High moisture extrusion of soybean protein isolate: Effect of β-glucan on physicochemical properties of extrudates

This study is focused on exploring the effect of twin-screw high-moisture extrusion technology on the physico-chemical properties of β-glucan-soybean protein isolate (SPI-BG) extrudates. Different proportions (0 %, 1 %, 2 %, 3 %, 4 %, 5 %) of oat β-glucan (BG) were added with soybean protein isolate (SPI) to prepare SPI-BG extrudates. Results showed that the addition of a high quantity of β-glucan (BG) decreased the elastic properties of soy protein isolate (SPI) extrudates and then increased. The strengthening of S1-S2-S3 interactions (hydrogen bonds, hydrophobic interactions, and disulfide bonds) was primarily responsible for this trend. Fourier transform infrared (FTIR) spectral analysis was conducted which revealed that BG did not significant affect random coil content of SPI. However, it was observed that α-helix content was increased significantly and the β-sheet content was decreased. An observation was noted in the value of enthalpy (ΔH) change that increased from 115.80 J/g to 159.68 J/g.

Mechanism of l-cysteine-induced fibrous structural changes of soybean protein at different high-moisture extrusion zones

In this study, the fibrous structure formation mechanism of soybean protein during high moisture extrusion processing was investigated using a dead-stop operation, and based on the interaction between soybean protein concentrate (SPC) and L-cysteine (CYS). The thermal properties, SDS-PAGE and particle size distribution of the samples from different extrusion zones were investigated. It was revealed that the addition of a moderate amount of CYS (0.1 %) promoted the fibrous structure formation in the SPC extrudates and optimised the textural properties of the SPC extrudates. In the extruder barrel, addition of CYS (0.1 %) promoted protein depolymerisation and unfolding in the mixing and cooking zones, and facilitated protein aggregation in the die and cooling zones. Protein solubility and raman spectroscopy revealed that disulfide bonds were principally responsible for fibrous structure formation; favoured when the intermolecular disulfide bonds (t-g-t mode) was increased. Finally, the transformation of protein conformation was revealed by secondary structure and surface hydrophobicity, which confirmed that the effect of CYS on protein conformation mainly occurred in the cooling zone. This study provides a theoretical basis for the application of CYS to regulate the fibrous structure of meat analogues.

Effect of high moisture extrusion on the structure and physicochemical properties of Tartary buckwheat protein and its in vitro digestion

Tartary buckwheat is rich in nutrients and its protein supports numerous biological functions. However, the digestibility of Tartary buckwheat protein (TBP) poses a significant limitation owing to its inherent structure. This study aimed to assess the impact of high moisture extrusion (HME, 60 % moisture content) on the structural and physicochemical attributes, as well as the in vitro digestibility of TBP. Our results indicated that TBP exhibited unfolded and amorphous microstructures after HME. The protein molecular weight of TBP decreased after HME, and a greater degradation was observed at 70 °C than 100 °C. In particular, HME at 70 °C caused an almost complete disappearance of bands near 35 kDa compared with HME at 100 °C. In addition, compared with native TBP (NTBP, 44.53 µmol/g protein), TBP subjected to HME at 70 °C showed a lower disulfide bond (SS) content (42.67 µmol/g protein), whereas TBP subjected to HME at 100 °C demonstrated a higher SS content (45.70 µmol/g protein). These changes endowed TBP with good solubility (from 55.96 % to 83.31 % at pH 7), foaming ability (20.00 %-28.57 %), and surface hydrophobicity (8.34-23.07). Furthermore, the emulsifying activity (EA) and in vitro digestibility are closely related to SS content. Notably, extruded TBP (ETBP) obtained at 70 °C exhibited higher EA and digestibility than NTBP, whereas ETBP obtained at 100 °C showed the opposite trend. Consequently, HME (especially at 70 °C) demonstrated significant potential as a processing technique for improving the functional and digestive properties of TBP.

Effects of the soy protein to wheat gluten ratio on the physicochemical and structural properties of Alaska pollock surimi-based meat analogs by high moisture extrusion

Surimi products have attracted much attention and are widely used in the food industry. Currently, the processing and exploitation of surimi products are mostly based on their gel characteristics. However, the abundant protein in surimi can be rearranged and integrated by high-temperature melting to generate a new surimi product with fibrous structures. In this study, meat analogs (new surimi product) were produced by high moisture extrusion (HME) using Alaska pollock surimi and plant protein (8:2), where the plant protein consisted of different ratios of soy protein and wheat gluten (9:1, 7:3, 5:5, 3:7 and 1:9). The product was marked as SSG because it was composed of Alaska pollock surimi, soy protein and wheat gluten. The structure and color results showed that the hardness and ΔE of SSG decreased, while the fibrous degree and lightness increased with increasing WG content. The observation of the macrostructure and microstructure also showed that the skeleton structure of SSG was more obvious with increasing WG addition, but the viscosity reflected a decreasing trend. Furthermore, an increase in the WG content raised the free water ratio and the total content of β-sheets, whereas the appropriate plant protein ratio reduced the SSG's thermal stability. In conclusion, Alaskan pollock surimi and the appropriate proportion of plant protein can form structurally stable meat analogs by high moisture extrusion.

Evaluating the potential of millets as blend components with soy protein isolate in a high moisture extrusion system for improved texture, structure, and colour properties of meat analogues

This study explored the use of millets flours as a secondary ingredient with soy protein isolate (SPI) to develop fibrous high moisture meat analogue (HMMA). Three millets (sorghum, pearl millet, and finger millet) with three incorporation levels (10%, 20%, and 30%) were extruded at 60%, 65%, and 70% moisture content. The results showed that millet type, incorporation level, and moisture content significantly influenced the system parameters and textural properties. Good visual texturization was achieved at addition of pearl millet up to 30% incorporation level and sorghum and finger millet up to 20% incorporation level. Furthermore, the textural properties of HMMA made from SPI-millet blends were compared against HMMA made from SPI-gluten blend and real chicken. The HMMA made from SPI-millet flour had lower hardness, chewiness, resilience, springiness, tensile strength, cutting strength than that for SPI and SPI-wheat gluten blend and were much closer to corresponding values for real chicken. The results also showed that each of the three millet types generated distinctly different fibre patterns (thick to thin fibres) and colour (whiter to darker) of HMMA. Thus, HMMA produced from SPI-millet flour blends can offer a wide textural, fibre pattern and colour space for different plant-based meat applications. Since millets do not have gluten, they also offer an opportunity to make gluten-free HMMA's.

Characterization of texturized meat analogues containing native lupin flour and lupin protein concentrate/isolate

Lupin is a nutritious, yet undervalued grain used as a fodder and food crop. In the present study, native lupin flour (LF), lupin protein concentrate (LPC), and lupin protein isolate (LPI) were combined (70% LPI:LPC blend ratios [30:70, 50:50, and 70:30] and 30% LF constant fraction), extruded at high moisture (45-55%), and shaped with a long cooling die (800 mm) to obtain texturized meat analogues (TMAs) with fibrous structures. The characteristics of TMAs (e.g., hardness, water hydration capacity) depended heavily on water content, blend ratios (LPI:LPC), and to a lesser extent, the long cooling die temperature. Color changes (i.e., L*, b*) were mostly attributed to variations in blend ratios (LPI:LPC). Microstructure analysis showed that TMAs with higher water content (55%) were more likely to have thinner walls and smaller void thickness. Fluorescence imagery revealed that TMAs with lower LPI content presented more homogeneous structures. These findings show that reasonable amounts (30% d.m.) of native lupin flour can be incorporated into meat analogues by maintaining a sufficiently high protein content (>50% d.m.) to trigger the formation of fibrous structures.