Performance of Drying Technologies to Ensure Microbial Safety of Dried Fruits and Vegetables

Abstract

Dried fruits, vegetables, herbs, and spices are produced in and sourced from many countries worldwide, but they have been increasingly reported to be involved in outbreaks and alerts due to the presence of foodborne pathogens such as Salmonella. These dried products are mainly produced by solar drying and conventional air drying, but a wide range of drying technologies are available. From a technological point of view the general trend is to optimize and standardize the drying process to ensure high-quality products to be offered. Drying technologies are mainly evaluated for their performance to reduce water activity at low energy cost while maintaining good sensorial quality of the dried product. However, as low water activity foods are increasingly recognized to support microbial survival and dried products are often consumed as they are, or are used as ingredients in many ready-to-eat foods, there is increasing attention to the microbiological quality and safety aspects of these products. This review presents traditional and emerging technologies to dry fruits, vegetables, herbs, and spices and discusses their potential to inactivate bacteria and viruses throughout the drying process. Overall, the microbial inactivation effect of the presented technologies has not yet been thoroughly assessed, even for traditional methods like solar drying, conventional air drying, or freeze-drying. Emerging technologies such as dielectric (assisted) drying and low-pressure superheated steam drying have been shown to reduce microbial populations; however, the number of studies is still low. Very few studies have focused on viral inactivation during drying processes.

Effect of superheated steam inactivation on naturally existent microorganisms and enzymes of highland barley

“…Indeed, drying occurs during SS processing and microbes are exposed to a low moisture environment, leading to high heat tolerance, especially for dried state (Lang et al ., ). This could be attributed to the thickening in the cell membrane resulting from the microbial cell shrinkage, which commonly increases the resistance to the heat and supports microbial cells survival (Smelt, ; Aronsson & Rönner, ; Bourdoux et al ., ). Tempering would induce high moisture content, thereby affecting the susceptibility of microbes to heat and to be inactivated easily.…”

Model discrimination for drying and rehydration kinetics of freeze‐dried tomatoes

“…For example, in plant cells—that is, fruits and vegetables, which are highly heat‐sensitive—over drying of the product may lead to the loss of the cell turgor and collapse of the food structure (Joardder, Kumar, & Karim, ), preventing the dried product regaining its initial moisture content (A. Marabi & Saguy, ; Marques et al, ). Due to the low processing temperatures – that also minimize the loss of flavor compounds and nutrients—freeze‐drying has found a wide field of application in fruits and vegetables processing (Bourdoux, Li, Rajkovic, Devlieghere, & Uyttendaele, ; Karathanos, Anglea, & Karel, ; Khalloufi & Ratti, ; Marabi & Saguy, ; Meda & Ratti, ).…”

High power ultrasound combined with supercritical carbon dioxide for the drying and microbial inactivation of coriander

“…It is worth pointing out that between 2007 and 2012, 7315 cases of bacterial infection and 63 deaths due to contaminated low-water activity foods were registered worldwide [3]. Indeed, even if traditional drying methods are efficient to obtain low water activity, they do not provide a strong microbial reduction during the dehydration [4]. Pasteurization of the dried products is possible but its efficacy might be inhibited because the heat resistance of microorganisms increases upon dehydration [5].…”