Research progress and application of ultrasonic- and microwave-assisted food processing technology.

Microwaves are electromagnetic waves of specific frequencies (300 MHz-3000 GHz), whereas ultrasonic is mechanical waves of specific frequencies. Microwave and ultrasonic technology as a new processing method has been widely used in food processing fields. Combined ultrasonic and microwave technology is exploited by researchers as an improvement technique and has been successfully applied in food processing such as thawing, drying, frying, extraction, and sterilization. This paper overviews the principle and characteristics of ultrasonic- and microwave-assisted food processing techniques, particularly their combinations, design of equipment, and their applications in the processing of agricultural products such as thawing, drying, frying, extraction, and sterilization. The combination of ultrasonic and microwave is applied in food processing, where microwave enhances the heating rate, and ultrasonic improves the efficiency of heat and mass transfer. The synergy of the heating effect of microwave and the cavitation effect of ultrasonic improves processing efficiency and damages the cell structure of the material. The degradation of nutrient composition and energy consumption due to the short processing time of combined ultrasonic and microwave technology is decreased. Ultrasonic technology, as an auxiliary means of efficient microwave heating, is pollution-free, highly efficient, and has a wide range of applications in food processing.

Improvement of extrudability and self-support of emulsion-filled starch gel for 3D printing: Increasing oil content.

This work investigated the mechanism of increasing oil content in synchronously enhancing extrudability and self-support of ß-carotene loaded starch-based emulsion-filled gels (S-EFG) during 3D printing in terms of gel properties. Increasing emulsion oil content enhanced the storage modulus, relaxation modulus, and hardness of gels, which indicated sodium caseinate-stabilized emulsions were active fillers in the starch gel. Thus, printed products with high oil content were less prone to collapse when selecting models with higher height. In addition, lower yield stress, relaxation time, and higher frequency dependence were observed in S-EFG with higher oil content (30-50 %) due to the lubricating/plasticizing effect of oils, which corresponded to the smoother extruded filament. Furthermore, the retention of ß-carotene in high oil content gel was higher after heat treatment due to denser microstructure. These results indicated that the extrudability and self-supporting of S-EFG were simultaneously improved by increasing oil content under the active filling effect and lubricating/plasticizing effect of emulsions.

Research progress in fluid and semifluid microwave heating technology in food processing.

Microwave is a form of electromagnetic radiation that has high penetration and heating efficiency in food processing. Uneven heating is the main problem of microwave processing, especially in solid foods. Fluid and semifluid media, which are good carriers in microwave processing, have uniform dielectric properties and good material fluidity. Herein, we review the development, application prospects, and limitations of microwave in fluid and semifluid food processing and the research progress in microwave heating with steam as carrier. The mixture of generated steam and tiny micro droplets from food material under the action of microwave can absorb microwave and transfer heat evenly, which effectively improves the uniformity of microwave heating. Due to the relatively uniform dielectric properties and consistent texture of fluid and semifluid food materials, uneven heating phenomenon during their microwave processing can be significantly inhibited. Based on the development of microwave heating technology and equipment design, the microbial inactivation and enzyme inhibition in fluid and semifluid food were improved and food product with better retention of nutrients and sensory profile were produced. Also, microwave radiation can be used to prepare the printing material or process the printed product for 3D food printing, which enhances the added value of 3D printed products and the personalization of food manufacturing. In future research, intelligent control technology can be applied in the microwave processing of fluid and semifluid food materials for various applications. Therefore, the processing conditions can be adjusted automatically.