Search

Plants store triacylglycerols in the form of oil bodies (OBs) as an energy source for germination and subsequent seedling growth. The interfacial biomaterials from these OBs are called OB membrane materials (OBMMs) and have several applications in foods, e.g., as emulsifiers. OBMMs are preferred, compared with their synthetic counterparts, in food applications as emulsifiers because they are natural, i.e., suitable for clean label, and may stabilize bioactive components during storage. This review focuses mainly on the extraction technologies for plant OBMMs, the functionality of these materials, and the interaction of OB membranes with other food components. Different sources of OBs are evaluated and the challenges during the extraction and use of these OBMMs for food applications are addressed.

Milk is commonly exposed to processing including homogenization and thermal treatment before consumption, and this processing could have an impact on its digestion behavior in the stomach. In this study, we investigated the in vitro gastric digestion behavior of differently processed sheep milks. The samples were raw, pasteurized (75 °C/15 s), homogenized (200/20 bar at 65 °C)–pasteurized, and homogenized–heated (95 °C/5 min) milks. The digestion was performed using a dynamic in vitro gastric digestion system, the human gastric simulator with simulated gastric fluid without gastric lipase. The pH, structure, and composition of the milks in the stomach and the emptied digesta, and the rate of protein hydrolysis were examined. Curds formed from homogenized and heated milk had much looser and more fragmented structures than those formed from unhomogenized milk, this accelerated the curd breakdown, protein digestion and promoted the release of protein, fat, and calcium from the curds into the digesta. Coalescence and flocculation of fat globules were observed during gastric digestion, and most of the fat globules were incorporated into the emptied protein/peptide particles in the homogenized milks. The study provides a better understanding of the gastric emptying and digestion of processed sheep milk under in vitro gastric conditions.

The natural structure of whole food plays an important role in the physiological impact of bioactive compounds present within the food, also known as the "matrix effect". Long-chain omega-3 polyunsaturated fatty acids (LCn-3PUFAs) are one example of a food-derived nutrient, mostly found in fish, that is believed to be influenced by the food matrix. However, most previous studies have compared only the long-term bioavailability of fish versus fish oil and have used commercial sources of fish oil. The present study aimed to investigate whether fish (salmon) matrix influences the transit of LCn-3PUFAs during in vitro digestion and affects bioavailability in healthy females. Meals containing intact salmon (intact structure), minced salmon (some structure) and defatted salmon + oil (no structure) with identical macronutrient compositions were developed. Healthy female participants (n = 13) consumed the meals in a postprandial crossover study and blood was collected at regular time points for 6 h post meal consumption. In parallel, in vitro digestion of the meals was performed using a human gastric simulator (HGS) and digesta samples were collected at regular time points for 6 h. Results: showed that plasma concentration of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were significantly higher after participants consumed intact salmon compared to the other meals (covariate analysis p < 0.001). The in vitro digestion results showed defatted salmon + oil meal had a faster decrease in pH and faster fat emptying from the HGS than the other two meals. The defatted salmon + oil meal more closely followed fat emptying of a homogeneous unstructured meal, whereas the other meals exhibited phase separation with a delay in fat emptying. Conclusion: The fish matrix (salmon) plays an important role in the bioaccessibility and bioavailability of EPA and DHA. The differences are partly explained by fat digestion and emptying from the stomach. This study suggests that the natural structure of fish has a functional effect on the absorption and bioavailability of fish oil.

Substitution of commercial milk powders by fluid milk concentrates as ingredients in dairy products, may improve product quality and increase sustainability. This study compared the functional properties of skim milk concentrates made by reverse osmosis (SMC) with standard reconstituted high- and low-heat skim milk powders (POW-SMC). SMC had larger Z-average size values, higher viscosities, wider particle size distributions and lower extent of whey protein denaturation than POW-SMC. During storage, SMC showed no acid-induced gelation, but improved rennet-induced gelation compared with POW-SMC. Emulsification activity improved at 20 compared with 10% solids in all concentrates, while emulsion stability was lowest for SMC. Better foaming was observed for high-heat POW-SMC, except after 30 days, where SMC showed highest overrun. In certain dairy products, SMC can thus replace commercial powders to reduce processing costs and improve functionality. SMC showed to be especially advantageous for rennet-gelled products.

In recent years, plant-based milk alternatives have become increasingly desirable because of their sustainability and proposed health benefits. There is a need to understand the behavior of plant-based milks during gastric digestion, including protein digestibility, structural changes, and macronutrient accessibility. The aim of this study was to investigate the gastric digestive behaviors of oat milk and an oat milk‒bovine skim milk blend (1:1, v/v), using an in vitro dynamic human gastric simulator. During gastric digestion with pepsin, the oat milk did not show significant changes in structure and physical stability. In contrast, the oat milk‒bovine skim milk blend formed coagulated, curd-like particles, which were induced by the action of pepsin on the milk proteins. The oat oil bodies were incorporated into the curd particles. This difference in gastric digestive behavior significantly altered the rate of gastric emptying. Coagulation of the oat milk‒bovine skim milk blend slowed the gastric emptying of macronutrients, leading to a delay in the release of protein and lipids into the small intestine compared with the oat milk. This study provides insight into the way the food structure modification during gastric digestion impacts nutrient delivery.

Soymilk (about 3% protein and 1.8% lipids), prepared by wet disintegration of soaked soybeans, was heated at 108 °C for 15 min and then subjected to in vitro gastric digestion using an advanced dynamic digestion model (i.e. a human gastric simulator). Microstructural changes, physicochemical stability and protein digestibility were studied; the release of protein and lipid during digestion was also quantified. Gastric digestion significantly influenced the colloidal stability of soymilk, resulting in coagulation of the soy proteins because of the action of pepsin and the acidic pH. The soymilk oil bodies appeared to be entrapped within the coagulated protein particles. With continued digestion, protein hydrolysis by pepsin resulted in the disruption of the coagulum structure, leading to an accelerated gastric emptying of both protein and lipid in the first 45 min. Gastric-induced coagulation did not have a significant impact on either protein or lipid emptying, except for an initial delay of lipid emptying in the first 15 min. No extensive coalescence of soymilk oil bodies was observed under a confocal microscope. This study provides further understanding of the fate of soymilk in the digestive tract and may be useful in the microstructural design of foods to achieve a controlled physiological response during digestion.

Bovine β-casein behaves as a chaperone at neutral pH, i.e., it inhibits aggregation of unfolded proteins, but chaperone effects have not been investigated at acidic pH. We examined chaperone effects during heating at pH 2 and 80 °C for mixtures of 1% (w/v) β-lactoglobulin (β-Lg) and β-Lg:β-casein molar ratios of 1:0.0625 to 1:1. These conditions hydrolyse β-Lg into peptides that self-assemble into amyloid-like nanofibrils. Hydrolysis rates in mixed solutions were unchanged from single-protein controls, according to sodium dodecyl sulphate polyacrylamide gel electrophoresis. At ratios ≥1:0.125, β-casein slowed fibril growth in a concentration-independent way, according to Thioflavin T fluorescence. We observed twisted irregular fibrils coexisting with long semiflexible fibrils when β-casein was heated with β-Lg, using transmission electron microscopy. We hypothesise that β-casein monomers and peptides can interact with growing β-Lg nanofibrils or assemble into micelles, with the latter pathway predominating at high β-casein concentrations.

A new iron&ndash, casein complex (ICC) has been developed for iron (Fe) fortification of dairy matrices. The objective was to assess the impact of ascorbic acid (AA) on its in vitro bioavailability in comparison with ferrous sulfate (FeSO4) and ferric pyrophosphate (FePP). A simulated digestion coupled with the Caco-2 cell culture model was used in parallel with solubility and dissociation tests. Under diluted acidic conditions, the ICC was as soluble as FeSO4, but only part of the iron was found to dissociate from the caseins, indicating that the ICC was an iron chelate. The Caco-2 cell results in milk showed that the addition of AA (2:1 molar ratio) enhanced iron uptake from the ICCs and FeSO4 to a similar level (p = 0.582, p = 0.852) and to a significantly higher level than that from FePP (p &lt, 0.01). This translated into a relative in vitro bioavailability to FeSO4 of 36% for FePP and 114 and 104% for the two ICCs. Similar results were obtained from water. Increasing the AA to iron molar ratio (4:1 molar ratio) had no additional effect on the ICCs and FePP. However, ICC absorption remained similar to that from FeSO4 (p = 0.666, p = 0.113), and was still significantly higher than that from FePP (p &lt, 0.003). Therefore, even though iron from ICC does not fully dissociate under gastric digestion, iron uptake suggested that ICCs are absorbed to a similar amount as FeSO4 in the presence of AA and thus provide an excellent source of iron.

This study investigated the self-assembly of purified β-lactoglobulin (β-Lg) genetic variants A, B and C into amyloid-like fibrils. β-Lg solutions (1%, w/v) were heated at 80 °C and pH 2 and were analysed for the presence of fibrils using the thioflavin T assay. Reducing sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) was used to follow heat-induced acid hydrolysis of β-Lg monomers. Fibrils separated from heated solutions were characterised by SDS-PAGE and transmission electron microscopy. The substitution of amino acid residues in β-Lg variants A, B and C did not significantly affect the kinetics of acid hydrolysis, self-assembly kinetics, or the morphology of the fibrils. The fibrils from β-Lg A, B and C were, however, slightly different in peptide compositions. These differences may be explained on the basis of amino acid substitutions, in particular the Asp64 of β-Lg A that is Gly in variants B and C.

Bovine β-lactoglobulin (β-Lg) self-assembles into long amyloid-like fibrils when heated at 80 °C, pH 2, and low ionic strength (0.015 mM). Heating β-Lg under fibril-forming conditions shows a lag phase before fibrils start forming. We have investigated the structural characteristics of β-Lg during the lag phase and the composition of β-Lg fibrils after their separation using ultracentrifugation. During the lag phase, the circular dichroism spectra of heated β-Lg showed rapid unfolding, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of samples showed increasing hydrolysis of β-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 β-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.

In this study we investigated the effects of different levels of glucosylation and lactosylation on β-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.

β-Lactoglobulin (β-lg) forms fibrils when heated at 80 °C, pH 2, and low ionic strength (0.015 mM). When formed at protein concentrations3%, these fibrils are made up of peptides produced from the acid hydrolysis of the β-lg monomer. The present study investigated the effects of the polyhydroxy alcohols (polyols) glycerol and sorbitol (0-50% w/v) on β-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 β-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 β-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.