Freeze-dried berry fruits are generally consumed as they are, whole and without peeling or cutting, as the conservation of their original shape and appearance is often desired for the final product. However, usually, berries are naturally wrapped by an outer skin that imparts a barrier to vapor flow during freeze-drying, causing berry busting. Photo-sequence, experimental, and theoretical methodologies were applied to evaluate the application of CO₂ laser microperforations to blueberry skin. Under the same set of freeze-drying conditions, blueberries with and without perforations were processed. The results showed that the primary drying time was significantly reduced from 17 ± 0.9 h for nontreated berries to 13 ± 2.0 h when nine microperforations per berry fruit were made. Concomitantly, the quality was also significantly improved, as the percentage of nonbusted blueberries at the end of the process increased from an average of 47% to 86%. From a phenomenological perspective, the analysis of the mass transfer resistance of nontreated fruits, in agreement with reported studies, showed a Type II curvature, with a sharp decrease at low time, followed by a linear increase. In contrast, blueberries with nine perforations depicted a Type III regime, with a saturation curvature toward the time axis. It was demonstrated that CO₂-laser microperforation has high potential as a skin pretreatment for the freeze-drying of blueberries.

Thermal processing is still the most important method to ensure food safety, however, there is a need for further improvements, from basic data to advanced optimization methods. Due to the competitive market, customer demands and environmental concerns, several challenges have been raised. In this review, some important topics are discussed, including inactivation kinetics, engineering properties, process design and control, packaging systems and regulatory, environmental, and economic aspects. This position paper describes our opinion about the main challenges associated with thermal processing (conventional and alternative technologies, as microwave and ohmic heating), as well as some possibilities to deal with them.