Effect of Intermittent Microwave Volumetric Heating on Dehydration, Energy Consumption, Antioxidant Substances, and Sensory Qualities of Litchi Fruit during Vacuum Drying

Effect of hot-air drying on drying characteristics and quality of tiger nut

BACKGROUND

The delayed drying of newly harvested tiger nuts can lead to mold and rancidity. Timely drying is therefore important. However, few studies have analyzed the impact of hot-air drying on the quality of tiger-nut oil and starch, making it essential to establish optimal drying conditions.

RESULTS

The results showed that the drying temperature was the most important factor affecting the drying speed, followed by drying airflow rate and loading capacity. A logarithmic model can describe the hot-air drying process of tiger nuts. The oil yield of tiger nut was highest after drying at 60 °C, reaching 22.40%. Meanwhile, the starch extracted from after drying at 60 °C had the highest solubility and expansion rate, 4.77% and 9.74%, respectively. Starch has the highest viscosity after drying at 70 °C, and it forms gel easily after aging.

CONCLUSION

High-quality tiger nuts should be produced under optimal conditions: a hot-air drying temperature of 60 °C, an airflow rate of 1.0 m s-1, and a loading capacity of 100 g. The results of this study have practical implications for the effective drying of tiger nuts. © 2024 Society of Chemical Industry.

Research Advances in Plant Protein-Based Products: Protein Sources, Processing Technology, and Food Applications

Plant proteins are high-quality dietary components of food products. With the growing interest in sustainable and healthy food alternatives, plant proteins have gained significant attention as viable substitutes for animal-based proteins. Understanding the diversity of protein sources derived from plants, novel processing technology, and multiple applications is crucial for developing nutritious and sustainable plant protein-based products. This Review summarizes the natural sources of traditional and emerging plant proteins. The classifications, processing technologies, and applications of plant protein-based products in the food industry are explicitly elucidated. Moreover, the advantages and disadvantages of plant protein-based food products are revealed. Strategies such as protein fortification and complementation to overcome these shortcomings are critically discussed. We also demonstrate several issues that need to be addressed in future development.

Multidirectional Polarization Impacts on Microwave Heating Efficiency: A Molecular Dynamics Research of Microwave Heating of Common Solvents

Energy efficiency has always been an inherent problem of microwave heating. In this work, the higher heating efficiency of the elliptically polarized microwave electric field is investigated via MD simulations, aiming to examine the multidirectional polarization effect during microwave heating. The MD results show that the heating efficiency growth rates of EtOH, AcOH, DMSO, H₂O, and DMF are 3.17%, 3.92%, 4.14%, 5.00%, and 27.06% sequentially larger with the elliptically polarized microwave electric field (EF) than those with the linearly polarized microwave EF. Energy analyses indicate that the utilization rate of microwave energy would be increased of the elliptically polarized microwave EF with the same electric field intensities. The higher decay speed of the rotation autocorrelation function curves of elliptically polarized EF presents that the sample molecules do have a more frequent rotational motion to align with the varying polarization directions. Additionally, dielectric properties analysis gave the relation between the heating efficiency growth rate and the loss tangent of the samples. This microwave heating method is expected to be a new route to improve the microwave heating efficiency.

Energy Consumption, Colour, Texture, Antioxidants, Odours, and Taste Qualities of Litchi Fruit Dried by Intermittent Ohmic Heating

To reduce the cost of dried litchi fruit, the processing characteristics and physicochemical properties of litchi were investigated using drying by intermittent ohmic heating (IOH) (intermittent air drying (IAD)) generated by BaTiO₃ resistance. Litchi fruit pulp were dried at 70 °C with an air velocity of 1.8 m/s; the drying intermittent profiles were as follows: (1) 20 min drying-on and 5 min drying-off; (2) 20 min drying-on and 10 min drying-off; and (3) 20 min drying-on and 15 min drying-off, which correspond to pulse ratios (PRs) of 1.2, 1.5, and 1.8, respectively. After drying, the water content, energy consumption, vitamin C content, total phenolic content, colour, taste, and odour qualities were assessed. The results suggested that IOH drying requires lower energy consumption and yields higher quality products. The energy consumption of intermittent air drying ranged from 341 kJ∙g^-1 to 427 kJ∙g^-1. The IAD of 1.2 and 1.5 PR reduced the browning of litchi fruits and gained better product quality. The major components of odour and tastes were explored in dried litchi. The rising PR of IAD enabled a lower retention of methane and sulphur-organic aroma and a higher assessing value of bitterness taste. This study revealed that BaTiO₃ is suitable for IOH drying and it resulted in more merits of dried litchi fruit.

Effect of Different Drying Techniques on Dehydration Kinetics, Physical Properties, and Chemical Composition of Lemon Thyme

Lemon thyme contains several bioactive health-promoting compounds of high antioxidant capacity—such as polyphenols, carotenoids, and chlorophyll—which may undergo degradation during drying in incorrect processing conditions. This work is aimed at evaluating the impacts of different drying techniques and parameters on the chemical and physical properties of lemon thyme. In the experiment, lemon thyme leaves are dried using two traditional hot-air methods, convective drying (temperature 70°C or 80°C, air velocity 2 m/s), and fluidized bed drying (temperature 70°C or 80°C, air velocity 5–10 m/s); as well as two innovative drying methods, microwave-assisted fluidized bed (MFB) drying (microwaves at a power of 240 or 440 W, air temperature 40°C, air velocity 5–10 m/s) and microwave-vacuum (MV) drying (microwaves at a power of 240 or 440 W, under vacuum at 4–6 kPa). The kinetics of water delivery are described using the Page Model. After drying, the nutritional composition of the material is analyzed: polyphenol (total content and polyphenols profile by ultra-performance liquid chromatography), carotenoid, and chlorophyll total content, as well as antioxidant capacity (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt [ABTS+] and ferric reducing antioxidant power [FRAP]). Color changes ( L*, a*, b*, ΔE) are also analyzed using the visible effects of lemon thyme pigment disintegration. It is found that the MV drying method is the best for lemon thyme preservation, as it has the shortest process time and the highest retention of polyphenols (78.90%-82.14%), chlorophylls (51.54%-52.68%), antioxidant capacity (47.83%-48.63% of ABTS+ and 20.85%-45.45% of FRAP), and presented the least color change ( ΔE = 25.57-28.32). For preserving carotenoids, the most protective method is MFB (retention 68.46%-70.61 %).