High-Moisture Shear Processes: Molecular Changes of Wheat Gluten and Potential Plant-Based Proteins for Its Replacement.

Nowadays, a growing offering of plant-based meat alternatives is available in the food market. Technologically, these products are produced through high-moisture shear technology. Process settings and material composition have a significant impact on the physicochemical characteristics of the final products. Throughout the process, the unfolded protein chains may be reduced, or associate in larger structures, creating rearrangement and cross-linking during the cooling stage. Generally, soy and pea proteins are the most used ingredients in plant-based meat analogues. Nevertheless, these proteins have shown poorer results with respect to the typical fibrousness and juiciness found in real meat. To address this limitation, wheat gluten is often incorporated into the formulations. This literature review highlights the key role of wheat gluten in creating products with higher anisotropy. The generation of new disulfide bonds after the addition of wheat gluten is critical to achieve the sought-after fibrous texture, whereas its incompatibility with the other protein phase present in the system is critical for the structuring process. However, allergenicity problems related to wheat gluten require alternatives, hence an evaluation of underutilized plant-based proteins has been carried out to identify those that potentially can imitate wheat gluten behavior during high-moisture shear processing.

Structure and activity of Aspergillus nidulans copper amine oxidase.

Aspergillus nidulans amine oxidase (ANAO) has the unusual ability among the family of copper and trihydroxyphenylalanine quinone-containing amine oxidases of being able to oxidize the amine side chains of lysine residues in large peptides and proteins. We show here that in common with the related enzyme from the yeast Pichia pastoris, ANAO can promote the cross-linking of tropoelastin and oxidize the lysine residues in α-casein proteins and tropoelastin. The crystal structure of ANAO, the first for a fungal enzyme in this family, has been determined to a resolution of 2.4 Å. The enzyme is a dimer with the archetypal fold of a copper-containing amine oxidase. The active site is the most open of any of those of the structurally characterized enzymes in the family and provides a ready explanation for its lysine oxidase-like activity.

Impact of water degumming and enzymatic degumming on gum mesostructure formation in crude soybean oil.

Phospholipid gum mesostructures formed in crude soybean oil after water degumming (WD) and enzymatic degumming (ED) were studied at a range of phospholipid and water concentrations. For ED, phospholipase C (PLC), phospholipase A2 (PLA2) and a mixture of phospholipases Purifine 3G (3G) were used. Both WD and ED resulted in lamellar liquid-crystalline phases, however, of different topology. The dependence of the bilayer spacings (as observed by SANS and SAXS) on the ratio between amount of water and amphiphilic lipids differed for WD and PLA2 ED vs PLC and 3G ED. This difference was also observed for dynamics at molecular scale as observed by time-domain (TD) NMR and attributed to partial incorporation of diglycerides and free fatty acids into gum bilayers after PLC and 3G ED. Feasibility of using TD-NMR relaxometry for quantification of the gum phase and estimation of degumming efficiency was demonstrated.

Microstructural investigation of monoglyceride-water coagel systems by NMR and CryoSEM.

Monoglyceride coagels consist of a network of plate-like crystals and are formed from a swollen gel state (alpha-gel). In order to resolve the transition mechanism, coagels were prepared with monoglycerides that differ in fatty acid composition (monomyristate and palmitate/stearate, respectively). Rheology provided information on kinetics of coagel formation and the strength of the resulting crystal network. From NMR measurements, the surface-to-volume ratio, tortuosity, and dimensionality of the network were obtained. These findings were in line with qualitative and quantitative structural information obtained from CryoSEM. As a model for the behaviour of non-monoglyceride species, the dynamics of (perdeuterated) palmitic acid was monitored in both alpha-gels and coagels. The experimental data support a two-stage mechanism. In the first stage, two-dimensional separation of D- and L-isomers in the monoglyceride bilayers of the alpha-gel occurs. This process depends primarily on lateral diffusion rate of the monoglycerides. Palmitic acid can be accommodated in the alpha-gel bilayer, but in the coagels it is separated into relative mobile and mechanically weak junction zones between the crystal plates. In the second stage of coagel formation, the crystal plates also grow in the third dimension. Both monoglyceride type and concentration determine the kinetics of this process.

Rheological characterization, crystallization, and gelation behavior of monoglyceride gels.

Saturated monoglycerides can form firm gels in water. These gels are networks of stiff plate-like beta-crystals of monoglycerides (a "cardhouse"), grown from a space-filling lamellar liquid-crystalline phase. The molecular mechanism of crystallization is discussed in the light of network formation. The concentration dependence of gel development of (shear-cooled) monoglyceride gels has been studied by rheology. A gelation mechanism has been proposed, consisting of two steps: (i) After formation of a nucleus, rapid crystallization in a lateral direction occurs (probably within one bilayer) by which the first space-filling network is formed. (ii) This is followed by reinforcement of the network by which stacks of crystalline bilayers are formed. The plate-like crystals are linked in connective domains or junction zones, probably containing all the material (cosurfactants, diglycerides, etc.) that does not fit in the crystalline array. Small deformation rheology shows that above about 2 wt% monoglyceride a percolating network is formed. The large deformation rheology is typical for a particle gel with a relatively small strain at failure (both in shear deformation and compression). The connective domains or junction zones already fail when relatively small deformations are put on the system.

Gastrointestinal metabolism of a vegetable-oil emulsion in healthy subjects.

BACKGROUND: Given the growing prevalence of overweight and obesity, weight-management strategies could be developed based on the effect of specific food ingredients on the gastrointestinal system to reduce food intake. OBJECTIVE: The aim of this study was to investigate the mechanisms by which a vegetable-oil emulsion may exert its effect on satiety by applying a multilumen tube to investigate digestion and absorption of lipids in the stomach and proximal jejunum. DESIGN: We gave 16 healthy, normal-weight subjects (in a double-blind, placebo-controlled crossover design) a test product (yogurt with a vegetable-oil emulsion) or an equal-calorie control by intragastric administration on 2 separate occasions. Gastric and intestinal samples were collected from the proximal jejunum during 180 min. RESULTS: We observed almost double amounts (P < 0.05) of total lipids, mainly as free fatty acids, from the test product (450 +/- 119 mg) in the proximal jejunum compared with amounts of total lipids from the control product (230 +/- 50 mg), and an over-time difference of free fatty acid concentrations was observed between the products (P < 0.05). To our knowledge, a novel and unexpected finding was the appearance of needle-shaped crystals in the jejunal samples that originated from the vegetable-oil emulsion and consisted of saturated fatty acids. Crystals were only rarely seen in the control samples. CONCLUSION: The higher amount of lipids in the proximal jejunum and the recovery of crystals in the intestinal samples after test-product infusion provide a plausible physiologic explanation for the ileal brake mechanism that leads to the increased satiety observed for this test product.