Concepción Romero

Antimicrobial activity of olive oil, vinegar, and various beverages against foodborne pathogens.

The survival of foodborne pathogens in aqueous extracts of olive oil, virgin olive oil, vinegar, and several beverages was evaluated. Vinegar and aqueous extracts of virgin olive oil showed the strongest bactericidal activity against all strains tested. Red and white wines also killed most strains after 5 min of contact, black and green tea extracts showed weak antimicrobial activity under these conditions, and no effect was observed for the remaining beverages (fruit juices, Coca-Cola, dairy products, coffee, and beer). The phenolic compound content of the aqueous olive oil and virgin olive oil extracts could explain their antibacterial activity, which was also confirmed in mayonnaises and salads used as food models. Virgin olive oil in mayonnaises and salads reduced the counts of inoculated Salmonella Enteritidis and Listeria monocytogenes by approximately 3 log CFU/g. Therefore, olive oil could be a hurdle component in certain processed foods and exert a protective effect against foodborne pathogens when contaminated foods are ingested.

Analysis of Total Contents of Hydroxytyrosol and Tyrosol in Olive Oils

The most abundant phenolic compounds in olive oils are the phenethyl alcohols hydroxytyrosol and tyrosol. An optimized method to quantify the total concentration of these substances in olive oils has been described. It consists of the acid hydrolysis of the aglycons and the extraction of phenethyl alcohols with a 2 M HCl solution. Recovery of the phenethyl alcohols from oils was very high (<1% remained in the extracted oils), and the limits of quantification (LOQ) were 0.8 and 1.4 mg/kg for hydroxytyrosol and tyrosol, respectively. Precision values, both intraday and interday, remained below 3% for both compounds. The final optimized method allowed for the analysis of several types of commercial olive oils to evaluate their hydroxytyrosol and tyrosol contents. The results show that this method is simple, robust, and reliable for a routine analysis of the total concentration of these substances in olive oils.

Anthocyanin and colour evolution during maturation of four port wines: effect of pyruvic acid addition

The formation of vitisin A-type compounds has been studied in four maturing fortified red port wines stored for 29 weeks at 15 °C. The anthocyanin concentrations were determined by high-pressure liquid chromatography (HPLC), and colour changes were monitored by spectrometric measurements. The losses of anthocyanins followed first-order reactions, and the concurrent formation of polymeric pigments was demonstrated. Vitisin A-type compounds were found to be in low concentration in these four naturally maturing fortified wines. The addition of pyruvic acid to the wines led to the formation of large concentrations of vitisin A derivatives. Up to 23 mg litre−1 vitisin A derivatives (vitisin A and its acylated forms acetylvitisin A and p-coumarylvitisin A) could be determined. Owing to their greater colour expression and greater stability than malvidin 3-glucoside, these new anthocyanins were shown to play an important role in the colour quality of the wines. An analytical survey of 32 port wines matured for between 2 and 6 years showed that vitisin A-type compounds were the main, and sometimes the only, anthocyanins present. © 2000 Society of Chemical Industry

Bactericidal Activity of Glutaraldehyde-like Compounds from Olive Products

The bactericidal effects of several olive compounds (nonenal, oleuropein, tyrosol, the dialdehydic form of decarboxymethyl elenolic acid either free [EDA] or linked to tyrosol [TyEDA] or to hydroxytyrosol [HyEDA]), other food phenolic compounds (catechin, epicatechin, eugenol, thymol, carvacrol, and carnosic acid), and commercial disinfectants (glutaraldehyde [GTA] and ortho-phthalaldehyde [OPA]), were tested against strains of Pseudomonas fluorescens, Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli. It was found that the bactericidal activities of olive GTA-like compounds (EDA, HyEDA, and TyEDA) were greater than those exerted by several food phenolic substances. Surprisingly, these olive antimicrobials were as active as the synthetic biocides GTA and OPA against the four bacteria studied. Thus, it has been proposed that the bactericidal activity of the main olive antimicrobials is primarily due to their dialdehydic structure, which is similar to that of the commercial biocides GTA and OPA. Our results clearly reveal that olive GTA-like compounds possess a strong bactericidal activity even greater than that of other food phenolic compounds or synthetic biocides.

Endogenous Enzymes Involved in the Transformation of Oleuropein in Spanish Table Olive Varieties

The main Spanish table olive varieties supplied by different olive cooperatives were investigated for their polyphenol compositions and the endogenous enzymes involved in their transformations during two growing seasons. Olives of the Manzanilla variety had the highest concentration in total polyphenols, followed by the Hojiblanca and Gordal varieties. The Gordal and Manzanilla cultivars showed the highest polyphenol oxidase activities. The Gordal cultivar presented a greater β-glucosidase and esterase activity than the others. An important influence of pH and temperature on the optimal activity of these enzymes was also observed. The polyphenol oxidase activity increased with temperature, and peroxidase activity was optimal at 35 °C. The β-glucosidase and esterase activities were at their maximum at 30 and 55 °C, respectively. The oxidase and β-glucosidase activities were at their maximum at the pH of the raw fruit. These results will contribute to the knowledge of the enzyme transformation of oleuropein in natural table olives.

Debittering of Olives by Polyphenol Oxidation

In this study, green olives preserved in acidified brine were debittered by subjecting them to an overpressure of oxygen or air for 1-3 days. It was demonstrated that fruits lost their bitter taste due to the enzymatic oxidation of the phenolic compounds, in particular, the glucoside oleuropein. Hence, the concentrations of both o-diphenols and, to a lesser extent, monophenols decreased in the olives with oxidation. This process also gave rise to a darkening effect on the superficial and interior color of the olives, which turned from yellow-brown to brown. Likewise, the effect of several variables on the oxidation rate of the olives, such as type of gas (oxygen, air), temperature, overpressure level, and size of the olives, was also studied. Results indicate that a new debittering method which could be a promising alternative to the treatment of fruits with NaOH is available to the industry. In addition, a new product with different color and texture from the traditional table olives is presented.

Inhibitors of lactic acid fermentation in Spanish-style green olive brines of the Manzanilla variety.

Frequently, a delay or lack of lactic acid fermentation occurs during the processing of Spanish-style green olives, in particular of the Manzanilla variety. Many variables can affect the progress of fermentation such as temperature, nutrients, salt concentration, antimicrobials in brines, and others. In this study, it was demonstrated that an inappropriate alkaline treatment (low NaOH strength and insufficient alkali penetration) allowed for the presence of several antimicrobial compounds in brines, which inhibited the growth of Lactobacillus pentosus. These substances were the dialdehydic form of decarboxymethyl elenolic acid either free or linked to hydroxytyrosol and an isomer of oleoside 11-methyl ester. Olive brines, from olives treated with a NaOH solution of low concentration up to 1/2 the distance to the pit, contained these antimicrobials, and no lactic acid fermentation took place in them. By contrast, a more intense alkaline treatment (2/3 lye depth penetration) gave rise to an abundant growth of lactic acid bacteria without any antimicrobial in brines. Therefore, the precise cause of stuck fermentation in Manzanilla olive brines was demonstrated for the first time and this finding will contribute to better understand the table olive fermentation process.

Assessment of Helicobacter pylori Eradication by Virgin Olive Oil

Background:  A recent study conducted by Medina et al. disclosed that virgin olive oil has a bactericidal effect in vitro against Helicobacter pylori because of its contents of certain phenolic compounds with dialdehydic structures. We carried out two clinical trials to evaluate the effect of virgin olive oil on H. pylori‐infected individuals.

Respiration and physicochemical changes in harvested olive fruits

SummaryThe effects of short storage time (up to two days), temperature and degree of ripeness on respiration rate, sugar metabolism and physicochemical characteristics of ‘Manzanilla’ and ‘Gordal’ olives (Olea europaea L.) were studied. Respiration rate declined rapidly during the first day and slowly from then. This decrease depended highly on the experimental temperature (10–40°C). Loss in firmness and weight of fruits increased at higher temperatures. The respiratory quotient was around 1 at harvest and declined parallel to the respiration rate for 2 d. Mannitol was the first sugar metabolized at all temperatures, followed by fructose. Glucose concentration decreased only with cv. Gordal and the highest temperature. Thus the metabolism of sugars by olives does not interfere with the further industrial fermentation processes which are based on the use of glucose as the main fermentable substrate. Loss of weight, colour changes and respiratory activity increased as more mature olives were used.

Composition of pigments and colour changes in green table olives related to processing type

Brownish colourations in Natural green table olives (non-treated with alkali) make this product less attractive to consumers than Spanish-style green table olives (treated with alkali), which develop a more appreciated bright golden-yellow colour. These colour differences were studied in relation to changes in the composition of chlorophyll and carotenoid pigments, as well as polyphenolic compounds and polyphenol oxidase enzyme (PPO) activity. Natural green olives showed a different chlorophyll profile than Spanish-style. However, all the chlorophyll pigments formed in both processing types were Mg-free derivatives (mostly pheophytins) with similar colourations, ranging from grey to green brownish. In the carotenoid fraction no appreciable differences were found between both processing types. The fruits brownish colour was mainly due to polymeric substances with a size of >1000 daltons and polyphenolic nature, resulting from an enzymatic oxidation by PPO of the o-diphenolic compounds present in the fresh fruits.