total lipid release was comparable between nuts after the in vitro intestinal phase (P > 0·05). Microstructural examination showed ruptured and fissured cell walls that would allow digestion of cellular contents, and this may be governed by internal cellular properties such as oil body state. Furthermore, the cell walls of walnuts tend to rupture rather than separate and as walnut tissue passes through the GI tract, lipids tend to coalesce reducing digestion efficiency.

Potential Impact of Oat Ingredient Type on Oral Fragmentation of Biscuits and Oro-Digestibility of Starch-An In Vitro Approach

The aim of the present study was to determine how variation in the biscuit matrix affects both the degree of in vitro fragmentation and the starch hydrolysis that occurs during the oral phase of digestion. Using three different oat ingredient types (oat flour, small flakes, and big flakes) and baking powder (or none), six biscuits with different matrices were obtained. The instrumental texture (force and sound measurements) of the biscuits was analyzed. The samples were then subjected to in vitro fragmentation. The particle size distribution and in vitro oral starch hydrolysis over time of the fragmented samples were evaluated. The results showed that the samples presented different fragmentation patterns, mainly depending on the oat ingredient type, which could be related to their differences in texture. The biscuits made with oat flour were harder, had a more compact matrix and showed more irregular fragmentation and a higher percentage area of small particles than those made with big oat flakes, which were more fragile and crumbly. The highest degree of starch hydrolysis corresponded to the biscuits made with flour. Conclusions: Differences in the mechanical properties of the biscuit matrix, in this case due to differences in the oat ingredient, play a role in the in vitro fragmentation pattern of biscuits and in the oral phase of starch hydrolysis.

Impact of cell wall encapsulation of almonds on in vitro duodenal lipolysis

•

Tissue microstructure controlled rate and extent of in vitro lipolysis in almonds.

•

Lipolysis methods using pH-stat and GC analysis were in good agreement.

•

Increasing lipid bioaccessibility led to increased levels of digestibility.

•

Almond cell walls restrict lipid release, thus hindering digestion kinetics.

Although almonds have a high lipid content, their consumption is associated with reduced risk of cardiovascular disease. One explanation for this paradox could be limited bioaccessibility of almond lipids due to the cell wall matrix acting as a physical barrier to digestion in the upper gastrointestinal tract. We aimed to measure the rate and extent of lipolysis in an in vitro duodenum digestion model, using raw and roasted almond materials with potentially different degrees of bioaccessibility. The results revealed that a decrease in particle size led to an increased rate and extent of lipolysis. Particle size had a crucial impact on lipid bioaccessibility, since it is an indicator of the proportion of ruptured cells in the almond tissue. Separated almond cells with intact cell walls showed the lowest levels of digestibility. This study underlines the importance of the cell wall for modulating lipid uptake and hence the positive health benefits underlying almond consumption.

The relationship between the fracture properties and the tissue structure of roasted sesame seeds

Using seven varieties of roasted sesame seeds, we examined the relationship between the fracture properties and the internal structure of roasted seeds. Analysis of fracture properties revealed significant differences across the samples in terms of fracture force and fracture strain at the biggest fracture point, and in the number of small fractures (p<0.05). Analysis of the cross-sectional structure revealed significant differences across the samples in the size of the void at the center of the sesame seed and in the overall thickness of the seed (p<0.05). Strong negative correlations were found for the center-void-to-seed thickness ratio against fracture force and fracture strain at the biggest fracture point. Moreover, fracture properties and cross-sectional structure were strongly correlated with sensory evaluations of crispness. Hence we concluded that the presence of a void in the central area of a seed decreases the necessary fracture force, resulting in a crispy texture.

Gastric digestion of raw and roasted almonds in vivo

Almonds are an important dietary source of lipids, protein, and α-tocopherol. It has been demonstrated that the physical form of almond kernels influences their digestion and absorption, but the role of thermal processes on the digestion of almonds has received little attention. The objectives of this study were to examine the gastric emptying and nutrient composition of gastric chyme from pigs (used as a model for the adult human) fed a single meal of either raw or roasted almonds over a 12-h postprandial period (72 pigs total, 6 pigs at each diet-time combination). Concentrations of glucose, triacylglycerols, and α-tocopherol in peripheral plasma during the 12-h postprandial period were determined. For dry matter and lipid, the gastric emptying profile was not different between raw and roasted almonds. Roasting almonds also did not influence gastric pH, or plasma glucose or triacylglycerols levels. In contrast, the gastric emptying of protein was more rapid for raw almonds compared to roasted almonds (P < 0.01) and intragastric protein content exhibited segregation (P < 0.001) throughout the stomach, with raw almonds having a higher level of segregation compared to roasted almonds. Postprandial plasma α-tocopherol levels were, on average 33% greater (P < 0.001) after consumption of raw almonds, most likely as a result of the higher concentration of α-tocopherol in raw almonds compared to roasted almonds. Roasting of almonds did not influence the overall gastric emptying process, but did lead to differences in the distribution of protein in the stomach and to the gastric emptying of protein.

Physical properties and microstructural changes during soaking of individual corn and quinoa breakfast flakes

The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (that is, milk or water) prior to consumption. The maximum rupture force (RF) of 2 types of breakfast flaked products (BFP)--corn flakes (CF) and quinoa flakes (QF)--were measured directly while immersed in milk with 2% of fat content (milk 2%) or distilled water for different periods of time between 5 and 300 s. Under similar soaking conditions, QF presented higher RF values than CF. Soaked flakes were freeze-dried and their cross section and surface examined by scanning electron microscopy. Three consecutive periods (fast, gradual, and slow reduction of RF) were associated with changes in the microstructure of flakes. These changes were more pronounced in distilled water than in milk 2%, probably because the fat and other solids in milk become deposited on the flakes' surface hindering liquid infiltration. Structural and textural modifications were primarily ascribable to the plasticizing effect of water that softened the carbohydrate/protein matrix, inducing partial collapse of the porous structure and eventually disintegration of the whole piece through deep cracks.

Digestion of Raw and Roasted Almonds in Simulated Gastric Environment

Knowledge of digestion kinetics of solid foods in human stomach, as affected by food processing methods, is critical in establishing processing conditions at the manufacturing stage to achieve desirable release of nutrients in the gastrointestinal tract. The objective of this study was to investigate how roasting affected disintegration and solid release properties of almond in simulated gastric environment. In vitro trials were performed for raw and roasted almonds by using static soaking method and a model stomach system. The changes in sample weight, dry mass, and moisture during the trials were determined. Both compression and penetration tests were used to investigate the texture of almonds with a focus on the influence of absorption of gastric juice. Light microscopy and transmission electronic microscopy were used to study the change in microstructure of the raw and roasted almonds after simulated digestion. The results suggested that the slow disintegration rate and the high amount of swelling of the almonds in the stomach may contribute to their high satiety property. Roasting significantly improved the disintegration rates of almonds and increased loss of solids during simulated digestion, which is well correlated with the decrease in the rigidity of almond samples after absorbing gastric juice. Microstructure of digested almonds showed breakage and breach of cell walls due to acid hydrolysis. Intercellular and intracellular channels formed in almonds during roasting are important for penetration of gastric juice that may facilitate an effective digestion.