Maarten A.I. Schutyser

Food Engineering at Multiple Scales: Case Studies, Challenges and the Future—A European Perspective

Abstract A selection of Food Engineering research including food structure engineering, novel emulsification processes, liquid and dry fractionation, Food Engineering challenges and research with comments on European Food Engineering education is covered. Food structure engineering is discussed by using structure formation in freezing and dehydration processes as examples for mixing of water as powder and encapsulation and protection of sensitive active components. Furthermore, a strength parameter is defined for the quantification of material properties in dehydration and storage. Methods to produce uniform emulsion droplets in membrane emulsification are presented as well as the use of whey protein fibrils in layer-by-layer interface engineering for encapsulates. Emulsion particles may also be produced to act as multiple reactors for food applications. Future Food Engineering must provide solutions for sustainable food systems and provide technologies allowing energy and water efficiency as well as waste recycling. Dry fractionation provides a novel solution for an energy and water saving separation process applicable to protein purification. Magnetic separation of particles advances protein recovery from wastewater streams. Food Engineering research is moving toward manufacturing of tailor-made foods, sustainable use of resources and research at disciplinary interfaces. Modern food engineers contribute to innovations in food processing methods and utilization of structure–property relationships and reverse engineering principles for systematic use of information of consumer needs to process innovation. Food structure engineering, emulsion engineering, micro- and nanotechnologies, and sustainability of food processing are examples of significant areas of Food Engineering research and innovation. These areas will contribute to future Food Engineering and novel food processes to be adapted by the food industry, including process and product development to achieve improvements in public health and quality of life. Food Engineering skills and real industry problem solving as part of academic programs must show increasing visibility besides emphasized training in communication and other soft skills.

Thermomechanical Morphology of Peas and Its Relation to Fracture Behaviour

Milling and subsequent air classification can be exploited for production of functional protein-enriched fractions from legumes and grains. Fracture behaviour is of large relevance to optimal disentanglement of protein and starch and is determined by the thermomechanical morphology of the seeds. Thermomechanical properties of peas were explored as a function of temperature and moisture content. Differential scanning calorimetry and thermal mechanical compression tests were carried out on pea protein and starch isolates yielding similar glass transition temperatures. Glass transition lines were successfully constructed using the Gordon–Taylor equation. Subsequently, three regions were identified in the state diagram; starch in the glassy and protein in the rubbery state, both components in the glassy state, and both components in the rubbery state. From single pea fracture experiments, it was found that the completely glassy peas fractured at a smaller critical compression distance compared to the peas in the other two regions. This can be explained by the elastic behaviour of the rubbery protein network, having a detrimental effect on the energy efficiency of milling processes. However, from scanning electron microscopy, it appeared that in rough fracture planes, visible when the protein was in the rubbery state, starch granules were present as more separate identities, suggesting increased disentanglement. Disentanglement of protein and starch by milling would then be optimal when protein is in the rubbery state. The latter can be achieved by milling at increased temperature and/or moisture content, which would be an attractive alternative.

Mimicking Spray Drying by Drying of Single Droplets Deposited on a Flat Surface

The inactivation of bioactive ingredients during spray drying is often matrix specific. Therefore, the design of new processes or the optimisation of existing spray drying processes is usually highly product specific and requires numerous experiments. Rapid experimentation methods that facilitate fast data generation are therefore desired. A novel method for drying single droplets to mimic spray drying is proposed. The approach involves droplet deposition on a hydrophobic flat surface followed by controlled drying. A heat and mass transfer model is applied to predict the drying history of the single droplets. The approach is successfully evaluated through studying the inactivation of β-galactosidase during drying. The heat and mass transfer model supplemented with inactivation kinetics provided reasonable prediction of the residual enzyme activity after drying. In addition, the inactivation kinetics could be directly extracted from single droplet experiments rather than using the kinetics from separate heating experiments. Finally, it was demonstrated that the inactivation kinetics found with the single-drop experiments could satisfactorily predict the residual activity of β-galactosidase dried with a laboratory-scale spray dryer.

Novel method for enumeration of viable Lactobacillus plantarum WCFS1 cells after single-droplet drying.

ABSTRACT Survival of probiotic bacteria during drying is not trivial. Survival percentages are very specific for each probiotic strain and can be improved by careful selection of drying conditions and proper drying carrier formulation. An experimental approach is presented, comprising a single-droplet drying method and a subsequent novel screening methodology, to assess the microbial viability within single particles. The drying method involves the drying of a single droplet deposited on a flat, hydrophobic surface under well-defined drying conditions and carrier formulations. Semidried or dried particles were subjected to rehydration, fluorescence staining, and live/dead enumeration using fluorescence microscopy. The novel screening methodology provided accurate survival percentages in line with conventional plating enumeration and was evaluated in single-droplet drying experiments with Lactobacillus plantarum WCFS1 as a model probiotic strain. Parameters such as bulk air temperatures and the carrier matrices (glucose, trehalose, and maltodextrin DE 6) were varied. Following the experimental approach, the influence on the viability as a function of the drying history could be monitored. Finally, the applicability of the novel viability assessment was demonstrated for samples obtained from drying experiments at a larger scale.

Porosity, Bulk Density, and Volume Reduction During Drying: Review of Measurement Methods and Coefficient Determinations

Several experimental methods for measuring porosity, bulk density, and volume reduction during drying of foodstuffs are available. These methods include, among others, geometric dimension, volume displacement, mercury porosimeter, micro-CT, and NMR. However, data on their accuracy, sensitivity, and appropriateness are scarce. This article reviews these experimental methods, areas of applications, and limits. In addition, the concept of porosity, bulk density, and volume reduction and their evolution as a function of moisture content during drying are presented. In this study, values of initial porosity (ϵ0) and density ratio (β) of some food products are summarized. It has been found that ϵ0 is highly dependent on the type of food products, while β ranges from 1.1 to 1.6. The possibility of calculating solid density based on food compositions has also been validated. The inter-predictions between porosity, bulk density, and volume density have been made mathematically evident.

Crust morphology and crispness development during deep-fat frying of potato

Crust formation is an important factor in determining the crispness of French fries. This study aimed at unravelling detailed structural and textural properties of the crust in relation to crispness during frying as a function of the process temperature and time. X-ray tomography showed a larger overall pore volume at higher frying times, while a lower final moisture content mainly resulted in an increase in the amount of large pores. Texture analysis revealed that the increase in porosity, due to the increased formation of pores, results in a more crispy behaviour after frying with oil of up to 180°C. At temperatures above 180°C crispness is actually found to decrease again, which is explained by the increased plastic behaviour of the crust. This may be related to the reduced glass transition temperature of the crust because of increased sugar degradation at a very high temperature.

Method Development to Increase Protein Enrichment During Dry Fractionation of Starch-Rich Legumes

A facile method was developed to establish milling settings that optimally separate starch granules from protein bodies and cell wall fibres for starch-rich legumes. Optimal separation was obtained for pea, bean, lentil and chickpea when the particle size distribution curve of flour and isolated starch granules overlap maximally. This outcome was based on scanning electron microscopy, protein content of the fine fraction and particle size distribution curves. Milling settings differed between legumes due to variances in seed hardness and starch granule size. The protein content of the fine fraction was legume specific as well and could be explained by differences in particle density, seed hardness, starch granule size, fat content and flour dispersibility.

Spray Drying of Lactobacillus plantarum WCFS1 Guided by Predictive Modeling

Shelf life of probiotic microorganisms can be retained by drying. Spray drying is an economically interesting alternative to freeze drying with that respect. However, the viability can decrease due to the drying process and testing it is laborious and expensive. This research shows that the viability of Lactobacillus plantarum WCFS1 during pilot scale drying can be predicted with kinetics gathered at a single droplet level. Using this approach, it could be demonstrated that the viability of L. plantarum WCFS1 during spray drying is mainly determined by the combination of temperature and moisture content during the first 0.5 seconds after atomization. The combination of a high moisture content and a high temperature appeared most detrimental to the residual viability. Moreover, it was found to be important to take into account the particle size distribution during atomization when predicting viability, since this has a large effect on the moisture content during this first 0.5 seconds. Finally, it was observed that shelf life during storage was mainly determined by the moisture content of the powder. A lower moisture content resulted in a higher viability. Above a moisture content of 6%, shelf life stability rapidly decreased in the applied maltodextrin (DE = 16) matrix.

Inactivation of Lactobacillus plantarum WCFS1 during spray drying and storage assessed with complementary viability determination methods

Survival of Lactobacillus plantarum WCFS1 spray-dried and stored under different conditions was investigated using complementary methods. One method involved a cell membrane integrity viability-based determination, the other assessed cell growth behavior in a liquid medium by means of detection time or by conventional plating. Survival decreased below 95% when spray drying was carried out at higher outlet spray drying temperatures (Tout>70°C). However, the membrane integrity method provided higher residual viability values compared to the detection time and conventional plating. This suggests that loss of viability may be due to a combination of damage to intracellular components and cell membrane. Also during storage viability based on growth behavior declined faster and was more temperature dependent compared to the viability as determined by the membrane integrity method. Also here additional damage to intracellular components is expected responsible to loss of viability. Major conclusion is that one should not only rely on a cell-membrane integrity based method to assess survival during spray drying and storage of bacteria. Previous studies that did so most probably underestimated viability as critical damage to intracellular components was not assessed.

Establishing guidelines to retain viability of probiotics during spray drying

We present the application of a model-based approach to map processing conditions suitable to spray dry probiotics with minimal viability loss. The approach combines the drying history and bacterial inactivation kinetics to predict the retention of viability after drying. The approach was used to systematically assess the influence of operational co-current spray drying conditions on residual viability. Moreover, two promising alternative drying strategies for probiotics were evaluated involving encapsulation in a hollow particle and using an “ideal-mixed” dryer system. Finally, a graph was constructed with the model to provide visual guidelines to optimize spray dying for probiotics in terms of viability and drying efficiency.