# Effect of Temperatures on Polyphenols during Extraction
## 6 Variance in Source  
It is also important to note that a plant's phenolic content itself may vary depending on plant growing conditions and plant genotypes [73]. Depending on the species, various forms of polyphenols and how they are bound to the plant tissue may vary and generate different effects on extraction temperature [57]. Heat treatment could aid in breaking the phenol-protein and phenol-polysaccharide bonds that increase extraction yield [22]. As the different phenolics in plant tissue are bound differently, the most effective method to extract the phenolic compounds will be different based on the plant species [17].  
[PERSON] et al. [36] performed a PLE for polyphenols from grape peels and seeds. They found that the temperature of extraction did not have a significant impact on the recovery rates from grape skin, but it did from the grape seed. As the breaking of bonds between the phenols and the plant matrix was facilitated at high temperatures, the authors suggested that the phenolic compounds in grape seed must have stronger bonds to the matrix compared with grape skin.  
[PERSON] et al. [50] studied the impact of PLE temperature on two types of sorghum trans and found that the optimum temperature was different for each type. As the profile of polyphenols within each type of sorghum bran is different, the optimal extraction temperature is also different. As seen in Table 2 above, the phenolic profile of each plant is very different, and due to this diversity, the hydrolysis that occurs during extractions at high temperatures may explain the variances reported in the literature.  
To better understand the impact of the source's plant matrix, we can specifically examine one well-studied source of polyphenols: honey. Many studies have investigated the impact of thermal processing on various types of honey, giving us insight into the behaviour of polyphenols.  
[PERSON] et al. [80] found that among four nectar honey variants tested, all four showed an increase in TPC and AOA with thermal treatment at 100 \({}^{\circ}\)C. However, the extent to which it increased depended on the honey variant. For example, The TPC in rapeseed honey increased 15%, while a 27% increase was observed for buckwheat honey [80]. In contrast, [PERSON] et al. [81] found that heat treatment at 60 \({}^{\circ}\)C caused a two-fold reduction in the TPC of eucalyptus honey.  
[PERSON] et al. [82] investigated the impact of thermal processing (82.2 \({}^{\circ}\)C for 10-12 s) on clover and buckwheat honey. There was no significant change in the TPC of clover honey, while the TPC in buckwheat honey showed a decrease. Another study [83] investigated the impact of thermal processing (90 \({}^{\circ}\)C up to 60 min) on honeyde, lime, acacia and buckwheat honey. The results, once again, varied depending on the origin of the honey. There was no significant change in TPC for acacia and buckwheat honey, while TPC increased for lime honey and decreased for honeydew honey [83]. [PERSON], [PERSON] and [PERSON] [84] compared the impact of liquefaction at 55 \({}^{\circ}\)C for 12 h and pasterisation at 90 \({}^{\circ}\)C for 15 s on astragalus and sunflower-cornflower honey. They concluded that the variation in the impact of the process on TPC and AOA is based on the type of honey. [PERSON] et al. [85] studied the influence of heat treatments on phenolic profiles of citrus, rosmary, polyfloral and honeydew honey and also concluded that the flavonoids reacted differently to the heat treatments depending on the origin of the honey.  
From the results of all the studies presented above, we can conclude that even within a single matrix (i.e., honey), the impact of temperature on polyphenols varies depending on the origin and type of honey.