Improving the functional properties of soy glycinin by enzymatic treatment. Adsorption and foaming characteristics

In this contribution we have determined the effect of limited enzymatic hydrolysis on the interfacial (dynamics of adsorption and surface dilatational properties) and foaming (foam formation and stabilization) characteristics of a soy globulin (glycinin, fraction 11S). The degree of hydrolysis (DH=0%, 2%, and 6%), the pH of the aqueous solution (pH=5 and 7), and the protein concentration in solution (at 0.1, 0.5 and 1 wt%) were the variables studied. The temperature and the ionic strength were maintained constant at 20 °C and 0.05 M, respectively. The rate of adsorption and surface dilatational properties (surface dilatational modulus, E, and loss angle) of glycinin at the air–water interface depend on the pH and DH. The adsorption decreased drastically at pH 5.0, close to the isoelectric point of glycinin, because of the existence of a lag period and a low rate of diffusion. The interfacial characteristics of glycinin are much improved by enzymatic treatment, especially in the case of acidic aqueous solutions. Hydrolysates with a low DH have improved functional properties (mainly foaming capacity and foam stability), especially at pH close to the isoelectric point (pI), because the native protein is more difficult to convert into a film at fluid interfaces at pH≈pI. The foam capacity depends on the rate of diffusion of protein to the interface and is much improved by the enzymatic treatment. Foam stability correlates with surface pressure and, to a minor extent, with surface dilatational modulus at long-term adsorption with few exceptions.     

Utilisation of chickpea protein isolates for production of peptides with angiotensin I‐converting enzyme (ACE)‐inhibitory activity

Chickpea protein isolates and the protease alcalase were used for the production of protein hydrolysates that inhibit angiotensin I‐converting enzyme (ACE). The highest degree of inhibition was found in a hydrolysate obtained by 30 min of treatment with alcalase. This hydrolysate was used as starting material for the purification of ACE‐inhibitory peptides. After Biogel P2 gel filtration chromatography and HPLC C₁₈ reverse phase chromatography, four peptides with ACE‐inhibitory activity were purified. Two of them were competitive inhibitors of ACE, while the other two were uncompetitive inhibitors. These results show that chickpea proteins are a good source of ACE‐inhibitory peptides when hydrolysed with the protease alcalase. © 2002 Society of Chemical Industry     

Isolation of Yersinia from raw meat (pork and chicken) and precooked meat (porcine tongues and sausages) collected from commercial establishments in Mexico City

A total of 160 meat product samples were collected from commercial outlets in Mexico City to investigate the presence of different species of Yersinia by the 4 degrees C enrichment method after 1, 3, 5, and 7 days of incubation using alkaline treatment and isolating in cefsulodin-Irgasan-novobiocin and MacConkey agars with Tween 80. Overall, Yersinia spp. were isolated from 27% of the samples analyzed, whereas 40% of the raw and only 13% of the precooked samples were contaminated. Although 2,970 colonies showed Yersinia characteristics, only 706 (24%) actually corresponded to this genus: 49% were Yersinia enterocolitica, 25% Yersinia kristensenii, 15% Yersinia intermedia, 9% Yersinia frederiksenii, and 2% Yersinia aldovae; 10% corresponded to biotype 2, 2% to biotype 3, and 4% to biotype 4. The presence of Yersinia in raw and cooked meat products represents a health risk for consumers in Mexico, where further clinical studies are needed to assess the epidemiological importance of this pathogen.     

Linear viscoelasticity and microstructure of heat-induced crayfish protein isolate gels

Linear dynamic viscoelastic properties have been used to evaluate the influence of heat processing on the microstructure of crayfish protein isolate (CFPI) in order to explore the potentials of crayfish in the production of surimi-like gel products. CFPI dispersions have been subjected to a temperature cycle that consisted of a constant heating rate temperature ramp and a rapid cooling step, following the transitions taking place in the system through the evolution of G′ and G″, under different CFPI concentrations and pH values. The influence of CFPI concentration and pH on linear viscoelasticity functions of CFPI aqueous systems before and after thermal processing has also been analysed. Occurrence of a gel-like behaviour has been found for CFPI dispersions. The mechanical spectra of CFPI gels have revealed a remarkable enhancement in gel strength by thermal processing. An apparent gel network enhancement has also been found by increasing the CFPI content or reducing the pH, excepting at the isoelectric point. The strong dependence of microstructure on pH found for thermally processed CFPI gels has been confirmed by Electron Microscopy.     

Sunflower protein hydrolysates for dietary treatment of patients with liver failure

A method is described to obtain hydrolysates with defined characteristics and a high Fischer ratio for patients with liver failure, using sunflower proteins (globulin fraction-II) as starting material. Protein with a branched chain amino acid (BCAA) concentration of 29.7±1.7% is treated in a first step with immobilized chymotrypsin (raw hydrolysate-1). Subsequent ultrafiltration (cut-off 3 kDa) of the hydrolysate gives sunflower protein hydrolysate-I (SFPH-I). In a second step, SFPH-I is treated with immobilized carboxypeptidase-A at alkaline pH for quasi-selective removal of aromatic amino acids (AAA). This sequential two-step process, followed by size exclusion chromatography on a Sephadex G-15 column, yields a product (SFPH-II) with a BCAA concentration of 37.4±2.2% and an AAA concentration of 0.5±0.1%, which gives a very high Fischer ratio (≈75). The product, comprising mainly peptides with molecular weights in the range of 3500 to 750 Da and free amino acids, is hypoallergenic and shows no or only a trace of bitterness. Any bitterness can be completely removed by treatment with Flavozyme^®, giving a hydrolysate that is composed mainly by tri- and dipeptides and free amino acids, and is termed highly hydrolyzed protein hydrolysate (HHPH). Both SFPH-II and HHPH can be used in enteral, parenteral, and oral nutrition for the treatment of patients with liver failure. This product presents all the conditions required for use in the treatment of patients with liver failure: high content in BCAA and low content in AAA, below 2%, and consequently, a very high Fischer ratio, ≈75.     

Hypocholesterolaemic and antioxidant activities of chickpea (Cicer arietinum L.) protein hydrolysates

BACKGROUND: Some dietary proteins possess biological properties which make them potential ingredients of functional or health‐promoting foods. Many of these properties are attributed to bioactive peptides that can be released by controlled hydrolysis using exogenous proteases. The aim of this work was to test the improvement of hypocholesterolaemic and antioxidant activities of chickpea protein isolate by means of hydrolysis with alcalase and flavourzyme. RESULTS: All hydrolysates tested exhibited better hypocholesterolaemic activity when compared with chickpea protein isolate. The highest cholesterol micellar solubility inhibition (50%) was found after 60 min of treatment with alcalase followed by 30 min of hydrolysis with flavourzyme. To test antioxidant activity of chickpea proteins three methods were used: β‐carotene bleaching method, reducing power and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical‐scavenging effect since antioxidant activity of protein hydrolysates may not be attributed to a single mechanism. Chickpea hydrolysates showed better antioxidant activity in all assays, especially reducing power and DPPH scavenging effect than chickpea protein isolate. CONCLUSION: The results of this study showed the good potential of chickpea protein hydrolysates as bioactive ingredients. The highest bioactive properties could be obtained by selecting the type of proteases and the hydrolysis time. Copyright © 2012 Society of Chemical Industry     

Effect of Alcalase™ on olive pomace protein extraction

The effect of Alcalase^™ treatment on olive pomace protein extraction has been studied. Alcalase improves protein extraction from 5 to 30% of total protein. This improvement is not accompained by an increase in degree of protein hydrolysis, probably because protease activity is inhibited by secondary metabolites and the substrate is highly denatured and resistant to hydrolysis. The increase in protein extraction is attributed to fiber solubilization as a result of secondary activities of Alcalase. Protein extracts with a high content of soluble fiber have improved functional properties, with respect to olive pomace, such as water and oil absorption. Emulsifying and foaming activities were inappreciable. The products obtained represent a suitable source of soluble fiber and protein and may contribute to the improvement of the economic status of olive pomace by-product.     

Factors affecting the in vitro protein digestibility of chickpea albumins

In vitro protein digestibility (IVPD) of chickpea albumins and its possible relationship to their structure and the presence of trypsin inhibitor activity (TIA) have been studied. Trypsin digestion of the albumin fraction under non‐reducing conditions was incomplete, while the reduction of inter‐ and intramolecular disulphide bonds caused an improvement in the accessibility of sites susceptible to trypsin digestion. Trypsin inhibitor activity in the chickpea albumin fraction was dependent upon both temperature and heating time. Although heating the albumin fraction at 100 °C for 30 min reduced the TIA by more than 50% with respect to the initial activity, an important TIA rate was attributable to heat‐resistant trypsin inhibitor. The TIA decrease was not related to an increase in the rate of IVPD. However, we observed a significant (P ≤ 0.05) increment in IVPD in the presence of β‐ME, confirming the essential role of disulphide bonds in stabilising the protein structure of the albumin fraction. © 2000 Society of Chemical Industry     

Production and characterization of an extensive rapeseed protein hydrolysate

Rapeseed protein isolate has been used as starting material for the generation of an extensive protein hydrolysate. Protein hydrolysis was produced by using sequentially an endopeptidase (Alcalase) and an exopeptidase (Flavourzyme). The final hydrolysate has a 60% degree of hydrolysis and was completely soluble between pH values 2.5 and 7. Molecular weight profile of the protein hydrolysate was characterized by gel filtration chromatography. A reduction in protein size was observed during the hydrolysis process with accumulation of small peptides and free amino acids after Flavourzyme digestion. Amino acid composition of fractions with different molecular weights of the final hydrolysate was analyzed. Some of these fractions, enriched or poor in certain amino acids, could be used for supplementation or treatment of determined clinical syndromes.     

Interaction of Lupinus angustifolius L. α and γ conglutins with 13-hydroperoxide-11,9-octadecadienoic acid

Food proteins suffer losses of functional and nutritional value due to reaction with lipid peroxidation products. The seed globulins conglutin α and γ from Lupinus angustifolius L. have been incubated with 13-hydroperoxide-11,9-octadecadienoic acid at pH 9 as a model of the interactions between seed storage proteins and lipid peroxidation products during storage and processing of protein-based products. The incubation lead to fragmentation and/or polymerization of the conglutins as determined by chromatographic and electrophoretic analysis. Losses of tryptophan, methionine, cysteine, proline, valine and leucine were shown by amino acid analysis. In vitro digestibility assays did not show clear differences between the digestibilities of the native conglutins before and after incubation with the hydroperoxide. Nevertheless, it is concluded that reaction with 13-hydroperoxide-11,9-octadecadienoic acid lead to a decrease in the nutritional value of the conglutins because the losses of essential amino acids were substantial. In addition, fragmentation and polymerization reactions most likely have a detrimental effect in the functional properties of the conglutins. These results highlight the deleterious effects that lipid peroxidation products have on products such as protein concentrates, isolates and hydrolysates obtained from lipid-rich seeds.