Glutinous rice (or sticky rice) has to be soaked in water over an extended period of time before cooking. Soaking provides some of the water needed for starch gelatinisation to occur during cooking. The extent of water uptake during soaking is known to be influenced by temperature. This paper explores the use of very high pressures up to 600MPa to accelerate water uptake kinetics during soaking. Changes occurring in length, diameter and moisture content were determined as a function of soaking time, pressure and temperature. The results show that length and diameter are positively correlated with all three parameters. However, the expansion ratios are not very high: the maximum length expansion ratio observed was 1.2, while the maximum diameter expansion ratio was 1.1. Given these low values, it was possible to model water uptake kinetics by using the well-known Fickian model applied to a finite cylinder, assuming uniform average dimensions and effective diffusion coefficient. The results showed that the overall rates of water uptake and the equilibrium moisture content increased with pressure and temperature. The effective diffusion coefficient, on the other hand, did not follow the same trend. Temperature influenced the effective diffusion coefficient below 300MPa, but had a marginal effect at higher pressures. Moreover, the effective diffusion coefficient increased with temperature between 20 and 50°C, but dropped at higher temperatures. This drop can be attributed to the gelatinisation of starch, which restricts the transport of water. Regardless, it is possible to increase the quantity of water absorbed by rice and the rate at which it is absorbed, by using high pressures and temperatures.

The effects of high pressure (to 800 MPa) applied at different temperatures (20-70 °C) for 20 min on beef post-rigor longissimus dorsi texture were studied. Texture profile analysis showed that when heated at ambient pressure there was the expected increase in hardness with increasing temperature and when pressure was applied at room temperature there was again the expected increase in hardness with increasing pressure. Similar results to those found at ambient temperature were found when pressure was applied at 40 °C. However, at higher temperatures, 60 and 70 °C it was found that pressures of 200 MPa caused large and significant decreases in hardness. The results found for hardness were mirrored by those for gumminess and chewiness. To further understand the changes in texture observed, intact beef longissimus dorsi samples and extracted myofibrils were both subjected to differential scanning calorimetry after being subjected to the same pressure/temperature regimes. As expected collagen was reasonably inert to pressure and only at temperatures of 60-70 °C was it denatured/unfolded. However, myosin was relatively easily unfolded by both pressure and temperature and when pressure denatured a new and modified structure was formed of low thermal stability. Although this new structure had low thermal stability at ambient pressure it still formed in both the meat and myofibrils when pressure was applied at 60 °C. It seems unlikely that structurally induced changes can be a major cause of the significant loss of hardness observed when beef is treated at high temperature (60-70 °C) and 200 MPa and it is suggested that accelerated proteolysis under these conditions is the major cause.

Oxymyoglobin in aqueous extracts of fresh beef longissimus dorsi muscles was initially oxidised to metmyoglobin during heat treatments at temperatures in the range 50-70 degreesC. The metmyoglobin then underwent reduction to a red pigment that was shown spectrally to be identical to oxymyoglobin. The formation of oxymyoglobin involved a heat induced precipitate that when removed from the solution, allowed oxidation to metmyoglobin to occur. However, on re-addition of the precipitate further reduction to oxymyoglobin took place. Dialysis of the muscle extract prior to heating markedly inhibited the reduction but addition of NADH to the dialysate permitted further reduction. The precipitate plus NADH caused oxymyoglobin formation in the presence of metmyoglobin but neither the precipitate nor NADH alone induced this formation. It is concluded that the initial conversion of oxymyoglobin to metmyoglobin on heating fresh beef muscle extracts was reversible and that the reverse reaction depended on the presence of both NADH and a muscle protein. (C) 2003 Elsevier Science Ltd. All rights reserved.

Intermediate moisture smoked beef was prepared by cook-soak/equilibration in a solution containing sodium chloride, sodium nitrite and potassium sorbate. Two further solutions contained glycerol and glycerol + 'onion' in addition to the above ingredients. Half the samples in each treatment group were smoked for 18 h (heavy smoking) and the others for 4 h (light smoking) at 50°C. All samples developed the pink-red colour of nitrite cured meat but those treated with glycerol were darker, presumably due to decreased moisture contents. Glycerol increased the apparent moisture, fat and sodium dodecyl sulphate (SDS) soluble protein contents and also improved the conversion of haemoproteins to the cooked cured form but decreased the percent soluble hydroxyproline. Smoking caused a marked decrease in moisture, SDS-soluble protein and soluble hydroxyproline contents and slightly decreased the available lysine and percent conversion of the haemoproteins to the cured nitrose forms. Smoking also caused increased darkening and hardness of the samples. Total viable aerobes, coliforms and fungi were below the levels of detection while TBA values were low and all samples possessed no detectable rancidity. Electrophoretograms of the samples indicated that cooking/equilibration had no significant effects on the proteins present but smoking led to a slight loss of some of the protein components.

Publisher Summary This chapter examines the transient movement of browning front through high-pressure treated potatoes. For experiment, potato cylinders are subjected to pressures of 200, 400 and 600 MPa for 5, 10, 20 and 30 min. After treatment, the samples are held at room temperature and a transverse cut is made at the time 0, and after 3, 6, 9, 12, 15, 18, 21 and 24 hours. Each experiment is done in triplicate and an untreated sample is used as a control. The depth of penetration of the browning front moving from the surface to the centre of the potato cylinder is measured. In the study, it is found that the net rate of movement of browning front in any high pressure treated vegetable is a balance between the extent of enzyme inactivation caused by the applied pressure, and the enhancement in oxygen diffusion rates caused by the opening up of tissue structure and higher solubility.

Textural properties and water holding capacity (WHC) of high-pressure (HP) induced gels were studied. At 20% protein concentration, soy protein isolate (SPI) and its major globulins: 7S and 11S, produced self-supporting gels at pressures in the range 300–700MPa. HP-induced gels gave significant lower values of adhesiveness and hardness when compared to the heat-treated gels. The WHC is enhanced by HP in the gels of 7S, and in some cases of SPI. Differential scanning calorimetry and electrophoresis (SDS–PAGE and native-PAGE) showed evidence of denaturation and aggregation during the formation of the gels. These effects are more intense with increasing pressures.

ABSTRACT: The diffusion coefficient of sucrose in potato cylinders was determinted at the various pressures (200 to 600 MPa) and temperatures (20, 40, and 60 °C). Application of pressure opened up the tissue structure and facilitated diffusion. However, higher pressures above 400 MPa also induced starch gelatinization and hindered diffusion. The maximum diffusion coefficient was therefore, dependent on which of the 2 effects dominated. In this study, the maximum value of diffusion coefficient observed represented an 8‐fold increase over ambient values. Thus, application of appropriate levels of pressure (100 to 400 MPa), can be used to accelerate mass transfer during ingredient infusion into foods.

Hydrated gluten and soy mixtures with concentrations of gluten-soy=20:80, 40:60, 60:40 and 80:20% were subjected to high pressure treatment at 700 MPa for 50 min at 20 and 60 degreesC. The treated samples were subsequently analysed for viscoclastic properties and electrophoretic patterns. A quadratic canonical polynomial model was used for the mixture design. Following high pressure treatment, the samples formed solid-like gel structures. In general, in the gels having high concentrations of gluten, both storage and loss moduli tended to increase with increasing pressure and temperature whereas, in the gels having high concentrations of soy. both moduli appeared to increase only slightly with increasing severity of the treatments. These results meant that the combined effect of temperature and pressure was much greater on the large complex gluten molecule than on the smaller soy globulins. (C) 2002 Elsevier Science Ltd. All rights reserved.

sSPI, 7S, and 11S globulin at 12% (w/v) protein concentration, at neutral pH, did not form gels when heat-treated (90 degreesC, 15 min) or when high pressure-treated (300-700 MPa), except for the I IS, which formed a gel when heat-treated. The combination of heat and pressure (that is heating the solutions in a water bath and then pressure-treating at room temperature or the reverse sequence), led to differences: when heat-treatment was before high-pressure treatment, only the I IS fraction formed a self-standing gel; however, when the solutions were pressurised before heat treatment, all the proteins formed self-standing gels. The textural and water-holding properties were measured on the gels formed with the three different soy proteins. (C) 2002 Elsevier Science Ltd. All rights reserved.

The different soy proteins studied, soy protein isolate (SPI), 7S globulin and 11S globulin are differently affected by high-pressure (HP). HP unfolds the proteins, exposing hydrophobic sites, leading to improve functional properties of the proteins. In our study, 7S showed the highest emulsifying activity index (EAI) and surface hydrophobicity after treatment at 400 MPa whereas 11S showed its highest EAI and surface hydrophobicity after treatment at 200 MPa. SPI showed the optimum value of EAI after treatment at 400 MPa although its surface hydrophobicity was low. It is suggested that pressure at 400 MPa dissociated the 7S of the SPI into partially or totally denatured monomers that enhanced the surface activity but at the same time, the unfolding of the polypeptides of the 11S within the hexamer led to aggregation, negatively affecting the surface hydrophobicity of the SPI.

In this study, high-pressure treatment (HPT) was applied to the mashing stage of beer production, which involves drying and milling of white malt and subsequent mixing with water. The following parameters were evaluated after pressurisation: P-glucanase activity, starch gelatinisation and sugar extraction. Evaluation of starch hydrolysis from the malted barley endosperm. after HPT was performed by measuring P-glucanase activity after pressurisation; this enzyme breaks down gums and beta-glucans in wort and is desirable to obtain a good-quality beer. Soaked malt samples pressurised at 200-600 MPa showed no increase in this activity compared with controls. Conversion of milled malt was evaluated indirectly by measuring the gelatinisation of starch, which began at 400 MPa. Soluble sugars were also measured in pressurised samples from the mashed liquid to investigate saccharification during the mashing stage. After 400 or 600 MPa treatment for 20min, both the sucrose (g per 100ml) and extract (1degreeskg (1)) values were the same as those found in mashed samples following the standard procedure used in the brewing industry (65degreesC,90 min). Starch gelatinisation was analysed at different high pressures (200-600 MPa) and it was shown that gelatinisation began at 400 MPa. The HPT time would have to be shorter to make the process commercially attractive. (C) 2002 Society of Chemical Industry.

Acid phosphatase activity was measured in whole milk, skim milk, acid and rennet wheys before and after subjecting samples to high hydrostatic pressures for 10 min. Whole and skim milks exhibited a significant drop in activity following treatment at pressures in excess of 200 MPa. While rennet whey exhibited similar characteristics, acid whey was more pressure resistant and required pressures in excess of 500 MPa before exhibiting a net loss in activity Most of the activity was lost in the first 10 min of pressurisation.

The influence of high pressure (HP) treatment (200–600MPa) on the emulsifying activity index (EAI) and emulsifying stability index (ESI) on the 7S and 11S globulins and soya protein isolate (SPI) at pHs 7.5 and 6.5, at different concentrations (0.25–0.75%) was studied. Solubility and surface hydrophobicity were used as indices of the degree of denaturation caused by HP. 7S showed the highest EAI and surface hydrophobicity after treatment at 400MPa, whereas 11S showed its highest EAI and surface hydrophobicity after treatment at 200MPa. No significant correlation (P>0.05) was found between solubility and EAI or hydrophobicity. SPI showed the optimum value of EAI after treatment at 400MPa although its surface hydrophobicity was low. It is suggested that pressure at 400MPa dissociated the 7S of the SPI into partially or totally denatured monomers that enhanced the surface activity but at the same time, the unfolding of the polypeptides of the 11S within the hexamer led to aggregation, negatively affecting the surface hydrophobicity of the SPI. The ESI values for the non-treated samples of SPI, 7S and 11S were higher at lower concentrations. At the same pH and concentration, the ESI decreased with increasing HP, except for the 7S at pH 7.5 and a protein concentration of 0.75%.

The emulsifying properties and the characteristics of heat-induced gels (texture and water-holding capacity) prepared from pressurised blood plasma solutions of different pH (5.5–7.5) were investigated. Changes in the plasma, that affected its behaviour as an emulsifier, occurred after pressurisation. The highest emulsifying activity was found for samples treated at 400 MPa. At pressures above 400 MPa, the emulsifying activity and stability, at all pHs, decreased with increasing pressure. The hardness of heat-induced gels decreased significantly as the pressure increased above 400 MPa, this effect being more noticeable with decreasing pH. However, although a 600 MPa pressurisation induced a further decrease in the firmness of gels from solutions at pH 6.5 and 7.5, it increased the hardness of gels at pH 5.5. For treatments up to 500 MPa, the highest elasticity was found in gels from solutions at pH 7.5. Pressure treatments above 400 MPa improve the water-holding capacity of heat-induced gels prepared from plasma solutions at pH ⩾6.5.

Probe spectrofluorimetry studies for ovalbumin (OVA) show an increase in surface hydrophobicity at pressures > 400 MPa. Pressure treatment of mixtures of OVA+ dextran sulphate (DS) greatly reduces the surface hydrophobicity. Size exclusion chromatography data indicate that stronger protein-polysaccharide complex(es) are formed during treatment at low ionic strength and pH 6.5. Emulsions made with pressurized (600 MPa) OVA in the presence of polysaccharide at pH 6.2 and low ionic strength exhibit the improved emulsifying efficiency and stabilizing properties of the protein. Under pressure treatment at pH less than or equal to 6.5, OVA forms reversible electrostatic complex(es) and the strength of interaction is related to the charge density on the polysaccharide (DS > iota -carrageenan (iota -CAR) > kappa -carrageenan (kappa -CAR)). Complexation of OVA with polysaccharide seems to protect the protein against loss of functionality from pressure-induced aggregation.

The influence of ι-carrageenan (ι-CAR) on the solution, interfacial and emulsifying properties of 11S globulin Viciafaba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200MPa for 20min. The total calorimetric enthalpy (ΔH) and size exclusion chromatography studies for the pure 11S indicate that there is subunit dissociation and extensive aggregation of the protein during or following treatment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphonate (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and apparent surface shear rheology experiments show that the molecules in the film adsorbed from the pressurised 11S are much more strongly interacting than those adsorbed from the native 11S. However, emulsions prepared with pressure processed 11S give substantially bigger droplets than those made with the untreated pure protein. Addition of ι-CAR to 11S reduces the denaturation temperature (Tm), the ΔH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic strength is indicative of complex formation. Tension measurements at the air–water interface are also consistent with the presence of a complex. Emulsions made with the simple 1:0.33 mixture of 11S+ι-CAR give emulsions with smaller droplets and pressure processing of the biopolymer mixture leads to emulsions with even smaller droplets. The presence of ι-CAR at low ionic strength appears to protect the globulin against pressure-induced aggregation.

The effect of high-pressure treatment (200-600 MPa for 20 min) on the texture of cherry tomatoes and on the key softening enzymes (pectinmethylesterase and polygalacturonase) was investigated. When subjected to high-pressure treatment whole cherry tomatoes showed increasing textural damage with increasing pressures up to 400 MPa. However, treatment at pressures above 400 MPa (500-600 MPa) led to less apparent damage than treatment at 300 and 400 MPa; the tomatoes appearing more like the untreated samples. These visual changes were reflected in the texture (firmness) and amount of cell rupture in the tomatoes, with the least firmness and the most cell rupture being seen after treatment at 400 MPa. Light and scanning electron microscopy supported these observations. Although a sample of purified commercial pectinmethylesterase was partially inactivated at pressures above 200 MPa, irrespective of pH (4-9), in the whole cherry tomatoes no significant inactivation was seen even after treatment at 600 MPa, presumably because other components in the tomato offered protection or the isoenzymes were different. Polygalacturonase was more susceptible to pressure, being almost totally inactivated after treatment at 500 MPa. It is concluded that the textural changes in tomato induced by pressure involve at least two related phenomena. Initially, damage is caused by the greater compressibilty of the gaseous phase (air) compared to liquid-solid components, giving rise to a compact structure which, on pressure release, is damaged as the air rapidly expands, leading to increases in membrane permeability. This permits egress of water, and the damage also enables enzymatic action to increase, causing further cell damage and softening. The major enzyme involved in the further softening is polygalacturonase, which is inactivated at 500 MPa and above, and not pectinmethylesterase, which in the whole fruit, is barotolerant.

The time-temperature profiles for cooking in-house made beef and lamb burgers were determined using a thermocouple placed in the centre of the burger. From these data the soluble myoglobin remaining in the burger was predicted using kinetic data from previously reported model experiments. First order kinetics were assumed for the denaturation of the myoglobin. A good correlation between observed and predicted data was observed. Thus the "degree of doneness"of different meats can be predicted when cooked under specified conditions.

The influence of sulphated polysaccharides (dextran sulphate (DS), i-cafiageenan (i-CAR) and kappa-carrageenan (kappa-CAR)) on the emulsifying properties of ovalbumin (OVA) has been investigated over a range of pressures and temperatures. Oil-in-water emulsions (10gl(-1) protein, 200ml(-1) n-tetradecane, pH 6.2) prepared with heat-treated (80 degrees C for 10min) mixtures of OVA + DS (1:0.25 by weight) had increased creaming stability but unchanged average droplet size compared to those made with untreated OVA and OVA + DS. Emulsions made with pressure-processed (600MPa for 20min) OVA + DS (1:0.25 or 1:0.5 by weight) mixtures had the best emulsifying efficiency and stability. Under similar experimental conditions, replacement of DS with either i- or kappa-CAR gave emulsions with larger droplets and more rapid serum separation, probably owing to depletion flocculation. High-pressure treatment (600 MPa) of the OVA and mixed biopolymer solutions at pH 6.2 in the presence of salt (>0.04M) led to unstable emulsions, and so the protective effect of DS was lost. High-pressure treatment (600MPa) of emulsions prepared with native OVA or OVA + DS mixtures induced significant levels of flocculation, as indicated by changes in the average droplet size and creaming behaviour. (C) 2000 Society of Chemical Industry.