Effect of high pressure (HP) on the quality and shelf life of red mullet (Mullus surmelutus)

The effect of different temperature/time/pressure high hydrostatic pressure (HP) treatment on the quality and shelf life of red mullet were studied. Different high pressure treatments (at 3, 7, 15 and 25 °C, 5 to 10 min and 220, 250 and 330 MPa) were tested to establish the best processing conditions for the quality of red mullet. The effect of the process on the quality of the sample was examined by colour, Trimethylamine nitrogen (TMA-N) and Thiobarbituric acid number (TBA) analysis. Based on the results of the parameters, the best combinations of HP treatments were determined as 220 MPa/5 min/25 °C and 330 MPa/5 min/3 °C for red mullet. The effects of this combination treatment on sensory, chemical and microbiological properties of red mullet stored at 4 °C were studied. The results obtained from this study showed that the shelf life of untreated and HP treated stored at 4 °C, as determined by overall acceptability of sensory and microbiological data, are 12 days for untreated red mullet and 14 days for treated red mullet at 220 MPa for 5 min at 25 °C and 15 days for treated red mullet at 330 MPa for 5 min at 3 °C.Industrial relevanceFresh fish have short shelf life. HP treatment has shown to be an effective method to control pathogen and spoilage microorganisms in fish and fish products. However, high pressure treatment can promote colour and oxidation changes that could modify their sensory characteristics. The main objective of the first part of this study was to detect the best combination among the applied pressure (220, 250 and 330 MPa), temperature (3, 7, 15 and 25 °C) and time (5 and 10 min) combinations. The treatment ranges were chosen according to the unchanging colour, lower TBA value and TMA stability by HP and considering the economical aspects of HP processing. In the second part of the study, HP was applied on the selected samples and a shelf-life study was performed by measuring the changes in the quality parameters, of the samples throughout their storage. The storage conditions were set so as to achieve refrigeration handling (4 °C). Shelf-life estimation was performed according to the data obtained. HP (at 220 MPa for 5 min at 25 °C and at 330 MPa for 5 min at 3 °C) treatment is the most effective treatment for shelf-life extension as compared to non-treated red mullet.     

High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation

Whole raw milk was processed using a 15 L h⁻¹ homogeniser with a high-pressure (HP) valve immediately followed by a cooling heat exchanger. The influence of homogenisation pressure (100–300 MPa) and milk inlet temperature T_in (4°C, 14°C or 24°C) on milk temperature T₂ at the HP valve outlet, on fat globule size distribution and on the reduction of the endogenous flora were investigated. The T_in values of 4–24°C led to milk temperatures of 14–33°C before the HP valve, mainly because of compression heating. High T_in and/or homogenisation pressure decreased the fat globule size. At 200 MPa, the d_4.3 diameter of fat globules decreased from 3.8±0.2 (control milk) to 0.80±0.08 μm, 0.65±0.10 or 0.37±0.07 μm at T_in=4, 14°C or 24°C, respectively. A second homogenisation pass at 200 MPa (T_in=4°C, 14°C or 24°C) further decreased d_4.3 diameters to about 0.2 μm and narrowed the size distribution. At all T_in tested, an homogenisation pressure of 300 MPa induced clusters of fat globules, easily dissociated with SDS, and probably formed by sharing protein constituents adsorbed at the fat globule surface. The total endogenous flora of raw milk was reduced by more than 1 log cycle, provided homogenisation pressure was ⩾200 MPa at T_in=24°C (T₂∼60°C), 250 MPa at T_in=14°C (T₂∼62°C), or 300 MPa at T_in=4°C (T₂∼65°C). At all T_in tested, a second pass through the HP valve (200 MPa) doubled the inactivation ratio of the total flora. Microbial patterns of raw milk were also affected; Gram-negative bacteria were less resistant than Gram-positive bacteria.     

Effects of high pressure treatment on indigenous enzymes in bovine milk: Reaction kinetics,inactivation and potential application

High pressure-induced inactivation of the indigenous milk enzymes alkaline phosphatase (ALP), γ-glutamyltransferase (GGT) and phosphohexoseisomerase (PHI) was studied in the pressure range 400–800 MPa at temperatures between 5 and 40 °C. With respect to pressure stability the following ranking was observed: ALP>GGT>PHI. PHI was inactivated after pressure treatment at 500 MPa and 20 °C for 10 min. In terms of reaction kinetics, inactivation of GGT followed first-order reaction kinetics in the range of 400–800 MPa whereas a reaction order of 1.5 was found for ALP. Reactivation of pressure-treated ALP was observed at low enzyme activity resulting from severe pressure treatment and 2 h storage at 35 °C. The influence of process temperature on the pressure-induced inactivation of GGT and ALP was limited in the range 5–40 °C.     

Conventional freezing plus high pressure–low temperature treatment: Physical properties,microbial quality and storage stability of beef meat

Meat high-hydrostatic pressure treatment causes severe decolouration, preventing its commercialisation due to consumer rejection. Novel procedures involving product freezing plus low-temperature pressure processing are here investigated. Room temperature (20 °C) pressurisation (650 MPa/10 min) and air blast freezing (−30 °C) are compared to air blast freezing plus high pressure at subzero temperature (−35 °C) in terms of drip loss, expressible moisture, shear force, colour, microbial quality and storage stability of fresh and salt-added beef samples (Longissimus dorsi muscle). The latter treatment induced solid water transitions among ice phases. Fresh beef high pressure treatment (650 MPa/20 °C/10 min) increased significantly expressible moisture while it decreased in pressurised (650 MPa/−35 °C/10 min) frozen beef. Salt addition reduced high pressure-induced water loss. Treatments studied did not change fresh or salt-added samples shear force. Frozen beef pressurised at low temperature showed L, a and b values after thawing close to fresh samples. However, these samples in frozen state, presented chromatic parameters similar to unfrozen beef pressurised at room temperature. Apparently, freezing protects meat against pressure colour deterioration, fresh colour being recovered after thawing. High pressure processing (20 °C or −35 °C) was very effective reducing aerobic total (2-log₁₀ cycles) and lactic acid bacteria counts (2.4-log₁₀ cycles), in fresh and salt-added samples. Frozen + pressurised beef stored at −18 °C during 45 days recovered its original colour after thawing, similarly to just-treated samples while their counts remain below detection limits during storage.     

Effects of high pressure processing on protein fractions of blue crab (Callinectes sapidus) meat

The studies about the effect of high pressure processing (HPP) on the myofibrillar proteins of crab meat are scarce in the literature. The aim of this study is to evaluate the effect of high pressure processing (HPP) at 100, 300 and 600 MPa (10 °C/5 min) on the muscular protein fractions of blue crab meat (Callinectes sapidus) and compares the effect of high pressure treatments and the thermal cooking process on the yielding of crab meat. Differential scanning calorimetry analysis of raw crab meat showed two peaks at 48.18 and 76.76 °C corresponding to myosin and actin denaturation. The increasing in the pressure level resulted in a decrease in denaturation enthalpy of both proteins. Data from Fourier transform infrared spectroscopy indicated changes in the secondary protein structures in which a reduction in α-helix and an increase in β-turn were observed as a result of denaturation induced by HPP. Electrophoresis analysis (SDS-PAGE) showed myofibrillar protein denaturation as the pressure level increased. The HPP at 100 and 300 MPa resulted in a significant increase in the yielding of meat extracted when compared to the thermal treatment (90 °C/20 min). Higher sensory scores were obtained in 300 and 600 MPa suggesting higher acceptance. Results suggest the feasibility of applying HPP as an alternative to the thermal treatment to process crab meat.Industrial relevanceHigh pressure processing (HPP) technology has been successfully applied to several seafood products. However, it is important to study the effect of HPP on the food components, mainly proteins in the crab meat to optimize the processing parameters to get high-quality products. In the present study, the benefit of using HPP as an alternative to the commercial thermal processing for extraction of crab meat has been confirmed. Applying 600 MPa (10 °C/5 min) to the whole blue crab resulted in a higher yield of extracted crab meat compared with the other treatments. However, using a range of 100–300 MPa (10 °C/5 min) also increases the yielding of extracted crab meat when compared to the thermal process, and moreover, the extraction procedure is faster. The quality and the functional properties of the crab meat with fresh appearance is preserved after the treatment at 100 MPa. These results could promote subsequent applications of pressurized crab meat in the crab industry, especially with the HPP treatments in a range between 100 and 300 MPa.     

Effect of high pressure, temperature, and storage on the color of porcine longissimus dorsi

The color of pork longissimus dorsi high pressure (HP) treated at 200 to 800MPa at 5 and 20°C for 10min was determined to a high degree by pressure level and to a lesser degree by temperature. Severe color changes appeared up to a threshold pressure at 400MPa. HP treatment at 20°C compared to 5°C resulted in meat, which was less red and slightly lighter. Storage at 2°C for 6days had no effect on lightness due to no further protein denaturation, but meat HP treated above 300MPa became significantly less red and more yellow within the first day of storage. Reflectance spectra showed that a short-lived ferrohemochrome myoglobin species was formed during HP treatment at 300 to 800, but transformed into a brown, ferric form of the pigment within the first day of storage. This explains the observed changes in the redness and yellowness after one day of storage.     

High pressure can reduce the antigenicity of bovine whey protein hydrolysates

The combined effect of high pressure (HP) and enzymatic treatments on the proteolysis and antigenicity of hydrolysates from bovine whey proteins (WP) was studied. Four food grade protease preparations (Alcalase, Neutrase, Corolase 7089 and Corolase PN-L) were used. Hydrolysis was performed at 40 °C for Corolase PN-L and 50 °C for the other enzymes, for 15 min, after or during HP treatment. The degree of hydrolysis and RP-HPLC peptide profile were evaluated. An indirect ELISA test using polyclonal rat anti β-lactoglobulin antibodies was used to determine the residual antigenicity. The results showed that HP treatment enhanced the hydrolysis of bovine WP. For most enzymes, the best results were obtained at a pressure of 300 MPa. For two enzymes, Corolase PN-L and Neutrase, differences in peptide profiles were obtained due to the pressure applied during the enzymatic hydrolysis. Based on these differences, the residual antigenicity of these preparations were determined. An important reduction was found in the antigenicity of the hydrolysates obtained with Corolase PN-L and Neutrase in combination with HP treatment (300 MPa), prior to or during enzymatic hydrolysis, respectively. These results suggest that HP can enhance the WP hydrolysis, and, depending on the choice of enzymes, reduce the residual antigenicity of the hydrolysates. The reduced antigenicity of hydrolysates obtained by the combined treatments could have a relevant application in the development of hypoallergenic infant formulae.     

Effect of high pressure processing and storage on the free amino acids in seedlings of Brussels sprouts

The potential of high pressure (HP) to affect the content of free amino acids (FAA) using seedlings of Brussels sprouts as a simple non-chopped vegetable system was examined. Firstly, the effect on FAA composition during growth was assessed and it was found that the composition of total free amino acids (TFAA) and individual FAA changed dramatically during growth of the seeds to the seedling at 7 days with the highest content of TFAA. Secondly, 7-day-old seedlings were HP-treated at various pressure levels (200–800 MPa for 3 min at 5 °C). As expected the HP-treatment did not affect the amino acids as no changes in TFFA were found immediately after pressurisation. In this line, HP-treatment up to 800 MPa had minor, but significant, effect on the FAA concentrations of 10 FAA (Ala, Asp, Glu, Gly, Leu, Phe, Pro, Ser, Trp and Tyr) and no significant changes were found for 7 of the FAA (Asn, Gln, His, Ile, Lys, Thr, and Val) concluding that the short pressure time (3 min) was insufficient to activate indigenous proteolytic enzymes. Furthermore, changes in the FAA content and composition of HP-treated seedlings during storage (0, 1, 2, and 4 days at 4 ± 2 °C) were evaluated in order to assess changes in the proteolytic enzyme activity. It was found that the changes in FAA differed according to the specific amino acids as well as the HP processing conditions and the subsequent storage time. These results suggest that HP treatment affects proteolysis and/or certain amino acids metabolism pathways in Brussels sprouts seedlings after HP treatment and during subsequent storage.     

The impact of high pressure on glucosinolate profile and myrosinase activity in seedlings from Brussels sprouts

The potential of high pressure (HP) to control bioactive components using seedlings of Brussels sprouts as a simple non-chopped vegetable system was examined. Enzyme activity in situ compared to purified enzyme and residual enzyme substrate in situ are used as three complementary measures for the HP effect. Purified myrosinase and seedlings of Brussels sprouts were submitted to HP 200–800 MPa at 5 °C for 3 min. The myrosinase activity decreased for both myrosinase systems upon increasing pressure to 800 MPa. Applying first-order kinetic to determine activation volumes revealed a linear relationship from 400 to 600 (ΔV^# = − 19.04 mL/mol) and 450–600 MPa (ΔV^# = − 37.79 mL/mol) for seedlings and purified myrosinase, respectively, indicating a protective effect of the plant matrix against enzyme inactivation. Purified myrosinase was activated at 200 MPa but at 800 MPa the glucosinolate degradation due to pressure induced disruption of the plant matrix seems to be partly counter-acted by myrosinase inactivation.Industrial relevanceHigh Pressure (HP) processing is an effective non-thermal preservation treatment for liquid and solid food. Moreover, over the last years, the potential of this technology to improve health and safety attributes of foods has been demonstrated. In particular, the ability of HP to preserve bioactive compounds has been established. There are only few studies evaluating the impact of HP on the complex bioactive glucosinolates-myrosinase. Therefore, this study opens the doors through the application of HP to preserve the bioactive glucosinolates in cruciferous vegetables by creating new processing solutions through controlled enzyme inactivation. Thus, HP could be an effective tool to achieve more effective solutions to obtain the new generation of convenient food and meet the need for new bioactive food products.     

High pressure–low temperature processing of beef: Effects on survival of internalized E. coli O157:H7 and quality characteristics

High pressure–low temperature (HPLT) processing was investigated to achieve Escherichia coli O157:H7 inactivation in non-intact, whole muscle beef while maintaining acceptable quality characteristics. Beef semitendinosus was internally inoculated with a four strain E. coli O157:H7 cocktail and frozen to − 35 °C, then subjected to 551 MPa for 4 min (HPLT). Compared to frozen, untreated control (F), HPLT reduced microbial population by 1.7 log colony forming units (CFU)/g on selective media and 1.4 log on non-selective media. High pressure without freezing (551 MPa/4 min/3 °C) increased pH and lightness while decreasing redness, cook yield, tenderness, and protein solubility. Aside from a 4% decrease in cook yield, HPLT, had no significant effects on quality parameters. It was demonstrated that HPLT treatment reduces internalized E. coli O157:H7 with minimal effect on quality factors, meaning it may have a potential role in reducing the risk associated with non-intact red meat.Industrial relevanceIn the current work, high pressure (551 MPa, 4 min) was applied to beef semitendinosus while it was at subfreezing temperatures (<− 30 °C). Most studies utilizing this high pressure–low temperature (HPLT) process employ subzero capable thermostatic high pressure equipment, which currently has no commercial equivalent. Successful HPLT runs were completed in this study using more conventional temperature control (1–3 °C) on pilot scale (20 L) high pressure processing equipment. The process yielded E. coli O157:H7 reductions of 1.4–1.7 log colony forming units (CFU)/g, which, while lower than conventional high pressure processing (HPP), may be sufficient to eliminate O157 populations typical of non-intact, whole muscle beef. Various quality factors, including color, purge losses and cooked tenderness, were unaffected by HPLT, while an equivalent HPP process at nonfreezing temperatures (551 MPa, 3 °C) induced color change (loss of redness), increased cook losses and decreased cooked tenderness compared to the control and HPLT beef. Producers of non-intact, whole muscle (blade tenderized or brine injected) meat, especially those that ship and sell frozen products, may look to HPLT processes to improve food safety.     

The effects of high hydrostatic pressure at subzero temperature on the quality of ready-to-eat cured beef carpaccio

We compared the application of high hydrostatic pressure (HHP) on unfrozen carpaccio (HHP at 20 °C) and on previously-frozen carpaccio (HHP at − 30 °C). HHP at 20 °C changed the color. The pressure increase from 400 to 650 MPa and the time increment from 1 to 5 min at 400 MPa increased L* and b*. a* decreased only with 650 MPa for 5 min at 20 °C. The prior freezing of the carpaccio and the HHP at − 30 °C minimized the effect of the HHP on the color and did not change the shear force, but increased expressible moisture as compared to the untreated carpaccio. HHP at 20 °C was more effective in reducing the counts of microorganisms (aerobic total count at 30 °C, Enterobacteriaceae, psychrotrophs viable at 6.5 °C and lactic acid bacteria) than HHP at − 30 º C. With HHP at 20 °C, we observed a significant effect of pressure and time on the reduction of the counts.     

Effect of modified atmosphere packaging,storage period,and storage temperature on the residual nitrate of sliced-pastırma,dry meat product,produced from fresh meat and frozen/thawed meat

The amount of nitrite in sliced-pastirma made, from fresh or frozen (which was stored at −18 °C for 240 days and then thawed at 10 °C for 24 h) M. Longissimus dorsi muscle was determined. Sliced-pastirma samples were stored in modified atmosphere packages (50% N₂ + 50% CO₂) at 4 and 10 °C for 150 days, and the amount of residual nitrite was measured after 0, 30, 60, 90, and 150 days of storage. The residual nitrite of pastirma samples made with frozen/thawed meat was higher than that of the pastirma made from fresh meat at both 0 day and at the end of the storage (150 days). The storage temperature (p < 0.01), storage period (p < 0.01) and the storage period × the storage temperature interaction (p < 0.01) had significant effects on the amount of the residual nitrite.     

Flavour profiles and survival of starter cultures of yoghurt produced from high-pressure homogenized milk

Volatile carbonyl compounds, organic acids and yoghurt bacteria counts were investigated in yoghurts made from ultra-high pressure homogenized milk. Yoghurts were manufactured from milk treated using ultra-high pressure homogenization at 200 or 300 MPa and at 30 °C or 40 °C, and compared with those produced from heat-treated milk with 3% added skim milk powder. To study the evolution of these parameters, samples were analysed after days 1, 14 and 28 of storage. Yoghurts from milk heat-treated or treated at 300 MPa had very similar profiles of organic acids and volatile compounds, as well as similar bacterial counts of both starter cultures. In comparison, yoghurts from milk treated at 200 MPa at either 30 °C or 40 °C gave different profiles, together with a sharp decrease in counts of lactobacilli. During storage, only slight differences in flavour compounds and yoghurt bacteria counts were detected, except in those samples from milk treated at 200 MPa.     

Effects of high pressure treatment on glycolytic enzymes of Lactococcus lactis subsp. lactis,Streptococcus thermophilus and Lactobacillus acidophilus

High pressure processing (HPP) reduces the glycolytic activity of lactic acid bacteria (LAB) and provides a means to control further production of acidic metabolites in fermented dairy products during storage. However, there is limited information on the effects of HPP on specific enzymes of dairy starter bacteria responsible for the metabolism of lactose. The aim of this study was to determine pressure-induced inactivation of glycolytic enzymes in Lactococcus lactis subsp. lactis C10, Streptococcus thermophilus TS1 and Lactobacillus acidophilus 2400. Cultures were grown for 16 h in M17 or MRS broth containing 5% (w/v) lactose at pH 6.5 (maintained by addition of 10 M NaOH). The cells were harvested by centrifugation, washed and resuspended in 100 mM phosphate buffer (pH 6.5) and pressure-treated at 300 and 600 MPa (≤ 22 °C, 5 min). The ability of pressure-treated resting cells of Lactococcus, incubated with 5% (w/v) lactose at 30 °C, to ferment lactose was evaluated by determining titratable acidity (TA) during incubation. The activities of phospho-β-galactosidase (P-β-gal), β-galactosidase (β-gal) and lactate dehydrogenase (LDH) were determined in cell-free extracts of untreated and pressure-treated cells. Resting cells of Lactococcus treated at 600 MPa had a substantially lower rate of acidification than the controls and those treated at 300 MPa. Both P-β-gal and β-gal were significantly inactivated (p < 0.01) in the starter cultures treated at 300 or 600 MPa. The LDH in Lactococcus and Lactobacillus was highly resistant to pressure treatment at 300 MPa. In contrast, the LDH in Streptococcus was almost completely inactivated at ≥ 300 MPa.Industrial relevanceContinuing production of acidic metabolites in fermented dairy products during storage can be a technological challenge that adversely affects product quality. The current study demonstrates that high pressure processing (HPP) offers the potential of controlling this problem by inactivation of glycolytic enzymes in various mesophilic and thermophilic starter cultures. The findings of this research will assist in establishing optimised operating parameters for HPP treatment of cultured products to extend shelf-life, by reducing acid production during storage.     

High pressure carbon dioxide combined with high power ultrasound processing of dry cured ham spiked with Listeria monocytogenes

Traditionally, thermal treatments for the inactivation of Listeria monocytogenes in meat products involve undesirable changes of the product quality. In recent years, efforts have been carried out to develop alternative methods to inactivate L. monocytogenes without affecting the product quality attributes. In this context, the feasibility of combined high pressure carbon dioxide and high power ultrasound (HPCO₂ + HPU) treatment to inactivate L. monocytogenes inoculated on the surface of dry cured ham was investigated. Inactivation data were determined at 6, 8 and 12 MPa, as a function of temperature (22, 35, 45 °C) and treatment time (0.5 to 30 min), and compared to those obtained after thermal and HPCO₂ treatments.Color, pH and acidity changes of the samples after both thermal and HPCO₂ + HPU treatments were measured and compared, sensorial profile of the treated samples was evaluated by a sensory panel and shelf-life was determined by a storage study for 4 weeks at 4 °C.The results clearly revealed that HPU alone was not able to induce any microbial inactivation while HPCO₂ + HPU treatment always assured a certain level of inactivation, variable with the process temperature used: the inactivation efficiency was demonstrated higher at 35 °C rather than 22 °C and no enhancement was observed at 45 °C compared to 35 °C. Process conditions of 12 MPa, 35 °C, at 10 W for 5 min assured inactivation to undetectable level of L. monocytogenes spiked on the surface of the product with an initial concentration of about 10⁹ CFU/g. No differences were detected between acidity, pH, color and sensory attributes of the untreated and HPCO₂ + HPU treated dry cured ham surface, while slight differences were measured between the values obtained for the untreated and thermally treated samples. Additionally, the storage study demonstrated that a full microbial and quality shelf-life was assured for 4 weeks at 4 °C. The results obtained may open the doors to the application of such an innovative process at industrial level, in particular to treat ham-type or meat products.     

Aging of red wines made from hybrid grape cv. BRS Violeta: Effects of accelerated aging conditions on phenolic composition,color and antioxidant activity

Aging is an enological technique usually employed with Vitis vinifera wines for improving and stabilizing wine sensory attributes like red wine color. However, red wines made from non-vinifera grape cultivars are considered not suitable for classic wine aging because they are prone to color loss during processing and storage, mainly due to the major occurrence of non-acylated anthocyanidin 3,5-diglucosides. The recently developed hybrid grape cv. BRS Violeta gives rise to deep red-purplish colored wines characterized by an important contribution of p-coumaroylated anthocyanidin 3,5-diglucosides. In this work, Violeta red wines were subjected to control (storage at 15 °C) and accelerated (storage at 25, 35 and 50 °C) aging for 120 days. Total phenolic content was only significantly decreased by 23% in accelerated aged wines at 50 °C, whereas antioxidant capacity was mainly reduced in the first 20 days of aging (around 35% for all the wines, except for 45% for wine aged at 50 °C) and then remained almost stable. In contrast, total anthocyanin content decreased following expected first-order kinetics and the variation of rate constants with regard to temperature fitted well with an Arrhenius-type equation. The calculated activation energy for disappearance of anthocyanins (47 kJ/mol) was close to the lower limit of the range of values reported for thermal degradation of anthocyanidin 3-glucosides. In addition, half-life values for p-coumaroylated anthocyanidin 3,5-glucosides of Violeta wine aged at 50 °C almost doubled those of their corresponding non-acylated derivatives. The latter result is suggested to be the main reason behind the relatively high resistance of Violeta wine towards the disappearance of anthocyanin under accelerated aging conditions. Finally, chromatic characteristics of Violeta wines did not significantly change their C* values during aging but L* and h* values increased as expected, the latter mainly due to higher increases of the yellow color component (b*) over lower decreases of the red color component (a*). These color changes were more drastic in the accelerated aged wines and the wine aged at 25 °C still maintained interesting color characteristics close to those of the control aged wine that did not change very much.     

Ultra high pressure homogenization of soymilk: Microbiological,physicochemical and microstructural characteristics

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa on soymilk was studied. A soymilk base product (BP) and ultra high temperature (UHT) treated soymilk were compared with UHPH treated soymilk. UHPH at 200 and 300 MPa reduced initial counts, spores and enterobacteria counts. Particle size analysis evidenced the intense reduction of particle size caused by UHPH, although the formation of aggregates was detected at 300 MPa. Colour differences between UHPH and BP or UHT soymilks were found. Treated soymilk (300 MPa) showed the lowest values of L¹, a¹ and b¹ coordinates. UHPH processed samples were more stable (showed less particle settling) than BP and UHT soymilks and these differences were also observed at days 30 and 60 of storage at 4 °C. Differential scanning calorimetry analysis indicated that soymilk proteins were partially denatured by 200 MPa, whereas UHPH treatment at 300 MPa showed the same extent of denaturation as UHT soymilk. Images of transmission electron microscopy showed the distribution and general characteristics of the colloidal particles and structures of UHPH, BP and UHT which were generally in accordance with the physicochemical parameters studied.     

Kinetics of destruction ofEscherichia coliandPseudomonas fluorescensinoculated in ewe's milk by high hydrostatic pressure

Ewe's1999199919991999 Academic PressAcademic PressAcademic PressAcademic Pressmilk standardized to 6% fat was inoculated with Escherichia coliand Pseudomonas fluorescensat a concentration of 10⁷and 10⁸ cfu ml⁻¹respectively, and treated by high hydrostatic pressure. Treatments consisted of combinations of pressure (50-300 MPa), temperature (2, 10, 25 and 50°C), and time (5, 10 and 15 min). Violet red bile agar and crystal-violet-tetrazolium count were used to determineE. coliandP. fluorescensrespectively. Pressurization at low and moderately high temperatures produced higher P. fluorescensinactivation than treatments at room temperature, while pressurization at only moderately high temperature produced high E. coliinactivation; low and room temperatures produced similar reductions. On E. coli,reductions of 6.055 log units were produced with 300 MPa for 15 min at 50°C, while on P. fluorescens,reductions of 5.059 log units were produced with 250 MPa for 15 min at 50°C. Both micro-organisms showed a first-order kinetics of destruction in the range 0-30 min, with D-values (at different temperatures and pressures from 150 to 300 MPa) between 2.055 and 18.058 min for E. coli,and 2.058-23.053 min for P. fluorescens.Abaroprotective effect of ewe's milk (6% fat) on both micro-organisms was observed, in comparison with other studies using different means and similar pressurization conditions.     

Comparison of ultra high pressure homogenization and conventional thermal treatments on the microbiological,physical and chemical quality of soymilk

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa in combination with different inlet temperatures (55, 65 and 75 °C) on soymilk was studied. UHPH-treated soymilk was compared with the base product (untreated), with pasteurized (95 °C for 30 s) and with ultra high temperature (UHT; 142 °C for 6 s) treated soymilks. Microbiological (total aerobic meshophilic bacteria, aerobic spores, and Bacillus cereus), physical (dispersion stability and particle size distribution) and chemical (lipoxygenase activity, hydroperoxide index and trypsin inhibitor activity) parameters of special relevance in soymilk were studied. Microbiological results showed that pressure and inlet temperature combination had a significant impact on the lethal effect of UHPH treatment. While most of UHPH treatments applied produced high quality of soymilks better than that pasteurized, the combination of 300 MPa and 75 °C produced a commercially sterile soymilk. UHPH treatments caused a significant decrease in particle size resulting in a high physical stability of samples compared with conventional heat treatments. UHPH treatment produced lower values of hydroperoxide index than heat treated soymilks although trypsin inhibitor activity was lower in UHT-treated products.     

Physical and structural changes induced by high pressure on corn starch,rice flour and waxy rice flour

The impact of high pressure (HP) processing on corn starch, rice flour and waxy rice flour was investigated as a function of pressure level (400 MPa; 600 MPa), pressure holding time (5 min; 10 min), and temperature (20 °C; 40 °C). Samples were pre-conditioned (final moisture level: 40 g/100 g) before HP treatments. Both the HP treated and the untreated raw materials were evaluated for pasting properties and solvent retention capacity, and investigated by differential scanning calorimetry, X-ray diffractometry and environmental scanning electron microscopy. Different pasting behaviors and solvent retention capacities were evidenced according to the applied pressure. Corn starch presented a slower gelatinization trend when treated at 600 MPa. Corn starch and rice flour treated at 600 MPa showed a higher retention capacity of carbonate and lactic acid solvents, respectively. Differential scanning calorimetry and environmental scanning electron microscopy investigations highlighted that HP affected the starch structure of rice flour and corn starch. Few variations were evidenced in waxy rice flour. These results can assist in advancing the HP processing knowledge, as the possibility to successfully process raw samples in a very high sample-to-water concentration level was evidenced.Industrial relevanceThis work investigates the effect of high pressure as a potential technique to modify the processing characteristics of starchy materials without using high temperature. In this case the starches were processed in the powder form - and not as a slurry as in previously reported studies - showing the flexibility of the HP treatment. The relevance for industrial application is the possibility to change the structure of flour starches, and thus modifying the processability of the mentioned products.