Manothermosonication Research Articles

Studies of ovalbumin gelation in the presence of carrageenans and after manothermosonication treatments

Ovalbumin is a key ingredient in many food products due to its ability to form a three-dimensional network after heat denaturation, that is, to form gels. We have explored two ways of modifying gels based on ovalbumin: (1) the addition of carrageenans, and (2) manothermosonication (MTS) treatments of ovalbumin suspensions prior to gelation. Ovalbumin gels showed elastic modulus ( G ′) values of 1216 Pa after a heating and a cooling period. The addition of kappa, lambda, and iota carrageenan enhanced G ′ values by 6, 1.7, and 1.7 fold, respectively. Kappa carrageenan was not only the most effective carrageenan in the improvement of ovalbumin gelation but changed also the gelation process at the end of the cooling phase. MTS treatments reduced G ′ values of ovalbumin gels by about 50% measured immediately after MTS treatments but only by ca. 25% after 24 h, which reveals that ovalbumin modifications introduced by ultrasound, whatever they are, are reversible. This reduction does not preclude the use of manothermosonicated liquid egg as gelling agent.

Microbial inactivation by new technologies of food preservation

The increasing consumer demand for 'fresh-like' foods has led to much research effort in the last 20 years to develop new mild methods for food preservation. Nonthermal methods allow micro-organisms to be inactivated at sublethal temperatures thus better preserving the sensory, nutritional and functional properties of foods. The aim of this review is to provide an overview of the microbiological aspects of the most relevant nonthermal technologies for microbial inactivation currently under study, including irradiation, high hydrostatic pressure, pulsed electric field and ultrasound under pressure. Topics covered are the mechanisms of inactivation, sensitivity of different microbial groups and factors affecting it and kinetics of inactivation.

Rheological properties of yoghurt made with milk submitted to manothermosonication.

Manothermosonication (MTS) treatments, the simultaneous application of heat and ultrasound under moderate pressure, of milk during 12 s at 20 kHz ultrasound amplitude, 2 kg pressure, and 40 degrees C allowed elaboration of yoghurts with rheological properties superior to those of control yoghurts elaborated with untreated milk. Measurements performed on intact samples (compression tests, relaxation tests, and texture profile analysis) and on slowly stirred samples (flow curves, apparent viscosity, yield stress, and viscoelastic properties) showed that MTS yoghurts had stronger structures, which resulted in higher values of almost all of the many relevant rheological parameters. Homogenization of fat globules brought about by MTS treatments is not responsible for the superior properties of MTS yoghurts, because the control yoghurt was also elaborated with homogenized milk. These results show that MTS could be a useful tool to improve the texture of yoghurts.

The effects of manothermosonication on tomato pectic enzymes and tomato paste rheological properties

The effect of manothermosonication (MTS), the simultaneous application of heat and high energy ultrasound waves under moderate pressure, on tomato juice rheology and on tomato pectinmethylesterase (PME) and polygalacturonase (PG) activity in tomato juice was examined. Tomato juice was subjected to MTS treatments (20 kHz, 2 kg pressure, 117 μm amplitude and 70 °C), or to control thermal treatments (TT), for 1 min. Flow curves, yield stress and apparent viscosity were measured on both kind of samples. Apparent viscosity of MTS samples were 1.6-fold higher than that of TT samples. Yield stress values were also 2.2-fold higher in MTS than in TT samples. Flow curve values were fitted to the power law equation; MTS samples showed about 1.9-fold higher consistency values and lower flow indexes, n=0.190 vs. n=0.126, than TT samples. MTS samples retained about 20% more serum than TT samples after centrifugation. TT inactivated about 38% of the initial PME activity whereas PME activity was undetectable in MTS-treated tomato juice. TT left PG unaffected whereas MTS treatments inactivated 62% of total PG activity. These results suggest, that MTS could be an useful technology to obtain high viscosity and consistency tomato juice.

Manothermosonication of heat-resistant lipase and protease from Pseudomonas fluorescens: effect of pH and sonication parameters.

The effect of different parameters (pH, ultrasonic amplitude and pressure) on the resistance to heat and manothermosonication (MTS) treatments of heat resistant lipase and protease produced by Pseudomonas fluorescens B52 and NCDO 2085, respectively, were studied. Lipase B52 thermoresistance decreases with an increase of pH. However, inactivation by MTS seems to be pH independent. There were only slight increases in the MTS efficiency when increasing pressure at UHT temperatures and the effect of amplitude was different depending on treatment temperature. Protease NCDO 2085, which was very resistant to MTS at 30 degrees C. was very sensitive to MTS at 76 degrees C. Increases in applied pressure had no effect on MTS efficiency at 140 degrees C and its inactivation by MTS was almost temperature independent between 76-109 degrees C. Data obtained are compared with previous published data and inactivation mechanisms are discussed.

The effects of manothermosonication on tomato endopolygalacturonase β-subunit

The ability of the β-subunit of tomato endopolygalacturonase I (PGI) to enhance the thermal resistance of endopolygalacturonase II (PGII) has been tested after PGI was inactivated by thermal or manothermosonication (MTS) treatments of similar intensity. The β-subunit retained a low converter activity (0.3–1%) after thermal treatments whereas this activity was fully destroyed by MTS treatments. The low amount of PGI activity restored in the heat treated samples could be due to a low assay efficiency or to the thermal inactivation of the β-subunit.

Inactivation of proteases and lipases by ultrasound

The inactivation of phospholipase A 2, α-chymotrypsin, trypsin and porcine pancreatic lipase by heat and manothermosonication (MTS), and the simultaneous application of heat and ultrasound under moderate pressure, has been studied in different treatment media. MTS sensitivity varied strongly for the different enzymes. Whereas phospholipase A 2 was almost insensitive to MTS treatments, α-chymotrypsin and porcine lipase MTS inactivation was much faster than heat inactivation. Trypsin heat inactivation was very different at low than at high temperatures. At low temperatures, it did not follow first order kinetics, contrary to what happened at high temperatures. MTS accelerated trypsin inactivation only at low temperatures. MTS changed also the inactivation order of trypsin (at low temperatures), α-chymotrypsin and porcine lipase; whereas heat inactivation of these enzymes did not follow first order kinetics, MTS inactivation fitted this well.

Manothermosonication of foods and food-resembling systems: effect on nutrient content and nonenzymatic browning.

The effect of manothermosonication (MTS), an emergent technology for food preservation, on thiamin, riboflavin, carotenoids, and ascorbic acid was evaluated in milk and orange juice. The effect of both heat treatment and MTS on several compounds produced in nonenzymatic browning in model systems was also studied. MTS does not affect significantly the nutrient content studied. However, it changes the behavior of nonenzymatic browning. No formation of 5-(hydroxymethyl)-2-furfuraldehyde (HMF) was detected in fruit juice model systems after heat and MTS treatments at the experimental conditions used. In a milk-resembling system, free HMF formation by MTS is higher compared to that by heat treatment. As the MTS temperature increases, free HMF production by both treatments equaled on another. For bound HMF the production rate is lower by MTS than by heat treatment under the experimental conditions used. Formation kinetics of brown pigments and that of fluorescent compounds are different for both treatments. Fluorescence and brown pigment production are faster in MTS.

Inactivation of heat-resistant pectinmethylesterase from orange by manothermosonication.

Pectinmethylesterase of navel oranges shows two fractions greatly differing in thermostability. The most thermostable fraction accounts for approximately 10% of total activity. The thermal inactivation of this fraction follows first-order kinetics both in 5 mM, pH 3.5, citrate buffer and in orange juice at the same pH, showing a z value of 5.1 degrees C and an activation energy (E(a)) of 435 kJ mol(-)(1) K(-)(1). The heat resistance of the enzyme is approximately 25-fold higher in the juice than in citrate buffer. When ascorbic acid, sucrose, glucose, and fructose are added to the citrate buffer at the concentrations found in orange juice, the heat resistance of the enzyme increases 3-fold. The addition of pectin at 0.01% concentration multiplies it by a factor of 50. Manothermosonication (MTS), the simultaneous application of heat and ultrasound under moderate pressure (200 kPa), at 72 degrees C, increases the inactivation rate 25 times in buffer and >400 times in orange juice. MTS inactivation shows a higher z value (35.7 degrees C) and lower E(a) (56.9 kJ mol(-)(1) K(-)(1)) than simple heating.

Inactivation of tomato pectic enzymes by manothermosonication

The resistance of tomato pectic enzymes to manothermosonication (MTS), a combined treatment of heat and ultrasound under moderate pressure, was studied. Pectinmethylesterase (PMF) and polygalacturonases (PG) I and II were inactivated much more efficiently by MTS than by simple heating. In MTS inactivation of these enzymes, the effect of heat and ultrasonic waves was synergistic. D values [the time required for the (original) enzyme activity to decrease by 90%] for PME heat inactivation at 62.5 °C were reduced 52.9-fold by MTS and those for PG I at 86 °C and PG II at 52.5 °C, 85.8-fold and 26.3-fold, respectively.

Free radical production by manothermosonication

The use of manothermosonication (MTS), a combined treatment of heat and ultrasound (20 kHz frequency) under moderate pressure, has been recently proposed as an alternative to conventional heat treatment of liquid foods. The efficiency of MTS has been proved on several enzymes of interest in food industry. One of the MTS enzyme inactivation mechanisms proposed is the interaction of free radicals produced by water sonolysis with some amino acid residues. In this paper we examine the rate of free radical production of the MTS system under different conditions of temperature, pressure and ultrasound amplitude using the terephtalate dosimeter. The ultrasound amplitude was varied between 20 and 145 μm at two different temperatures and pressures ( 70 ° C 200 kPa and 130 ° C 500 kPa ). In both cases, free radical production rate increases linearly with increasing ultrasound amplitude. The pressure effects on free radical production was studied under two different conditions at 117 μm: 70 °C and 130 °C. At 70 °C an increase of hydrostatic pressure results in an increase in free radical production rate, whereas increasing hydrostatic pressure at 130 °C had a negligible effect on free radical production rate. Temperature effects were studied between 30 and 140 °C at 117 μm ultrasound amplitude. Results show that increasing temperature results in a decrease in hydroxyl radical rate production.

Lipoxygenase Inactivation by Manothermosonication: Effects of Sonication on Physical Parameters, pH, KCl, Sugars, Glycerol, and Enzyme Concentration

Manothermosonication (MTS) efficiency in lipoxygenase (LOX) inactivation, in phosphate buffer, pH 6.5, increases with ultrasound amplitude in the range 0-104 μm at any temperature from 67.5 to 76.3 o C. Activation energy (E a ) is lower in MTS than in thermal enzyme inactivation and decreases with increasing ultrasound amplitude. Thermal and MTS resistance of the enzyme raises with decreasing pH in the range 5.2-8, but more so thermal than MTS resistance. Differences of E a between thermal and MTS enzyme inactivation increase with decreasing pH. Glucose, sucrose, and glycerol increase both thermal and MTS LOX resistance. Neither of these enzyme stabilizers deviates the MTS inactivation course from first-order kinetics but all of them transform in biphasic the thermal inactivation course. LOX concentration does not affect thermal stability but increasing concentration of the enzyme increases MTS resistance. These results are discussed in terms of the possible inactivation mechanism added to heat by ultrasonic waves in MTS