Manuel Brenes

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.

Transformation of oleuropein and its hydrolysis products during Spanish‐style green olive processing

Products obtained from elenolic acid glucoside hydrolysis during the storage of Spanish-style green olive brines were elenolic acid and glucose. The disappearance of elenolic acid glucoside from brines followed a first-order kinetics rate and was influenced by the storage temperature. Hydrolysis of this glucoside also occurred in brines ultrafiltered at 10000 Da pore size, indicating that no enzymatic action was needed to break the glycoside bond. Inoculation experiments with microorganisms obtained from a Spanish-style green olive brine demonstrated that this microflora was able to use the glucose formed from elenolic acid glucoside hydrolysis, although in our experiments only yeasts could grow in the assayed brines. It needs to be stressed that the glucose liberated by elenolic acid glucoside hydrolysis may represent about 20% of the total initial glucose in brines at the start of the fermentation step in Spanish-style green olive processing.

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.

Improvement of phenolic compound content in virgin olive oils by using enzymes during malaxation

Abstract The effect of enzyme addition to the olive paste on the phenolic composition of virgin olive oil has been studied. The experiments were carried out with both Picual and Arbequina cultivars, using the continuous two-phase extraction system at industrial scale and for three consecutive seasons. Phenolic compounds, in particular orthodiphenols, increased their concentration in oils when enzymes were added to the olive paste before the malaxation stage. Among non-orthodiphenols, the lignans 1-acetoxypinoresinol and pinoresinol slightly increased their concentration. In general, the positive effect of enzymes was more marked for Arbequina than for the Picual cultivar. The peroxide index and “Rancimat” stability of oils were also positively affected when using enzymes. Besides, wash waters from the vertical centrifuge showed a higher concentration of phenolics when the pastes were treated with enzymes. Therefore, the use of enzymatic formulations during the extraction process of olive oil may not only increase the oil yield but also the nutritional quality of the oil.

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.

Antimicrobial activity of olive solutions from stored Alpeorujo against plant pathogenic microorganisms.

The aim of this work was to assess the in vitro antimicrobial effects that wastewaters from alpeorujo oil extraction have against phytopathogenic bacteria and fungi. Alpeorujo was stored for 6 months and then processed to extract its oil, pomace, and a new liquid waste (OWSA), which was characterized by its content in phenolic compounds. OWSA at 20% decreased bu >4 log the population of Erwinia spp., Pseudomonas spp., and Clavibacter spp. viable cells in test tubes, whereas OWSA at 50% in agar medium was necessary to inhibit mycelial growth of most fungi. It was found that the bactericidal effect was due to the joint action of low molecular mass phenolic compounds, although neither hydroxytyrosol, its glucosides, hydroxytyrosol glycol, nor a glutaraldehyde-like compound individually explained this bioactivity. Hence, OWSA constitutes a promising natural solution to fight plant phytopathogenic bacteria and fungi.

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.

Fermentation of washing waters of Spanish-style green olive processing

Abstract Washing waters of Spanish-style green olive processing are heavily contaminated waste streams that represent an important environmental problem that needs to be solved. These liquids are only generated for 2 months a year and a storage period is needed if high-value substances are to be extracted from them. Fermentation of the washing waters under acidic conditions was studied throughout a year. A lactic acid fermentation took place in vessels with either no initial correction of pH, or pH corrected to 4. When the pH was initially lowered to 3, only yeasts grew and a significant concentration of ethanol was generated. The concentration of phenolic compounds decreased slightly during the fermentation process, particularly hydroxytyrosol, which was found in high concentration in these waste waters. If this orthodiphenol is to be recovered from washing waters, time is required to hydrolyse the elenolic acid glucoside. The glucoside was hydrolysed under the acidic conditions of the washing waters, and the reaction was affected by temperature and pH. Thus, fermentation of washing waters under certain conditions may give rise to solutions with no off-odours and a high concentration of lactic acid and hydroxytyrosol, which are economically interesting products.

Lactobacillus plantarum Survival During the First Days of Ripe Olive Brining

Summary The effects of time (1, 3, 5, 7 and 9 days after brining), NaCl concentration (3% and 0% w/v) and glucose on Lactobacillus plantarum inoculum survival in directly brined olives were studied. Maintenance of the inoculum population was only possible when inoculation was carried out after three days of brining if the covering solution was tap water, and after seven days if a 3 % NaCl solution was used. Presence of glucose improved the survival rate, especially for the Cacerena cultivar. The inhibitory effect of diffused polyphenols on Lactobacillus plantarum during these days was significant only when it was associated with NaCl (3% NaCl brines). The combined effect of 6% NaCl and the polyphenol concentration caused a marked decrease in survival in 7 days of Hojiblanca brines. Thus, the two effects with greatest influence on survival were the period of brining (which must be sufficient to provide nutrients) and salt concentration which caused a substantial decrease in survival when nutrients were scarce. Low levels of salt enhanced fermentability as was demonstrated by the spontaneous flora growth in the brines of all treatments. Microorganisms formed were not only Gram-negative rods and yeasts, but also lactic acid bacteria (Leuconostoc paramesenteroides and Lactobacillus plantarum) in the 0% salt Hojiblanca brines.

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.