Nutritional assessment of plant-based beverages in comparison to bovine milk.

Plant-based beverages (PBB) are often marketed and used by consumers as alternatives to ruminant milks, particularly bovine milk (hereafter referred to as milk). However, much research has established that there is variation in nutritional composition among these products, as well as demonstrating that they are largely not nutritional replacements for milk. A survey of the prices and nutrition labels of PBB available in New Zealand supermarkets was undertaken. Selected almond, coconut, oat, rice, and soy PBB products were then analyzed for nutritional content, including energy, fat, protein, amino acid, bioavailable amino acid, and trace element contents. Finally, the protein and calcium contents of well-mixed and unshaken products were analyzed to ascertain the impact of colloidal stability on nutrient content. All PBB groups were more expensive than milk on average, while their declared nutrient contents on package labels was highly variable within and between groups. Analyses of selected PBB revealed that soy products had the most similar proximate composition to milk, while all other PBB groups contained less than 1.1 g protein per 100 mL on average. Many PBB were fortified with calcium to a similar concentration as that in milk. Shaken and unshaken samples showed divergent protein and calcium content for several PBB products but had no effect on the composition of milk, indicating that the nutrient content of PBB at the point of consumption will be dependent on whether the product has been shaken. Only the soy PBB had comparable amino acid content and bioavailability to milk. Overall, our results demonstrate the diversity in composition and nutritional properties of PBB available in New Zealand. While the existent environmental footprint data on PBB shows that they generally have lower carbon emissions than milk, milk currently accounts for approximately 1% of the average New Zealand resident's consumption-based emissions. Except for calcium-fortified soy PBB, none of the commercially available PBB had nutritional compositions that were broadly comparable to milk.

Structural changes in milk from different species during gastric digestion in piglets.

This study investigated the structural and physicochemical changes that occur in milk, a naturally designed complex structured emulsion, during gastric digestion using the bottle-fed piglet as an animal model. The gastric digestions of cow, goat, and sheep milk were compared in male piglets euthanized at different postfeeding times to collect the stomach chyme. The cow and noncow milks separated into curd (aggregated caseins) and liquid (mostly soluble whey) phases in the piglet's stomach. For milk from all the species, the curd remained longer in the stomach because of its slow disintegration, whereas the liquid phase emptied readily. The majority of the fat globules were found to be entrapped within the protein network of the curd. The rate of release of fat globules was strongly dependent on the breakdown of the surrounding protein network of the curd. The consistency of the gastric curds changed as digestion progressed, with goat and sheep milk curds having relatively softer curd consistency and less fused protein networks, especially toward the end of digestion. This might have led to the lower protein and fat retention in the goat and sheep milk curds and relatively faster gastric emptying of these nutrients from goat and sheep milk in comparison to cow milk. This in vivo study provided new and enhanced understanding of the mechanisms of the gastric digestion of milk from different species. It may have implications for developing bioinspired structures for the controlled digestion and delivery of nutrients.

Structural and interfacial characteristics of oil bodies in coconuts (Cocos nucifera L.).

This study investigated the structural characteristics of oil bodies from mature coconut (Cocos nucifera L.) fruit. The ultrastructure and the distribution of oil bodies in coconut endosperm were investigated using cryo-scanning electron microscopy. The interfacial characteristics of the oil bodies in suspensions isolated using two different protocols were studied using confocal laser scanning microscopy (CLSM), and the oleosins stabilizing the oil bodies were characterized using sodium dodecyl sulfate polyacrylamide electrophoresis. The oil bodies were found to be preferentially accumulated in endosperm tissues away from the inner endosperm and had a polydisperse size distribution, both intracellularly and in suspensions. The CLSM of oil bodies revealed uniform distribution of proteins and phospholipids at the interface along with glycolipids. Six different proteins were found to be associated with oil bodies some of which were disulfide-linked. This work provides new insights into the structure of coconut oil bodies and mechanisms for their stabilization.

Glycation as a Tool To Probe the Mechanism of ß-Lactoglobulin Nanofibril Self-Assembly.

In this study we investigated the effects of different levels of glucosylation and lactosylation on ß-Lg self-assembly into nanofibrils at 80 °C and pH 2. Fibrils in heated samples were detected with the thioflavin T assay and transmission electron microscopy, while SDS-PAGE was used to investigate the composition of the heated solutions and fibrils. Glycation had different effects in the nucleation and growth phases. The effect of glycation on the nucleation phase depended on the degree of glycation but not the sugar type, whereas both the type of sugar and the degree of glycation affected the rate of fibril growth. Glycation by either sugar strongly inhibited self-assembly in the growth phase, and lactosylation produced a much stronger effect than glucosylation. We suggest that the varying glycation susceptibility of different lysine residues can explain these observations. The large, polar sugar residues on the glycated fibrillogenic peptides may inhibit fibril assembly by imposing steric restrictions and disrupting hydrophobic interactions.

Modulating ß-lactoglobulin nanofibril self-assembly at pH 2 using glycerol and sorbitol.

ß-Lactoglobulin (ß-lg) forms fibrils when heated at 80 °C, pH 2, and low ionic strength (<0.015 mM). When formed at protein concentrations <3%, these fibrils are made up of peptides produced from the acid hydrolysis of the ß-lg monomer. The present study investigated the effects of the polyhydroxy alcohols (polyols) glycerol and sorbitol (0-50% w/v) on ß-lg self-assembly at pH 2. Glycerol and sorbitol stabilize native protein structure and modulate protein functionality by preferential exclusion. In our study, both polyols decreased the rate of ß-lg self-assembly but had no effect on the morphology of fibrils. The mechanism of these effects was studied using circular dichroism spectroscopy and SDS-PAGE. Sorbitol inhibited self-assembly by stabilizing ß-lg against unfolding and hydrolysis, resulting in fewer fibrillogenic species, whereas glycerol inhibited nucleation without inhibiting hydrolysis. Both polyols increased the viscosity of the solutions, but viscosity appeared to have little effect on fibril assembly, and we believe that self-assembly was not diffusion-limited under these conditions. This is in agreement with previous reports for other proteins assembling under different conditions. The phenomenon of peptide self-assembly can be decoupled from protein hydrolysis using glycerol.

Β-lactoglobulin self-assembly: structural changes in early stages and disulfide bonding in fibrils.

Bovine ß-lactoglobulin (ß-Lg) self-assembles into long amyloid-like fibrils when heated at 80 °C, pH 2, and low ionic strength (<0.015 mM). Heating ß-Lg under fibril-forming conditions shows a lag phase before fibrils start forming. We have investigated the structural characteristics of ß-Lg during the lag phase and the composition of ß-Lg fibrils after their separation using ultracentrifugation. During the lag phase, the circular dichroism spectra of heated ß-Lg showed rapid unfolding, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of samples showed increasing hydrolysis of ß-Lg. The SDS-PAGE profiles of fibrils separated by ultra centrifugation showed that after six hours, the fibrils consisted of a few preferentially accumulated peptides. Two-dimensional SDS-PAGE under reducing and nonreducing conditions showed the presence of disulfide-bonded fragments in the fibrils. The sequences in these peptide bands were characterized by in-gel digestion electrospray ionization (ESI)-MS/MS. The composition of solubilized fibrils was also characterized by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS/MS. Both MS analyses showed that peptides in fibrils were primarily from the N-terminal region, although there was some evidence of peptides from the C-terminal part of the molecule present in the higher molecular weight gel bands. We suggest that although the N-terminal region of ß-Lg is almost certainly involved in the formation of the fibrils, other peptide fragments linked through disulfide bonds may also be present in the fibrils during self-assembly.