Pretreatment is widely used before drying of agro-products to inactivate enzymes, enhance drying process and improve quality of dried products. In current work, the influence of various pretreatments on drying characteristics and quality attributes of fruits and vegetables is summarized. They include chemical solution (hyperosmotic, alkali, sulfite and acid, etc.) and gas (sulfur dioxide, carbon dioxide and ozone) treatments, thermal blanching (hot water, steam, super heated steam impingement, ohmic and microwave heating, etc), and non-thermal process (ultrasound, freezing, pulsed electric field, and high hydrostatic pressure, etc). Chemical pretreatments effectively enhance drying kinetics, meanwhile, it causes soluble nutrients losing, trigger food safety issues by chemical residual. Conventional hot water blanching has significant effect on inactivating various undesirable enzymatic reactions, destroying microorganisms, and softening the texture, as well as facilitating drying rate. However, it induces undesirable quality of products, e.g., loss of texture, soluble nutrients, pigment and aroma. Novel blanching treatments, such as high-humidity hot air impingement blanching, microwave and ohmic heat blanching can reduce the nutrition loss and are more efficient. Non-thermal technologies can be a better alternative to thermal blanching to overcome these drawbacks, and more fundamental researches are needed for better design and scale up.

Chemical and physical pretreatments of fruits and vegetables: Effects on drying characteristics and quality attributes - a comprehensive review.

In food processing, the applications of ultrasound can be divided into two categories, namely replacing traditional technologies and assisting traditional technologies In the latter case, the processing efficiency is enhanced and the disadvantageous of traditional technologies during processing are improved These ultrasonic effects can be defined as ultrasonic enhancement of food processes This review is focused on the use of ultrasound to enhance various food processes, including extraction, freezing, thawing, brining, oxidation, filtration, and drying/dehydration The major functions of ultrasound in enhancing these processes and the factors which can affect the ultrasonic enhancement are elucidated In the meantime, the strategies of modeling these processes enhanced by ultrasound are provided Future studies should pay more attention to elucidate the ultrasonic effects during freezing, thawing, brining, oxidation, and filtration processes Furthermore, when it comes to design the ultrasound equipment at the industrial level, it is better to quantify the ultrasonic effects through numerical stimulation

Enhancement of Food Processes by Ultrasound: A Review

The demand for convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives, has spurred the need for the development of a number of non-thermal approaches to food processing, of which ultrasound technology has proven to be very valuable. Increasing number of recent publications have demonstrated the potential of this technology in food processing. A combination of ultrasound with pressure and/or heat is a promising alternative for the rapid inactivation of microorganisms and enzymes. Therefore, novel techniques like thermosonication, manosonication, and manothermosonication may be a more relevant energy-efficient processing alternative for the food industry in times to come. This review aims at identifying the opportunities and challenges associated with this technology. In addition to discussing the effects of ultrasound on foods, this review covers various areas that have been identified as having great potential for future development. It has been realized that ultrasound has much to offer to the food industry such as inactivation of microorganisms and enzymes, crystallization, drying, degassing, extraction, filtration, homogenization, meat tenderization, oxidation, sterilization, etc., including efficiency enhancement of various operations and online detection of contaminants in foods. Selected practical examples in the food industry have been presented and discussed. A brief account of the challenges in adopting this technology for industrial development has also been included.

Opportunities and challenges in application of ultrasound in food processing

Energy and exergy analyses of solar drying system of red seaweed

Direct and indirect power ultrasound assisted pre-osmotic treatments in convective drying of guava slices

Effect of ultrasound on banana cv Pacovan drying kinetics

The effect of ultrasound and osmotic dehydration pretreatments on papaya drying kinetics was investigated. The ultrasound pretreatment was carried out in an ultrasonic bath at 30 °C. The osmotic pretreatment in sucrose solution was carried out in an incubator at 34 °C and agitation of 80 rpm for 210 min. The drying process was conducted in a fixed bed dryer at 70 °C. Experimental data were fitted successfully using the Page model for dried fresh and pretreated fruits, with coefficient of determination greater than 0.9992 and average relative error lower that 14.4 %. The diffusional model was used to describe the moisture transfer, and the effective water diffusivity was identified in the order of 10−9 m2 s−1. It was found that drying rates of osmosed fruits were the lowest due to the presence of infused solutes, while the ultrasound pretreatment contributed to faster drying rates. Evaluation of the dried fruit was performed by means of total carotenoids retention. Ultrasound treatments in distilled water prior to air-drying gave rise to dried papayas with retention of carotenoids in the range 30.4–39.8 % and the ultrasonic-assisted osmotic dehydration of papayas showed carotenoids retention values up to 64.9 %, whereas the dried fruit without pretreatment showed carotenoids retention lower than 24 %.

Sofia Sorelly Belém Oliveira

Papers

Effect of ultrasound on banana cv Pacovan drying kinetics

Improvement of water transport and carotenoid retention during drying of papaya by applying ultrasonic osmotic pretreatment