How much do process parameters affect the residual quality attributes of dried fruits and vegetables for convective drying?

Abstract

Drying processes reduce the amount of available essential nutrients in dried plant-based foods to a large extent compared to fresh produce. This reduction is much larger than the differences in the final quality of products dried using various processing parameters and, in most cases, different drying methods. This aspect is, however, rarely highlighted. Here, the extent to which different convective drying methods reduce the nutritional content, namely vitamin C, carotenoids and phenolic content of dried fruits and vegetables, compared to fresh produce was quantified using literature data. The impact of different drying process parameters, such as air temperature, airspeed and relative humidity on the nutritional content of fruits and vegetables were compared. Results revealed that convective drying reduced the amount of vitamin C, carotenoids and the phenolic content of dried fruits and vegetables by up to 70%. The reduction in the residual vitamin C and carotenoid content of dried fruits and vegetables due to differences in air temperature (∼40%), airspeed (∼20%), and relative humidity (∼20%) is much less than the nutritional quality losses due to the drying process. The residual vitamin C, carotenoids and phenolic contents in convective-dried fruits and vegetables are ∼30% less than those in freeze-dried products. This study confirms that little absolute gains in nutritional quality can be achieved by opting for either an alternative drying method or optimizing processing parameters since the drying process already results in a low nutritional quality of dried products. As such, the remaining micronutrient concentration of dried products should not necessarily be a decisive criterion in selecting the most appropriate drying method or processing parameters for fruits and vegetables. Instead, other key performance indicators such as the drying time, energy consumption, or sensory properties such as color, texture, and rehydration capacity could eventually have a greater influence on the decision-making process.