Influence of Alkaline Treatment on Structural Modifications of Chlorophyll Pigments in NaOH—Treated Table Olives Preserved without Fermentation

Abstract

Alkaline treatment is a key stage in the production of green table olives and its main aim is rapid debittering of the fruit. Its action is complex, with structural changes in both the skin and the pulp, and loss of bioactive components in addition to the bitter glycoside oleuropein. One of the components seriously affected are chlorophylls, which are located mainly in the skin of the fresh fruit. Chlorophyll pigments are responsible for the highly-valued green color typical of table olive specialties not preserved by fermentation. Subsequently, the effect on chlorophylls of nine processes, differentiated by NaOH concentration and/or treatment time, after one year of fruit preservation under refrigeration conditions, was investigated. A direct relationship was found between the intensity of the alkali treatment and the degree of chlorophyll degradation, with losses of more than 60% being recorded when NaOH concentration of 4% or greater were used. Oxidation with opening of the isocyclic ring was the main structural change, followed by pheophytinization and degradation to colorless products. To a lesser extent, decarbomethoxylation and dephytylation reactions were detected. An increase in NaOH from 2% to 5% reduced the treatment time from 7 to 4 h, but fostered greater formation of allomerized derivatives, and caused a significant decrease in the chlorophyll content of the olives. However, NaOH concentrations between 6% and 10% did not lead to further time reductions, which remained at 3 h, nor to a significant increase in oxidized compounds, though the proportion of isochlorin e4-type derivatives was modified. Chlorophyll compounds of series b were more prone to oxidation and degradation reactions to colorless products than those of series a. However, the latter showed a higher degree of pheophytinization, and, exclusively, decarbomethoxylation and dephytylation reactions.

Assessment of different debittering techniques to valorize orange peel

“…Alkali treatment and subsequence washing, and soaking, has been reported as an efficient method to debitter OPs (Yıldız Turgut et al ., 2016). Also, similar treatments have been used for debittering olives, showing a loss of bioactive compounds such as phenolic compounds (TPC) when compared to fresh olives (Alexandraki et al ., 2014; Berlanga‐Del Pozo et al ., 2020). Results of the present study seemed to confirm the utility of alkali blanching to decrease TPC as well as bitterness perception in OP, although the other methods seemed to lead to a greater decrease in TFC (e.g., salt blanching or lactic acid fermentation).…”

Chlorophyllides: Preparation, Purification, and Application

“…Hynninen and Hyvärinen further demonstrated the allomerization pathways of chlorophylls under essentially anhydrous chlorophyll and thoroughly dried methanol [150]. The treatment of 2-5% NaOH from 7 to 4 h increased the formation of allomerized derivatives of chlorophyll [149,152,153]. Some examples of chlorophyllides purification by chromatography are shown in Table 4.…”

“…At the chiral C13 2 -position, chlorophyll(ide)s are transformed to epimers via stereoinversion and allomers via oxidation [146][147][148]. It is well known that the epimerization and allomerization occur easily under basic conditions and an alcoholic solution [149,150]. Hynninen et al reported a free-radical allomerization mechanism of chlorophyll [151].…”

Characterization and Processing of Table Olives: A Special Issue

“…However, its action is complex and structural changes in the olive, and loss of bioactive components, also occur. Because chlorophylls are one of the bioactive components seriously affected, Berlanga-Del Pozo et al [ 10 ] designed a work aimed to investigate the effect of the alkaline treatment on these pigments that are responsible for the characteristic bright green color of table olives not preserved by fermentation. Specifically, the authors investigated the effect of nine combinations of two important parameters of the alkali treatment (NaOH concentration and treatment time) on green table olives processed in the Campo Real style and preserved for 1 year under refrigerated conditions.…”

“…To conclude, the present special issue consists of 10 original research papers and two review articles. The research papers, focused on recent research advances related to characterization and processing of table olives, have covered microbiological and chemical changes in table olives during spontaneous or controlled fermentation employing different cultivars [ 3 ], characterization of their composition of volatiles and the sensory profile [ 5 , 6 , 7 ], mineral composition [ 8 ] and bioavailability [ 9 ], changes in bioactive components (chlorophylls) by processing [ 10 ], optimized use of starter cultures for the improvement of the different fermentative processes [ 4 , 5 ], and new strategies to reduce sodium and additives, to stabilize the organoleptic properties and avoid defects [ 11 , 12 ].…”