Numerical modelling of conjugate heat and mass transfer during hydrofluidisation food freezing in different water solutions

A novel method of hydrofluidisation food freezing is numerically investigated in this paper. This technique is based on freezing small food products in a liquid medium under highly turbulent flow conditions when the heat transfer coefficient is higher than 1 000 W⋅m⁻²⋅K⁻¹, which depends on the operating and flow conditions. A numerical model was developed to characterise the freezing process in terms of the heat transfer and diffusion of liquid solution components into the food product. The study investigates the freezing process of spherical samples in binary solutions of ethanol (30%) and glycerol (40%) and ternary solution of ethanol and glucose (15%/25%). The developed model was employed to determine the concentration of the liquid solution in food samples and to quantify the effect of sample size, heat transfer coefficient, solution temperature and concentration on the process. The food sample size varied from 5 to 30 mm, and the heat transfer coefficients varied from 1 000 to 4 000 W⋅ m⁻²⋅ K⁻¹. The results confirm that a freezing time of 15 min for 30 mm diameter samples or less than 1 min for 5 mm diameter samples can be achieved with the hydrofluidisation method. The solution uptake was influenced by the solution type, sample size and process parameters and varied from 8.9 to 35 g of solute per kg of product for ethanol-glucose and glycerol solutions, respectively. This paper quantifies the advantages and possible limitations of hydrofluidisation, which has not yet been entirely studied, especially in terms of the mass absorption of different solutes.     

New insights into the thermodynamics and kinetics of triacylglycerols crystallization

Understanding the transition from an isotropic liquid state to an organized crystalline state of triacylglycerols has great significance when designing lipid-based materials in general and food products in particular. In the current research, the balance between the demand for the tuning-fork (Tf) conformation, which is the suitable conformation for most crystalline organizations, and the supply of these molecules was discussed. Based on the negative dependency of the nucleation rates and the induction times on temperature, it was suggested that the limiting factor for the nucleation process is the conversion from the Tf conformation to any other conformation. On the other hand, based on the positive dependency of the melting temperatures and enthalpies on crystallization temperature, and the organized morphologies obtained at higher temperatures, it was suggested that the limiting factor during the crystal growth process is the conversion to the Tf conformation from another conformation.     

Simultaneous stone-milling and extraction enables efficient one-step extraction of hard plant materials

Extraction of plant materials is an essential practice in various fields using natural compounds. Nevertheless, it is challenging to perform complicated extraction efficiently and consistently on materials with hard-to-crush structures. This work presents a new method called simultaneous stone-milling and extraction (SME) to achieve one-step extraction of hard materials. SME under its optimal conditions was confirmed to produce high quality extracts from whole spice seeds (anise seeds, dill seeds, fennel seeds) and coarse-cut star anise. Compared to other extraction methods like maceration, heat-assisted extraction and ultrasound-assisted extraction, SME extracts contained comparable or higher concentrations of general (polyphenols, flavonoids, antioxidants) and specific (enzyme inhibitors) bioactive groups. Hence, SME with its one-step operation is expected to simplify the task of plant extraction and contribute to the advances in studies using plant-derived phytochemicals.     

Dry Fractionation Approach in Concentrating Tocopherols and Tocotrienols from Palm Fatty Acid Distillate: A Green Pretreatment Process for Vitamin E Extraction

Palm fatty acid distillate (PFAD) is a rich source of vitamin E. As compared to other vegetable oil, PFAD has higher tocotrienol (70–80%) over tocopherol content, which makes it a valuable source for vitamin E extraction. Current vitamin E extraction methods are not sustainable due to the intensive usage of chemical and high operational cost. Hence, the present study investigated for the first time using dry fractionation process as a green and economical pretreatment method for separating solid fraction (stearin) and liquid fraction (olein) in order to concentrate vitamin E from PFAD in olein fraction. We examined the dry fractionation conditions: crystallization ending temperature (36–44 °C), cooling rate (0.3 and 1.5°C min⁻¹), stirring speed (20–125 rpm), and holding time (0–60 min) on the composition of unsaturated and saturated fatty acids as well as vitamin E content in liquid fraction (olein) and solid fraction (stearin) using gas chromatography and high performance liquid chromatography, respectively. In most of these conditions, vitamin E was ultimately higher in olein fraction as compared to stearin fraction, which is correlated with the high degree of unsaturation. Under a cooling rate of 0.3°C min⁻¹, 90 rpm stirring speed, and ending crystallization of 38 °C, the highest vitamin E rich olein fraction was attained with 1479 ± 10.51 ppm in 50 g olein fraction as compared to 1366 ± 7.94 ppm in 500 g of unfractionated PFAD.     

Nutrient enrichment of dairy curd by incorporation of whole and ruptured microalgal cells (Nannochloropsis salina)

This work investigated incorporation of Nannochloropsis salina into renneted dairy gels and curd. Whole and ruptured microalgal cells did not impair κ-casein macropeptide cleavage by the rennet enzyme. However, insoluble components of ruptured cells impeded gelation, presumably by hindering interactions between renneted casein micelles. Confocal imaging showed that whole cells were retained and homogenously distributed within the protein network of the gels and cooked curd, whereas ruptured algae formed large aggregates that altered the protein matrix. Eicosapentaenoic acid (EPA) in the whole microalgal cells was incorporated within the curds, with considerably less EPA retained for ruptured cells. Soluble algal debris did not impair gelation, however EPA wasn't retained in the curd. The study demonstrates that nutrient enrichment of renneted dairy products is possible by incorporating whole microalgal cells to displace milk fat with protein and the beneficial long-chain omega-3 fatty acid EPA. Future research into the optimisation of product organoleptic properties is required.     

High pressure assisted extraction of proteins from wet biomass of Arthrospira platensis (spirulina) – A kinetic approach

The application of high-pressure technology (100–600 MPa, 20 °C for up to 20 min) for cell disruption and consequent extraction of proteins -including C-phycocyanin- from the cyanobacteria Arthrospira platensis (spirulina), was investigated. Wet spirulina biomass was suspended in three different aqueous systems (deionized water, phosphate buffer, 10% sodium chloride solution). During a-24 h post processing storage period at 20 °C, the concentration of total soluble proteins and C-phycocyanin content and purity were measured. Color-spectrum and chroma analyses were also performed. The use of deionized water and phosphate buffer as processing/extraction media favoured the extraction process compared to the NaCl solution. Proteins extraction was significantly assisted by pressure. Equal/higher intensity than 400 MPa led to lower C-phycocyanin extraction yields, probably due to denaturation of proteins. High pressure conditions at 300 MPa for 10 min -using deionized water or phosphate buffer as medium- were selected as optimum, leading to higher extraction yields and purity extracts within ~2 h after processing.     

Olfactory responses of Stegobium paniceum to different Chinese medicinal plant materials and component analysis of volatiles

Stegobium paniceum (L.) (Coleoptera: Anobiidae) is among the major pests of stored products, causing great damage to stored Chinese medicinal plant materials (CMPMs) in China. Effective control strategies are urgently needed. The aim of this study was to explore the role of volatile organic compounds in the host preference of S. paniceum. First, the olfactory behavioral responses of S. paniceum adults to volatiles from four CMPMs (Panax notoginseng, Angelica sinensis, Gastrodia elata, and Peucedanum praeruptorum) were tested in Y-tube olfactometer experiments. Then, the volatile composition of these plant materials were analyzed by gas chromatography-mass spectrometry (GC-MS). S. paniceum showed significant preferences for volatiles from the four CMPMs, compared with clean air (CA). When S. paniceum was presented with choices among different CMPMs, it showed the strongest preference for P. notoginseng, followed by A. sinensis, then G. elata, and P. praeruptorum. GC-MS analysis identified 43, 34, 28 and 60 components in the volatile profiles of P. notoginseng, A. sinensis, G. elata, and P. praeruptorum, respectively. Falcarinol (14.4%), 3-n-butyl phthalide (78.7%), p-cresol (40.1%), and β-pinene (29.1%) were the most abundant components of the volatiles of P. notoginseng, A. sinensis, G. elata, and P. praeruptorum, respectively. The olfactory responses of S. paniceum to the four CMPMs demonstrated that host-related volatiles play an important role in the host-searching process by adult beetles. This information will be useful for the development of safe and effective trapping strategies for this pest.     

Gas-assisted exfoliation of boron nitride nanosheets enhancing adsorption performance

A gas exfoliation strategy for controllable preparation of boron nitride (BN) nanosheets with few-layered structure were reported. The green exfoliation process provides the BN nanosheets remarkable increment of adsorption capacities to organic contaminants, which is ascribed to better exposure of active sites originating from the larger surface area and thinner layer. Moreover, the prepared BN also exhibits outstanding recyclability.     

Professional design of chemical plants based on problem-based learning on a pilot plant

This work describes a novel teaching methodology and its application in a subject framed in the last course of the master’s degree in Chemical Engineering at the University of Seville. The main aim consists of promoting a way to facilitate professional practice in this field to the students. Authors also aim at guiding the transition to the new learning requirements demanded by the European Higher Education Area (EHEA).The novel methodology is based on the development of a detailed design of a pilot plant that can be further evaluated by the students themselves. Students are also allowed to run experiments at the facility and carry out several standard tests to verify the quality of the results of their works. The novelty of this proposal consists of incorporating a real installation available in our department to drive new learning methodologies applied in Chemical Engineering curricula. The methodology is distributed across several tasks: training (self-learning), project execution and supervision, comparison with a real installation and pilot plant experiences. The application of the proposed teaching methodology provided quality didactic material production, high satisfaction of the students with the new learning approach and the fact that they gained practical experience at industrial scale.