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UC Davis UC Davis Previously Published Works Title Reducing Phenolics Related to Bitterness in Table Olives Permalink https://escholarship.org/uc/item/66x5590m Authors Johnson, RL Mitchell, AE Publication Date 2018 DOI 10.1155/2018/3193185 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Hindawi Journal of Food Quality Volume 2018, Article ID 3193185, 12 pages https://doi.org/10.1155/2018/3193185 Review Article Reducing Phenolics Related to Bitterness in Table Olives Rebecca L. Johnson and Alyson E. Mitchell Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA Correspondence should be addressed to Alyson E. Mitchell; [email protected] Received 21 May 2018; Revised 9 July 2018; Accepted 24 July 2018; Published 13 August 2018 Academic Editor: Amani Taamalli Copyright © 2018 Rebecca L. Johnson and Alyson E. Mitchell. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Olives are one of the oldest food products in human civilization. Over the centuries, numerous methods have been developed to transform olives from a bitter drupe into an edible fruit. Methods of processing table olives rely on the acid, base, and/or enzymatic hydrolysis of bitter phenolic compounds naturally present in the fruit into nonbitter hydrolysis products. Today, there are three primary methods of commercial table olive processing: the Greek, Spanish, and Californian methods, in addition to several Artisanal methods. is review focuses on the technological, microbiological, chemical, and sensory aspects of table olive processing and the inherent benets and drawbacks of each method. e table olive industry is facing challenges of environmental sustainability and increased consumer demand for healthier products. Herein, we examine current research on novel technologies that aim to address these issues. 1. Introduction e consumption of table olives increased globally by 182% [4], and olive oil consumption increased by 76% e olive tree (Olea europaea L.) was rst cultivated ap- between 1990 and 2016 [5]. is increase is attributed to the proximately 5000–6000 years ago in the early bronze age and popularity of the Mediterranean diet, which is linked to is one of the oldest known cultivated plants [1]. Ripe olives reducing cardiovascular disease [6], Alzheimer’s disease contain high levels of bitter phenolic compounds including [7, 8], and other age-related conditions [9]. Consumption of oleuropein and ligstroside that make the fruit inedible [2, 3]. olive oil is an essential component of the Mediterranean diet In order for olives to be considered suitable for human due to presence of mono-unsaturated fatty acids and phe- consumption, the fruit must undergo some form of pro- nolic compounds that are unique to Olea europaea and cessing, fermentation, or curing to reduce the concentration exhibit antioxidant [10], anti-in£ammatory [11], anticancer of these bitter phenolic compounds. Various methods are [12], antimicrobial, and antiviral properties [13, 14]. is used worldwide to debitter olives. Many of these methods phenolic fraction is also present in table olives. Current have roots in ancient antiquity (e.g., salt curing), while commercial table olive processing methods remove many of others employ recent technological developments (e.g., these bitter phenolic compounds and as a result, can alter the California black ripe processing). health-promoting potential of various table olive products Today, there are three main commercial approaches used [15, 16]. Additionally, current commercial table olive pro- for debittering olives which include Greek, Spanish, and cessing methods are some of the most water intensive California processing methods (Table 1; Figure 1). In ad- methods used in commercial food processing and can re- dition, there are several artisanal methods used to produce quire more than 7,571 liters of water per ton of olives table olives with limited industrial scalability (e.g., salt curing (e.g., California and Spanish methods) and generate highly or air-dried olives). Each method of debittering produces toxic wastewater. Increased consumer demand for healthier a dierent style of table olives with a unique texture and food products that are produced in an environmentally chemical, microbial, and sensorial proles. sustainable manner, as well as industrial interest in 2 Journal of Food Quality Table 1: Comparison of Greek natural, Spanish green, and California style black ripe table olives processing parameters. Method Greek natural Spanish green Californian style black ripe Raw fruit Purple maturation Green maturation Green maturation Debittering mechanism Diusion Base hydrolysis + diusion Base hydrolysis Debittering time 6–12 months 1–7 months 1 week Final pH ∼4 ∼4 5.8–7.9 Final color Purple or dark brown Green or pale yellow Black (articial color) Flavor Salty, acidic, and fermented Salty, acidic, and fermented Soapy, earthy, and buttery Wastewater per ton olive 0.9–1.9 m3/t 3.9–7.5 m3/t 8.0 m3/t Sterilization required No No Yes Drawbacks Long processing time — Carcinogenic acrylamide Greek Spanish California Purple olives harvested Green olives harvested Green olives harvested Stored in brine Lye treatment Lye treatment Washing Washing and air oxidation Brine (4–10% NaCl) Brine (4–10% NaCl) Repeat (3-4x) until pH>8 (3-4x) until Repeat Fermentation (pH<4) Fermentation (pH<4) 5 g/L ferrous gluconate Pasteurization Pasteurization Pasteurization at 80°C for 8 min at 80°C for 8 min at 121°C for 8 min Figure 1: Diagram of Greek natural, Spanish green, and California style black ripe table olives processing methods. decreasing processing time, water usage, and cost, demon- compounds that contribute to the green color in olives de- strates the need for innovation in olive processing technolo- crease (i.e., chlorophylls and carotenoids) and the compounds gies. is review focuses on the technological, microbiological, that contribute to red and purple colors increase chemical, and sensory aspects of table olive processing, in- (i.e., anthocyanins) [19]. As olives transition from green to cluding the benets and drawbacks of each processing purple, the cell wall of the fruit begins to rupture, softening the method, and examines proposed novel technologies to im- texture, and releasing enzymes, including the endogenous prove table olive quality and industry sustainability. β-glucosidases and esterases [20, 21]. Endogenous enzymes within the olive fruit hydrolyze oleuropein and ligstroside into 2. Olive Fruit Maturation derivative compounds (i.e., oleuropein aglycone, ligstroside aglycone, oleocanthal, oleacein, hydroxytyrosol, tyrosol, Olive fruits are spherical or oval drupes, classied as small oleoside methyl ester, and elenolic acid) that can then (less than 3 grams), medium (3–5 grams), or large (over 5 themselves be further hydrolyzed [22]. (Figure 2) As a result, grams) [17]. During growth, olive drupes are green, and they the phenolic prole of green stage olives is dierent than accumulate bitter phenolics including oleuropein and lig- purple stage olives, with the former containing a higher stroside within the £esh and skin. Oleuropein and ligstroside concentration of bitter phenolics [23, 24]. Although the are secoiridoids (i.e., a subclass of monoterpenoid iridoid purple olive fruit is less bitter than the green, both green and compounds) that accumulate in the £esh and skin of olives purple fruit of most varieties are far too bitter to be consumed as a protective mechanism against insect, pathogen, and raw without some form of processing or curing to reduce herbivore attack (Figure 2) [18]. levels of these bitter phenolic compounds. Green olives undergo three maturation stages on the tree e olive fruit intended for table olive processing can be which include (1) the green stage, (2) the turning color stage, picked at any time during the maturation cycle, and olives and (3) the purple stage [17]. Color change occurs as the intended for Greek fermentation, salt curing, or air drying Journal of Food Quality 3 Glucose R O R Esterase/ Glucose OH OH ester hydrolysis O O O O + HO O OH R=OH for hydroxytyrosol R=OH for oleuropein R=H for tyrosol O O Oleoside methyl ester R=H for ligstroside O O Beta-glucosidase/ hydrolysis OH R R OH OH O O OH Esterase/ ester hydrolysis O O O + HO OH O O R=OH for hydroxytyrosol R=OH for oleuropein aglycone R=H for tyrosol R=H for ligstroside aglycone O O Elenolic acid Esterase/ ester hydrolysis OH R OH O O O R=OH for oleacein R=H for oleocanthal Figure 2: Olive secoiridoids and their hydrolysis products. are generally harvested when purple, whereas olives phenolic compounds found in very few edible plants apart intending for Spanish and California processing methods are from olives and are among the more important compounds in harvested in the green stage [17]. Choice of the harvest stage regard to sensory perception of bitterness [2, 26]. Secoiridoids will have an impact on the textural, sensorial, and chemical are characterized by an exocyclic 8,9-olenic functionality, aspects of the nal product. comprised of an elenolic acid and a glucosidic residue, also known as an oleosidic skeleton. Notable secoiridoids in olives 3. Phenolic Compounds in Olives include oleuropein, ligstroside, and dimethyl oleuropein, as well as their phenolic derivatives

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