Effect of ultrasonication on microbial quality, colour and ascorbic acid of passion-fruit juice during storage

Passion fruit juice (PFJ) has a delicate flavour very susceptible to thermal degradation. This study pursued to test the effect of sonication as non-thermal preservation method on some quality parameters of PFJ. The effect of ultrasound (20 kHz, 263 W, 89.25 µm) on the indigenous microflora, colour and ascorbic acid content of PFJ was studied. Firstly, the kinetic of microbial inactivation was determined for aerobic mesophilic counts and yeasts counts. Data was fitted to Weibull model, and a treatment time of 8 min was selected for stability studies. To this, untreated and sonicated juice was stored at 4 and 10 ºC up to 10 days and microbial quality, instrumental colour, pH and ascorbic acid content were evaluated. In general, ultrasound kept juice microbiologically stable for up to 10 days at 4 ºC without markedly affecting other parameters evaluated. Ultrasound seems suitable to stabilize microbiologically PFJ.Ciencias de la Alimentació

Fruit characterization of high oil content avocado varieties

To expand the data bank on avocado (Persea americana Mill.) varieties all over the world, and to select good varieties for commercial or improving purposes, a partial fruit characterization of 13 high oil content (11.23-18.80%) was performed. The chosen varieties are growing in a Venezuelan germplasm bank: Fuerte, Peruano, Lula, Ortega, Red Collinson, Alcemio, Araira 1, Pope, Ettinger, Gripiña 5, Barker, Duke, and Ryan. They were characterized for pulp oil and moisture; weight (whole fruit, seed, pulp and peel); length, width and fruit shape; peel characteristics (roughness, color and hand peeling); and ripeness time. The variety Ryan showed the highest oil content (18.80%) and calorific value (191 Kcal/100 g wet flesh). Avocado varieties grown in Venezuela have generally less oil content and are generally lighter than those from other countries. Most of the varieties had low pulp proportion, and were pyriform, with rough green peel and difficult to hand peel. Red Collinson had an uncommon reddish peel. The ripening time was between 4 and 10 days after harvest.O teor de óleo de abacates (Persea americana Mill.)é uma característica importante para seu consumo in natura e para a indústria. Treze variedades de abacate de alto teor de óleo (11,23-18,80%) de um pomar venezuelano: Fuerte, Peruano, Lula Ortega, Red Collison, Alcemio, Araira 1, Pope, Ettinger, Gripiña 5, Barker, Duke e Ryan, foram caracterizados pelo teor de óleo da polpa e umidade; peso (fruto inteiro, semente, polpa e casca); comprimento, largura e forma; características da casca (rugosidade, cor e soltura); e tempo de maturação. A variedade Ryan mostrou os maiores teor de óleo (18,80%) e valor calórico (191 kcal/100 g de peso fresco). As variedades venezuelanas têm, em geral, teor mais baixo de gordura e proporção de polpa, e são em geral mais leves que aquelas de outros países. A maioria das variedades é periforme, com casca verde áspera e difíceis de serem descascadas manualmente. A variedade Red Collison tem uma cor avermelhada incomum. A maturação esteve entre 4 e 10 dias após a colheita

Pulsed light inactivation of mushroom polyphenol oxidase: a fluorometric and spectrophotometric study

Polyphenol oxidase (PPO) is one of the most important food enzymes, it is responsible for the browning of many foods. Pulsed light (PL) is a non-thermal method of food preservation that is able to inactivate PPO. The aim of this work was to gain insight into the mechanism of PPO inactivation by PL. To this, the kinetics of PPO inactivation by PL was measured, together with associated changes in tryptophan fluorescence, KI fluorescence quenching and turbidity; and results were analysed by parameter A and phase diagram methods. Enzyme inactivation followed the Weibull model. Tryptophan fluorescence decreased during PL treatment, as well as the parameter A, while Stern-Volmer constants increased and turbidity was constant. The phase diagram showed only two populated states. There was a high correlation between the loss of activity and parameter A. Results indicate that under the experimental conditions, the inactivation of PPO by PL is an all-or-none process where the enzyme progressively unfolds with no evidence of aggregation.Fundación Universitaria San Antonio de CartagenaCiencias de la Alimentació

An Approach to Standardize Methods for Fluence Determination in Bench-Scale Pulsed Light Experiments

Pulsed light (PL) is a fast non-thermal technology for decontamination based on the application of pulses of highintensity polychromatic light including UV-C light. Continuous-wave (CW) ultraviolet (UV) light technology is based on the application of monochromatic or polychromatic low-intensity light for long times. Appropriate UV dosimetry is fundamental in order to intercompare results and for scaling up. There are standard methods for bench-top CW UV treatments but not for tests involving PL dosimetry. The present article introduces the fundamentals of photochemistry and photophysics, adapts a protocol for CW UV dosimetry to PL tests, and critically revises current ways of reporting results of PL tests.Ciencias de la Alimentació

Pulsed light inactivation of horseradish peroxidase and associated structural changes

Pulsed light (PL) is a non-thermal preservation method in which foods are subjected to one or several intense pulses of wide-spectrum light. Peroxidase (POD) is an enzyme that needs to be inactivated or inhibited because of its deleterious effects on the quality of fruits and vegetables. The feasibility of using PL to inactivate POD was tested and results explained based on measurements of UV–vis spectrum, farUV circular dichroism and tryptophan fluorescence, and the phase-diagram method. PL reduced the activity of POD by more than 95% after applying 128 J cm 2 . There was observed a decrease in the Reinheitzahl value and ellipticity and an increase in tryptophan fluorescence at incremental fluences, as well as linear phase diagrams. The study indicates that the inactivation of POD by PL is an all-or-none process related to loss of helical structure, weak unfolding and ejection of the prostetic group.Ciencias de la Alimentació

A review of quantitative methods to describe efficacy of pulsed light generated inactivation data that embraces the occurrence of viable but non culturable state microorganisms

The purpose of this timely review is to critically appraise and to assess the potential significance of best-published microbial inactivation kinetic data generated by pulsed light (PL). The importance of selecting different inactivation models to describe the PL inactivation kinetics is highlighted. Current methods for the detection of viable-but-nonculturable (VBNC) organisms post PL-treatments are outlined along with the limitations of these methods within food microbiology. Greater emphasis should be placed on elucidating appropriate inactivation kinetic model(s) to cater for the occurrence of these VBNC organisms that are underestimated in number using traditional culture-based enumeration methods. Finally, the importance of further molecular and combinational research to tackle the potential threat posed by VBNC organisms with regard to kinetic inactivation modelling and nexus to public health and food safety is presented.Ciencias de la Alimentació

A novel electrochemical device as a disinfection system to maintain water quality during washing of ready to eat fresh produce

Electrolyzed water (EW) is known by its bactericidal efficacy and capability to oxidize organic matter. The present research evaluated the efficacy of recently developed electrolytic cells able to generate higher concentration of reactive oxygen species using lower power and salt concentration than conventional cells. This study tested the inactivation of Escherichia coli O157:H7, the organic matter depletion and trihalomethane (THM) generation by EW in process wash water under dynamic conditions. To achieve this, clean tap water was continuously added up to 60 min with artificial process water with high chemical oxygen demand (COD) inoculated with E. coli O157:H7, in experiments performed in a pilot plant that recirculated water through one electrolytic cell. Plate counts of E. coli O157:H7, COD, THMs, free, combined and total chlorine, pH, temperature and oxidation-reduction potential were determined. Results indicate that the novel electrolysis system combined with minimal addition of NaCl (0.05%) was able to suppress E. coli O157:H7 population build-up and decreased the COD accumulation in the process wash water. THM levels in the water were relatively high but its concentration in the washed product was marginal. Highly effective electrolysis has been proven to reduce the occurrence of foodborne diseases associated to cross-contamination in produce washers without having an accumulation of THMs in the washed product.Ciencias de la Alimentació

Pulsed light inactivation of polygalacturonase

Pulsed light is a non-thermal technology capable to inactivate enzymes. This study investigated the effect of pulsed light on the activity of polygalacturonase, and on the structure of the enzyme by means of fluorescence emission spectra, free sulphydryl detection and analysis of changes in parameter A and phase-diagram. The results showed that pulsed light is able to inactivate polygalacturonase in buffer, with > 90 % reduction of enzyme activity after applying 128 J/cm2 and a first-order kinetic constant of 0.0426 cm2/J under the experimental conditions. The free sulfhydryl detection revealed the rupture of sulfhydryl bridges. Fluorescence spectra analysis showed that the tertiary structure of polygalacturonase was changed. Phase diagram analysis shows the existence of only two populated states. It is suggested that the inactivation of polygalacturonase by pulsed light is an all-or-none process where disulfide bridges are broken and the enzyme is unfolded.Ciencias de la Alimentació

Pectin methylesterase inactivation by pulsed light

Pectinmethylesterase (PME) is a degradative enzyme of the cloudiness of fruit juices. Pulsed light (PL) is a non-thermal technology able to inactivate enzymes. This work aimed to assess the potential inactivation of PME by PL and to explain how it occurs. To this, a suspension of the enzyme was treated with PL up to 128 J/cm2. The inactivation curve was built and structural changes were determined by far-UV circular dichroism, intrinsic and extrinsic fluorescence and spectrophotometry. Furthermore, the presence/absence of unfolding intermediaries was assessed by phase-diagram analysis. PL was able to inactivate PME with a first-order kinetic rate of 0.034 cm2/J. The inactive protein seemed to have a molten-globule structure, due to the conserved secondary structure and modified tertiary structure. Phase diagram data fitted a single line, which is consistent with absence of unfolding intermediaries. A significant increase in absorbance at 420 nm (p<0.05) showed that PL promoted enzyme aggregation.Ciencias de la Alimentació