Abstract
Spontaneous fermentation constitutes the basis of the chief natural method of processing of table olives, where autochthonous strains of lactic acid bacteria (LAB) play a dominant role. A thorough literature search has unfolded 197 reports worldwide, published in the last two decades, that indicate an increasing interest in table olive-borne LAB, especially in Mediterranean countries. This review attempted to extract extra information from such a large body of work, namely, in terms of correlations between LAB strains isolated, manufacture processes, olive types, and geographical regions. Spain produces mostly green olives by Spanish-style treatment, whereas Italy and Greece produce mainly green and black olives, respectively, by both natural and Spanish-style. More than 40 species belonging to nine genera of LAB have been described; the genus most often cited is Lactobacillus, with L. plantarum and L. pentosus as most frequent species—irrespective of country, processing method, or olive type. Certain LAB species are typically associated with cultivar, e.g., Lactobacillus parafarraginis with Spanish Manzanilla, or L. paraplantarum with Greek Kalamata and Conservolea, Portuguese Galega, and Italian Tonda di Cagliari. Despite the potential of native LAB to serve as starter cultures, extensive research and development efforts are still needed before this becomes a commercial reality in table olive fermentation.
Highlights
Olives are drupes characterized by bitter taste, low carbohydrate content (2.5–6% w/w), and high oil content (10–15% w/w), depending on time of the year and cultivar [1]
To be used in food fermentation, microorganisms should be selected at the strain level—since not all strains are suitable for use as starters, nor are all well-adapted to food substrates [102,103]
The thorough search conducted on fermentation of table olives reveals that most scientific publications originate in countries of the Mediterranean basin—especially Italy, Greece, Portugal, and Spain
Summary
Olives are drupes characterized by bitter taste, low carbohydrate content (2.5–6% w/w), and high oil content (10–15% w/w), depending on time of the year and cultivar [1]. 80% of those carbohydrates, whereas glucose, fructose, sucrose, xylose, and rhamnose account for the remainder. Despite a lower richness in sugars than other drupes, olives can still support active microbial fermentation, provided that sufficiently long timeframes are allowed. The aforementioned bitterness is due to the presence of phenolic compounds, oleuropein—which appears to play a defense role against predators. The main natural method of table olive processing is fermentation, which starts spontaneously owing to the presence of native microorganisms. The underlying microbial ecosystem is complex and variable; its dynamics throughout fermentation is determined by parameters that influence metabolism, Foods 2020, 9, 948; doi:10.3390/foods9070948 www.mdpi.com/journal/foods
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