Quantitative analysis of 3D food printing layer extrusion accuracy: Contextualizing automated image analysis with human evaluations: Quantifying 3D food printing accuracy.

3D food printing can customize food appearance, textures, and flavors to tailor to specific consumer needs. Current 3D food printing depends on trial-and-error optimization and experienced printer operators, which limits the adoption of the technology by general consumers. Digital image analysis can be applied to monitor the 3D printing process, quantify printing errors, and guide optimization of the printing process. We here propose an automated printing accuracy assessment tool based on layer-wise image analysis. Printing inaccuracies are quantified based on over- and under-extrusion with reference to the digital design. The measured defects are compared to human evaluations via an online survey to contextualize the errors and identify the most useful measurements to improve printing efficiency. The survey participants marked oozing and over-extrusion as inaccurate printing which matched the results obtained from automated image analysis. Although under-extrusion was also quantified by the more sensitive digital tool, the survey participants did not perceive consistent under-extrusion as inaccurate printing. The contextualized digital assessment tool provides useful estimations of printing accuracy and corrective actions to avoid printing defects. The digital monitoring approach may accelerate the consumer adoption of 3D food printing by improving the perceived accuracy and efficiency of customized food printing.

Metabolomics and sensory evaluation of white asparagus ingredients in instant soups unveil important (off-)flavours.

Split-stream processing of asparagus waste stream is a novel approach to produce spray-dried powder and fibre. Asparagus ingredients processed by this method and a commercial asparagus powder were compared by evaluating their flavour profile in a soup formulation. Professional sensory panel and untargeted metabolomics approaches using GC-MS and LC-MS were carried out. Unsupervised and supervised statistical analyses were performed to highlight discriminatory metabolites and correlate these to sensory attributes. The spray-dried powder scored higher on asparagus flavour compared to the commercial powder. The fibre negatively impacted the taste and mouthfeel of the soups. GC-O-MS confirmed the role of dimethyl sulphide, 2-methoxy-3-isopropyl pyrazine and 2-methoxy-3-isobutyl pyrazine in asparagus odour. Seven new volatile compounds are also proposed to contribute to asparagus flavour notes, most of which were more abundant in the spray-dried powder. This research demonstrates the feasibility of upcycling asparagus waste streams into flavour-rich ingredients with good sensorial properties.

The effect of partial replacement of maltodextrin with vegetable fibres in spray-dried white asparagus powder on its physical and aroma properties.

Asparagus concentrate was spray-dried in different carrier formulations in which maltodextrin was partially replaced by cellulose-based carriers, i.e. asparagus fibre, citrus fibre or microcrystalline cellulose. This replacement was limited to a maximum level of 3% w/w for asparagus and citrus fibres, and 10% w/w for microcrystalline cellulose, due to fibre insolubility and increased viscosity of the feed. Powders obtained from feed solutions with an initial solids content of 40% w/w showed better physical properties and aroma retention than 30% w/w. Partial replacement of maltodextrin by cellulose-based carriers resulted in powders with similar physical properties as the control and did not detrimentally influence the aroma profiles as analyzed by headspace solid-phase microextraction and gas chromatography-mass spectrometry. This research shows that fibre obtained from asparagus waste streams could potentially be used as a carrier to produce spray-dried asparagus powder with retained key asparagus volatiles such as 2-methoxy-3-isopropyl pyrazine.

Thermal inactivation kinetics of ß-galactosidase during bread baking.

In this study, ß-galactosidase was utilized as a model enzyme to investigate the mechanism of enzyme inactivation during bread baking. Thermal inactivation of ß-galactosidase was investigated in a wheat flour/water system at varying temperature-moisture content combinations, and in bread during baking at 175 or 205°C. In the wheat flour/water system, the thermostability of ß-galactosidase increased with decreased moisture content, and a kinetic model was accurately fitted to the corresponding inactivation data (R2=0.99). Interestingly, the residual enzyme activity in the bread crust (about 30%) was hundredfold higher than that in the crumb (about 0.3%) after baking, despite the higher temperature in the crust throughout baking. This result suggested that the reduced moisture content in the crust increased the thermostability of the enzyme. Subsequently, the kinetic model reasonably predicted the enzyme inactivation in the crumb using the same parameters derived from the wheat flour/water system. However, the model predicted a lower residual enzyme activity in the crust compared with the experimental result, which indicated that the structure of the crust may influence the enzyme inactivation mechanism during baking. The results reported can provide a quantitative understanding of the thermal inactivation kinetics of enzyme during baking, which is essential to better retain enzymatic activity in bakery products supplemented with heat-sensitive enzymes.

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.

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

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.

Aspergillus oryzae in solid-state and submerged fermentations. Progress report on a multi-disciplinary project.

We report the progress of a multi-disciplinary research project on solid-state fermentation (SSF) of the filamentous fungus Aspergillus oryzae. The molecular and physiological aspects of the fungus in submerged fermentation (SmF) and SSF are compared and we observe a number of differences correlated with the different growth conditions. First, the aerial hyphae which occur only in SSFs are mainly responsible for oxygen uptake. Second, SSF is characterised by gradients in temperature, water activity and nutrient concentration, and inside the hyphae different polyols are accumulating. Third, pelleted growth in SmF and mycelial growth in SSF show different gene expression and protein secretion patterns. With this approach we aim to expand our knowledge of mechanisms of fungal growth on solid substrates and to exploit the biotechnological applications.