Main Challenges Expected from the Impact of Climate Change on Microbial Biodiversity of Table Olives: Current Status and Trends

Abstract

Climate change is a global emergency that is affecting agriculture in Mediterranean countries, notably the production and the characteristics of the final products. This is the case of olive cultivars, a source of olive oil and table olives. Table olives are the most important fermented vegetables in the Mediterranean area, whose world production exceeds 3 million tons/year. Lactic acid bacteria and yeast are the main microorganisms responsible for the fermentation of this product. The microbial diversity and population dynamics during the fermentation process are influenced by several factors, such as the content of sugars and phenols, all of which together influence the quality and safety of the table olives. The composition of fruits is in turn influenced by environmental conditions, such as rainfall, temperature, radiation, and the concentration of minerals in the soil, among others. In this review, we discuss the effect of climate change on the microbial diversity of table olives, with special emphasis on Spanish and Portuguese cultivars. The alterations expected to occur in climate change scenario(s) include changes in the microbial populations, their succession, diversity, and growth kinetics, which may impact the safety and quality of the table olives. Mitigation and adaptation measures are proposed to safeguard the authenticity and sensorial features of this valuable fermented food while ensuring food safety requirements.

Keywords: climate change; mitigation measures; safety; spoilage; table olives.

Figure 1

Photo of the Iberian Peninsula showing the impact of the dry weather on vegetation, created using data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) between 7 April and 22 April 2005. Brown represents those regions where vegetation was thin and less dense than average. Source: NASA Earth Observatory [5].

Figure 2

Effect of a 4 °C increase in ambient temperature on fruit anthocyanins (cyaniding-3-glucoside equivalent kg⁻¹ FW) and polyphenols (mg caffeic acid kg⁻¹ pulp) content. AT: ambient temperature (in 2015, the average ambient temperatures ranged from 7 °C to 30 °C (with a minimum temperature of 1 °C and a maximum temperature of 38 °C), in 2016, they varied between 11 °C and 32 °C (with a minimum of 7 °C and a maximum of 40 °C), and in 2017, they spanned from 8 °C to 30 °C (with a minimum of 2 °C and a maximum of 38 °C)); AT + 4 °C: 4 °C increase in ambient temperature; the average within each column followed by different letters is significantly different at p ≤ 0.05 by F-test. The coefficient of variation (%) is represented as dashed lines in green and blue (right axis), where a higher value indicates greater relative variability compared to the mean, whereas a lower coefficient of variation indicates less variability in relation to the mean (Source: [25]).

Figure 3

Daily values of maximum (red) and minimum (blue) temperature (°C) and rainfall (grey) (L/m²), measured in the Arahal region (Seville, Spain) over four years (2019–2022) [28].

Figure 4

Table olive production (tons) from 1990 to 2022. (a) World production; (b) Spanish production; and (c) Portuguese production. The dashed line refers to the production trend.

Figure 5

Projected impact of high temperatures and low rainfall on microbial populations in Spanish-style table olives.