A.H. Sánchez

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.

Chemical profile of industrially fermented green olives of different varieties

Over 160 fermented brines, from green olives of Manzanilla, Hojiblanca, and Gordal varieties processed in five companies in two consecutive seasons, were analysed for physicochemical characteristics, organic acids, sugars, and volatile components. The composition of the brine following fermentation was assumed to be identical to that of the aqueous phase of the olives. Olive variety and processor were found to have a greater influence than season on both physicochemical characteristics and chemical composition. Hojiblanca olives presented values of pH, combined acidity, and volatile acidity significantly (P<0.05) higher than those of Manzanilla and Gordal, reflecting different processing conditions. The volatile/total acidity ratio, which did not differ between varieties or seasons, appeared to correlate with development of the “fourth stage” of fermentation. The major compounds were lactic, acetic, succinic and formic acids, ethanol, and methanol, with the contents of ethanol and formic acid being significantly different in all three varieties. Residual fermentation substrates, such as mannitol, glucose, sucrose, and citric acid, in addition to propanol, propionic acid, 2-butanol, and acetaldehyde, were found in low concentrations.

A Comparison of Simulation and Hardware-in-the- Loop Alternatives for Digital Control of Power Converters

Debugging digital controllers for power converters can be a problem because there are both digital and analog components. This paper focuses on debugging digital controllers to be implemented in Field Programmable Gate Arrays or Application Specific Integrated Circuits, which are designed in hardware description languages. Four methods are proposed and described. All of them allow simulation, and two methods also allow emulation-synthesizing the model of the converter to run the complete closed-loop system in actual hardware. The first method consists in using a mixed analog and digital simulator. This is the easiest alternative for the designer, but simulation time can be a problem, specially for long simulations like those necessary in power factor correction or when the controller is very complex, for example, with embedded processors. The alternative is to use pure digital models, generating a digital model of the power converter. Three methods are proposed: real type, float type and fixed point models (in the latter case including hand-coded and automatic-coded descriptions). Float and fixed point models are synthesizable, so emulation is possible, achieving speedups over 20 000. The results obtained with each method are presented, highlighting the advantages and disadvantages of each one. Apart from that, an analysis of the necessary resolution in the variables is presented, being the main conclusion that 32-bit floating point is not enough for medium and high switching frequencies.

Analysis of zapatera olives by gas and high-performance liquid chromatography

Abstract Gas chromatography and high-performance liquid chromatography were applied to normal and “zapatera” olive brines obtained from typical fermentation brines of green table olives after different treatments. The zapatera samples were obtained by pH adjustment to 5.1 followed by inoculation with a suspension of sediment from a zapatera brine and incubation at 30°C for 40 days. The compounds determined were lactic acid, C 2 -C 6 fatty acids, acetaldehyde, methanol, ethanol, 2-butanol and n -propanol. Normal and zapatera brines were compared to identify components that indicated spoilage. One of these components was found in the gas chromatogram of the volatile fatty acids from the zapatera samples and identified as cyclohexanecarboxylic acid by gas chromatography-mass spectrometry. A comparison of the corresponding aromagrams revealed quantitative differences in aroma composition. Various relationships calculated from the peak areas of selected unknown components in these aromagrams were so distinct as to provide a basis for characterizing zapatera spoilage.