Rework Potential of Soy and Pea Protein Isolates in High-Moisture Extrusion.

High-moisture extrusion (HME) is an effective process to make fibrous products that can be used as meat analogues. In this study, the effect of extrusion of already extruded products (i.e., re-extrusion) was tested with the aim to explore the potential of rework in HME. The rework of material is important because it is a route to reduce waste, which is always produced, for example during the start or at the end of a production run. Pea and soy protein isolates (PPI and SPI) were first extruded, then freeze-dried and ground, and extruded again. The visual and textural properties of the fibrous products were evaluated. Also, the rheological properties, solubility, and water-holding capacity (WHC) of the ingredients and the products after the first and second extrusion were quantified. The obtained freeze-dried powders after the first HME cycle had a reduction in solubility of 15% for PPI and 74% for SPI. Furthermore, WHC was reduced by 65% and 17% for PPI and SPI, respectively. After the second HME cycle, the reduction in solubility and WHC was augmented to 22% and 90% for PPI, and 79% and 63% for SPI. No effect on stock and loss moduli after heating and cooling were found, even after two HME cycles. SPI fibrous products did not differ in cutting strength, anisotropy index, or visual appearance after re-extrusion. Only, a decrease in hardness was detected, from 62.0 N to 51.1 N. For PPI, re-extrusion did reduce the cutting force and hardness but not the anisotropy index. It was concluded that even though HME induces a loss of solubility and WHC, this did not affect the fibrous texture formation of the protein. This means that the texture formed during HME does not depend on the process history and that rework is thus possible for fibrous products.

Flavor-protein interactions for four plant proteins with ketones and esters.

The interaction between flavors and proteins results in a reduced headspace concentration of the flavor, affecting flavor perception. We analyzed the retention of a series of esters and ketones with different chain lengths (C4, C6, C8, and C10) by protein isolates of yellow pea, soy, fava bean, and chickpea, with whey as a reference. An increase in protein concentration led to a decrease in flavor compound in the headspace as measured with atmospheric pressure chemical ionization time-of-flight mass spectroscopy (APCI-TOF-MS). Flavor retention was described with a flavor-partitioning model. It was found that flavor retention could be well predicted with the octanol-water partitioning coefficient and by fitting the hydrophobic interaction parameter. Hydrophobic interactions were highest for chickpea, followed by pea, fava bean, whey, and soy. However, the obtained predictive model was less appropriate for methyl decanoate, possibly due to its solubility. The obtained models and fitted parameters are relevant when designing flavored products with high protein concentrations.

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.