Protein recovery from rainbow trout (Oncorhynchus mykiss) processing byproducts via isoelectric solubilization/precipitation and its gelation properties as affected by functional additives

Solubility of rainbow trout proteins was determined between pH 1.5 and 13.0 and various ionic strengths (IS). Minimum solubility occurred at pH 5.5; however, when IS = 0.2, the minimum solubility shifted toward more acidic pH. Isoelectric solubilization/precipitation was applied to trout processing byproducts (fish meat left over on bones, head, skin, etc.), resulting in protein recovery yields (Kjeldahl, dry basis) between 77.7% and 89.0%, depending of the pH used for solubilization and precipitation. The recovered protein contained 1.4-2.1% ash (dry basis), while the trout processing byproducts (i.e., starting material) 13.9%. Typical boneless and skinless trout fillets contain 5.5% ash, and therefore, the isoelectric solubilization/precipitation effectively removed impurities such as bones, scales, skin, etc., from the trout processing byproducts. The recovered proteins retained gel-forming ability as assessed with dynamic rheology, torsion test, and texture profile analysis (TPA). However, the recovered proteins failed to gel unless beef plasma protein (BPP) was added. Even with BPP, the recovered protein showed some proteolysis between 40 and 55 degrees C. Addition of potato starch, transglutaminase, and phosphate to the recovered proteins resulted in good texture of trout gels as confirmed by torsion test and TPA. Higher ( P < 0.05) shear stress and strain were measured for gels developed from basic pH treatments than the acidic counterparts. However, proteins recovered from acidic treatments had higher ( P < 0.05) lipid content than the basic treatments. This is probably why the gels from acidic treatments were whiter ( L* - 3 b*) ( P < 0.05) than those from the basic ones. Our study demonstrates that functional proteins can be efficiently recovered from low-value fish processing byproducts using isoelectric solubilization/precipitation and subsequently be used in value-added human foods.     

Conformational and rheological changes in catfish myosin as affected by different acids during acid-induced unfolding and refolding

Changes in the conformation of catfish (Ictalurus punctatus) myosin due to (i) anions, (ii) acid pH, and (iii) salt addition were determined using tryptophan fluorescence, hydrophobicity measurements, differential scanning calorimetry, and circular dichroism. The relationship between conformation and storage modulus (G') of acid-treated myosin was studied. Three acids, HCl, H2SO4, and H3PO4, were used for unfolding myosin at three acidic pH conditions, 1.5, 2.0, and 2.5. Unfolded myosin was refolded to pH 7.3. Denaturation and unfolding of myosin was significantly (p < 0.05) lower when salt (0.6 M NaCl) was present during acid unfolding than in the absence of salt. When salt was added before unfolding, the alpha-helix content of myosin treated at pH 1.5 was significantly lower than that treated at pH 2.5. When salt was added after refolding, the alpha-helix content of myosin was unaffected by different pH treatments. The G' of myosin increased with an increase in myosin denaturation. The G' of myosin was significantly (p < 0.05) higher when salt was added to myosin after refolding than before acid unfolding. Among the different anion treatments, the G' of acid-treated myosin decreased in the order Cl- approximately SO42- > PO43-. Among the different pH treatments, the G' of myosin treated at pH 1.5 was significantly (p < 0.05) higher than myosin treated at pH 2.5. The conditions that would result in maximum myosin denaturation and maximum G' were unfolding of myosin at pH 1.5 using Cl- (from HCl) followed by refolding at pH 7.3 and subsequent addition of 0.6 M NaCl.     

Recovery of functional proteins from herring (Clupea harengus) light muscle by an acid or alkaline solubilization process

Proteins from herring (Clupea harengus) light muscle were extracted using acidic or alkaline solubilization; 92 and 89% of the initial muscle proteins were solubilized at pH 2.7 and 10.8, respectively, of which 96 and 94% were recovered during precipitation at pH 5.5. Consistency of the pH-adjusted muscle homogenates increased with increased raw material age and homogenization intensity; it declined following holding on ice. Some hydrolytic myofibrillar protein degradation occurred during cold storage of the acidified (pH 2.7) homogenates. With alkalized homogenates, hydrolysis was negligible. The total lipid content changed from 0.13 g/g of protein in the muscle to 0.04 g/g of protein in both the acid- and alkali-produced protein isolates. Corresponding values for the phospholipid content were from 0.037 to 0.02 g/g of proteins. Acid- and alkali-produced proteins made gels with equal strain and color. Stress values were equal or lower in acid- versus alkali-produced protein gels. When ice-stored raw material was used, strain and stress values of gels were reduced.     

Soybean glycinin subunits: Characterization of physicochemical and adhesion properties

Soybean proteins have shown great potential for applications as renewable and environmentally friendly adhesives. The objective of this work was to study physicochemical and adhesion properties of soy glycinin subunits. Soybean glycinin was extracted from soybean flour and then fractionated into acidic and basic subunits with an estimated purity of 90 and 85%, respectively. Amino acid composition of glycinin subunits was determined. The high hydrophobic amino acid content is a major contributor to the solubility behavior and water resistance of the basic subunits. Acidic subunits and glycinin had similar solubility profiles, showing more than 80% solubility at pH 2.0-4.0 or 6.5-12.0, whereas basic subunits had considerably lower solubility with the minimum at pH 4.5-8.0. Thermal analysis using a differential scanning calorimeter suggested that basic subunits form new oligomeric structures with higher thermal stability than glycinin but no highly ordered structures present in isolated acidic subunits. The wet strength of basic subunits was 160% more than that of acidic subunits prepared at their respective isoelectric points (pI) and cured at 130 degrees C. Both pH and the curing temperature significantly affected adhesive performance. High-adhesion water resistance was usually observed for adhesives from protein prepared at their pI values and cured at elevated temperatures. Basic subunits are responsible for the water resistance of glycinin and are a good starting material for the development of water-resistant adhesives.     

Extraction of proteins with low fluoride level from Antarctic krill (Euphausia superba) and their composition analysis

The extraction of proteins with low fluoride level (LFP) from Antarctic krill (Euphausia superba) was investigated in this work. The optimal conditions for protein solubilization were determined to be pH 11.5 and 4 °C. The proteins were solubilized two times; a water/krill ratio (mL/g) of 6 and a time of 30 min were used for the first step, whereas the second used a water/krill residue ratio (mL/g) of 3 and a time of 30 min. The optimum pH for protein precipitation was 4.6. A LFP with fluoride content of 9.86 mg/kg (dry weight) was finally obtained through a fluoride removal program. The protein yield of LFP was 52.68%. Composition analysis of LFP indicated it was composed of 66.96% of crude proteins (dry weight) and 33.01% of total lipids (dry weight),, and all nine essential amino acids were in sufficient amounts to meet FAO/WHO/UNU requirements for adults and infants. In addition, LFP could be taken as a good source of EPA and DHA for consideration of use as a food item for human consumption.     

Inhibition of protease in intact fish fillets by soaking in or injection of recombinant soy cystatin or bovine plasma

Arrowtooth flounder (AF) fillets are known to contain a heat-activated cysteine protease similar to that found in Pacific whiting, which results in soft texture upon cooking. A crude recombinant soy cystatin (CRSC) produced by Escherichia coli, which has been shown to inhibit the protease(s) in Pacific whiting, was introduced into AF fillets by immersion or injection at one of three levels of inhibitory activity: 10 times less than, equal to, or 10 times greater than that of a 20% bovine plasma protein (BPP) solution, a known inhibitor of AF protease(s). Fillets treated with CRSC or BPP at equal inhibitory strength subsequently exhibited the same degree of protection against textural degradation during cooking. Fillets treated with CRSC at lesser or greater levels of inhibitory activity than those of BPP exhibited lesser or higher protection, accordingly. As revealed by SDS-PAGE, the outer portion of fillets soaked with inhibitory solutions was more effectively protected than the inner portion. Such differences between the outer and inner portions of the fillets were not evident when inhibitory solutions were injected into the fillets.     

Acid-induced gelation of enzymatically modified, preheated whey proteins

Low-pH whey protein gels are formulated using a sequential protocol of heat treatment, enzyme incubation, and cold-set acidification. The heat-induced disulfide and enzyme-catalyzed epsilon-(gamma-glutamyl)lysine linkages, both at neutral pH, produce a polymerized protein solution. The molecular weights of these samples show an exponential increase with protein concentration. The additional enzyme-catalyzed cross-links cause little change in molecular weight from that of heat-treated samples at low protein concentrations, indicating predominant intramolecular cross-linking. Enzyme treatment at higher protein concentration however causes increase in molecular weight, possibly due to formation of intermolecular cross-links. Acidification of the polymerized protein solutions through glucono-delta-lactone acid leads to gel formation at pH 4. The elastic (G') and viscous (G' ') moduli of gels with and without enzyme treatment show similar frequency dependence, indicating comparable microstructures, consistent with all samples exhibiting similar fractal dimensions of approximately 2 obtained independently using rheology and confocal microscopy. A substantial increase in fracture strain and stress of the gel is achieved by enzyme treatment. However, the elastic modulus (G') is only slightly larger after enzyme treatment compared with heat-treated samples. These results indicate that factors responsible for fracture properties may not be apparent in the gel microstructure and linear viscoelastic properties.     

Gelation of chicken pectoralis major myosin and heat-denatured beta-lactoglobulin

Thermal, rheological, and microstructural properties of myosin (1 and 2% protein) were compared to mixtures of 1% myosin and 1% heat-denatured beta-lactoglobulin aggregates (myosin/HDLG) and 1% myosin and 1% native beta-lactoglobulin (myosin/beta-LG) in 0.6 M NaCl and 0.05 M sodium phosphate buffer, pH 6.0, 6.5, and 7.0 during heating to 71 degrees C. Thermal denaturation patterns of myosin and myosin/HDLG were similar except for the appearance of an endothermic peak at 54-56 degrees C in the mixed system. At pH 7.0, 2% myosin began to gel at 48 degrees C and had a storage modulus (G') of 500 Pa upon cooling. Myosin/HDLG (2% total protein) had a gel point of 48 degrees C and a G' of 650 Pa, whereas myosin/beta-LG had a gel point of 49 degrees C but the G' was lower (180 Pa). As the pH was decreased, the gel points of myosin and myosin/HDLG decreased and the G' after cooling increased. The HDLG was incorporated within the myosin gel network, whereas beta-LG remained soluble.     

Physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate

The amino acid composition and physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were evaluated and compared with those of soy protein isolate (SPI). Edestin, a kind of hexameric legumin, was the major protein component. HPI had similar or higher levels of essential amino acids (except lysine), in comparison to those amino acids of SPI. The essential amino acids in HPI (except lysine and sulfur-containing amino acids) are sufficient for the FAO/WHO suggested requirements for 2-5 year old children. The protein solubility (PS) of HPI was lower than that of SPI at pH less than 8.0 but similar at above pH 8.0. HPI contained much higher free sulfhydryl (SH) content than SPI. Differential scanning calorimetry analysis showed that HPI had only one endothermic peak with denaturation temperature (T(d)) of about 95.0 degrees C, attributed to the edestin component. The T(d) of the endotherm was nearly unaffected by 20-40 mM sodium dodecyl sulfate but significantly decreased by 20 mM dithiothreitol (P < 0.05). The emulsifying activity index, emulsion stability index, and water-holding capacity of HPI were much lower than those of SPI, and the fat adsorption capacity was similar. The data suggest that HPI can be used as a valuable source of nutrition for infants and children but has poor functional properties when compared with SPI. The poor functional properties of HPI have been largely attributed to the formation of covalent disulfide bonds between individual proteins and subsequent aggregation at neutral or acidic pH, due to its high free sulfhydryl content from sulfur-containing amino acids.     

Pasting properties of gamma-irradiated rice starches as affected by pH.

Changes in the viscosity properties of gamma-irradiated rice starches (from 1 to 25% amylose content) from four genotypes (JY293, Jiayu 293; XS, Xiushui; ZF504, Zhefu 504; and ZXN, Zaoxiannuo) during pasting in water (pH 7) or in different pH solutions were studied using a rapid visco analyzer. Peak viscosity (PV) of all native rice starches was little affected at pH 4 and 10, while hot paste viscosity (HPV) and cool paste (final) viscosity (CPV) were generally lower at pH 4 and higher at pH 10 as compared with that at pH 7. The PV, HPV, and CPV of gamma-irradiated starches were higher at pH 4 and lower at pH 10 than pH 7. All viscosity characteristics of native rice starches were reduced in stronger alkali (pH 11.5) or acidic (pH 2.5) solutions. However, the gamma-irradiated starches were substantially higher at pH 2.5 but lower at pH 11.5, indicating that the effect of irradiation was highly pH dependent. The swelling volume of irradiated ZF504 and JY293 starch at all irradiation levels was higher at pH 4 than pH 7, while the values were lowest at pH 2.5. The irradiated ZXN and XS starches had higher swelling volumes at pH 4 and pH 2.5 than pH 7. Differential scanning calorimetry analysis showed that gamma-irradiation caused progressively lower gelatinization peak temperature (T(p)) and higher gelatinization range (T(r)) at pH 7. T(p) was higher and T(r) was lower at a much stronger acidic condition (pH 1) for both native and irradiated starches. The possibility of using viscosity changes in low pH for the detection of irradiated starch was discussed.     

Removal of lipids and diarrhetic shellfish poisoning toxins from blue mussels (Mytilus edulis) during acid and alkaline isolation of proteins

Diarrhetic shellfish poisoning (DSP) toxins pose a serious health risk for consumers of bivalves and other shellfish, as well as a huge economic burden for the bivalve-producing farmers. In this work, the aim was to utilize a solubilization-based protein-isolation method to produce a low-DSP toxin protein isolate from toxic blue mussels that are unsuitable for the whole shellfish market. A homogenate of whole mussel meat was solubilized at low pH (2.8) or high pH (11.1), followed by centrifugation and reprecipitation of the solubilized mussel proteins at the isoelectric pH. In a second centrifugation, precipitated proteins were collected. These processes resulted in 81 (acid solubilization) and 72% (alkaline solubilization) reduction in the initial DTX-1 toxin content of the mussel meat. No other DSP toxins were found in the protein isolates. Acid processing of mussel meat resulted in 50% reduction in the total lipid content, while alkaline treatment did not significantly affect the lipid content. The effect of citric acid and calcium chloride addition to the mussel meat-water homogenate on lipid and toxin content was also investigated. A poor correlation factor was surprisingly obtained between reductions in DTX-1 toxin and lipids in protein isolates from processed toxic mussels. Results from an analytical mass balance of the DTX-1 toxin during acid processing showed that 61% of this toxin ended up in the aqueous supernatant after the second centrifugation. The present study presents a promising alternative way of utilizing mussels for food production in periods when they are toxic.     

Solubilization of Fe (III) from humic-Fe complexes,humic/Fe-oxide mixtures and from poorly ordered Fe-oxide by organic acids - consequences for P adsorption

The effect of organic acids on the solubility of Fe from humic Fe complexes, poorly ordered Fe-oxides and humic/Fe-oxide mixtures was investigated at pH 4 and 7. After reaction, the suspensions were filtered through a 20 000 D membrane and Fe and humic concentrations were determined in the filtrate. Among four organic acids, citric acid had the strongest effect on Fe-solubility and solubilized up to 25% of total Fe from the humic complexes at pH 4. Humic substances were solubilized by citrate too, the proportions being higher at pH 7 than at pH 4. Malic and tartaric acid solubilized substantial but lower amounts of Fe from humic complexes than citric acid, whereas phthalic acid did not solubilize Fe and humics. Citrate added to poorly ordered Fe-oxide and its mixtures with humics, aged for 65 days, increased 20 000 D filtrable Fe, the effect being higher for humic/Fe-oxide complexes. Adding citrate to humic/Fe-oxide mixtures and to Fe-oxide strongly decreased the P sorption, the extent, being higher for the former adsorbent.     

Preparation of interesterified plastic fats from fats and oils free of trans fatty acid

Interesterified plastic fats were produced with trans-free substrates of fully hydrogenated soybean oil, extra virgin olive oil, and palm stearin in a weight ratio of 10:20:70, 10:40:50, and 10:50:40, respectively, by lipase catalysis. The major fatty acids of the products were palmitic (32.2-47.4%), stearic (12.0-12.4%), and oleic acid (33.6-49.5%). After storage at 5 degrees C (refrigerator temperature) or 24 degrees C (room temperature) for 16 h, the physical properties were evaluated for solid fat content, texture, melting, and crystallization behavior, viscoelastic properties, crystal polymorphism, and crystal microstructure. The interesterified fats contained desirable crystal polymorphs (beta' form) as determined by X-ray diffraction spectroscopy. They exhibited a wide plastic range of solid fat content of 52-58% at 10 degrees C and 15% at 40 degrees C. The physical properties were influenced by the ratio of palm stearin and olive oil. Harder and more brittle texture, crystallization and melting at higher temperature, higher solid fat contents, and more elastic (G') or viscous (G') characteristics were observed in the produced fats containing a higher content of palm stearin and lower content of olive oil. The produced fats stored at 5 degrees C consisted mostly of beta' form crystal together with a small content of beta form, while those at 24 degrees C had only beta' form. The produced fat with a higher amount of palm stearin appeared to have more beta' form crystal and small size crystal clusters. Thus, the physical properties of the produced plastic fats may be desirable for use in a bakery product.     

Antioxidant activity of peptides obtained from porcine myofibrillar proteins by protease treatment

Hydrolysates obtained from porcine myofibrillar proteins by protease treatment (papain or actinase E) exhibited high antioxidant activity in a linolenic acid peroxidation system induced by Fe(2+). Hydrolysates produced by both papain and actinase E showed higher activities at pH 7.1 than at pH 5.4. The antioxidant activity of the papain hydrolysate was almost the same as that of vitamin E at pH 7.0. These hydrolysates possessed 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and chelating activity toward metal ions. Antioxidant peptides were separated from the papain hydrolysate by ion exchange chromatography. The acidic fraction obtained by this method exhibited higher activity than the neutral or basic fractions. Antioxidant peptides in the acidic fraction were isolated by high-performance liquid chromatography on an ODS column and shown to possess the structures DSGVT, IEAEGE, DAQEKLE, EELDNALN, and VPSIDDQEELM. The DAQEKLE peptide showed the highest activity among these peptides.     

Functional Characteristics of Extruded Blends of Whey Protein Concentrate and Corn Starch

The aim of this work was to study the effects of extrusion barrel temperature (70–180°C), feed moisture (18–30%), pH (3–8), different proportions of corn starch (75–95%), and whey protein concentrate (WPC, 80% protein concentration) (25–5%) on the preparation of functional blends. Expansion index (EI), bulk density (BD), compression force (CF), color, water absorption index (WAI), water solubility index (WSI), gel strength (GS), syneresis of the gel, and in vitro digestibility were evaluated. Barrel temperature and the proportion of WPC had significant effects on BD; at higher temperatures, BD was lower. Feed moisture and pH had significant effects on EI; with lower moisture and higher pH, the EI increased. An interaction of barrel temperature and feed moisture had an effect on WAI; at lower moisture content, the temperature effect was nonexistent, whereas at higher temperatures and feed moisture content, the WAI increased. The pH level had a significant effect on WSI, showing high WSI when lower pH levels were used. Color analysis showed that higher protein content and pH generated higher δE values; low feed moisture and low pH resulted in gel syneresis. Higher in vitro digestibility was obtained when a higher WPC proportion and pH were used. Extruded WPC-CS blends under alkaline and acidic conditions were affected by the preparation of diverse formulations that potentially can be used in foods to improve some functional and protein content.     

Unfolding and refolding of beta-lactoglobulin subjected to high hydrostatic pressure at different pH values and temperatures and its influence on proteolysis

The unfolding of beta-lactoglobulin during high-pressure treatment and its refolding after decompression were studied by 1H NMR and 2H/1H exchange at pH 6.8 and 2.5 and at 37 and 25 degrees C. The extent of unfolding increased with the pressure level. The structure of beta-lactoglobulin required higher pressures to unfold at pH 2.5 than at pH 6.8. More flexibility was achieved at 37 degrees C than at 25 degrees C. Results indicated that the structural region formed by strands F, G, and H was more resistant to unfold under acidic and neutral conditions. The exposure of Trp19 at an earlier time, as compared to other protein regions, supports the formation of a swollen structural state at pH 2.5. Refolding was achieved faster when beta-lactoglobulin was subjected to 200 MPa than to 400 MPa, to 37 degrees C than to 25 degrees C, and to acidic than to neutral pH. After treatment at 400 MPa for 20 min at neutral pH, the protein native structure was not recovered. All samples at acidic pH showed that the protein quickly regained its structure. Hydrolysis of beta-lactoglobulin by pepsin and chymotrypsin could be related to pressure-induced changes in the structure of the protein. Compared to the behavior of the protein at atmospheric pressure, no increased proteolysis was found in samples with no increased flexibility (100 MPa, 37 degrees C, pH 2.5). Slightly flexible structures were associated with significantly increased proteolysis (100 MPa, 37 degrees C, pH 6.8; 200 MPa, 37 degrees C, pH 2.5). Highly flexible structures were associated with very fast proteolysis (>or=200 MPa, 37 degrees C, pH 6.8; >or=300 MPa, 37 degrees C, pH 2.5). Proteolysis of prepressurized samples improved only when the protein was significantly changed after the pressure treatment (400 MPa, 25 degrees C, 20 min, pH 6.8).     

Raman spectroscopy determines structural changes associated with gelation properties of fish proteins recovered at alkaline pH

Structural changes of alkali-treated rockfish protein isolate (AKPI) during frozen storage were elucidated using a Raman spectrometer and scanning electron microscope (SEM). The results were compared to conventional surimi (CS). No significant textural difference was noted between AKPI stored at pH 5.5 and 7.0. The strongest texture was found for AKPI frozen with cryoprotectants and CS, while the weakest texture was observed in AKPI frozen without cryoprotectants. SEM revealed the most discontinuity in gels of AKPI with no cryoprotectants and a more aggregated microstructure after storage at pH 5.5 than at neutral pH. Raman spectral analysis demonstrated refolding of AKPI by pH readjustment to 7.0, although the refolded structure was not identical to that before the pH shift. CS showed higher alpha-helix content (approximately 50%) than AKPI (approximately 20-30%). Frozen storage induced a decrease and an increase in the alpha-helix content of CS and AKPI samples, respectively. AKPIs were slightly less stable than CS during frozen storage.     

Enzyme-aided modification of chicken-breast myofibril proteins: effect of laccase and transglutaminase on gelation and thermal stability

The effect of laccase and transglutaminase (TG) on cross-linking, gelation, and thermal stability of salt-soluble chicken-breast myofibril proteins was investigated at pH 6. Both enzymes modified the protein pattern detected by SDS-PAGE. Identification of proteins by peptide mass mapping showed that myosin heavy chain (MHC) and troponin T were the most affected proteins. These proteins faded or disappeared as a function of the incubation time with both enzymes on SDS-PAGE. The molecular weight of actin was not, however, affected by either enzyme. The effects that the enzymes had on the gel formation of chicken-breast myofibrils were studied in 0.35 and 0.60 M NaCl solutions at 3% protein content and a constant temperature of 40 degrees C by using a small deformation viscoelastic measurement. TG substantially increased the storage modulus (G') of 3% protein in 0.35 M NaCl. Without the enzymes, gelation was insignificant in 0.35 M NaCl. The increased solubility of the proteins at 0.60 M NaCl intensified gelation with TG. G' increased 32 and 64% at dosages of 10 and 100 nkat of TG, respectively. Also, laccase increased G' of the gel in 0.60 M salt concentration. However, a high laccase dosage decreased the magnitude of G' below the control level. Differential scanning calorimetric (DSC) measurements indicated slightly reduced myosin heat stability after TG pretreatment and increased actin heat stability with both enzymes. Maximum transition temperatures did not alter with either enzyme.     

Heat-induced gel formation by soy proteins at neutral pH

Heat-induced gel formation by soy protein isolate at pH 7 is discussed. Different heating and cooling rates, heating times, and heating temperatures were used to elucidate the various processes that occur and to study the relative role of covalent and noncovalent protein interactions therein. Gel formation was followed by dynamic rheological measurements. Heat denaturation was a prerequisite for gel formation. The gelation temperature (84 degrees C) was just above the onset denaturation temperature of glycinin. The stiffness of the gels, measured as the elastic modulus, G', increased with the proportion of denatured protein. An increase in G' was also observed during prolonged heating at 90 degrees C. This increase is explained by the occurrence of rearrangements in the network structure and probably also by further incorporation of protein in the network. The increase in G' upon cooling was thermoreversible indicating that disulfide bond formation and rearrangements do not occur upon cooling.     

高压均质-酶解改性提高酸性条件下花生蛋白的溶解性及其稳定性研究

花生蛋白在酸性条件下会絮凝沉淀,溶解性降低,限制了其在酸性饮料加工领域的应用。本研究通过利用高压均质-中性蛋白酶酶解复合改性提高花生蛋白在pH值4.0条件下的溶解度,并根据Turbiscan多重光散射稳定性分析仪的背散射光强值和体系不稳定指数(TSI)分析不同浓度改性蛋白添加量对酸性果汁稳定性的影响。响应面分析结果表明,高压均质-中性蛋白酶酶解复合改性的最优工艺为:均质压力79.74 MPa,料液比7.23%,加酶量517 U·g^-1,酶解时间48.20 min,此时,花生蛋白在pH值4.0条件下氮溶指数(NSI)从由4.04%提升至37.49%。将改性后蛋白加入pH值3.88的果汁中,改性后蛋白添加量为3%和4%的果汁稳定性指数(TSI)分别为1.95和2.23,显著优于蛋白质添加量为5%的样品(TSI为3.29)。研究表明高压均质-中性蛋白酶酶解改性可以显著提高花生蛋白在pH值4.0条件下的溶解度且改性后蛋白在酸性饮料中稳定性良好,为植物蛋白在酸性饮料中的应用提供了参考。