Influence of NaCl concentration and high pressure treatment on thermal denaturation of soybean proteins

In the present work the effect of high pressure (HP) treatment in the presence of NaCl on the thermal behavior of soybean proteins was analyzed by differential scanning calorimetry. The thermograms obtained have shown that NaCl addition increased the thermal stability – increase in temperatures of denaturation (Td) – of both glycinin and β-conglycinin. HP treatments increased thermal stability of glycinin, but decreased that of β-conglycinin. High NaCl concentrations decreased (in glycinin) or inverted (in β-conglycinin) the effects of HP on thermal stability. Cooperativity of denaturation of glycinin was enhanced by NaCl and HP. Cooperativity of denaturation of β-conglycinin was enhanced by HP and also by NaCl at 0.2 mol/L but decreased with the combination of treatments. Salt addition increased the enthalpy, ΔH, of denaturation of glycinin and β-conglycinin, being this effect stronger on glycinin. HP treatment provoked the denaturation of both protein fractions. The presence of NaCl protected glycinin against HP-denaturation at any assayed salt concentration and pressure level, while β-conglycinin was only protected at 200 and 400 MPa, but was more denaturated at 600 MPa in the presence of 0.6 mol/L of NaCl.

Industrial relevance

The knowledge provided by this work may be useful in the handling of high pressure-treated food with high NaCl content (e.g. meat emulsions, smallgoods) where soybean proteins are used as additives, in order to choose high pressure values to achieve their denaturation or predict the effects of ulterior thermal treatments. Thus, this knowledge may be useful to increase the use of high pressure in food industry.     

Cold-set gelation of high pressure-treated soybean proteins

The ability of soybean proteins to form cold-set gels, using high pressure (HP) processing as denaturing agent and calcium incorporation was evaluated. Different protein preparations were assayed: soybean protein isolate (SPI), a β-conglycinin enriched fraction (7SEF) and a glycinin enriched fraction (11SEF). 7SEF formed aggregated gels with low water holding capacity whereas 11SEF did not form self-standing gels. SPI formed the better gels: ordered and with high water holding capacity. SPI gels were relatively soft and their visual aspect, rheological and texture properties, and water holding capacity depended on HP level (400–600 MPa), CaCl₂ concentration (0.015–0.020 mol L⁻¹) and protein concentration (85–95 g L⁻¹), thus gels with different characteristics may be obtained. The gels comprised a three dimensional network stabilized by non-covalent interactions with spaces filled of proteins in aqueous solution. The results indicate that it is possible to use HP and subsequent calcium incorporation to form self-standing cold-set gels from soybean proteins. These gels may be of interest to incorporate heat-labile compounds or probiotics during the gelation step.     

Effects of Calcium and Pressure Treatment on Thermal Gelation of Soybean Protein

ABSTRACT:  The effect of calcium and high-pressure (HP) treatment on the heat gelation of soybean proteins was investigated. In the presence of calcium (2 to 25 mM), the gelation of dispersions of soybean protein isolate (SPI), a β-conglycinin-enriched fraction (7SEF), and a glycinin-enriched fraction (11SEF) started with protein having a lower degree of denaturation. The gels from these dispersions had greater stiffness than the samples without added calcium. HP treatment had different effects on heat-induced gelation depending on the presence of calcium and on the nature of the proteins. In the absence of calcium, gels with low stiffness were formed after HP treatment, compared with untreated samples, and regardless of the sample type (SPI, 7SEF, 11SEF). In the presence of calcium, gel stiffness was increased after HP treatment of dispersions containing β-conglycinin (SPI and 7SEF), while the opposite effect was observed for 11SEF. In the presence of calcium, HP treatment promoted a greater contribution of hydrophobic interactions in SPI and 7SEF. In the dispersions containing β-conglycinin, these conditions also promoted the appearance of a heterogeneous distribution of molecular sizes, from enormous aggregates to dissociated species. Our results suggest that, in the presence of calcium, HP treatment has an opposite effect on the ability of glycinin and β-conglycinin to participate in the formation of a 3-dimensional network upon heating.     

Effects of transglutaminase treatment on the thermal properties of soy protein isolates

The effects of covalent cross-linking of microbial transglutaminase (MTGase) on the thermal properties of soy protein isolates (SPI), including the thermal denaturation and glass transition were investigated by conventional and modulated differential scanning calorimetry (DSC). The MTGase treatment significantly increased the thermal denaturation temperatures (including the on-set temperature of denaturation, T_m and the peak temperature of denaturation, T_d) of glycinin and β-conglycinin components of SPI (P ⩽ 0.05), and the thermal pretreatment of SPI further increased the extent of this improvement. The MTGase treatment also improved the ability of SPI to resist the urea-induced denaturation. Modulated DSC analysis showed that there were two glass transition temperatures (T_g) in the reversible heat flow signals of native SPI (about 5% moisture content), approximately corresponding to 45 and 180 °C, respectively. These T_g values of SPI were significantly decreased by the MTGase treatment (at 37 °C for more than 2 h) (P ⩽ 0.05). The improvement in the hydration ability of protein and the formation of high molecular biopolymers may account for the changes of thermal properties of soy proteins caused by the MTGase cross-linking.     

Gelation of soybean proteins induced by sequential high-pressure and thermal treatments

The effect of high-pressure treatment on structural and rheological properties of soybean protein dispersions was studied. A sequential high-pressure/thermal treatment was also analyzed. Dissimilar effects on soy protein isolate (SPI) and the enriched soybean protein fractions: β-conglycinin (βCEF) and glycinin (GEF) were observed. High pressure (600 MPa) promoted βCEF gelation, but did not modify the rheological properties of GEF in spite of its complete denaturation. Pressure treatment also induced the establishment of hydrophobic interactions and disulfide bonds that allowed the formation of soluble high molecular mass aggregates from the different polypeptides of both β-conglycinin and glycinin. Protein strands formation was detected in matrix microstructure of HP-treated SPI and βCEF dispersions in accordance with their rheological behavior of weak gels. In the case of GEF modifications induced by HP in the microstructure (apparition of large granules) were not accompanied by rheological changes.     

High-pressure treatment effects on proteins in soy milk

Effects of high-pressure treatment on the modifications of soy protein in soy milk were studied using various analytical techniques. Blue shifts of λ_max could be observed in the fluorescence spectra. Spectrofluorimetry revealed that the soy protein exhibited more hydrophobic regions after high-pressure treatment. Electrophoretic analysis showed the change of soy protein clearly and indicated that soy proteins were dissociated by high pressure into subunits, some of which associated to aggregate and became insoluble. High-pressure denaturation occurred at 300 MPa for β-conglycinin (7S) and at 400 MPa for glycinin (11S) in soy milk. High pressure-induced tofu gels could be formed that had gel strength and a cross-linked network microstructure. This provided a new way to process soy milk for making tofu gels.     

Formation and properties of glycinin-rich and β-conglycinin-rich soy protein isolate gels induced by microbial transglutaminase

The gelation and gel properties of glycinin-rich and β-conglycinin-rich soy protein isolates (SPIs) induced by microbial transglutaminase (MTGase) were investigated. At the same enzyme and protein substrate concentrations, the on-set of gelation of native SPI and the viscoelasticity development of correspondingly formed gels depended upon the relative ratio of glycinin to β-conglycinin. The turbidity analysis showed that the glycinin components also contributed to the increase in the turbidity of SPI solutions incubated with MTGase (at 37 °C). Textural profile analysis indicated that the glycinin components of SPIs principally contributed to the hardness, fracturability, gumminess and chewiness values of corresponding gels, while the cohesiveness and springness were mainly associated with the β-conglycinin components. The strength of MTGase-induced gels of various kinds of SPIs could be significantly improved by the thermal treatment. The protein solubility analyses of MTGase-induced gels, indicated that besides the covalent cross-links, hydrophobic and H-bondings and disulfide bonds were involved in the formation and maintenance of the glycinin-rich SPI gels, while in β-conglycinin-rich SPI case, the hydrophobic and H-bondings were the principal forces responsible for the maintenance of the gel structure. The results suggested that various kinds of SPI gels with different properties could be induced by MTGase, through controlling the glycinin to β-conglycinin ratio.     

Assessment of the protein quality of fourteen soybean [Glycine max (L.) Merr.] cultivars using amino acid analysis and two-dimensional electrophoresis

The protein quality of commercial soybeans varieties can be determined from their total protein content, their amino acid composition and from the ratio of glycinin to β-conglycinin, the major seed storage protein components. In this study 14 commercial soybean cultivars were assessed. There were significant differences in storage protein composition (P < 0.05) and in their valine, proline and phenylalanine contents (P < 0.01 to P < 0.001). Mean protein values among these varieties ranged from 29.8% to 36.1%. The total amino acid nitrogen (AAN) ranged from 89.6 to 95.1 g AA/16 g of nitrogen, corresponding to nitrogen values from 16.5 to 17.9 g AAN/100 g protein. All varieties contained a good balance of essential amino acids (EAA₉), limited only in methionine. Two-dimensional gel electrophoretic (2-DE) separations, led to the establishment of high-resolution proteome reference maps, enabling polypeptide chain identification and calculation of the ratio of the constituent glycinin and β-conglycinin storage proteins of soybean. This method enables the assessment of the genetic variability of the soybean cultivars, which can then be correlated with their protein quality and food processing properties. These three methods can be used as very effective tools for assisting plant breeders in their selection of high quality soybean varieties.     

Protein quality and identification of the storage protein subunits of tofu and null soybean genotypes,using amino acid analysis,one- and two-dimensional gel electrophoresis,and tandem mass spectrometry

The protein quality of 11 null and 2 tofu soybean genotypes were determined from their total protein content, their amino acid composition, and their glycinin and β-conglycinin contents. There were highly significant differences (P < 0.001) in their total storage proteins, and amino acid contents. Total protein among these genotypes ranged from 33 to 37%, with arginine being the third highest amino acid (7.4–10.9 g/100 g protein) followed by glutamic and aspartic acids. Methionine accounted for only 1.6–2.4 g/ 100 g of protein. All genotypes contained a good balance of essential amino acids (EAA₉), ranging from 43.5 to 47.3% of the total protein, limited only in methionine and possibly threonine and valine. Two-dimensional gel electrophoretic (2-DE) reference maps, using narrow range immobilized pH gradient (IPG) strips, revealed unique differences in the proteome, and subunit expression of glycinin and β-conglycinin, among these null genotypes, which can then be correlated with their protein quality. Out of a total of 111 basic (pH 6–11), and 223 acidic (pH 4–7) protein spots separated by 2-DE, 41 soybean storage protein spots were excised, and identified by liquid chromatography on-line with electro spray LCQ DecaXP tandem quadrupole time-of-flight mass spectrometry (LC/MS/MS). These methods will enable accurate evaluation of protein quality in soybeans, based on their protein digestibility-corrected amino acid score, assessment of the genetic variability of soybean genotypes, and serve as very effective tools for assisting plant breeders in their selection of high quality soybean varieties.     

β-Conglycinin (7S) and glycinin (11S) exert a hypocholesterolemic effect comparable to that of fenofibrate in rats fed a high-cholesterol diet

The hypocholesterolemic effect of isolated soybean proteins and fenofibrate in rats was compared. Forty-five rats were divided into five groups: standard (STD; casein), high cholesterol (HC; STD plus 1% cholesterol/0.5% cholic acid), HC + β-conglycinin, HC + glycinin and HC + fenofibrate. The proteins and the drug were administered by gavage for 28 days. The proteins decreased total cholesterol (TC) and triacylglycerol (TG) in the plasma of the rats fed HC diet, to values very close to those fed on fenofibrate. High density lipoprotein cholesterol (HDL-C) levels in the plasma were increased by the β-conglycinin, glycinin and fenofibrate groups. The largest TC reduction in the liver was observed in the fenofibrate group; in contrast, the β-conglycinin and glycinin groups exhibited reduced the levels of hepatic TG and TC. Based on these data, it could be suggested that the oral daily administration of isolated soybean proteins, in the range of 2.75% of the protein ingested daily, can promote a reduction in TC and TG in the plasma of rats fed hypercholesterolemic diets.     

In vitro glycation and antigenicity of soy proteins

Soy protein isolate (SPI) was glycated with fructose or fructooligosaccharides (FOS) through the Maillard reaction in powder and liquid systems. A reduction in primary free amino groups of SPI up to 85% and 96% was observed in the powder and liquid system, respectively. Following heating at 95 °C for 1 h under liquid conditions, the electrophoretic behavior of allergenic 7S (β-conglycinin) and 11S (glycinin) fractions of SPI was modified when glycated with FOS (molar ratio primary amino groups to FOS of 1:74) as shown by SDS-PAGE analysis. The antigenicity of this glycated protein was also largely reduced (up to ∼90%) compared with that of the unglycated form. Glycation reactions with fructose in a powder and liquid system also reduced the antigenicity of the glycated proteins.     

Soybean β-conglycinin constituent subunits: Isolation,solubility and amino acid composition

A protocol to purify soybean β-conglycinin constituent subunits (α, α′, β) from soybean (Glycine max Linn. Merr.) was investigated. The combination of anion exchange chromatograph and Immobilized Metal Ion Affinity Chromatography (IMAC), under 6 M urea was used. The subunits were evaluated by SDS–PAGE, Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC). The subunits α, α′ and β exhibited isoelectric precipitation at pH 4.0–5.0, 4.0–5.0 and 4.0–6.0, respectively. β subunit exhibited constant solubility around 56% at pH ? 6. Total Essential Amino Acid (TEAA) and Essential Amino Acid Index (EAAI) revealed that both TEAA and EAAI of α′ subunits were lower than α and β subunits. This new fractionation method has practical significance for the researchers to prepare enough suitable amounts of samples to study the structure–physicochemical function relationships of β-conglycinin constituent subunits, and to supply enough diet for animal experiments to study the physiological function of single β-conglycinin constituent subunit.     

Ultra-High Pressure Homogenization enhances physicochemical properties of soy protein isolate-stabilized emulsions

The effect of Ultra-High Pressure Homogenization (UHPH, 100–300 MPa) on the physicochemical properties of oil-in-water emulsions prepared with 4.0% (w/v) of soy protein isolate (SPI) and soybean oil (10 and 20%, v/v) was studied and compared to emulsions treated by conventional homogenization (CH, 15 MPa). CH emulsions were prepared with non-heated and heated (95 °C for 15 min) SPI dispersions. Emulsions were characterized by particle size determination with laser diffraction, rheological properties using a rotational rheometer by applying measurements of flow curve and by transmission electron microscopy. The variation on particle size and creaming was assessed by Turbiscan® analysis, and visual observation of the emulsions was also carried out. UHPH emulsions showed much smaller d_3.2 values and greater physical stability than CH emulsions. The thermal treatment of SPI prior CH process did not improve physical stability properties. In addition, emulsions containing 20% of oil exhibited greater physical stability compared to emulsions containing 10% of oil. Particularly, UHPH emulsions treated at 100 and 200 MPa with 20% of oil were the most stable due to low particle size values (d_3.2 and Span), greater viscosity and partial protein denaturation. These results address the physical stability improvement of protein isolate-stabilized emulsions by using the emerging UHPH technology.     

The dominating effect of ionic strength on the heat-induced denaturation and aggregation of β-lactoglobulin in simulated milk ultrafiltrate

The denaturation/aggregation behaviour of heated (78 °C, 10 min) β-lactoglobulin (1%, w/w) was examined as a function of heating pH (5.0–7.0), in the presence of different salts. Heating β-lactoglobulin in the presence of calcium (5 mm) significantly increased the level of aggregated protein at most heating pH values, compared to heating in water or sodium chloride (100 mm). Heating β-lactoglobulin in the presence of calcium (5 mm) and phosphate (5 mm), resulted in similar denaturation levels in the pH range 5.0–5.8 as in the presence of calcium (5 mm) alone but reduced denaturation in the pH range 6.0–7.0, probably due to the formation of insoluble calcium phosphate. The addition of NaCl (100 mm) counteracted the aggregation promoting properties of the calcium and calcium/phosphate systems. Heating β-lg in a simulated milk ultrafiltrate solution was similar to heating in NaCl alone. This suggested that Ca²⁺ effects alone may not explain the heat-induced denaturation/aggregation behaviour of β-lactoglobulin in milk whey systems.     

Effect of high intensity ultrasound on physicochemical and functional properties of soybean glycinin at different ionic strengths

In this work, soybean glycinin was treated by high intensity ultrasound (HIU; 20 kHz at 80 W cm^− 2 from 0 to 40 min) in three ionic strengths (I = 0.06, 0.2 and 0.6) at pH 7.0. At all three ionic strengths, HIU of glycinin increased emulsion stability and decreased the turbidity. However, the effects of HIU on the particle size, particle distribution, solubility, emulsifying activity index, and surface hydrophobicity showed different characteristics in three ionic strengths. For example, after HIU, surface hydrophobicity of glycinin increased at I = 0.06 and 0.2, but remained unchanged at I = 0.6. The effects of HIU on glycinin were more pronounced at I = 0.2 than the other two ionic strengths. Furthermore, HIU influenced the glycinin aggregates, but remained the secondary and tertiary structures almost unchanged, which could be demonstrated by circular dichroism and the intrinsic fluorescence spectra.Industrial relevanceSoy protein is a plant protein which is widely employed in food products due to its high nutritional value, low price as well as its good functional properties. However, soy protein, especially glycinin, is easy to form aggregates and therefore limits soy proteins'application in some aspects. High intensity ultrasound (HIU) waves are generally considered as safe, non-toxic, and environmentally friendly. The results of this study suggested that HIU could dissociate soy glycinin and improve some functional properties of soybean glycinin, indicating that HIU can be considered as a potential tool to change soy glycinin's functional property. Moreover, this work found that the effects of HIU on physicochemical and functional properties of soybean glycinin were different in three ionic strengths, which could provide some fundamental information on how HIU influences the soy glycinin structures in different ionic strength and increase the application of HIU in the soy bean industry.     

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 800 MPa at 5 and 20 °C for 10 min 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 400 MPa. HP treatment at 20 °C compared to 5 °C resulted in meat, which was less red and slightly lighter. Storage at 2 °C for 6 days had no effect on lightness due to no further protein denaturation, but meat HP treated above 300 MPa 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.     

Skim milk protein distribution as a result of very high hydrostatic pressure

This work studies the micellar size and the distribution of caseins, major and minor whey proteins in different fractions of skim milk treated up to 900 MPa for 5 min. Transmission electron microscopy showed that the smallest casein micelles were formed around 450 MPa with no variations at higher pressures. The changes found in micellar size correlated with the concentration of soluble casein, because treatments at 250 MPa significantly enhanced the level of non-sedimentable casein while, between 700 and 900 MPa, there were no further increases with respect to lower pressures. There was a severe β-lactoglobulin (β-Lg) denaturation at pressures ≥ 700 MPa, which reached 77–87%. α-Lactalbumin (α-La) was stable up to 550 MPa, but it denatured at higher pressures. The content of soluble lactoferrin (Lf) decreased with pressure, particularly from 550 to 800 MPa, while that of secretory IgA (sIgA) progressively decreased from 250 up to 700 MPa. Our results indicated that treatment of milk at very high pressures, from 700 to 900 MPa, did not reduce micellar size nor released more soluble casein with respect to treatments at lower pressures (250–550 MPa). However, these treatments led to a severe denaturation of the whey proteins, in particular of β-Lg and the minor proteins Lf and sIgA. The possibility of using high hydrostatic pressure to obtain a soluble milk fraction with a casein and whey protein composition similar to that of human milk is discussed.     

Effect of high-pressure treatment on microbiology,proteolysis, lipolysis and levels of flavour compounds in mature blue-veined cheese

The effect of high-pressure (HP) treatment (400 MPa, 600 MPa) on ripening of mature 42-day-old Irish blue-veined cheese was studied. Counts of non-starter lactic acid bacteria, lactococci, yeasts, moulds, enterococci and total aerobic bacteria significantly decreased due to HP, with moulds being most sensitive and 600 MPa the most effective treatment. The levels of pH 4.6-soluble nitrogen and (12%) trichloroacetic acid-soluble nitrogen increased immediately after both HP treatments; however, after 28 days of storage, values were lower in HP-treated cheeses than in the control cheese. Urea-polyacrylamide gel electrophoresis showed increased breakdown of β-casein due to HP treatment at both 400 MPa and 600 MPa. Levels of free fatty acids were lower in HP-treated cheese than in the control, but not significantly so, and no significant changes could be observed in the level of flavour compounds of blue-veined cheese. Overall, HP treatment of blue-veined cheese reduced microbiological activity and decelerated proteolysis, with no statistically significant effects on development of flavour compounds.Industrial relevanceHigh-pressure treatment has been studied for the past 100 years; nevertheless, it was not applied in dairy industry, until recently, for a cheese spread. In this study, HP-induced inactivation of microbes and enzymes, which could arrest the ripening of high-quality mature (i.e., ripened) Irish farmhouse blue-veined cheese and thus extend shelf-life at optimal quality, was examined.     

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.     

Microstructural and morphological behaviors of asparagus lettuce cells subject to high pressure processing

To explore the mechanisms of texture change under high pressure (HP) processing, the effects of different pressures on cell microstructure and cell morphological behaviors of asparagus lettuce were investigated using different microscopy approaches. Pectin immunofluorescence labeling was adopted to analyze cell morphological change in vivo by in situ visualization of cell wall. Image analysis showed that cells in asparagus lettuce treated at lower pressures (100 MPa, 200 MPa and 300 MPa) exhibited rounder and smaller than the untreated samples. However, the shapes of cells in asparagus lettuce treated at 500 MPa were close to the control. The in situ analysis on pectin distribution by CLSM indicated that pectin was mainly restricted in the corners of tricellular junctions in the samples treated at 200 MPa and 300 MPa, whereas pectin uniformly distributed around the whole cell wall at 500 MPa. The results of cell activity staining were consistent with that of ultrastructure change of cell wall and membrane observed by TEM, which suggested that plasma membrane was ruptured at the pressure of 200 MPa, 300 MPa and 500 MPa. Meanwhile, the integrity of cell wall structure was retained under all HP conditions. Based on the above results, a 7-cell tissue model has been proposed to show the cell morphological behavior. On the one hand, moderate HP (100 MPa–300 MPa) caused an initial texture loss of asparagus lettuce tissue, probably due to the loss of turgor pressure and the loose skeleton of cell wall. On the other hand, HP (500 MPa) caused less apparent texture loss of asparagus lettuce due to the unchanged pectin distribution, which can maintain the rigid and flexible cell wall.