Rheological Properties of Rice Starch Dispersions in Dimethyl Sulfoxide

The steady and dynamic shear rheological properties of rice starches dispersed in dimethyl sulfoxide (DMSO) solution (90% DMSO‐10% water) were evaluated at various concentrations (7, 8, 9 and 10%, w/w). Rice starch dispersions in DMSO solution at 25°C showed a shear‐thinning flow behavior (n=0.44–0.60) and their consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The apparent viscosity over the temperature range of 25–70°C obeyed the Arrhenius temperature relationship, indicating that the magnitudes of activation energy (E_a) were in the range of 11.7–12.7 kJ/mol. The Carreau model provided better fit on the shear rate‐apparent viscosity data than the Cross model. Dynamic frequency sweep test showed that both storage modulus (G′) and loss modulus (G′′) of rice starch dispersions increased with the increase in concentration. G′′ showed a higher dependence on frequency (ω) compared to G′ due to the higher G′′ slopes. All rice starch dispersions showed the plateau of G′ at high frequencies. Intrinsic viscosity of rice starch dispersions in DMSO was 104.1 mL/g.     

The physico-chemical properties of commercial canola protein isolate-guar gum gels

Biopolymer mixtures impart desirable texture to foods. Dynamic rheology was used to characterize canola protein isolate (CPI)‐guar gum gels. The effects of pH, salt, guar gum and protein concentrations on the gelling ability of CPI were evaluated. Factorial and response surface optimization models were used to identify the optimum conditions (20%, w/v CPI; pH 10; 1.5%, w/v guar gum; 0.05 m NaCl) that would simultaneously maximize G′ (≥28 000 Pa) and minimize tan δ (<0.17) values of CPI‐guar gum gels. Although pH > 8 is unconventional in food systems, strong and elastic CPI‐guar gum gels (G′ =56 440 Pa; tan δ = 0.18) were produced at pH 10, whereas gels prepared at pH 6 were less elastic (G′ = 2726 Pa; tan δ = 0.2). Under the optimum conditions, CPI alone formed a stronger gel (G′ = 64 575 Pa; tan δ = 0.15) than CPI‐guar gum mixture, suggesting that guar gum interfered with protein gelation.     

Channel catfish (Ictalurus punctatus) muscle protein isolate performance processed under different acid and alkali pH values

Abstract: Channel catfish (Ictalurus punctatus) muscle was subjected to 6 protein extraction and precipitation techniques using acid solubilization (pH 2.0, 2.5, and 3.0) or alkaline solubilization (pH 10.5, 11.0, 11.5) followed by precipitation at pH 5.5. The catfish protein isolate was compared with ground defatted white muscle. Alkali‐processed catfish showed increased gel rigidity, gel strength, and gel flexibility compared to acid‐processed catfish, which exhibited inconsistent functional performance, increasing and decreasing gel rigidity, gel strength, and gel flexibility. The gel rigidity (G′) at pH 3.0 in the absence of salt had the highest G′ of the acid treatments and was not significantly different from the alkaline‐treated catfish muscle (P > 0.05). However in the presence of added salt pH treatment it had the lowest G′ and was different from alkaline treatments (P < 0.05) during break force testing. These results show that pH‐shift processing of channel catfish muscle provides highly functional isolates with a potentially broad range of applications. This range of applications is possible due to the modification of the textural properties of catfish muscle protein produced using different acidic or alkaline pH solubility treatments.     

Effect of Fortification with Various Types of Milk Proteins on the Rheological Properties and Permeability of Nonfat Set Yogurt

ABSTRACT: Yogurt base was prepared from reconstituted skim milk powder (SMP) with 2.5% protein and fortified with additional 1% protein (wt/wt) from 4 different milk protein sources: SMP, milk protein isolate (MPI), micellar casein (MC), and sodium caseinate (NaCN). Heat‐treated yogurt mixes were fermented at 40 °C with a commercial yogurt culture until pH 4.6. During fermentation pH was monitored, and storage modulus (G′) and loss tangent (LT) were measured using dynamic oscillatory rheology. Yield stress (σ_yield) and permeability of gels were analyzed at pH 4.6. Addition of NaCN significantly reduced buffering capacity of yogurt mix by apparently solubilizing part of the indigenous colloidal calcium phosphate (CCP) in reconstituted SMP. Use of different types of milk protein did not affect pH development except for MC, which had the slowest fermentation due to its very high buffering. NaCN‐fortified yogurt had the highest G′ and σ_yield values at pH 4.6, as well as maximum LT values. Partial removal of CCP by NaCN before fermentation may have increased rearrangements in yogurt gel. Soluble casein molecules in NaCN‐fortified milks may have helped to increase G′ and LT values of yogurt gels by increasing the number of cross‐links between strands. Use of MC increased the CCP content but resulted in low G′ and σ_yield at pH 4.6, high LT and high permeability. The G′ value at pH 4.6 of yogurts increased in the order: SMP = MC < MPI < NaCN. Type of milk protein used to standardize the protein content had a significant impact on physical properties of yogurt. Practical Application: In yogurt processing, it is common to add additional milk solids to improve viscosity and textural attributes. There are many different types of milk protein powders that could potentially be used for fortification purposes. This study suggests that the type of milk protein used for fortification impacts yogurt properties and sodium caseinate gave the best textural results.     

Rheological properties and permeability of soy protein-stabilised emulsion gels made by acidification with glucono-δ-lactone

BACKGROUND: Soy protein, an important efficient emulsifier, is widely used by the food industry for incorporation into milk, yogurts, ice cream, salad dressings, dessert products, etc. The objective of this study was to investigate the rheological and physical properties of soy protein‐stabilised emulsion gels as affected by protein concentration and gelation temperature. RESULTS: The rheological properties and permeability were determined using oscillatory rheometry, permeability and whey separation. The modulus (G′ and G″), fracture stress and fracture strain of acid‐induced emulsion gels after 20 h of glucono‐δ‐lactone addition depended strongly on soy protein concentration and gelation temperature. At increasing soy protein concentrations, acid‐induced emulsion gels had shorter gelation times but higher storage moduli (G′), fracture stresses and strains. Increasing gelation temperature decreased the gelation time, G′, fracture stresses and strains. Permeability and whey separation were significantly affected by the protein concentration and the gelation temperature. A significant positive correlation was observed between whey separation and permeability coefficient in emulsion gels formed at different temperatures. CONCLUSION: The rheological properties and permeability of soy protein‐stabilised emulsion gels were significantly influenced by protein concentration and gelation temperature. Copyright © 2011 Society of Chemical Industry     

Rheological properties of soy protein hydrolysates obtained from limited enzymatic hydrolysis

Soy protein products hexane-defatted soy flour, extruded-expelled soy flour, soy protein concentrate and soy protein isolate, were modified by using the enzyme bromelain to 2% and 4% degrees of hydrolysis (DH). Peptide profiles, water solubility, and rheological properties including dynamic shear, large deformation, and apparent viscosities of resulting hydrolysates were determined. Protein subunits profiles for the hydrolysed isolates and concentrates were extensively altered by the treatment while only minor changes were observed for the hydrolysed flours. Water solubility profiles of all hydrolysates in the pH range of 3.0-7.0 were enhanced by hydrolysis. For the unhydrolysed controls, the isolate had the highest storage modulus (G′), followed by the concentrate, the extruded-expelled flour and the hexane-defatted flour. The hydrolysates retained some of their gelling ability even though the losses in storage modulus (G′) were substantial. After heating step to 95 °C, the G′ values of all substrates at 25 °C decreased with increase in DH. Texture profile analyses of the soy protein gels were also lower in hardness after hydrolysis. The Power Law model provided excellent fit to hydrolysate dispersions flow (R²>0.99). Hydrolysis decreased the consistency coefficients of dispersion and increased flow behavior index resulting in thinner dispersions. These results suggest that limited protease hydrolysis of various soy protein meals with bromelain produce soy protein ingredients with modified rheological properties.     

Effect of grinding on the structure of pea protein isolate and the rheological properties of its acid-induced gels

The purpose of this study was to expand the application range of pea protein isolates by improving the rheological properties of their acid-induced gels. A pea protein isolate was ground for different durations, and changes in the structure and properties of its gels were studied. Furthermore, the influence mechanism of grinding on gelation was revealed. The results showed that grinding slightly changed the secondary structure of the pea protein isolate and had a great impact on its tertiary structure. Compared with the unground pea protein isolate, the solubility of the ground pea protein isolate increased from 45.89% to 69.84%, and the water-holding capacity of the gels increased from 52.04% to 94.67% at 7.5 min of grinding. After grinding for 15 min, the particle size of the pea protein isolate decreased from 1292.4 to 945.7 nm, and the polydispersity index decreased from 0.387 to 0.321. Rheological measurements showed that the storage modulus (G′), viscosity and recovery of protein gel samples improved after grinding. Thus, grinding enhanced the potential of protein gels for new applications.     

Dynamic rheological measurements on heat-induced myosin gels: Effect of ionic strength,protein concentration and addition of adenosine triphosphate or pyrophosphate

Myosin solutions and suspensions have been monitored during heating at pH 6.0 by using dynamic rheological measurements. The storage modulus (G′), the loss modulus (G) and the phase angle (δ) all showed a marked dependence on ionic strength in the temperature range 25–75°C. The filamentous gels (ionic strength <0.34) displayed a temporary reduction in G′ at temperatures between 50 and 60°C, presumably due to denaturation in parts of the rod portion of the myosin molecule. In the same temperature region the concentration dependence of G′ changed by a power of 2. The loss modulus also showed a marked concentration dependence, while the phase angle varied with concentration primarily at low (<50°C) temperatures. For the final gels, heated to 75°C, only G′ indicated marked differences due to different protein concentrations and ionic strengths; all gels were almost completely elastic (δ?1°). Adenosine triphosphate was shown to have a pronounced temporary effect on the filamentous gel formed at low temperatures, i.e. on the gel with the highest concentration dependence, while pyrophosphate had no such effect. However, both adenosine triphosphate (or rather its hydrolysis product: adenosine diphosphate) and pyrophosphate appeared to have a small, lasting effect on the heat-gelling ability of myosin: the former a detrimental effect, the latter an improvement.     

Dynamic Rheology of Rice Starch‐Galactomannan Mixtures in the Aging Process

The effect of galactomananns (guar gum and locust bean gum) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) on the dynamic rheological properties of aqueous rice starch dispersions (5%, w/w) was investigated by small‐deformation oscillatory measurements during aging. Magnitudes of storage (G′) and loss (G′′) moduli measured at 4°C before aging increased with the increase in gum concentration in the range of 0.2–0.8%. G′ and G′′ values of rice starch‐locust bean gum (LBG) mixtures, in general, were higher than those of rice starch‐guar gum mixtures. G′ values of rice starch‐guar gum mixtures as a function of aging time (10 h) at 4°C increased rapidly at initial stage and then reached a plateau region at long aging times. However, G′ values of rice starch‐LBG mixtures increased steadily without showing a plateau region. Increasing the guar gum concentration resulted in an increase in plateau values. The rate constant (K) for structure development during aging was described by first‐order kinetics. K values in rice starch‐guar gum mixtures increased with the increase in guar gum concentration. G′ values of rice starch‐galactomannan mixtures after aging were greater than those before aging.     

Rheological properties of modified lupin proteins

The properties of acetylated, succinylated and phosphorylated protein isolates extracted from the flour of yellow lupins (L. luteus) were studied by means of oscillatory rheology. The flow behaviour of protein dispersions (15% w/w) and the properties of thermotropic gels were distinctly influenced by the modification. Succinylation increased the viscosity of the dispersions of unmodified protein isolate (LPI) from 99 mPas to 515 mPas and results in the lowest gel point (T = 30.5°C). Acetylation and phosphorylation enhance the pseudoplastic flow behaviour of the dispersions. Acylated lupin samples formed the strongest gels with a small visco‐elastic range while phosphorylation leads to weak and “rubber‐like” gels.     

Physical properties of emulsion gels formulated with sonicated soy protein isolate

This study aimed to determine the effect of high-intensity ultrasound (HIU) on physical properties of soy protein isolate dispersions (SPI) and their addition to emulsion gels (EG) containing soybean oil (SBO), inulin (IN) and carrageenan (CAR). Sonicated and non-sonicated SPI dispersions were mixed with CAR, IN and SBO and heated at 90 °C for 30 min to gel the emulsion. An increase in solubility and oil binding capacity was observed in sonicated SPI dispersions (S-SPI) compared to the non-sonicated ones. HIU changed the molecular weight of SPI and decreased apparent viscosity in the dispersions. The use of S-SPI in the EG reduced the droplet size and increased the hardness and G′ values. The use of S-SPI allowed a reduction of 75% of carrageenan in the EG without affecting the hardness of the gel. The results suggest that HIU can be used to improve rheological properties of functional EG.     

Curtailing Oxidation‐Induced Loss of Myosin Gelling Potential by Pyrophosphate Through Shielding the S1 Subfragment

In muscle food processing, where oxidation is inevitable, phosphates are usually added to improve water binding. This present study attempted to investigate the interactive roles of protein oxidation and pyrophosphate (PP) during thermal gelation of myosin. Myosin isolated from pork muscle was solubilized in 0.5 M NaCl at pH 6.2 then oxidatively stressed with an iron‐redox cycling system that produces hydroxyl radicals with or without 1 mM PP and 2 mM MgCl₂ at 4 °C for 12 or 24 h then heated to 50 °C at 1.3 °C/min. Protein conformational stability was measured by differential scanning calorimetry, and covalent cross‐linking was examined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis following chymotrypsin digestion. The binding of PP to myosin suppressed disulfide bond formation in myosin subfragments 1 and 2 and partially inhibited oxidation‐initiated cross‐linking of heavy meromyosin during myosin gelation with a lesser effect on light meromyosin. In the presence of PP, myosin exhibited less loss of conformational integrity upon oxidation than myosin without PP. Rheological analysis from 20 to 75 °C indicated up to 32% decreases (P < 0.05) in elastic modulus (G′) of myosin gels due to oxidation. However, the presence of 1 mM PP, which also lowered the gelling capacity of myosin, inhibited the oxidation‐induced G′ by nearly half (P < 0.05). These results suggest that the protection of myosin head from oxidative modification by PP can be a significant factor for the minimization of gelling property losses during cooking of comminuted meats.     

Effects of oligosaccharides on phase transition temperatures and rheological characteristics of waxy rice starch dispersion

BACKGROUND: The creation of starch‐based foods incorporated with functional ingredients such as probiotics is of great current interest in the food industry. This study aimed to investigate the effects of prebiotic oligosaccharides on the phase transition temperatures and rheological characteristics of waxy rice starch dispersions. Four oligosaccharides were applied to the rice starch dispersions: chitooligosaccharides, fructooligosaccharides, isomaltooligosaccharides and xylooligosaccharides. RESULTS: The addition of 125 g kg^?1 oligosaccharides elevated the onset and peak temperatures for gelatinisation of 200–400 g kg^?1 waxy rice starch dispersions. The temperature of the storage modulus (G′) for gelatinisation increased markedly on adding fructooligosaccharides to 200–300 g kg^?1 waxy rice starch. For gelatinisation of 300 g kg^?1 rice starch dispersion the effectiveness of the oligosaccharides in changing the above parameters was as follows: chitooligosaccharides > fructooligosaccharides > isomaltooligosaccharides > xylooligosaccharides. Moreover, their effectiveness was dependent on the amylose content, as illustrated by comparing waxy and non‐waxy rice starches (amylose contents 9–256 g kg^?1). Importantly, the logarithmic G′₉₅ change was linearly and negatively correlated with amylose content. CONCLUSION: The results suggest that oligosaccharide‐containing rice starch dispersions may potentially be used for the formulation of oligosaccharide‐containing starchy functional foods owing to the rheological changes of these starch dispersions. Copyright © 2011 Society of Chemical Industry     

Dynamic rheology of wheat flour dough. II. Assessment of dough strength and bread‐making quality

Controlled stress rheometry revealed that differences in wheat flour dough strengths could be observed by means of dynamic rheological measurements in the region of higher stress amplitude (ie >100 Pa). At lower stress amplitude (τ_o) the values of elastic modulus G′ for weak doughs were higher than those for strong doughs, but they decreased substantially beyond 100 Pa stress amplitude (τ_o), such that the G′ values for strong doughs crossed over the G′ values for weak doughs. Beyond a critical value of stress amplitude (ie 100 Pa), true differences in dough strengths could be seen on the basis of their elastic characteristics, because at large deformations protein–protein interactions played a more dominant role in the rheological behaviour of flour doughs. Dynamic rheological analysis demonstrated a very weak inverse relationship (R² = 0.16) between the G′ values of flour doughs and loaf volume data for 12 wheat cultivars of diverse bread‐making performance. However, the G′ values of glutens showed significant positive relationships with bread‐making performance, explaining 73% of the variation in loaf volume. © 2002 Society of Chemical Industry     

Thermal and viscoelastic properties of starch gels from maize varieties

The aim of this work was to determine the thermal, functional and rheological properties of maize (Zea mays) starch isolated from seven varieties. Chemical analysis was undertaken in all starch samples. The gelatinization and retrogradation temperature at different storage times, as well as the enthalpy of the isolated starches, were determined using differential scanning calorimetry (DSC). Swelling and solubility were also measured in individual samples. Dynamic oscillatory tests (amplitude and frequency sweeps) were undertaken on starch samples with 10% (w/v) of total solids during a cycle of three stages (kinetics) of heating/cooling, using a strain‐controlled rheometer. The samples presented an amylose content which ranged from 22% to 29%, typical in normal starches, the lipid values were under 1%, while the protein contents were just over 1%. The calorimetric profile for the studied starches showed a peak temperature (gelatinization) over the temperature range from 72.5 to 75.7 °C and enthalpy values between 13.68 and 17.58 J g^?1. Four starches presented enthalpy values of the retrogradation transition that increased with the storage time, showing differences among the starches analysed. Maximum swelling and solubility were usually found at the second stage of the above‐mentioned cycle. The rheological profile showed that the gels formed during the first stage of the above‐mentioned kinetics presented the behaviour of weak viscoelastic gels with the storage or elastic modulus (G′) higher than the loss or viscous modulus (G″) over the applied strain and frequency ranges. All samples showed a more elastic character as the kinetics progressed. Starches isolated from diverse maize varieties showed differences in their characteristics studied, and might produce different functional properties in the products where they are used. Copyright © 2006 Society of Chemical Industry     

Rheological properties of starches from grain amaranth and their relationship to starch structure

Amaranth starch (Amaranthus cruentus L. and Amaranthus hypochondriacus L.) in this investigation possessed a relatively small and uniform granule size of a type “A” pattern obtained by X‐ray diffraction, with the degree of crystallinity ranging from 24.5 to 27.9%. This was followed by work on steady and dynamic rheological properties on shear of seven native amaranth starches. Aqueous pastes (5% solids) exhibited shear‐thinning behavior, and the flow behavior was fitted with the Herschel–Bulkley equation (regression coefficients were over 0.99). Cultivar V69 showed much higher G′ (storage modulus) and G″ (loss modulus) than the other samples and produced a solid‐like gel, which could be attributed to the high amylose content of its network. Correlation analysis revealed that amylose content was positively correlated with G′ and negatively with the loss tangent (tan δ) of the material.     

Impact of ultrafiltration/diafiltration sequence on the production of soy protein isolate by membrane technologies

In previous studies, the advantages of combining electrodialysis using a bipolar-cationic membranes configuration to acidify a soy protein extract to pH 6 with ultrafiltration/diafiltration (UF/DF) using a 100 kDa membrane to produce a soy protein isolate with low phytic acid content and improved solubility between pH 2 and 4 was demonstrated, when compared to the production of soy protein isolates by isoelectric precipitation and by UF/DF of a soy protein extract at pH 9. However, limited work was done to establish the impact of the UF/DF sequence for the purification of the pH 6 extract. Therefore, the purpose of this work was to study the impact of four different UF/DF sequences with a total permeate volume of 1.5–1.6 times the initial volume, on membrane fouling and permeate flux, as well as on the isolate protein, ash and phytic acid contents and solubility profile. Of the investigated UF/DF sequences, the VCR 5, VD 4 sequence was shown to be the one with the most severe fouling and consequently the most severe permeate flux decline. At the same time, it was also the VCR 5, VD 4 sequence which was the most efficient in terms of ash and phytic acid removal, followed by the VCR 5, re-VCR5 sequence, the VCR 2, VD 2 sequence and the VCR 2, (re-VCR 2)X 2 sequence, respectively. It was also observed that isolate with low phytic acid content resulted in narrower protein solubility profiles around the isoelectric point and higher protein solubility for the pH range of 2 to 4.Industrial relevancePlant proteins have made up a higher proportion of the human diet in recent years. Soybeans are the most important source of plant protein ingredients accounting for some 68% of global plant protein consumption in the world. Soy protein isolate is traditionally prepared by isoelectric precipitation process. This process has high productivity, however, it results in products with poor functional properties due to protein denaturation and to the presence of phytic acid (1–3% w/w) which alters the solubility of the isolates especially for the pH below the proteins' isoelectric point. In this work, we combined electrodialysis using a bipolar-cationic membranes configuration to acidify a soy protein extract to pH 6 with ultrafiltration/diafiltration (UF/DF) using a 100 kDa membrane to produce soy protein isolates with low phytic acid content. The impact of four different UF/DF sequences on membrane fouling, permeate flux, isolate composition and solubility profile was studied. Of the investigated UF/DF sequences, the VCR 5, VD 4 sequence was shown to be the one with the most severe fouling but at the same time the most efficient in terms of ash and phytic acid removal. It was also observed that the isolate produced by the VCR 5, VD 4 sequence shows narrower protein solubility profiles around the isoelectric point and higher protein solubility for the pH range of 2 to 4 than isolates produced by alternative UF/DF sequences. This isolate could be considered as a valuable ingredient for the formulation of fruit juice beverages or power juices, considering that the pH of these liquid food products is around 3.5.     

Xanthan Enhances Water Binding and Gel Formation of Transglutaminase-Treated Porcine Myofibrillar Proteins

ABSTRACT: In this study, the effect of xanthan on dynamic rheological properties, textural profile, and water binding of transglutaminase (TG)-treated myofibrillar protein (MP) gels was investigated. In experiment 1, MP suspensions (40 mg/mL protein, 0.6 M NaCl) at pH 6.45 with or without 0.05% xanthan were treated with 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% TG; in experiment 2, MP suspensions (40 mg/mL protein, 0.6 M NaCl) at pHs 6.13, 6.30, 6.45, 6.69 with or without 0.05% xanthan were treated with 0.3% TG. Treated samples were analyzed with differential scanning calorimetry for thermal stability and oscillatory rheometry and Instron penetration tests for gelation properties. The TG treatments lowered the transition temperature (T_m) of MP by as much as 6 °C (P < 0.05) but increased apparent enthalpy of denaturation. However, there was no detectable thermal stability difference between MP samples with or without xanthan. The shear storage modulus (G′) of MP gels increased markedly upon treatments with ≥0.3% TG, and the presence of xanthan further enhanced the gel strength (P < 0.05). The addition of 0.05% xanthan decreased cooking loss of TG-treated MP gels by 17% to 23% when compared with gels without xanthan at all pH levels evaluated (6.13 to 6.67). Thus, the combination of TG and xanthan offered a feasible means to promote cross-linking and gelation of MP while reducing cooking losses.     

Gelation of single heated vs. double heated whey protein isolate

Gelation of single and double heated whey protein dispersions was investigated using Ca²⁺ as inducing agents. Whey protein isolate (WPI) dispersions (10% w/w) were single heated (30 min, 80 °C at pH 7.0) or double heated (30 min, 80 °C at pH 8.0 and 30 min, 80 °C at pH 7.0) and diluted to obtain the desired protein and/or calcium ions concentration (4–9% and 5–30 mm, respectively). Calcium ions were added directly or by using a dialysis method. Double-heated dispersions gelled faster at lower protein and calcium ion concentrations than single-heated dispersions. Gels obtained from double-heated dispersions had lower values of shear strain and shear stress at fracture than gels obtained from single-heated dispersions. Double heating caused a significant complex modulus (G*) increase at 4% WPI and 15 mm calcium ions in comparison with gels obtained from single-heated dispersion. Less significant differences between gels made from double and single-heated dispersions were observed at 6% WPI, however a higher value of complex modulus was obtained for 8% protein gels from the single-heated solution. Native and non-reduced SDS–PAGE did not show clearly the effect of different procedures of heating on the quantities of polymerised proteins. Proteins in double-heated dispersions had higher hydrophobicity. Increased calcium concentration caused decreased protein hydrophobicity for both single and double-heated solutions.     

Increasing nutrient availability of feather meal for ruminants and non‐ruminants using an ammonia pressurisation/depressurisation process

An ammonia pressurisation/depressurisation process (PDA) was evaluated for efficacy in enhancing solubility and digestibility of feather meal (FM) protein. Commercial FM was processed for 5 min with variable ammonia loadings (0.5–2 g g⁻¹ DM), moisture contents (10–50%) and temperatures (75–90 °C). Dry matter and protein solubility were determined in a 0.15 M NaCl solution (6 h, 39 °C) and soluble protein content was determined by the Lowry method. Ruminal solubility was determined by the Kjeldahl method as protein lost in the rumen (1 min) of a cannulated steer. Protein digestibility (crude protein by Kjeldahl analysis) was determined using the in situ dacron bag and pepsin techniques. Protein solubility in the untreated FM was low (13.3 and 7.2%, in NaCl and in rumen fluid, respectively) and increased (p < 0.05) to 39.4 and 23.0%, respectively, in the treated FM at the optimal conditions (50% moisture, 2 g ammonia g⁻¹ dry FM and 90 °C). Ruminal and pepsin protein digestibilities increased (p < 0.05) with increasing moisture content, ammonia loading and temperature. Protein digested in the rumen at 12 h increased from 21.9 (untreated) to 43.0%. Highest digestibility value at 48 h was 54.8%. Pepsin protein digestibility increased (p < 0.05) from 35.4% in the untreated FM to 89.3% in the optimal treatment. Protein solubility in NaCl correlated very well (0.98) with pepsin digestibility. The 3‐fold increase in solubility and 2‐fold increase in digestibility could improve nutrient availability of FM and increase its value as a protein source for both ruminants and non‐ruminants. © 1999 Society of Chemical Industry