# Impact of Frost on the Morphology and Chemical Composition of _cv_. [PERSON]
## 1 Introduction  
Olive oil, the main source of fat in the Mediterranean diet, is a food with an exceptional balance between saturated and unsaturated fatty acids, containing other important minor compounds such as polyphenols, tocopherols, carotenoids, sterols, and chlorophylls. Fruit cultivar, agronomic practices, fruit ripeness, weather, and geographical origin (soil conditions, latitude, and altitude) greatly influence the physicochemical and sensory profiles of the olive oils [1; 2; 3; 4; 5; 6].  
Establishing the \"right time\" to harvest is of utmost significance. During the ripening process of the fruit, several chemical and enzymatic reactions change the color, pulp-to-stone ratio, weight, oil content, and phenolic compound concentration, reflecting the final olive oil composition [7; 8] and conditioning its yield, sensory characteristics, shelf-life, and color. Olive color can be used to assess the ripeness index of the olive fruit because the photosynthetic activity decreases along with ripeness, reducing the concentration of chloroplast pigments, and changing the green olive fruit coloration to purple shades [8]. Later harvest will also deliver olives with a higher percentage of oil per mass of the fruit (lower moisture content), increasing the olive oil extraction yield per fruit mass, although not necessarily per tree. However, these olive oils have low bitterness and lack green fruit aromas compared to oils extracted from olives at earlier ripeness stages, showing a shorter shelf-life imposed by a reduction on its natural antioxidants and being, therefore, moreprone to the appearance of defects such as rancidity [9]. On the other hand, too early a harvest leads to reduction of the extraction yield and, occasionally, to the extraction of unacceptable oils from an organoleptic point of view, due to an excessive bitterness imposed by its high concentration of polyphenols [7; 8; 10]. Thus, olive farmers and olive oil producers face a dilemma in establishing the best harvest time-period, which would allow farmers to obtain a satisfactory yield without compromising the olive oil physicochemical quality.  
In addition to all these expected biological evolutions of the plant, the weather conditions are of utmost importance for the ripening evolution, and consequently, the definition of harvest. Climate change and unexpected weather events, particularly unpredicted early frosts or other extreme weather phenomena, have increased the complexity of these decisions. While natural weather variations are known to influence the composition of olive oils, with a higher proportion of monounsaturated fatty acids at lower temperatures [11; 12], among other known variations, the effect of frost on olive oil yield and quality has only been recently addressed [13; 14; 15; 16].  
Frost occurs every year across southern and eastern agricultural geographical regions. Mediterranean countries like Portugal are also affected by frost. This phenomenon is particularly problematic in the Tras-os-Montes region (northeast of Portugal), the second-largest Portuguese production area of olive trees for oil extraction. Olive oils from the Tras-os-Montes region are well-known for their high physicochemical quality and distinctive sensory characteristics. One example is the olive oils extracted from Santulhana cultivar, whose olives have medium-high weight, are large and symmetric, with an interesting oil yield and high levels of antioxidants [17]. Unfortunately, olive groves with Santulhana trees are mainly located in the northeast of Portugal, a geographical area with optimal conditions (i.e., clear, cold nights, without wind or at higher altitudes) for frost occurrences.  
In this sense, and to truly understand the frost impact on the quality of \(\varpi\). Santulhana olives, several morphological and chemical parameters were evaluated in olives subjected or not subjected to frost conditions, aiming to provide a decision basis regarding its harvest and quality impact.