Effects of high‐pressure processing and enzymatic dephosphorylation on phosvitin properties

BACKGROUND: Egg phosvitin could be a good source of functional peptides. Enzymatic dephosphorylation and high‐pressure processing combined with thermal treatment applied before proteolysis could produce phosvitin hydrolysates with different properties compared to its native form. RESULTS: Phosvitin structure was maintained overall during high‐pressure treatment of 600 MPa applied at an initial temperature of 65 °C regardless of the pH and duration of treatment, confirming the high structural stability of this phosphoprotein. Treatment of phosvitin with phosphatase increased the degree of dephosphorylation from 24% to 63%, after 2 and 18 h, respectively. Moderate dephosphorylation of phosvitin prior to proteolytic digestion improved its hydrolysis, allowing formation of peptides with a molecular weight lower than 17,000 kDa as determined by size exclusion chromatography. Angiotensin‐converting enzyme (ACE) inhibition and antioxidant activity of dephosphorylated and protease‐treated phosvitin was increased by 52% and 39%, respectively, as compared to protease‐digested native phosvitin. CONCLUSION: Enzymatic dephosphorylation before proteolysis mimicking in vivo gut conditions improved ACE inhibition and antioxidant activity of phosvitin hydrolysates. Copyright © 2012 Society of Chemical Industry     

Original article: Modelling the effects of food ingredients and pH on high‐pressure processing inactivation of Bacillus cereus spores: a laboratorial study

The combination of high pressure and heat on Bacillus cereus spores in food matrix was investigated with the purpose of achieving a predictive model of microbial inactivation. The high‐pressure processing (HPP) conditions were fixed at 540 MPa and 71 °C for 16.8 min, which were determined as the optimum conditions considering six‐log‐cycle reductions of B. cereus spores. The effects of soybean protein, sucrose, soybean oil and pH on the inactivation of B. cereus spores by HPP were evaluated, and a quadratic predictive model for the effects of food ingredients and pH on the reductions of B. cereus spores by HPP was built using response surface methodology. The experimental results showed that soybean protein, sucrose and pH significantly affected the reductions of B. cereus spores. The predictive model is significant, because the level of significance was P < 0.0001 and the calculated F‐value is much greater than the tabulated F‐value. The adequacy of the predictive model equation was verified effectively using the experimental test data that were not used in the development of the model.     

Effects of high‐pressure homogenisation on physicochemical characteristics of partially skimmed milk

The changes in partially skimmed milk (0.5% fat) physicochemical properties and proteins after high‐pressure homogenisation (HPH) at 100, 200 and 300 MPa were investigated. Processing parameters and changes in pH, ethanol precipitation stability, lightness, whey protein denaturation, hydrophobicity and viscosity were evaluated. No significant differences were found between milk pH and nonprotein nitrogen content before and after HPH. Ethanol stability, lightness and hydrophobicity increased when pressure was increased from 100 MPa to 300 MPa. Whey protein denaturation, evaluated through noncasein nitrogen, occurred only at 200 to 300 MPa, and viscosity increased just at 300 MPa. Therefore, HPH changed some milk physicochemical characteristics, mainly those related to protein content. These results highlight that HPH processing is a promising technology to improve partially skimmed milk mouth feel being suitable for dairy products manufacturing.     

Synergistic effects of high pressure processing and slightly acidic electrolysed water on the inactivation of Bacillus cereus spores

Bacillus spores are concerns for their resistance to heat, high pressure processing (HPP), and disinfectants. We examined the effects of HPP and slightly acidic electrolysed water (SAEW) on inactivation of B. cereus spores. Spores' suspensions were prepared with 2‐(N‐morpholino) ethanesulfonic acid (MES) buffer or SAEW with available chlorine content (ACC) of 24, 35, 44 or 55 mg L^?1, and then subjected to HPP. The individual effects of HPP or SAEW on spores were negligible (<1.0 log CFU mL^?1). With factorial design and anova analysis, HPP + SAEW treatment was shown to have significantly positive effects on spores’ inactivation. The optimal conditions were 300 MPa HPP + SAEW with 44 mg L^?1 ACC or 200 MPa HPP + SAEW with 44 mg L^?1 ACC + 500 MPa HPP, producing reductions of 3.27 and 3.99 log CFU mL^?1, respectively. HPP + SAEW have potentials to serve as two effective hurdle techniques for inactivating B. cereus spores.     

The impact of high pressure and temperature on bacterial spores: inactivation mechanisms of Bacillus subtilis above 500 MPa

Abstract: High‐pressure thermal sterilization (HPTS) is an emerging technology to produce shelf stable low acid foods. Pressures below 300 MPa can induce spore germination by triggering germination receptors. Pressures above 500 MPa could directly induce a Ca⁺²‐dipicolinic acid (DPA) release, which triggers the cortex‐lytic enzymes (CLEs). It has been argued that the activated CLEs could be inactivated under HPTS conditions. To test this claim, a wild‐type strain and 2 strains of Bacillus subtilis spores lacking germinant receptors and one of 2 CLEs were treated simultaneously from 550 to 700 MPa and 37 to 80 C (slow compression) and at 60 to 80 C up to 1 GPa (fast compression). Besides, an additional heat treatment to determine the amount of germinated cells, we added TbCl₃ to detect the amount of DPA released from the spore core via fluorescent measurement. After pressure treatment for 120 min at 550 MPa and 37 °C, no inactivation was observed for the wild‐type strain. The amount of released DPA correlated to the amount of germinated spores, but always higher compared to the belonging cell count after pressure treatment. The release of DPA and the increase of heat‐sensitive spores confirm that the inactivation mechanism during HPTS passes through the physiological states: (1) dormancy, (2) activation, and (3) inactivation. As the intensity of treatment increased, inactivation of all spore strains also strongly increased (up to ?5.7 log₁₀), and we found only a slight increase in the inactivation of one of the CLE (sleB). Furthermore, above a certain threshold pressure, temperature became the dominant influence on germination rate. Practical Application: The continuous increase of high‐pressure (HP) research over the last several decades has already generated an impressive number of commercially available HP pasteurized products. Furthermore, research helped to provoke the certification of a pressure‐assisted thermal sterilization process by the U.S. FDA in February 2009. However, this promising sterilization technology has not yet been applied in industrial settings. An improved understanding of spore inactivation mechanisms and the ability to calculate desired inactivation levels will help to make this technology available for pilot studies and commercialization at an industrial scale. Moreover, if the synergy between pressure and elevated temperature on the inactivation rate could be identified, clarification of the underlying inactivation mechanism during HP thermal sterilization could help to further optimize the process of this emerging technology.     

Effect of high‐pressure processing on immunoreactivity,microbial and physicochemical properties of hazelnut milk

This study investigated the effects of high‐pressure processing (HPP) and thermal processing (TP) on the overall quality attributes of hazelnut milk. HPP achieved the same microbial safety as TP, and the pH, °Brix and sugar contents were maintained at the levels of fresh hazelnut milk. Although HPP caused colour changes, the ?E was smaller than that of the TP sample. Increasing pressure significantly decreased the immunoreactivity of the hazelnut milk by 70%, while simultaneously reducing the levels of essential and non‐essential amino acids and chemical score (CS) and the essential amino acid index (EAAI) values. However, neither HPP nor TP significantly affected the fatty acid composition of hazelnut milk. HPP retained higher total phenolic and flavonoid levels of the hazelnut milk, with a better antioxidant capacity than TP samples. Thus, the HPP maintained microbial safety during cold storage, and physicochemical properties of the treated hazelnut milk were not significantly different from those of the fresh hazelnut milk.     

Evaluation of plasma,high‐pressure and ultrasound processing on the stability of fructooligosaccharides

Fructooligosaccharides (FOS) are among the main carbohydrates with prebiotic activity, and they are the most applied functional carbohydrate ingredient in the food industry. FOS are known to hydrolyse when subjected to thermal processing, thus partially losing its functional properties. In this study, we evaluate whether three nonthermal technologies are suitable for processing FOS regarding its stability after processing. FOS were subjected to ultrasound, high‐pressure processing (HPP) and atmospheric cold plasma (ACP). The FOS solution, 70 g L^?1, was set at a concentration recommended for human intake. The treatments were carried out at operating conditions usually used for microbial inactivation in foods (HPP at 450 MPa for 5 min; US at 600–1200 W L^?1 for 5 min; ACP at 70 kV for 15–60 s). NMR and HPLC analysis of the FOS components showed that ACP, ultrasound and HPP have not induced any significant change on FOS concentration (<2.0%) nor on the degree of polymerisation of the FOS (<3.3%). Contrarily to what is reported for thermal treatments, these nonthermal technologies were considered suitable for FOS processing.     

Effect of high‐pressure processing on myofibrillar protein structure

Modification of myofibrillar proteins induced by high‐pressure processing has been investigated at pressures ranging from 50 to 600 MPa for 10 min at 20 °C. Analysis by spectroscopic methods and circular dichroism of myofibrillar proteins in phosphate buffer pH 6.0 containing 0.6 M KCl showed no changes in the secondary structure of proteins. However, study of protein conformation by quasielastic light scattering and gel filtration chromatography proved the emergence of aggregation after treatment at pressures higher than 300 MPa. This aggregation was accompanied by enhanced binding of anilino‐1‐naphthalene‐8‐sulphonic acid, which indicated an increase in hydrophobic bonding of myofibrillar proteins. Modification of the tertiary and quaternary structures of proteins may induce a molten globule state. Copyright © 2003 Society of Chemical Industry     

Effects of sodium tripolyphosphate on functional properties of low‐salt single‐step high‐pressure processed chicken breast sausage

Influences of sodium tripolyphosphate (STPP) contents (0.1, 0.2, 0.3 and 0.4%) on water holding capacity (WHC) and texture properties of low‐salt (1.2% NaCl) single‐step high‐pressure processed chicken breast sausages (LSSS‐HPP sausages) were evaluated. Results showed that WHC was improved (4–5%) by the addition of STPP. However, the STPP contents customarily used for cooked sausages (0.3–0.5%) were excessive for LSSS‐HPP sausages, causing a soft and tacky texture. Sausages containing 0.1% of STPP had the best taste according to the sensory evaluations. Chemical interactions plus Raman spectroscopic analysis revealed that STPP addition partly changed native structures of myofibrillar proteins. Furthermore, higher STPP contents in the meat batter prevented those proteins from high pressure denaturing and aggregating in the subsequent single‐step HPP procedure. Increased hydrogen bonds and decreased hydrophobic interactions explained the better WHC and softer texture. Therefore, 0.1% of STPP is the optimal content in the processing of new‐type LSSS‐HPP sausages.     

The use of mechanical analyses,scanning electron microscopy and ultrasonic imaging to study the effects of high‐pressure processing on multilayer films

The effects of high‐pressure processing (HPP) on the mechanical and physical characteristics of eight high‐barrier multilayer films were investigated. These films were PET/SiO_x/LDPE, PET/Al₂O₃/LDPE, PET/PVDC/nylon/HDPE/PP, PE/nylon/EVOH/PE, PE/nylon/PE, metallised PET/EVA/LLDPE, PP/nylon/PP and PET/PVDC/EVA. In addition, PP was evaluated as a monolayer film for comparison purposes. Pouches made from these films were filled with distilled water, sealed, then pressure processed at 600 and 800 MPa for 5, 10 and 20 min at a process temperature of 45 °C. Pouches kept at atmospheric pressure were used as controls. Prior to and after HPP, all films were tested for tensile strength, percentage elongation and modulus of elasticity (at 50 cm min^?1) and imaged by scanning electron microscopy (SEM) and C‐mode scanning acoustic microscopy (C‐SAM). Results showed no significant changes in tensile strength, elongation and modulus of elasticity of all films after HPP. However, significant physical damage to metallised PET (MET‐PET) was identified by SEM and C‐SAM. Thus it could be concluded that MET‐PET is not suitable for batch‐type high‐pressure‐processed food packaging. It can also be concluded that the other materials investigated during this study are suitable for batch‐type high‐pressure‐processed food packaging. Copyright © 2003 Society of Chemical Industry     

Changes on colour parameters caused by high‐pressure processing of apple juice made from six different varieties

The colour changes caused by high‐pressure processing at different temperatures of apple juice were investigated. Six apple varieties were used (Braeburn, Fuji, Gala, Golden Delicious, Granny Smith and Red Delicious), searching for the influence of the variety from two different approaches: a kinetic study, finding the best model for each one of them, and a multivariate study consisting of a principal component analysis of data. Although it had lower initial values, redness (a*) was more influenced by high pressure than yellowness (b*). The pattern followed by colour changes was found to be definitively dependent on the variety. High‐pressure processing affects in a stronger way the absorbances located near 400 nm (i.e. 400.5 nm in Fuji and 434.0 nm in Braeburn).     

Mathematical modeling of Saccharomyces cerevisiae inactivation under high‐pressure carbon dioxide

High‐pressure carbon dioxide inactivation curves of Saccharomyces cerevisiae at different temperatures were analysed using the modified Gompertz model. Comparable λ and μ values were obtained under pressure treatment as function of temperature. The phase of disappearance (λ) and the inactivation rate (μ) of S. cerevisiae were inversely related. Higher μ values were obtained at 50°C than at 40, 30, and 20°C under 10.0 MPa CO₂ pressure. Increased pressure and temperature had significant effects on the survival of S. cerevisiae. Arrhenius, linear and square‐root models were used to analyse the temperature dependence of the inactivation rate constant. For the Arrhenius model the activation energy (E_μ) was 56.49 kJ/mol at 10.0 MPa, and 55.70, 53.83, and 52.20 kJ/mol at 7.5, 5.0, and 2.5 MPa, respectively. Results of this study enable the prediction of yeast inactivation exposed to different CO₂ pressures and temperatures.     

Influence of ethanol/water ratio in ultrasound and high‐pressure/high‐temperature phenolic compound extraction from agri‐food waste

The valorisation and management of agri‐food waste are currently hot investigation topics which probe the recovery of valuable compounds, such as polyphenols. In this study, high‐pressure/high‐temperature extraction (HPTE) and ultrasound‐assisted extraction (UAE) have been used to study the recovery of phenolic compounds from grape marc and olive pomace in hydroalcoholic solutions. The main phenolic compounds in both extracts were identified by HPLC‐DAD. Besides extraction yield (total polyphenol and flavonoid content) and the antiradical power, polyphenol degradation under HPTE and UAE has also been studied. HPTE with ethanol 75% gave higher phenolic extraction yields: 73.8 ± 1.4 mg of gallic acid equivalents per gram of dried matter and 60.0 mg of caffeic acid equivalents per gram of dried matter for grape marc and olive pomace, respectively. In this study, the efficient combination of ethanol/water mixture with HPTE or UAE has been used to enhance the recovery of phenolic compounds from grape marc and olive pomace. HPLC‐DAD showed that UAE prevents phenolic species degradation damage because of its milder operative conditions.     

High pressure processing combined with selected hurdles: Enhancement in the inactivation of vegetative microorganisms

High pressure processing (HPP) as a nonthermal processing (NTP) technology can ensure microbial safety to some extent without compromising food quality. However, for vegetative microorganisms, the existence of pressure-resistant subpopulations, the revival of sublethal injury (SLI) state cells, and the resuscitation of viable but nonculturable (VBNC) state cells may constitute potential food safety risks and pose challenges for the further development of HPP application. HPP combined with selected hurdles, such as moderately elevated or low temperature, low pH, natural antimicrobials (bacteriocin, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils), or other NTP (CO₂, UV-TiO₂ photocatalysis, ultrasound, pulsed electric field, ultrafiltration), have been highlighted as feasible alternatives to enhance microbial inactivation (synergistic or additive effect). These combinations can effectively eliminate the pressure-resistant subpopulation, reduce the population of SLI or VBNC state cells and inhibit their revival or resuscitation. This review provides an updated overview of the microbial inactivation by the combination of HPP and selected hurdles and restructures the possible inactivation mechanisms.