In-line rheological and microstroctural characterization of high moisture content protein vegetable mixtures in single screw extrusion

Characterisation of the Enzymatically Extracted Oat Protein Concentrate after Defatting and Its Applicability for Wet Extrusion

An oat protein concentrate (OC1) was isolated from oat flour through starch enzymatic hydrolysis, by subsequent defatting by ethanol and supercritical fluid extraction (SFE) reaching protein concentrations of 78% and 77% by weight in dry matter, respectively. The protein characterisation and functional properties of the defatted oat protein concentrates were evaluated, compared and discussed. The solubility of defatted oat protein was minor in all ranges of measured pH (3-9), and foamability reached up to 27%. Further, an oat protein concentrate defatted by ethanol (ODE1) was extruded by a single screw extruder. The obtained extrudate was evaluated by scanning electron microscope (SEM), texture and colour analysers. The extrudate's surface was well formed, smooth, and lacking a tendency to form a fibrillar structure. Textural analysis revealed a non-unform structure (fracturability 8.8-20.9 kg, hardness 26.3-44.1 kg) of the oat protein extrudate.

Properties of Texturized Vegetable Proteins from Edible Mushrooms by Using Single-Screw Extruder

This research aimed to determine the feasibility of using mushrooms as an alternative ingredient in texturized vegetable protein (TVP) production using a single-screw extruder. TVPs from King Oyster (TVP-KO) and Pheonix mushroom (TVP-PH) were successfully developed and characterized. The visual appearance of TVP was reddish-brown, with a distinct roasted mushroom-soybean aroma. When rehydrated and cooked, both TVPs provided a minced meat-like appearance and chewy meat texture comparable to commercial TVP (TVP-Com); however, they had inferior water and oil holding and rehydration capacities. TVPs contained comparable protein content to TVP-Com (45–47 wt%), slightly lower carbohydrate content (33–36 wt% vs. 39 wt%), and ash (3–4 wt% vs. 8 wt%), but higher lipid content (7–8 wt% vs. 0.84 wt%) than TVP-Com. Sai-aua prepared from TVP-KO gained the highest overall acceptability. Mushrooms proved to be a potential source for TVP production due to their availability, low cost, nutritional value, and health benefits. Moreover, this finding helps add value to traditional meat products, which offer an opportunity for developing non-animal products with satisfactory sensory properties and low cost. In addition, the study would provide scientific resources for developing plant-based meat products that address health awareness and economic and environmental sustainability concerns.

Fibrous Structures from Starch and Gluten

Starch is added to meat analogues for binding and water holding. In this study, we investigate whether starch can have an additional role as a structuring agent. Therefore, different types of starch were combined with wheat gluten at various amounts and sheared in a High Temperature Shear Cell to determine how starch influences the structuring behavior of gluten–starch blends. The starches were chosen based on their diverse amylose contents, leading to different technological properties. Remarkable differences were found between the starches investigated. The addition of Amioca starch (containing 1% amylose) had a strong negative influence on the ability of gluten to form fibers. Maize starch (25% amylose) and Hylon VII (68% amylose) formed fibrous materials up to high starch additions. The pre-gelatinizing of maize starch further increased the ability of gluten–starch mixtures to form fibrous structures. The influence of the different types of starch on the hardness, deformability, and stiffness of the sheared samples was also assessed, revealing a spectrum of achievable properties through the addition of starch. Most remarkable was the formation of a material with anisotropy in Young’s modules. This anisotropy is also found in chicken meat, but not in protein-based fibrous materials. Furthermore, it was observed that the pre-gelatinization of starch facilitated fiber formation. A similar effect of pre-gelatinizing the starch was found when using faba bean meal with added wheat gluten, where fibrous structures could even be formed in a recipe that previously failed to produce such structures without pre-treatment.

Blending Proteins in High Moisture Extrusion to Design Meat Analogues: Rheological Properties, Morphology Development and Product Properties

High moisture extrusion (HME) of meat analogues is often performed with raw materials containing multiple components, e.g., blends of different protein-rich raw materials. For instance, blends of soy protein isolate (SPI) and another component, such as wheat gluten, are used particularly frequently. The positive effect of blending on product texture is well known but not yet well understood. Therefore, this work targets investigating the influence of blending in HME at a mechanistic level. For this, SPI and a model protein, whey protein concentrate (WPC), were blended at three different ratios (100:0, 85:15, 70:30) and extruded at typical HME conditions (55% water content, 115/125/133 °C material temperature). Process conditions, rheological properties, morphology development, product structure and product texture were analysed. With increasing WPC percentage, the anisotropic structures became more pronounced and the anisotropy index (AI) higher. The achieved AI from the extrudates with a ratio of 70:30 (SPI:WPC) were considerably higher than comparable extrudates reported in other studies. In all extrudates, a multiphase system was visible whose morphology had changed due to the WPC addition. The WPC led to the formation of a much smaller dispersed phase compared to the overlying multiphase structure, the size of which depends on the thermomechanical stresses. These findings demonstrate that targeted mixing of protein-rich raw materials could be a promising method to tailor the texture of extruded meat analogues.

Extrusion of wheat gluten-peanut oil complexes and their rheological characteristics

In order to clarify the effects of extrusion treatment on the processing properties of extrudates, providing a theoretical basis for the production of gluten-based extrudates with favorable sensory quality. This study examined the effects of various extrusion temperatures on the rheological properties of wheat gluten-peanut oil complexes (WPE) and wheat gluten (WG). At the extrusion temperature conditions of this study, the dynamic moduli of gluten in WG and WPE reached the maximum, and the creep strain reached a minimum at 160 °C. Extrusion treatment resulted in the decrease in β-sheet and α-helix content and an increase in the amount of β-turns and random coils. The secondary structural changes and increase in the number of disulfide bonds led to gluten aggregation, thus affecting their rheological properties. These results enhance our understanding of the variations in the rheological properties of extrudates and promote the potential application of gluten-based complexes in extrusion.

Thermo-mechanical processing of plant proteins using shear cell and high-moisture extrusion cooking

Consumption of plant-based meat analogues offers a way to reduce the environmental footprint of the human diet. High-moisture extrusion cooking (HMEC) and shear cell processing both rely on thermo-mechanical treatment of proteins to product fibrous meat-like products. However, the mechanisms underlying these processes are not well understood. In this review we discuss the effect of thermo-mechanical processing on the physicochemical properties and phase behavior of proteins and protein mixtures. The HMEC and shear cell processes are comparable in their basic unit operations, which are (1) mixing and hydration, (2) thermo-mechanical treatment, and (3) cooling. An often overlooked part of the extruder that could be crucial to fibrillation is the so-called breaker plate, which is situated between the barrel and die sections. We found a lack of consensus on the effect of heat on protein-protein interactions, and that the experimental tools to study protein-protein interactions are limited. The different mechanisms for structure formation proposed in literature all consider the deformation and alignment of the melt. However, the mechanisms differ in their underlying assumptions. Further investigation using novel and dedicated tools is required to fully understand these thermo-mechanical processes.

Effect of extrusion temperature on the protein aggregation of wheat gluten with the addition of peanut oil during extrusion

The influence of extrusion temperature on protein components and aggregation of wheat gluten (WG) and wheat gluten-peanut oil complexes (WPE) during extrusion with the addition of peanut oil was studied. Gliadin content and wheat gluten extractability decreased and glutenin content increased as extrusion temperature increased. At the same extrusion temperature, the gliadin content in WPE was higher than that in WG. The addition of peanut oil also resulted in the higher gluten extractability of WPE than WG. Increasing extrusion temperature also increased the average molecular weight of glutenin and gliadin. The decreased free sulfhydryl (SH) and increased disulfide bonds (SS) indicated that wheat gluten aggregation was promoted, via disulfide cross-linking, when extrusion temperature increased. Furthermore, increased temperature promoted the aggregation of gluten by increasing sulfhydryl-disulfide bond (SH-SS) interchange during extrusion. When the secondary structure of wheat gluten was analyzed by circular dichroism, the relative gluten α-helix content was decreased and the relative β-sheet content was increased. Also, the results of scanning electron microscopy (SEM) showed the size of the resultant particles increased with temperature, and the mean particle size of WPE was higher than WG. This research shows that extrusion temperature promotes gluten aggregation of WG and WPE. It provides basic data to support the study of gluten-lipid extrusion in the field of protein processing.

Physical and Microstructure Properties of Oyster Mushroom-Soy Protein Meat Analog via Single-Screw Extrusion

Single-screw extrusion of a fibrous-structured meat analog from soy proteins added with low-grade oyster mushroom was successful. Satisfactory extrudates were obtained at a barrel temperature of 140 °C, screw speed range of 100-160 rpm, and oyster mushroom addition at 0%, 7.5%, and 15% via factorial experiments. Single-screw extrusion equipped with a slit die successfully produced expanded oyster mushroom-soy protein extrudates. However, the increase in the oyster mushroom content significantly decreased (p ≤ 0.05) the expansion ratio of the extrudate from 1.26 to 0.98. This result indicated that adding more oyster mushroom restrained the expansion ratio. The extrudates had a medium density range (max of 1393.70 ± 6.30 kg/m3). By adding oyster mushroom, the extrudates attained a higher moisture content (range = 34.77% to 37.93%) compared with the extrudates containing the protein mixture only (range = 26.99% to 32.33%). The increase in screw speed and oyster mushroom significantly increased (p ≤ 0.05) the water absorption index. The increase in the texturization index was significantly influenced (p ≤ 0.05) by oyster mushroom addition rather than the screw speed. A defined fibrous structure supported the high texturization index and small shape of air cells observed in the extrudates.