Traditional and industrial oven-dry processing of olive fruits: influence on textural properties,cell wall polysaccharide composition,and enzymatic activity

The preparation of table olives according to the Italian traditional “Ferrandina” method (Fer) includes an initial blanching step of black Cassanese olives, followed by salting and oven-drying. Its industrial implementation, also called the “Sybaris” method (Syb), replaces the blanching procedure by cutting the olives followed by immersion in water. The measurement of tensile properties showed that the Fer processing increased the weakness, softness, and deformability of the skin and the flesh of olive fruits, while the flesh of the Syb fruits became stronger and stiffer. These differences are probably correlated to the degradation and/or reorganisation of cell wall polysaccharides in the fruits. The degradation of pectic and hemicellulosic polysaccharides in the Fer olives was inferred by their increased solubility in aqueous solutions. Contrarily, retention of pectic polysaccharides was observed in Syb olives. As no correlation was found between cell wall degrading enzymatic activities and cell wall polysaccharides extractability, it is probable that these modifications were driven by heat.     

Naturally fermented black olives: Effect on cell wall polysaccharides and on enzyme activities of Taggiasca and Conservolea varieties

Black olives of Taggiasca (Ta) and Conservolea (Co) varieties were processed according to the Greek style method in order to investigate the effect of this type of table olive processing on cell wall composition. Naturally black processing involves the storage in brine of fully ripe olives for several months, allowing a spontaneous fermentation by a mixed flora followed by fermentation by the lactic acid bacteria and yeasts. The smaller fruits of Ta variety are richer in pectic polysaccharides, accounting for half of total cell wall polysaccharides (12 mg/fruit), whereas in Co they accounted for one third (23 mg/fruit). Fresh Co olives had higher proportion of glucuronoxylans and xyloglucans (33%), whereas these polysaccharides accounted for 22% in Ta. The processing did not cause significant variations in the cell wall polysaccharide composition of Ta fruits, although pectic polysaccharides became more soluble in aqueous solutions. Conversely, processed Co olives had slightly higher amounts of galacturonan-rich pectic polysaccharides than the unprocessed fruits, suggesting that the long stage in brine might have contributed to the stabilisation and/or the biosynthesis of new polysaccharides. The changes caused by processing on cell wall polysaccharides appear to be closely related to the activity and availability of cell wall degrading enzymes.     

Oven‐dried table olives: textural properties as related to pectic composition

The effects of processing treatments on the microscopic structure, pectic fractions and firmness of ripe olives (Olea europaea L Cassanese variety), processed by the ‘Ferrandina’ method for oven‐dried table olive production, were studied. The process included a first heating step, a salting step and a final oven‐drying process. Scanning electron microscopic observations of olive tissue structure revealed that heat treatment was highly damaging, affecting the intercellular pectic substances and producing cell separation. Epicuticular waxes were barely affected and limited the shrivelling of the fruit during the oven dehydration process. The pectin content was higher in the oven‐dried olives than in the fresh samples. The sodium hydroxide‐soluble fraction was the main pectin fraction in the olive tissues. Its content decreased markedly after the heating step, while it increased after the oven dehydration step. The softening of the olive tissues increased after heat treatment, and a correlation was found between protopectin content and firmness. In oven‐dried olives a firming of the olive tissues was observed due to the de‐esterification of pectin and to its decreased solubility resulting from an increase in cell wall calcium bridging. © 2000 Society of Chemical Industry     

Cell wall polysaccharides implied in green olive behaviour during the pitting process

Olive fruits processed as “Spanish green olives” were sorted into two batches depending on their pitting behaviour: those that broke under punch pressure, and those that were pitted without damage. Cell wall polysaccharides from both batches were isolated. The main changes were lower amounts of carbonate-soluble and 24 % KOH-soluble polysaccharides and a higher proportion of 4% KOH-soluble polysaccharides in broken olives. The carbonate-soluble fraction from broken olives was poorer in homogalacturonans, polysaccharides that could help in increasing texture. The 24% KOH-soluble fraction from the same olive batch was poorer in xylans and xyloglucans, the former being present in a higher proportion in the 4% KOH-soluble fraction and the last in cellulose residue. The new xylans of the 4% KOH-soluble fraction were of high (around 250 kDa) and low (6–40 kDa) molecular weights. Carbonate-soluble and 24% KOH-soluble fractions are very important in maintaining cell wall structure, which is responsible for vegetable product firmness. Received: 28 September 1999     

Influence of olive tree irrigation and the preservation system on the fruit characteristics of Hojiblanca black ripe olives

In this study, the effect of olive tree irrigation, the use of salt in preservation liquids and the reuse of sodium hydroxide solutions (lye) on the weight, shriveling, firmness and phenolic content of Hojiblanca processed olives was investigated. A weight loss in fruits of up to 5% during the preservation stage was observed, particularly for olives from irrigated trees and stored in brines. By contrast, a weight gain of up to 7% was achieved during the darkening stage, whose intensity was increased by using fruits from non-irrigated trees and preserved in a salt-free environment as well as fresh lye for the debittering step. Moreover, shriveling particularly appeared in fruits from non-irrigated olive trees, this defect being more intense if lye was reused. Firmness was also affected by the studied variables, and natural rainfed irrigation and the reuse of lye and salt in the preservation solutions gave rise to firmer olives. The content in phenolic compounds of black processed olives was higher in fruits from non-irrigated than irrigated trees, in particular those of hydroxytyrosol, tyrosol and luteolin 7-glucoside. Overall, these results will contribute to the knowledge of table olives processing and the industrial optimization of this sector.     

Factors affecting the changes in texture of dressed ("aliñadas") olives

The effect of the natural components of dressing during the conservation of olives on their texture was studied. Significant differences in texture between preparations with and without dressing were detected, although the texture in both preparations continued to diminish with time of conservation until the difference between textures was eliminated. These facts suggest that the enzymes coming from the constituents of the dressing (garlic, lemon, etc), as well as those endogenous enzymes in the olive fruit itself influence the changes in the texture, the olive becoming more susceptible to dressing and to enzymatic action as the stage of maturation progresses. Changes in the composition of polysaccharides and significant decreases in texture were related. Degradation of important polysaccharides in the structure of cell walls, such as !-cellulose, carbonate-soluble pectin and 4% KOH-soluble hemicelluloses were detected. This noticeable degradation could be explained perfectly by the combined action of the cell wall degrading enzymes, cellulase and polygalacturonase, present.     

Effect of Cooking and Pre-Cooking on Cell-Wall Chemistry in Relation to Firmness of Carrot Tissues

The aim of this work was to investigate heat-induced changes in cell wall polysaccharides of carrot in relation to texture. Discs of fresh carrot (Daucus carota cv Amstrong) tissue were subjected to cooking (100°C, 20 min), with or without a pre-cooking treatment (50°C, 30 min). Alcohol-insoluble residues were prepared from the tissues and were extracted sequentially with water, NaCl, CDTA, Na₂CO₃ and 0·5 M KOH to leave a residue. These were analysed for their carbohydrate compositions, their degree of methyl esterification and the molecular size of selected soluble polysaccharides. Cooking caused tissues to soften. This involved cell separation, an increase in water- and salt-soluble, high-molecular-weight pectic polysaccharides and a concomitant decrease in the pectic polymers in all wall extracts and the residue. Pre-cooking prior to cooking enhanced cell–cell adhesion and reduced the extent of softening. This was accompanied by a general reduction in the degree of methylesterification of cell-wall pectic polymers, and a decrease in the cooking-induced modification to all pectic fractions. The firming effect of pre-cooking could be reversed by extracting the precooked+cooked tissue with CDTA, a chelating agent. The role of Ca²⁺ cross-linked polymers and pre-cooking in the enhancement of firmness are discussed. © 1997 SCI.     

Ripening‐related changes in the cell walls of olive (Olea europaea L.) pulp of two consecutive harvests

Olive fruits, harvested in two consecutive seasons at green, cherry and black stages, were used to study compositional changes in the cell walls during ripening. Ripening‐related changes in both harvests were characterised mainly by an increase in the solubilisation of pectic and hemicellulosic polysaccharides, an increase in the relative amount of arabinose in pectic polysaccharides and a decrease in the degree of methylesterification of pectic polysaccharides. Further to degrading processes, the data obtained suggest the synthesis of new polysaccharides. The analysis of olive cell wall phenolics showed mainly the presence of p‐coumaric acid, which increased in one harvest, whereas in the other the values did not differ. The samples of the second harvest, although presenting green, cherry and black colours, had less distinct ripening characteristics than those of the previous harvest. Different activity levels of polyphenol oxidase, polygalacturonase and pectin methylesterase might have contributed to the differences observed between the two harvests. The results showed the distinct extension of ripening‐related changes in the cell walls of the two harvests, indicating that the olive colour, although characteristic of the stage of ripening, cannot be strictly used for its evaluation and definition. Copyright © 2006 Society of Chemical Industry     

L‐Phenylalanine ammonia‐lyase activity and concentration of phenolics in developing olive (Olea europaea L cv Arbequina) fruit grown under different irrigation regimes

Changes in L ‐phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5) activity and total phenolic, ortho‐diphenolic and fat contents of olive flesh in response to different irrigation treatments applied to olive tree cv Arbequina were studied during fruit ripening. Results indicate that the fat content of olive flesh at harvest was not affected by irrigation, although olives from the most heavily irrigated treatment reached their final fat content (dry weight) earlier than those from other irrigation treatments. PAL activity and phenolic content, expressed on a dry weight basis, decreased during fruit development and were affected by irrigation, being lowered as the water supplied increased. Good correlations were established between PAL enzymatic activity and the polyphenol and ortho‐diphenol contents of olive flesh, indicating that PAL is involved in the phenolic metabolism of olive fruit. The phenolic content of the oil depends on the PAL activity in the fruit, which varies with changes in water status. © 2002 Society of Chemical Industry     

Use of a lactic acid bacteria starter culture during green olive (Olea europaea L cv Ascolana tenera) processing

Among the Italian olive germplasm, ‘Ascolana tenera’ is one of the best varieties for table olive production. This research addressed the impact of different processing types (Greek‐style and Spanish‐style) on the fermentation and phenolic composition of olive fruit. In particular, the effects of a lactic acid bacteria (LAB) starter culture on the fermentation of naturally green olives processed according to the traditional Greek method were studied. Results revealed that Spanish‐style processing produced a dramatic loss of total phenolics, while natural olive processing favoured a higher retention of biophenols. Oleoside 11‐methylester, a phenol‐related compound, and hydroxytyrosol, tyrosol, vanillic acid, 3,4‐dihydroxyphenylglycol, oleuropein and oleuropein aglycons, as the main phenols, were detected in olive fruit. More interestingly, this research indicated that inoculation with LAB affected the pH, total acidity, microbial profile and palatability of olives. Olives fermented with the LAB starter culture were perceived by panellists to be less bitter and more aromatic than those spontaneously fermented. Thus the use of LAB inoculants during olive fermentation could be applied with the currently available technology. Copyright © 2005 Society of Chemical Industry     

紫薯果胶类多糖的成分分析及稳定性研究

以超声波辅助酶法提取及纯化紫薯果胶类多糖,并对其主要成分及稳定性进行分析.结果表明:所得紫薯果胶类多糖的干燥减量、酸不溶灰分、pH值、总半乳糖醛酸、酯化度、总糖、蛋白质含量分别为4.32％、0.32％、4.22、65.24％、31％、65％、1.02％,符合相关标准.测出所得紫薯果胶类多糖的重均分子量为70745 Da...     

The Influence of pH and Sodium Hydroxide Exposure Time on Glucosamine and Acrylamide Levels in California‐Style Black Ripe Olives

Acrylic acid, N‐acetyl‐glucosamine and glucosamine were investigated for their role in the formation of acrylamide in California‐style black ripe olives [CBROs]. Levels of acrylic acid and glucosamine are reported for the first time in fresh (333.50 ± 21.88 and 243.59 ± 10.06 nmol/g, respectively) and in brine‐stored olives (184.50 ± 6.02 and 165.88 ± 11.51 nmol/g, respectively). Acrylamide levels significantly increased when acrylic acid (35.2%), N‐acetyl‐glucosamine (29.9%), and glucosamine (124.0%) were added to olives prior to sterilization. However, isotope studies indicate these compounds do not contribute carbon and/or nitrogen atoms to acrylamide. The base‐catalyzed degradation of glucosamine is demonstrated in olive pulp and a strong correlation (r² = 0.9513) between glucosamine in olives before sterilization and acrylamide formed in processed CBROs is observed. Treatment with sodium hydroxide (pH > 12) significantly reduces acrylamide levels over 1 to 5 d without impacting olive fruit texture.     

An explorative study on the cell wall polysaccharides in the pulp and peel of dragon fruits (Hylocereus spp.)

The pectic and hemicellulosic cell wall polysaccharides from the pulp and the peel of white-flesh and red-flesh dragon fruits (Hylocereus spp.) were isolated and compared in terms of degree of methoxylation (DM), solubility properties (relative content of uronic acids and neutral sugars in different fractions), neutral sugar composition, molar mass distribution, and affinity toward some specific anti-pectin antibodies. Hereto, the alcohol-insoluble residues were extracted and sequentially fractionated using hot water, a chelating agent, sodium carbonate, and potassium hydroxide solutions to obtain different pectin fractions and a hemicellulose fraction. Chemical analyses were used to characterize these polysaccharide fractions. The results show that cell wall polysaccharides of the pulp and especially of the peel from white-flesh and red-flesh dragon fruits contain significant amounts of pectic substances that are lowly methyl-esterified. The cell wall polysaccharides of the peel as well as those of the pulp contain high amounts (38–47 %) of loosely bound (water-soluble) pectic substances. In the water-soluble fraction (WSF) of the peel samples, uronic acids are the predominant monomers. On the contrary, rhamnogalacturonan-I type neutral sugars, and especially arabinose and galactose, contribute equally, as compared to uronic acid, to the WSF of the pulp samples. Despite the low average DM value of pulp and peel pectin, pectic substances in both samples showed affinity for antibodies with different specificities indicating that a wide range of epitopes, including long blocks of unesterified galacturonic acids (GalA) residues as well as (short) blocks of esterified GalA residues, is present. No large differences between the pectic substances among the different dragon fruit varieties were observed.     

Tunisian table olive phenolic compounds and their antioxidant capacity

ABSTRACT:  For the 1st time, 4 olive cultivars, the Meski, Chemlali, Besbessi, and Tounsi, from the Tunisian market were investigated to evaluate the phenolic compounds' contribution in nutritional value of table olives. From the Meski cultivar, we have chosen 4 different samples to evaluate differences within the same cultivar. Basic characteristics and total phenolic content were evaluated in flesh and kernel. The highest value of flesh phenolic content was observed in sample M4 of the Meski cultivar; however, the lowest value was observed in the Besbessi cultivar and they were 1801 and 339 mg GA/100 g dry weight, respectively. The main simple phenolic compounds identified in flesh extracts are hydroxytyrosol, tyrosol, and vanillic acid. Oleuropein was not detected in any samples. The antioxidant activity of Tunisian olive flesh varies between 212 and 462 μM TEAC/g of dry weight. Antioxidant activity of olives was related to their phenolic content but we found a low correlation between phenolic content and TEAC.     

Extraction of pectic polysaccharides from sugar‐beet cell walls

Previous methods of extracting pectin from sugar‐beet have used pulp as the starting material. As the temperature and pressure of the pulping process may modify the architecture of the cell wall, we have adapted a relatively non‐disruptive method to characterise cell wall material (CWM) isolated directly from the sugar‐beet. Cell walls from mature sugar‐beets (Beta vulgaris L Aztec) were sequentially extracted four times with imidazole and twice with sodium carbonate to produce six heterogeneous pectic polysaccharide extracts, and with KOH to produce a hemicellulosic extract which was predominantly xylans. Heterogeneity of the extracted pectins was indicated by differences in FTIR spectra, uronic acid content, % methyl esterification, % feruloylation, % acetylation, molecular weight distribution and neutral sugar composition. The highest proportion of feruloyl esters was found in polysaccharides solubilised by the second sodium carbonate extraction. Anion exchange chromatography of these polysaccharides gave three fractions, one of which contained most of the feruloyl ester. These results indicate that feruloyl esters are not randomly distributed among the different pectic polysaccharides in the sugar‐beet cell wall, and that esterification is likely to be dependent on the local sugar sequence or conformation. © 2000 Society of Chemical Industry     

CELL WALL COMPOSITIONS AND ENZYMES OF POTATOES, JICAMAS AND CHINESE WATER CHESTNUTS

Cell wall compositions and the levels of ten enzymes of potatoes, jicamas and Chinese water chestnuts were determined to explain the differences in thermal softening of these vegetables. Cell walls were prepared from the tissues by sieving of ethanolic homogenates to remove most of the starch and analyzed for neutral sugars and uronic acids. Jicamas and water chestnuts contain less galactose but more arabinose and glucuronic acid and much more xylose than potatoes. Water chestnuts contain less galacturonic acid than jicamas and potatoes and this was confirmed by extraction of pectin under various conditions. The results suggest that resistance to thermal softening may be related to cell wall polysaccharides rich in arabinose, glucuronic acid and xylose rather than to pectic polysaccharides. The major differences in enzyme compositions are much higher β-amylase and exopolygalacturonase in jicamas and water chestnuts than in potatoes. Water chestnut exopolygalacturonase is unusually heat-stable, but the relationship of this enzyme or of β-amylase to thermal softening is not clear.     

Effect of pH on the colour formed by Fe-phenolic complexes in ripe olives

The effects of the pH in the flesh of ripe olives processed for table olive production, the type of acid used to correct it, the heating process used and the iron content of the flesh on the colour of the final product were studied. The best colour was obtained by bottling the fruits at pH 7. Additions of acids, especially citric acid, always caused discoloration when olives were bottled at a pH of around 7. On the other hand, when the fruits were packed at a pH higher than 7 the addition of certain amounts of acids produced darker olives. Darker colours are related to higher iron contents in the flesh, but treatment of olives with ferrous gluconate before neutralising the pH of the flesh yielded better colours than those treated after neutralising for the same iron concentration in the olives. Results obtained after adding iron to the oxidation solutions did not show the same pattern as those obtained using fruits. These results suggest that the fixation of the colour formed is not only due to the phenol-iron complexes.     

Optimization of Ripe Olive Processing with a Single Lye Treatment

The development of a method for darkening black ripe olives during the washing step with a single NaOH treatment and preservation liquid was studied. Olives of the Hojiblanca cultivar were darkened at pilot plant scale, packed, sterilized, and analyzed after 2 mo of storage at ambient temperature. It was found that the use of a mixture of preservation liquid:water at a ratio of 1:1 during the first washing gave rise to darker olives with slightly better firmness and no effect on sensory quality. However, care must be taken with the concentration of acetic acid in the preservation solution, as a content of this organic acid higher than 25 g/L can cause adverse effects on olive color due to the low pH that can be reached in the flesh of the fruit. Additionally, the re‐use of the preservation solution in the first washing resulted in enrichment in antioxidant compounds of the packed product. Black ripe olives processed with preservation liquid had a total phenolic content of 629 mg/kg, whereas those with only tap water had 376 mg/kg, in particular hydroxytyrosol and hydroxytyrosol‐4‐glucoside. These findings mean that it is possible to get darker olives with higher contents in bioactive substances by reusing the preservation liquid during the darkening step of black ripe olives.     

The isolation and analysis of cell wall material from the alcohol-insoluble residue of cabbage (Brassica oleracea var. capitata)

Cell wall material (CWM) was isolated from the wet ball-milled alcohol-insoluble residue of cabbage by treatment with Pronase, phenol-acetic acid-water and 90% aqueous dimethyl sulphoxide to remove precipitated proteins, starch and other intracellular compounds. Some solubilisation (mainly of pectic material) occurred during the purification stages. Methylation analysis of the cold water-soluble polysaccharides showed that the main neutral glycosidic linkages in descending order of concentration, were: non-reducing terminal arabinose groups, 5-linked arabinose and 4-linked galactose. The CWM contained a high level of arabinose-containing pectic polysaccharides. The main linkages present in the non-cellulosic polysaccharides were 4-linked galacturonic acid, non-reducing terminal arabinose groups and 5-linked arabinose; doubly branched arabinose residues were also present. Sequential extraction of the CWM by aqueous inorganic solvents yielded further information on the types of polysaccharides present. The general structural features of the CWM are discussed in the light of these results.     

Colour fixation in ripe olives. Effects of type of iron salt and other processing factors

A detailed study has been made of the colour fixation stage of ripe olive processing. The effects of the degree of iron oxidation and the colour‐fixing liquid on iron availability have been investigated and an explanation is given for the greater effectiveness of ferrous salts compared to ferric salts. Likewise, a 2⁴ factorial design was used to study the influence on olive colour of the pH of the aeration solution, the type of colour‐fixing liquid, the type of ferrous salt and the aeration system. The data were analysed by multivariate and univariate analysis of variance (MANOVA/ANOVA), the best results being obtained with low pH (4.0), tap water, ferrous lactate and no aeration during the first 3 h of immersion in the colour‐fixing solution. These results can be explained by the iron availability averages having been altered by differences in the concentration of organic matter, the pH of the solution and the diffusion of iron into the olive flesh. The results can be used to reduce iron residues in ripe olives. © 2001 Society of Chemical Industry