Effects of shear stress on the microalgae Chaetoceros muelleri

The effect of shear stress on the viability of Chaetoceros muelleri was studied using a combination of a rheometer and dedicated shearing devices. Different levels of shear stress were applied by varying the shear rates and the medium viscosities. It was possible to quantify the effect of shear stress over a wide range, whilst preserving laminar flow conditions through the use of a thickening agent. The threshold value at which the viability of algae was negatively influenced was between 1 and 1.3 Pa. Beyond the threshold value the viability decreased suddenly to values between 52 and 66%. The effect of shear stress was almost time independent compared to normal microalgae cultivation times. The main shear stress effect was obtained within 1 min, with a secondary effect of up to 8 min

Quantifying water distribution between starch and protein in doughs and gels from mildly refined faba bean fractions

The development of novel and sustainable food products, such as cheese- and meat analogues, requires a better understanding of the use of less refined ingredients. We investigated the distribution of water between the protein and starch phase of doughs and heat-induced gels made from air-classified faba bean fractions by developing a method suited for investigation of such multi-component ingredients. The moisture contents of the protein and starch phases in the dough were determined using a method based on partial sorption isotherms of mixed doughs of protein- and starch-rich fractions at high water activity. Water content of the protein phase is higher than that of the starch phase in dough, showing that protein takes up more water than starch at room temperature. Also, the moisture content of the protein phase in the gels was calculated using a model based on the denaturation temperature of legumin. From the experiments and the modelling, it became evident that the moisture content of the protein phase in the gel is lower than the moisture content of the protein phase in the dough, showing the importance of considering moisture migration from the protein to the starch during heating

Effect of L-cysteine and L-ascorbic acid addition on properties of meat analogues

Currently, studies are underway to use pea protein isolate (PPI) for the production of meat analogues because it is considered as a more sustainable alternative to soy. The potential of PPI has been demonstrated in extrusion and PPI in combination with wheat gluten has been studied in the shear cell. To enlarge the possibilities to make meat analogues with a broader range of properties, the effects of L-cysteine (CYS) and L-ascorbic acid (AA) on PPI and wheat gluten (WG) blends were examined at different concentrations (0, 100, 500, 1000 and 2000 ppm). The results showed that both CYS and AA altered the properties of the products formed by the high-temperature shear cell (HTSC). Both additives altered the fibrousness and the mechanical properties of the products obtained after processing. Especially CYS revealed an increase in tensile stress, tensile strain and Young's modulus as its concentration increased. However, products containing CYS depicted a relatively stable anisotropic index of 1, which corresponded to a densely packed matrix that was observed by microstructural analysis. A small elevated anisotropic index (>1) of products containing AA at concentrations of 500–2000 ppm could be attributed to the formation of pores parallel to the shear flow direction in these samples visualized by a confocal laser scanning microscope (CLSM) and the scanning electron microscope (SEM). In the products containing 2000 ppm of AA and 2000 ppm CYS, small and large fibers were formed, respectively. Therefore, this research pointed out the potential application of CYS and AA to alter and control the textural attributes of products. This application could aid in improving the consumer acceptance of meat analogues and, thus, contribute to being able to feed the increasing population of the world

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

Water-binding capacity of protein-rich particles and their pellets

The water-binding capacities (WBCs) of pea protein isolate, soy protein isolate, lupin protein concentrate and vital wheat gluten particles were investigated by hydrating them in excess water, centrifuging these dispersions, and calculating the WBCs from the weight of the pellets. It was found that, except for pea proteins, the pellet consisted of a notable amount of interstitial water. Furthermore, it seems that when particles were largely deformable a (semi-)continuous protein network was formed in which individual particles could not be distinguished anymore. Then, the WBC of the pellet did not represent the WBC of the original particles anymore. Consequently, it was concluded that the WBC of the pellet (WBC-P) differs from the WBC of the particles. Therefore, the characteristics of the particles and their pellets were further investigated with, among others, time domain nuclear magnetic resonance (TD NMR). TD NMR turned out to be a useful additional tool to do this, and has the potential to give an indication of the amount of water present in each water domain. From the information obtained about the characteristics of the particles and their pellets, it could be concluded that variations in the WBC-P were the result of differences in the deformability of the particles (i.e., their capability to swell and to withstand the centrifugal force), and their ability to bind water interstitially.</p

Type of pectin determines structuring potential of soy proteins into meat analogue applications

The addition of pectin to soy protein isolate (SPI) is a route to create fibrous products using shear cell technology. In this study, we investigated pectins derived from soybean, sugar beets, and citrus (two variants) that vary in sugar composition, degree of methylation and acetylation. The objective was to examine how these different pectins impact the functional properties of the SPI dispersions. The SPI-pectin blends were shear structured and their visual appearance, microstructural, rheological, and mechanical properties were analyzed. The addition of pectins from citrus (the highly methyl-esterified form) and soybean resulted in fibrous products when mixed with SPI. The addition of the low methyl-esterified pectin derived from citrus led to less pronounced fibrous product, and pectin from sugar beet did not lead to fibrous products. To explain the effect, several properties of the blends and products were tested. It was found that the fibrous products contained more air (i.e. higher void fraction) than products that were not fibrous, and that air bubbles were deformed in the shear direction. The rheological measurements of the blends revealed that the pectins lowered the yield and flow point of SPI, and the flow transition index. The blend with the highest elasticity after heating also had the highest deformation of air bubbles. Based on all results it was concluded that pectin influenced the structure formation in two ways: 1) affecting the ability to facilitate air inclusion and 2) influencing the storage modulus and elasticity of the matrix

Recovery of protein from green leaves : Overview of crucial steps for utilisation

Plant leaves are a major potential source of novel food proteins. Till now, leaf protein extraction methods mainly focus on the extraction of soluble proteins, like rubisco protein, leaving more than half of all protein unextracted. Here, we report on the total protein extraction from sugar beet leaves (Beta vulgaris L.) by a traditional thermal extraction method consisting of mechanical pressing, heating to 50 °C and centrifugation. The resulting streams (i.e. supernatant, green-protein pellet and fibrous pulp) were characterised in terms of composition, physical structure and processing options. The protein distributed almost equally over the supernatant, pellet and pulp. This shows that thermal precipitation is an unselective process with respect to fractionation between soluble (rubisco) and insoluble (other) proteins. About 6% of the total protein could be extracted as pure rubisco (90% purity) from the supernatant. Surfactants commonly used for protein solubilisation could hardly re-dissolve the precipitated proteins in the pellet phase, which suggested that irreversible association was induced between the co-precipitated proteins and cell debris. Thus, the extraction of this protein will require prevention of their co-precipitation, and should take place in the original juice solution.</p

Flavor-protein interactions for four plant protein isolates and whey protein isolate with aldehydes

Aldehydes are important flavor molecules to consider in plant-based products. Here, the flavor retention of a series of saturated aldehydes and mono-unsaturated aldehydes (2-alkenals) with different chain lengths (C4, C6, C8, and C10) in dispersions with protein isolates of pea, soy, fava bean, chickpea, and whey (as reference) was analyzed with APCI-TOF-MS. The headspace concentrations of alkenals were lower than aldehydes, meaning alkenals were retained more than saturated aldehydes. The retention was modeled by assuming hydrophobic interactions and covalent interactions. The ratio between the hydrophobic interaction parameter and the covalent parameter showed that covalent interactions are mainly important for butanal and butenal (C4). For the other aldehydes, hydrophobic interactions became increasingly important. Correlations were found between the chemical interaction parameters and the cysteine and methionine content of the different proteins. The obtained model parameters for each set of proteins and flavors allow the prediction of flavor retention when developing a flavored product with high protein content

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