## 3 Effect of Food Processing and Culinary Preparations on PAs, TAs and OAs
### Thermal Treatment
also confirmed the stability of these compounds at 100 \({}^{\circ}\)C by performing a stability study with standard solutions of PAs [70]. However, [PERSON] (2007) evaluated the thermal stability of retrosine (a 1,2-unsaturated PA) in contaminated maize flour while preparing maize porridge. The flour was boiled with water for 3 h. After this thermal process, a slight reduction in the content of retrosine was observed in the maize porridge, suggesting its degradation by heat application [71]. Nonetheless, these results were not conclusive, as it was not clear if the reduction observed in the retrosine content was due to heat degradation or to an extraction inefficiency caused by the formation of emulsions [71]. On the other hand, [PERSON] et al. also reported degradation of both PAs and PANOs during tea manufacturing, specifically during the drying stage [72]. However, the degradation of PANOs was sharper than the degradation of PAs, with degradative percentages in the ranges 58.2-79.2% and 0.8-26.4%, respectively [72]. Nonetheless, they also showed a simultaneous increase in PAs with a reduction in PANOs during the withering step, suggesting PANOs would be transformed to their corresponding PAs [72]. Accordingly, it is important to highlight that although these compounds may not degrade or completely disappear at high temperatures, they do not remain unchanged either. In this context, some works have described that the tertiary PAs/PANOs ratio and the total content of PAs can be modified with the application of heat [73; 74]. Likewise, the transformation of monoester PAs to diesters by heat action has also been reported [58; 59]. In the work carried out by [PERSON] et al. it was confirmed that the content of these alkaloids in a contaminated pollen sample decreased when it was dried with heat [75]. However, the degradation was mainly observed in the PANO content (up to 30%). However, a concomitant increase (150-190%) was determined in the PA free bases [75]. This was attributed to the fact that PANOs were degraded by heat into their corresponding free base primary PAs, maintaining the total levels of PAs [75]. In the same line, [PERSON] et al. confirmed the heating process, such as drying, contributed to PANO reduction and their transformation to their related PAs, while PAs were more stable so they were difficult to oxidize to their corresponding PANOs [72]. In contrast, it was observed that storing contaminated honey with PAs at 20 \({}^{\circ}\)C long-term did not decrease the content of PANOs [76]. Likewise, no inter-conversion to their corresponding PAs was observed under these conditions [76]. [PERSON] et al. (2019) also evaluated the stability of PAs at two different temperatures (15 and 30 \({}^{\circ}\)C) in bee bread samples [77]. It was observed that the overall PA content remained relatively stable at 15 \({}^{\circ}\)C, while at 30 \({}^{\circ}\)C it decreased by 33-39%, mainly due to a reduction in the PANO content. Thus, it seems from the data of these works, that heat may produce a certain degree of thermal degradation, but it can also induce the reduction of PANOs into their corresponding free base primary PAs. Nonetheless, since in the work of [PERSON] et al. (2019) the content of tertiary PAs did not increase accordingly in the stored bee bread, authors excluded a simple reduction of PANOs into their corresponding tertiary PAs. Thus, they suggested that PANO reduction might be caused by the digestive enzymes that bees added to their honey during the production of bee bread [77]. Overall, as can be deduced from all these works, there is much controversy about the effect of heat on the content of PAs and PANOs. Many of the results published are uncertain and inconclusive. One of the main reasons is that many of these works have not carried out an exhaustive control of the variables and parameters that can affect this process. Likewise, none of these works include the study of kinetics and thermodynamic parameters related to the thermal degradation of PAs.