Degradation kinetics of the antioxidant additive ascorbic acid in packed table olives during storage at different temperatures

The kinetics of ascorbic acid (AA) loss during storage of packed table olives with two different levels of added AA was investigated. Three selected storage temperatures were assayed: 10 degrees C, ambient (20-24 degrees C), and 40 degrees C. The study was carried out in both pasteurized and unpasteurized product. The effect of pasteurization treatment alone on added AA was not significant. In the pasteurized product, in general AA degraded following a first-order kinetics. The activation energy calculated by using the Arrhenius model averaged 9 kcal/mol. For each storage temperature, the increase in initial AA concentration significantly decreased the AA degradation rate. In the unpasteurized product, AA was not detected after 20 days in samples stored at room temperature and AA degradation followed zero-order kinetics at 10 degrees C, whereas at 40 degrees C a second-order reaction showed the best fit. In both pasteurized and unpasteurized product, the low level of initial dehydroascorbic acid disappeared during storage. Furfural appeared to be formed during storage, mainly at 40 degrees C, following zero-order kinetics.

Utilization at high pH of starter cultures of lactobacilli for Spanish-style green olive fermentation

Inoculation at alkaline pH (above 9) of lye-treated green olives with starter cultures of Lactobacillus pentosus CECT 5138 was studied. Despite an initial loss of viability in the order of 1-2 log cycles on average, depending mainly on time of application, cultures grew and initiated an accelerated fermentation process. Inoculation reduced the population of Enterobacteriaceae, and thereby potential spoilage, and produced a quicker acidification of brines and decrease of pH, when compared with control uninoculated batches. Results obtained throughout three consecutive seasons demonstrated that utilization at high pH of starter cultures of lactobacilli is feasible, provided that the inoculum size takes into account the initial low survival.

Comparative study on chemical changes in olive juice and brine during green olive fermentation

Changes in physicochemical characteristics, substrate depletion, and product formation during fermentation were followed in both brine and olive juice in order to achieve a complete knowledge of fermentation chemistry in Spanish-type green olives. Both spontaneous and controlled fermentations were investigated. Fermentation rate, irrespective of the type of fermentation, was lower in olive juice than in brine, but the main acid products eventually reached equilibrium. Final free acidity remained significantly (p < 0.05) higher, and combined acidity remained lower, in brine than in olive juice in both fermentations, but differences in final pH were not significant in controlled fermentation. Final concentrations of lactic and formic acids were significantly (p < 0. 05) higher, and those of ethanol and succinic acid were lower, in controlled fermentation than in spontaneous fermentation. Butanediol, attributable to Enterobacteriaceae growth, was formed only in the latter case. Calculated carbon recoveries were not significantly (p < 0.05) different in any case, giving a mean of some 78%.

Lactic acid fermentation and storage of blanched garlic

The controlled fermentation of peeled, blanched garlic, using a starter culture of Lactobacillus plantarum, was studied and compared with that of unblanched garlic. Blanching was carried out in hot water (90 degrees C) for 15 min. The starter grew abundantly in the case of blanched garlic, producing mainly lactic acid and reaching a pH of 3.8 after 7 days, but its growth was inhibited in unblanched garlic. Ethanol and fructose, coming from enzymatic activities of the garlic, and a green pigment were formed during the fermentation of unblanched garlic, but not of blanched garlic. The blanched garlic fermented by L. plantarum, even without a preservation treatment (pasteurization), was microbiologically stable during storage at 30 degrees C in an acidified brine (approximately 3% (w/w) NaCl and pH 3.5 at equilibrium), but fructans were hydrolyzed. The packed fermented product and that obtained by direct packing without fermentation were not significantly different with regard to flavour.

Processing and storage of lye-treated carrots fermented by a mixed starter culture

A mixed culture of Lactobacillus plantarum and Saccharomyces cerevisiae was compared with a single culture of L. plantarum as starter for the fermentation of lye-treated carrots. Using the mixed culture, more than 95% of glucose, fructose and malic acid was consumed after 7 days of fermentation in a brine containing 2.5% w/v NaCl and 0.7% acetic acid, but only 54% of sucrose was degraded. The fermentation products quantified were lactic acid, ethanol and acetic acid and carbon recovery was 88%. Using the single culture of L. plantarum, substrate consumption was lower, and carbon recovery almost 100%. In uninoculated lye-treated carrots, heterofermentative bacteria grew, with the production of considerable amounts of mannitol. In all cases, the stability, sensorial characteristics and carotenoid content of the packed product were studied during 9 months of storage at 30 degrees C, and two different preservation systems were compared: addition of preservatives, approximately 500 and 1000 mg/kg of sorbic and benzoic acid, respectively, and pasteurization at 80 degrees C for 10 min. The pasteurized samples were microbiologically stable during the storage period, while lactic acid bacteria grew in the samples with preservatives. Storage time significantly (P < 0.05) affected the texture and colour parameters (L*, a*, b*) of the carrots, but not the amounts of alpha- and beta-carotene. The type of fermentation had no significant effect on texture, colour parameters or carotenoid content. The preservation method had no significant effect on texture or carotenoid content, but did affect colour (parameter a*). The flavour of carrots fermented by the mixed culture was significantly (P < 0.05) preferred to that of those fermented with a single culture of L. plantarum.

Determination of benzoic and sorbic acids in packaged vegetable products. Comparative evaluation of methods

Three analytical methods for determining sorbic and benzoic acids in various packaged vegetable products were evaluated, with special attention being paid to green olives. Two of these methods used a simple, isocratic, reversed-phase HPLC technique for separating and detecting the preservatives, but differed in the preparation of the sample (extraction with 60% methanol or steam distillation). The third method was based on separation by steam distillation and determination of the acids in the distillate by spectrophotometry. For the olives, while this method proved to be excellent (total error < 25%) for high concentrations (> 100 ppm), the HPLC methods were more efficient for the whole range of concentrations studied (5-500 ppm). Both HPLC methods had detection limits of approximately 1 ppm for the two preservatives. With other sample matrices (tomatoes, cucumbers, caperberries, silver-skinned onions and hot peppers), the three methods proved to be excellent for high concentrations of preservatives (500 ppm), but at low levels (20 ppm), the spectrophotometric method and the HPLC method with extraction by 60% methanol proved to be unacceptable (total error > 50%) in some cases.