Atze Jan van der Goot

Shear‐Induced Inactivation of α‐Amylase in a Plain Shear Field

A newly developed shearing device was used to study shear‐induced inactivation of thermostable α‐amylase in a plain shear field, under conditions comparable to extrusion. The results show that the inactivation can be described well with a first‐order process, in which the inactivation energy largely depends on the shear stress, instead of specific mechanical energy or strain history. The resulting dependency of the rate of inactivation on the shear stress is very strong and nonlinear, which leads to the conclusion that in many cases the maximally applied shear stress determines the inactivation. Quantification of the inactivation rates gives design criteria for the application of enzymes in more viscous systems than conventionally used, provided that the reactor is designed such that no peak shear stresses occur.

The use of exergetic indicators in the food industry – A review

ABSTRACT Assessment of sustainability will become more relevant for the food industry in the years to come. Analysis based on exergy, including the use of exergetic indicators and Grassmann diagrams, is a useful tool for the quantitative and qualitative assessment of the efficiency of industrial food chains. In this paper, we review the methodology of exergy analysis and the exergetic indicators that are most appropriate for use in the food industry. The challenges of applying exergy analysis in industrial food chains and the specific features of food processes are also discussed.

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.

Understanding leaf membrane protein extraction to develop a food-grade process

Leaf membrane proteins are an underutilised protein fraction for food applications. Proteins from leaves can contribute to a more complete use of resources and help to meet the increasing protein demand. Leaf protein extraction and purification is applied by other disciplines, such as proteomics. Therefore, this study analysed proteomic extraction methods for membrane proteins as an inspiration for a food-grade alternative process. Sugar beet leaves were extracted with two proteomic protocols: solvent extraction and Triton X-114 phase partitioning method. Extraction steps contributed to protein purity and/or to selective fractionation, enabling the purification of specific proteins. It was observed that membrane proteins distributed among different solvents, buffers and solutions used due to their physicochemical heterogeneity. This heterogeneity does not allow a total membrane protein extraction by a unique method or even combinations of processing steps, but it enables the creation of different fractions with different physicochemical properties useful for food applications.

Covalent Bonding of Chlorogenic Acid Induces Structural Modifications on Sunflower Proteins

Proteins and phenols coexist in the confined space of plant cells leading to reactions between them, which result in new covalently bonded complex molecules. This kind of reactions has been widely observed during storage and processing of plant materials. However, the nature of the new complex molecules and their physicochemical properties are largely unknown. Therefore, we investigated the structural characteristics of covalently bonded complexes between sunflower protein isolate (SFPI, protein content 85 wt %) and the dominant phenol in the confined space of a sunflower seed cell (chlorogenic acid, CGA). It was shown that the efficiency of bond formation goes through a maximum as a function of the SFPI:CGA ratio. Moreover, the bonding of CGA with proteins resulted in changes in the secondary and tertiary structure of the protein. It was also shown that the phenol bound strongly to the protein, which resulted in new crosslinks between the polypeptide chains. As a result, secondary structures like α-helices and β-sheets diminished, which in turn resulted in more disordered domains and a subsequent modification of the tertiary structure of the proteins. These findings are relevant for establishing future protocols for extraction of high-quality proteins and phenols when utilizing plant material and offer insight into the impact of processing that these ingredients endure.

Protein Oxidation in Plant Protein-Based Fibrous Products: Effects of Encapsulated Iron and Process Conditions

Plant protein-based fibrous structures have recently attracted attention because of their potential as meat replacer formulations. It is, however, unclear how the process conditions and fortification with micronutrients may affect the chemical stability of such products. Therefore, we aimed to investigate the effects of process conditions and the incorporation of iron (free and encapsulated) on protein oxidation in a soy protein-based fibrous product. First, the physicochemical stability of iron-loaded pea protein particles, used as encapsulation systems, was investigated when exposed to 100 or 140 °C. Second, protein oxidation was measured in the iron-fortified soy protein-based fibrous structures made at 100 or 140 °C. Exposure to high temperatures increased the carbonyl content in pea protein particles. The incorporation of iron (free or encapsulated) did not affect carbonyl content in the fibrous product, but the process conditions for making such products induced the formation of carbonyls to a fairly high extent.

Sustainable protein technology : an evaluation on the STW Protein programme and an outlook for the future

In 2013 a new STW research programme was started on sustainable protein recovery. This STW Protein Programme consisted of five sustainable protein technology projects, which aimed at developing innovative methods to extract proteins from plant leaves, microalgae and insects to meet the increasing demand for food proteins for humans and livestock. The aim of the additional STW-project ‘Meer en Beter Eiwit’ was to summarize and evaluate the main results and conclusions of these five projects. Besides, some more recent additional insight on protein extraction was supplemented. Project partners including WUR, knowledge institutes and industry were interviewed to obtain their opinion on the project performed and future research needs. This has led to a vision document that gives direction to future research in the field of protein and technology. The approach of this project was to study the topic from start (biomass) via technology to finish (product). It was further put into a larger perspective, looking at the entire chain. When relevant, additional aspects such a soil quality and global protein demands were included.