The Impact of Thermosonication and Pulsed Electric Fields on Staphylococcus aureus Inactivation and Selected Quality Parameters in Orange Juice

The effect of yeast concentration on ultraviolet (UV) inactivation of five strains of Escherichia coli O157: H7 from different sources, inoculated both individually and simultaneously in orange juice, was analyzed and mathematically modeled. The presence of yeast cells in orange juice decreases the performance of UV radiation on E. coli inactivation. UV absorption coefficients in the juice increased with increasing yeast concentration, and higher UV doses were necessary to inactivate bacterial strains. UV intensities of I=3.00±0.3 mW/cm 2 and exposure times (t) between 0 and 10 min were applied; radiation doses (energy, E=I×t) ranging between 0 and 2 J/cm 2 were measured using a UV digital radiometer. All the tested individual strains showed higher resistance to the treatment when UV radiation was applied at 4°C in comparison to 20°C. UV inactivation of E. coli O157:H7 individual strain was satisfactory fitted with a first order kinetic model. A linear relationship was found between UV absorptivities and D values (radiation doses required to decrease microbial population by 90%) for each strain. The dose required to reach 5-log reduction for the most unfavorable conditions that is the most UV resistant strain, and maximum background yeast concentration was 2.19 J/cm 2 at 4°C (corresponding to 11 min of UV treatment) and 2.09 J/cm 2 at 20°C (corresponding to 10.55 min of UV treatment). When a cocktail of strains was inoculated in orange juice, the logistic equation was the best model that fits the experimental results due to the deviation from the log-linear kinetics. The UV resistance between strain cocktail and single strain were mathematically compared. Slopes of the decline curves for strain cocktail at high UV doses were lower than the slopes of the log-linear equation calculated for the individual strains, even for the most resistant one. Therefore, microbial inactivation tests using a cocktail of strains are particularly important to determine the performance of the UV inactivation treatment.

Section: Introductionmentioning

confidence: 99%

Ultraviolet Treatment of Orange Juice to Inactivate E. coli O157:H7 as Affected by Native Microflora

Oteiza

Giannuzzi

Zaritzky

2009

“…The sonicated and the thermal treated samples showed ascorbic acid values in the same range. Thermosonication treatment also retained high levels of ascorbic acid in a study with orange juice reported by Walkling-Ribeiro et al (2007). Murcia et al (2000), in a study in which broccoli florets were industrially processed, showed that blanching for 60 s at 92-96°C maintained about 50% of vitamin C content and reduced 99% of peroxidase activity.…”

mentioning

confidence: 81%

Impact of Thermal Blanching and Thermosonication Treatments on Watercress (Nasturtium officinale) Quality: Thermosonication Process Optimisation and Microstructure Evaluation

Cruz

Vieira

Fonseca

et al. 2009

The objectives of the present work were to optimise watercress heat and thermosonication blanching conditions, in order to obtain a product with better quality for further freezing, and to evaluate the effects of thermosonication on the microstructure of watercress leaves. In a chart of optimal time-temperature conditions for a 90% peroxidase inactivation (imposed constraint), vitamin C (objective function) and a-value (improvement toward green) were mathematically predicted for both heat and thermosonication blanching treatments. Two optimal thermosonication combinations were selected: 92°C and 2 s, retaining 95% of vitamin C content and 5% a-value improvement, and a better condition in terms of practical feasibility, 86°C and 30 s, allowing a 75% vitamin C retention and 8% a-value improvement. The experimental values, for each thermosonication optimal time-temperature zone, were in good agreement with the models' predicted responses. In terms of microstructure, thermosonicated watercress at 86 and 92°C showed similar loss of turgor and release of chloroplasts. The proposed optimal thermosonication blanching conditions allow the improvement of the blanched watercress quality and consequently contribute for the development of a high-quality new frozen product. However, a suitable scale-up is mandatory for industrial implementation.

“…The effect of thermo-sonication (TS) and PEF on inactivation of S. aureus and selected quality aspects in orange juice was investigated (Walkling-Ribeiro et al 2009). TS (10 min at 55°C) applied in combination with PEF (40 kV/cm for 150 μs) resulted in a comparable inactivation of S. aureus to that achieved by conventional HTST.…”

Section: Orange Juicementioning

confidence: 99%

Critical Issues Pertaining to Application of Pulsed Electric Fields in Microbial Control and Quality of Processed Fruit Juices

Ortega‐Rivas

2009

Pasteurisation of fruit juices is normally carried out by thermal means. Heat treatment is an efficient technology for pasteurisation, but may also cause impairment of nutritive and sensory attributes. High-voltage pulsed electric field (PEF) treatment is a promising nonthermal processing method for pasteurisation of liquid foods. Sensory quality of fruit juices is important for consumers. PEF lends itself to be employed as an alternative to produce fruit juices of high quality and safe for consumption, and yet its practical application has been really limited. This paper reviews research carried out recently about the potential use of PEF to different fruit juices, aimed at employing the technology at industrial scale in order to search for wider commercialisation.