Effect of high hydrostatic pressure on the structure of the soluble protein fraction in Porphyridium cruentum extracts

High hydrostatic pressure (HHP) treatments are trending as “green” stabilization and extraction process. The extraction of B-phycoerythrin from microalgae is getting more and more interest due to its numerous potentialities in foods, cosmetics and medicine. Thus, the effects of high pressure on the structural characteristics of B-phycoerythrin extracted from Porphyridium cruentum are explored in this paper.Spectrophotometric methods allowed to measure B-phycoerythrin content (UV–visible) and gave an indication on the protein structure (fluorescence). Micro-DSC analysis and electrophoresis complemented this structural investigation for all the protein fractions of P. cruentum extracts.Applying high hydrostatic pressure treatments up to 300 MPa during 5 min had no significant effect on B-phycoerythrin content and structure in P. cruentum extracts. Nevertheless, conformational changes of the protein are suggested by fluorescence yield decrease at 400 MPa, and protein aggregation of B-phycoerythrin, observed by Micro-DSC and electrophoresis, occurred at 500 MPa.Industrial relevanceThe HHP process is an emerging technology for the microbiological stability of various food matrices, including the proteins of microalgae as natural colorant. The target pressure to stabilize is around 400 MPa. High hydrostatic pressure can be used on P. cruentum extracts up to 300 MPa without any change in protein structure, as the threshold of protein aggregation is observed at 400 MPa. The observed changes of the proteins structure after applying HHP above 400 MPa can have a strong impact at macroscopic scale on the food matrices: increase of turbidity, change of texture, stability of emulsion.     

Effects of high hydrostatic pressure on physicochemical and functional properties of walnut (Juglans regia L.) protein isolate

BACKGROUND: Walnut (Juglans regia L.) is a good source of protein that has potential application in new product formation and fortification. The main objectives of this study were to investigate the effects of high hydrostatic pressure (HHP) treatment (300–600 MPa 20 min) on physicochemical and functional properties of walnut protein isolate (WPI) using various analytical techniques at room temperature. RESULTS: The results showed significant modification of solubility, free sulfhydryl content and surface hydrophobicity with increased levels of HHP treatment, indicating partial denaturation and aggregation of proteins. Differential scanning calorimetry and fluorescence spectrum analyses demonstrated that HHP treatment resulted in gradual unfolding of protein structure. Emulsifying activity index was significantly (P < 0.05) increased after HHP treatment at 400 MPa, but significantly decreased (P < 0.05) relative to the untreated WPI with further increase in pressure. HHP treatment at 300–600 MPa significantly decreased emulsion stability index. Additionally, HHP‐treated walnut proteins showed better foaming properties and in vitro digestibility. CONCLUSION: These results suggest that HHP treatment could be applied to modify the properties of walnut proteins by appropriate of pressure levels, which will help in using walnut protein as a potential food ingredient. © 2012 Society of Chemical Industry     

Effects of high hydrostatic pressure on microstructure,physicochemical properties and in vitro digestibility of oat starch/β-glucan mixtures

Oats do not contain gluten protein, and oat dough structure is formed mainly through the hydrogen bonding of starch and β-glucan. As a non-thermal processing technology, high hydrostatic pressure (HHP) is mainly used to modify starch and protein in food processing. This study investigated the effects of HHP treatment on the morphological, structural, thermal, pasting and in vitro digestion properties of oat starch/β-glucan mixtures. Results showed that β-glucan interconnects with amylose through hydrogen bonding and has a protective effect on the crystalline region of oat starch. Effect of HHP treatment on the crystal structure of mixture system goes through crystal structure perfection stage, crystallisation disintegration and gelatinisation stage. After 300–400 MPa treatment, the changes in particle surface were not obvious, the phase transition temperature, the ΔH_gel and the PT of mixtures increased, while the particle size, viscosity and BD values decreased. After 500–600 MPa treatment, mixtures were completely gelatinised, most of the particles swelled and deformed, the particle size increased significantly. The principal component analysis results show that the complexes were distributed in the same region with similar properties after the 300–400 MPa and 500–600 MPa treatments, respectively.     

Selective-Targeted Effect of High-Pressure Processing on Proteins Related to Quality: a Proteomics Evidence in Atlantic Mackerel (Scomber scombrus)

The effect of high hydrostatic pressure (HHP) treatment (150, 300, and 450 MPa for 0, 2.5, and 5 min) on total sodium dodecyl sulfate (SDS)-soluble and sarcoplasmic proteins in frozen (?10 °C for 3 months) Atlantic mackerel (Scomber scombrus) was evaluated. Proteomics tools based on image analysis of SDS-polyacrylamide gel electrophoresis (SDS-PAGE) protein gels and protein identification by tandem mass spectrometry (MS/MS) were applied. Total SDS-soluble proteins, composed in high proportion of myofibrillar proteins, were stable under pressurization treatment in terms of solubility and electrophoretic gel profiles. However, pressurization reduced sarcoplasmic proteins’ solubility, modified their one-dimensional (1-D)/two-dimensional (2-D) SDS-PAGE patterns in a direct-dependent manner, and exerted a selective effect on particular sarcoplasmic proteins depending on processing conditions. Thus, protein bands assigned to creatine kinase, fructose-bisphosphate aldolase A, glycogen phosphorylase, and β-enolase were degraded at 300–450 MPa. Additionally, the stability of triosephosphate isomerase B, phosphoglucomutase, and phosphoglycerate kinase-1 was found to be HHP-reduced when submitted at 450 MPa. HHP processing (300–450 MPa) also induced a cross-linking product formation of pyruvate kinase and two compounds derived from tropomyosin at 450 MPa. Frozen storage time of pressurized samples induced an additional lessening in protein solubility, but electrophoretic patterns were not modified. The present investigation emphasizes the higher lability of sarcoplasmic proteins under HHP treatment and the important role of these proteins in the sensory quality enhancement provided by milder HHP conditions on frozen mackerel. HHP technology is expected to boost the development of novel tailored processing approaches to tackle food quality challenges.     

Effect of high hydrostatic pressure on the structure,physicochemical and functional properties of protein isolates from cumin (Cuminum cyminum) seeds

The effect of high hydrostatic pressure (HHP) treatment on the structure, physicochemical and functional properties of cumin protein isolate (CPI) was investigated. More aggregates, pores, irregular conformations and bigger particle size were observed for HHP-treated CPI. HHP resulted in an increase in α-helix, a decrease in β-strand and fluorescence intensity of CPI. Surface hydrophobicity (H_o) of CPI significantly increased after HHP treatment, from 343.35 for native CPI to 906.22 at 600 MPa (P < 0.05). HHP treatment at 200 MPa reduced zeta-potential and solubility of CPI, while had little effect at 400 and 600 MPa. Emulsifying activity and stability of CPI decreased after HHP treatment, of which droplet size of emulsions significantly increased (P < 0.05). HHP-treated CPI could form heat-induced gelation at lower temperature (68.5 °C) and improved storage modulus (G′) comparing to native one (80.6 °C), suggesting that CPI might be potential protein resources as gelation substitute in food system.     

Effect of high pressure processing on heat-induced gelling capacity of blue crab (Callinectes sapidus) meat

There has been increasing use of High pressure processing (HPP) in the fishery industry since this technology facilitates shellfish shucking. Nevertheless, there is limited information about the effect of HPP on protein functional properties of some shellfish. The aim of this study was to evaluate the effect of 100, 300 and 600 MPa/5 min on the gelling capacity of heat-induced (40 °C/30 min + 90 °C/20 min) blue crab (Callinectes sapidus) meat. HPP treatment resulted in crab meat gels with a lighter and reddish colour as compared to the control. HPP at 600 MPa induced the formation of high molecular aggregates from the denaturation-aggregation of myosin heavy chain. Pressurization at 100 MPa promoted the shift of α-helix structures to β-sheet and β-turn as compared with the other pressure levels. TPA values were higher in gels made at 100 MPa than at 300 or 600 MPa. Low pressure levels, then, increased the heat-induced gelling capacity of crab meat, improving the texture through modification of its protein structure.Industrial relevanceHigh pressure processing (HPP) technology has been successfully applied to several seafood products, both for processing and storage. However, in the case of blue crab meat it is important to study the effect of HPP on protein functional properties such as gelling capacity in order to optimize processing parameters for the preparation of high-quality restructured products. This paper reports the development of a HPP process (100, 300 and 600 MPa/5 min 40 °C/30 min + 90 °C/20 min) prior to thermal gelling for the preparation of crab meat gels. The application of 600 MPa produced considerable protein aggregation of gels, whereas with pressures below 300 MPa protein functionality can be modified to produce crab meat gels with adequate brightness, TPA values and a fresh, high-quality appearance. These results could provide a basis for further pressurization applications in the crab industry to create new seafood product analogues based on this kind of crab meat.     

Effects of high hydrostatic pressure on the conformational structure and the functional properties of bovine serum albumin

Non-thermal technologies, such as High Hydrostatic Pressure (HHP), are able to induce extensive changes in the structure of biological macromolecules, namely proteins. HHP treatments disrupt the electrostatic interactions, which stabilize the quaternary and the tertiary structure of the proteins, and activate the reactions of sulfhydryl-disulfide bond exchange. These structural changes result in the dissociation and refolding of proteins during HHP treatments, and consequently in the modification of protein functional properties, namely physicochemical properties (solubility, binding and surfactant properties, water and oil absorption capacity, emulsifying and foaming properties). The technological behavior of the proteins in food preparation, processing, storage, as well as their contribution to determine quality perception of foods mainly depends on these functional properties.This work aims at investigating the effects of HHP treatments on the conformational (quaternary, tertiary and secondary) structure and the functional properties of a globular water soluble protein, the Bovine Serum Albumin (BSA). BSA (50–100 mg/mL) solutions in Sodium Phosphate Buffer were processed at different pressure levels (100–500 MPa) and treatment times (15, 25 min). BSA unfolding and refolding were analyzed in terms of free sulfhydryl (SH) groups, changes of secondary structure, foaming and emulsifying properties.Analyzing the experimental data it can be concluded that the unfolding of BSA samples with a concentration of 50 mg/mL occurred in the pressure range between 100 and 400 MPa. In fact an increased number of the free SH groups as well as an improved foaming and emulsifying ability were detected in the treated samples. Pressure levels above 400 MPa promoted the interactions between adjacent polypeptide chains and the formation of soluble high molecular mass aggregates. The concentration of the protein in the samples, also, controlled the occurrence of unfolding and aggregation. Extensive changes in BSA secondary structure were observed at pressure level above 300 MPa, for longer processing times and higher protein concentrations. In these processing conditions β-sheet aggregates were likely to replace the initial α-helixes.Industrial relevanceThe paper consists in the study of the Effects of High Hydrostatic Pressure processing (HHP) on the conformational structure and the functional properties of Bovine Serum Albumin.he work proposes an innovative technology for Food Industries that can be widely used for food conservation and to induce protein modifications in the same time. For this reason the technology represents a good tool for the production of hypoallergenic compounds especially in the field of dairy products and infant formula companies.     

Effects of High Hydrostatic Pressure on the Physical,Microbial, and Chemical Attributes of Oysters (Crassostrea virginica)

The change in the quality attributes (physical, microbial, and chemical) of oysters (Crassostrea virginica) after high hydrostatic pressure (HHP) treatment at 300 MPa at room temperature (RT, 25 °C) 300, 450, and 500 MPa at 0 °C for 2 min and control oysters without treatment were evaluated over 3 wk. The texture and tissue yield percentages of oysters HHP treated at 300 MPa, RT increased significantly (P < 0.05) compared to control. Aerobic and psychrotrophic bacteria in control oysters reached the spoilage point of 7 log CFU/g after 15 d. Coliform counts (log MPN/g) were low during storage with total and fecal coliforms less than 3.5 and 1.0. High pressure treated oysters at 500 MPa at 0 °C were significantly higher (P < 0.05) than oysters HHP treated at 300 MPa at 0 °C in lipid oxidation values. The highest pressure (500 MPa) treatment in this study, significantly (P < 0.05) decreased unsaturated fatty acid percentage compared to control. The glycogen content of control oysters at 3 wk was significantly higher (P < 0.05) when compared to HHP treated oysters [300 MPa, (RT); 450 MPa (0 °C); and 500 MPa (0 °C)]. HHP treatments of oysters were not significantly different in pH, percent salt extractable protein (SEP), and total lipid values compared to control. Based on our results, HHP prolongs the physical, microbial, and chemical quality of oysters.     

Microbiological stabilization of Aloe vera (Aloe barbadensis Miller) gel by high hydrostatic pressure treatment

The effect of high hydrostatic pressure (HHP) treatment (300, 400 and 500MPa for 1 and 3min at 20°C) on the microbiological shelf-life and microbiota composition of Aloe vera gel during 90days of storage at 4°C was investigated. Aerobic mesophilic and psychrotrophic bacteria, as well as moulds and yeasts, were enumerated after HHP treatment and through cold storage. Randomly selected isolates from the count plates were identified by standard methods and the API identification system. Results showed that HHP treatment at or over 400MPa for 3min were effective to keep the microbial counts to undetectable levels during the whole storage period, and consequently the microbiological shelf-life of A. vera gel was extended for more than 90days at 4°C. The microbiota in the untreated A. vera gel was dominated by Gram-negative bacteria (mostly Rahnella aquatilis) and yeasts (mostly Rhodotorula mucilaginosa). In contrast, Gram-positive bacteria tentatively identified as Arthrobacter spp. and Micrococcus/Kocuria spp. were the predominant microorganisms in samples pressurized at 300MPa for 1 and 3min, while Bacillus megaterium predominating in samples treated at 400MPa for 1min. At 400MPa for 3min and above, the microbial growth was completely suppressed during at least 90days; however, viable spore-formers were detected by enrichment.     

Evaluation of the technological properties of rice starch modified by high hydrostatic pressure (HHP)

This aim of the study was to evaluate the technological properties of rice starch modified by high hydrostatic pressure (HHP). Black rice starch (BRS) was dispersed in 20% water and then HHP was applied at pressures of 200, 400 and 600 MPa for 30 min, where morphological, structural, functional and thermal parameters were evaluated. High pressure (BRS600) provided greater morphological damage, such as surface cavities and loss of crystallinity. The treatment HHP > 400 MPa the type of diffraction pattern was changed from type A to type V. The FT-IR spectra showed differences in intensity, especially for control, which revealed better defined peaks of greater intensity. The modified starch showed a greater affinity for water and oil absorption than the native starch as well as for milk absorption, exhibiting a higher binding capacity for the whole milk. HHP treatment is a fast and efficient non-thermal method to improve the technological properties of BRS.     

High hydrostatic pressure modification of whey protein concentrate for improved functional properties

Whey protein concentrate (WPC) has many applications in the food industry. Previous research demonstrated that treatment of whey proteins with high hydrostatic pressure (HHP) can enhance solubility and foaming properties of whey proteins. The objective of this study was to use HHP to improve functional properties of fresh WPC, compared with functional properties of reconstituted commercial whey protein concentrate 35 (WPC 35) powder. Fluid whey was ultrafiltered to concentrate proteins and reconstituted to equivalent total solids (8.23%) as reconstituted commercial WPC 35 powder. Solutions of WPC were treated with 300 and 400 MPa (0- and 15-min holding time) and 600 MPa (0-min holding time) pressure. After HHP, the solubility of the WPC was determined at both pH 4.6 and 7.0 using UDY and BioRad protein assay methods. Overrun and foam stability were determined after protein dispersions were whipped for 15 min. The protein solubility was greater at pH 7.0 than at pH 4.6, but there were no significant differences at different HHP treatment conditions. The maintenance of protein solubility after HHP indicates that HHP-treated WPC might be appropriate for applications to food systems. Untreated WPC exhibited the smallest overrun percentage, whereas the largest percentage for overrun and foam stability was obtained for WPC treated at 300 MPa for 15 min. Additionally, HHP-WPC treated at 300 MPa for 15 min acquired larger overrun than commercial WPC 35. The HHP treatment of 300 MPa for 0 min did not improve foam stability of WPC. However, WPC treated at 300 or 400 MPa for 15 min and 600 MPa for 0 min exhibited significantly greater foam stability than commercial WPC 35. The HHP treatment was beneficial to enhance overrun and foam stability of WPC, showing promise for ice cream and whipping cream applications.     

Effect of high hydrostatic pressure (HHP) on structure and activity of phytoferritin

High hydrostatic pressure (HHP) has drawn considerable attention because of its potential application in food industry. Ferritin, an iron storage protein, is widely distributed in food made from legume seeds, which is highly stable due to its shell-like structure. Therefore, it is of special interest to know whether or not high HHP treatment has effect on this protein. In this study, the structure and activity of soybean seed ferritin (SSF) were examined by circular dichroism spectrum (CD), UV–VIS and fluorescence spectrophotometry in conjunction with stopped-flow light scattering upon treatment with HHP at 400 MPa for 10 min. Results revealed that such treatment has little effect on the primary and secondary structure of SSF, but pronouncedly altered its tertiary and quaternary structure. As a result, the protein aggregation property and iron release activity were dramatically changed, while its activity of iron oxidative deposition was kept unchanged.     

Study of the Effect of High Hydrostatic Pressure (HHP) on the Osmotic Dehydration Mechanism and Kinetics of <Emphasis Type="Italic">Wumei</Emphasis> Fruit (<Emphasis Type="Italic">Prunus mume</Emphasis>)

Osmotic dehydration (OD) is the most important procedure for obtaining candied wumei (Prunus mume), which is a very popular snack in Eastern Asian countries. This study aims to evaluate the effects of high hydrostatic pressure (HHP) pre-treatment (50–400 MPa) on the mass transfer kinetics and on the water diffusivity of wumei fruit during OD and to investigate the effect on water distribution and cell viability aspects. The results showed that HHP increased initial rate and effective diffusivity of mass transfer values compared to non-treated samples. Time domain nuclear magnetic resonance revealed that, upon HHP treatment, the water redistributed in vacuole, cytoplasm/extracellular spaces, and cell wall/membrane. The application of 400 MPa probably caused some irreversible damages to the cell membranes. The cell viability study determined by fluorescein diacetate staining showed a loss of cell viability at pressures higher than 200 MPa. HHP exhibited an effective pre-treatment to increase mass transfer of wumei fruit during OD process.     

Effects of high hydrostatic pressure on structure and colour of red ginseng (Panax ginseng)

BACKGROUND: The conventional method of processing ginseng (Panax ginseng) roots into red ginseng involves mainly heating and drying processes. In the present study, this method was modified by using high hydrostatic pressure (HHP) to improve the physicochemical characteristics of red ginseng. RESULTS: The HHP process (600 MPa for 1 min) significantly improved the histological properties of red ginseng by increasing cellular disruption and release of cell contents. The total reducing sugar content was significantly (P < 0.05) higher (increased from 10.67 to 15.25 mg g^?1) in red ginseng processed at 600 MPa for 1 min. Similarly, the total free amino acid content also increased significantly (from 2.81 to 7.77 mg g^?1). The HHP process resulted in superior and more even colouration and gave an attractive visual appearance to red ginseng. The optical density at 420 nm and Hunter's colour a value (redness) of extracts prepared from red ginseng increased significantly (P < 0.05) with the application of HHP. CONCLUSION: HHP‐processed red ginseng has significantly higher reducing sugar and free amino acid contents together with a more compact cell structure and superior visual quality (brighter red colour). Hence the application of HHP in red ginseng processing can result in ginseng products of improved quality compared with those obtained by the conventional method. Copyright © 2012 Society of Chemical Industry     

Identification and characterization of antioxidant peptides from sweet potato protein hydrolysates by Alcalase under high hydrostatic pressure

Sweet potato protein hydrolysates (SPPH) were generated by Alcalase under high hydrostatic pressure (HHP, 100, 200 and 300 MPa). HHP significantly improved the degree of hydrolysis (DH) and antioxidant activity, and increased the < 3 kDa fraction content of SPPH (P < 0.05). SPPH by Alcalase at 300 MPa for 60 min exhibited the highest DH and antioxidant activity and was separated into three fractions by ultrafiltration. The most active fraction FIII (< 3 kDa) was further separated into fifty four fractions by semi-preparative RP-HPLC and measured using the ORAC assay. In addition, more active fractions were examined by LC–MS/MS, and diverse peptides were identified, matching sequences of Sporamins A and B. To evaluate the structure–activity dependences, twenty sequences were synthesized, of which the antioxidant activity was assessed. Five peptides showed good activity: HDSASGQY ≥ YYMVSA ≥ HDSESGQY ~ YYIVS ~ RYYDPL, with the contribution of His and Tyr.Industrial relevanceThis study will give a novel technique for using industrial waste slurry, a byproduct in the process of sweet potato starch manufacturing, which contains various bioactive components (such as protein, minerals, etc.) since most of them are normally discarded. The present study is focused on assessing the effects of enzymatic hydrolysis by Alcalase under high hydrostatic pressure (HHP) on the release of antioxidant peptides from sweet potato protein (SPP). The results of this work provide a potential application of enzymatic hydrolysis assisted by HHP on the development of ingredients from SPP in functional foods.     

Effect of high hydrostatic pressure to sweet potato flour on dough properties and characteristics of sweet potato‐wheat bread

The effect of high hydrostatic pressure (HHP, 100–400 MPa) for 20 min at 25 °C to sweet potato flour (SPF) on dough properties and characteristics of sweet potato‐wheat bread was investigated. The particle size of SPF after HHP was decreased significantly. The obvious rupture was observed in granules of SPF after HHP at 300 and 400 MPa by scanning electron microscopy (SEM). After HHP, significant differences on endothermic peak temperatures (T_P) of SPF were observed by differential scanning calorimetric (DSC), of which the enthalpy change (ΔH) had a slight increase, expect that at 200 MPa. Gas retention of dough with SPF after HHP increased markedly from 1199 (0.1 MPa) to 1246 ml (100 MPa). Specific loaf volume of bread with SPF at 400 MPa was increased significantly, while the hardness and chewiness were reduced. Thus, SPF treated with HHP at 400 MPa could be potentially used in wheat bread production.     

High hydrostatic pressure effect on chemical composition,color, phenolic acids and antioxidant capacity of Cape gooseberry pulp (Physalis peruviana L.)

The aim of this study was to evaluate the effects of high hydrostatic pressure (HHP) at 300, 400 and 500 MPa/1, 3 and 5 min on nutritional and antioxidant properties of Cape gooseberry pulp after immediate application and after 60 days of storage. Proximal analysis, color, phenolic acids content and antioxidant capacity were determined. When analyzing the immediate effect of different treatments, a clear influence of HHP was observed in all the components of the proximal analysis. Regarding color, none of the three chromatic parameters showed significant differences with control leading to a minimum ΔE at 300 MPa/3 min. Changes in bound and free phenolic acids were evidenced after treatments. The maximum levels of TPC as well as antioxidant capacity were observed at 500 MPa/5 min. By the end of storage, all treated samples discolored leading to ΔE = 14.9 at 500 MPa/5 min. The profile of free and bound phenolic acids presented differences compared to Day 0. The antioxidant capacity by means of ORAC increased for treatments above 300 MPa/5 min indicating the effectiveness of these treatments for the production of functional products based on gooseberry pulp. For treatments above 400 MPa/3 min, molds and yeasts were not detected.     

Effect of Osmotic Dehydration Under High Hydrostatic Pressure on Microstructure, Functional Properties and Bioactive Compounds of Strawberry (Fragaria Vesca)

Sliced strawberries were subjected to combined osmotic dehydration (40 °Brix) and high hydrostatic pressure (HHP) at 100, 200, 300, 400 and 500 MPa for 10 min. This research was carried out to study the effects of pressure on firmness, polysaccharides, total dietary fibre and microstructure, functional properties (rehydration ratio and water holding capacity) and bioactive compounds (anthocyanins, flavonoid and total phenolic). HHP affected the texture of the fruits leading to soft fruits due to increasing pressure. Fruit microstructure evidenced influence of pressure presenting the pressurised samples irregular matrices compared to samples treated at 0.1 MPa (control samples). Polysaccharides increased with pressure. Total dietary fibre, anthocyanins, flavonoids and total phenolic content showed a decrease with pressure when compared to control samples. Based on results, minor alterations of the mentioned quality parameters were evidenced when working in the range of 300–500 MPa.     

Impact of Radio Frequency,Microwaving, and High Hydrostatic Pressure at Elevated Temperature on the Nutritional and Antinutritional Components in Black Soybeans

In this study, the effects of high hydrostatic pressure (HHP) at elevated temperature (60 °C) and 2 dielectric heating (DH) methods (radio frequency [RF], and microwaving [MW]) on the nutritional compositions and removal of antinutritional factors in black soybeans were studied. Each treatment caused <2% reduction in protein, and 3.3% to 7.0% decline in total amino acid content. However, the proportion of essential amino acid slightly increased in DH treated samples. The treatment decreased fat content (14.0% to 35.7%), but had small influence on fatty acid proportion. Antinutritional factors including trypsin inhibitor, tannins, saponins, and phytic acid were all declined by the 3 treatments, and DH treatment was generally more efficient. The most abundant saponins was decreased >22% in DH treated samples. MW and HHP led to higher in vitro protein digestibility, RF and MW promoted protein aggregation from atomic force microscope topography, but HHP caused more damages on protein subunits as seen from SDS‐PAGE image.     

Chemical Forces,Structure, and Gelation Properties of Sweet Potato Protein as Affected by pH and High Hydrostatic Pressure

Sweet potato is one of cheap sources for starch industries worldwide, and exploiting starch wastewater as an alternative protein source is mainly environmental and economic concerns. In this study, the effects of high hydrostatic pressure (HHP; 250, 400, and 550 MPa) on chemical forces, structure, and gelation properties of sweet potato protein (SPP) at pH 3.0, 6.0, and 9.0 were investigated. The values of surface hydrophobicity (H_o) and absolute value of zeta potential of SPP significantly increased from 250 to 550 MPa (p?<?0.05) at all three pH conditions. The total amount of sulfhydryl (-SH-) groups in SPP decreased after HHP at pH 9.0, whereas the amount of free -SH- increased. High molecular mass aggregates (>?180 kDa) were observed in SPP after HHP at pH 6.0 and 9.0 by SDS-PAGE. Regarding elastic rheological behaviors, storage modulus (G′) values of SPP were significantly strengthened after HHP treatment. In addition, textural properties and water-holding capacity of gels made from SPP after 250 and 400 MPa at pH 9.0 were significantly improved, and the gels showed a compact and uniform gel network with the contribution of immobilized water fractions. The gel properties exhibited by SPP after HHP treatment at different pH levels, in particular after 400 MPa at pH 9.0, suggested that it could be potential protein resources as new gelling reagent in the food system.