Sylvie L. Turgeon

Protein/polysaccharide complexes and coacervates in food systems

Since the pioneering work of Bungenberg de Jong and co-workers on gelatin-acacia gum complex coacervation in the 1920-40s, protein/polysaccharide complexes and coacervates have received increasing research interest in order to broaden the possible food applications. This review focuses on the main research streams followed in this field during the last 12 years regarding: i) the parameters influencing the formation of complexes and coacervates in protein-polysaccharide systems; ii) the characterization of the kinetics of phase separation and multi-scale structure of the complexes and coacervates; and iii) the investigation of the functional properties of complexes and coacervates in food applications. This latter section encompasses various technological aspects, namely: the viscosifying and gelling ability, the foaming and emulsifying ability and finally, the stabilization and release of bioactives or sensitive compounds.

Protein-polysaccharide interactions: phase-ordering kinetics, thermodynamic and structural aspects

Abstract If the most important parameters affecting protein–polysaccharide interactions are now well documented, recent advances concern the structure-building kinetics, thermodynamics and structure of mixtures. As far as complex coacervation is concerned, experimental tools such as light scattering techniques, confocal and electron microscopy and high-sensitivity or isothermal titration calorimetry have brought insights on the molecular structure of the systems and gave access to thermodynamic parameters. These experimental data, combined with intensive numerical simulations on polyelectrolyte systems, are used to build up various models of protein–polysaccharide interaction taking into account both intrinsic and extrinsic parameters. In the case of thermodynamic incompatibility, probing interfaces of phase-separated systems is bringing some insights on the spatial and temporal behavior of such systems. The recent use of w/w emulsion like approach successfully allowed better control of the morphology of segregative phase-separated systems.

Rheology of κ-carrageenan and β-lactoglobulin mixed gels.

Abstract Gel formation and the melting of κ-carrageenan in the presence of β-lactoglobulin were investigated using dynamic rheological techniques as well as a sequence of experimental sweeps of time–temperature, frequency, and strain. The blends, initially prepared at 45°C, show homogeneous mixtures, which then lead to the formation of a gelled κ-carrageenan network containing inclusions of native β-lactoglobulin during the controlled cooling phase from 45 to 20°C. In its native state, the protein seems to weaken the polysaccharide network, particularly when present in high concentration. Upon subsequent heating to 90°C, mixed gels presented a biphasic profile: the first phase, characterized by a decrease in the storage modulus, involves a heat-induced meltdown of the κ-carrageenan network, whereas the second phase, exhibiting an increase in the storage modulus, corresponds to the build up of a protein network. The DSC analysis showed that each biopolymer undergoes specific conformational changes. These results are highly indicative of the lack of association between the biopolymers and suggest a phase separation and gelation in β-lactoglobulin and κ-carrageenan mixtures. The final cooling phase of the mixed gels, from 90 to 20°C, induces a consolidation of the protein network and a gelation of κ-carrageenan. This rheological behaviour suggests that gelation of κ-carrageenan in the presence of a gelled protein network would lead to the formation of a phase-separated bicontinuous network. The strain sweep results for mixed gels obtained at the end of the experiments support that hypothesis.

Structural characterization of laminaran and galactofucan extracted from the brown seaweed Saccharina longicruris.

Brown seaweed contains several polysaccharides like laminaran, fucoidan and alginate. Laminaran is a beta-glucan that has shown anti-apoptotic and anti-tumoral activities, while galactofucan (fucoidan) is a sulfated polysaccharide that has displayed anticoagulant, anti-tumor, anti-thrombosis, anti-inflammatory and antiviral properties. In this study, crude laminaran and galactofucan (fucoidan) were extracted from the brown seaweed Saccharina longicruris at four harvest periods (M05, A05, N05 and J06). The galactofucan M05 and N05 fractions were depolymerized (RDP) over 2 or 4h to give 4 RDP fractions (M05 RDP 2H, M05 RDP 4H, N05 RDP 2H and N05 RDP 4H) whose molecular weights, monosaccharide compositions and glycosidic linkages were determined by GC-MS. The laminaran fraction gave a molecular weight range from 2900 to 3300 Da and contained between 50.6% and 68.6% d-glucose and an average of 1.3% D-mannitol. The presence of a beta-(1,3) linkage between D-glucose in the main chain was observed, with branching at positions 6 and 2. The M05 fraction contained less branching than other laminaran fractions, which might have influenced its conformation in solution and thus its activity. The crude galactofucan fractions displayed a molecular weight range from 638 to 1529 kDa, whereas the RDP fractions had molecular weights <30 kDa. The structure of the galactofucan fractions remained complex after depolymerization, with these also being more sulfated (30-39%) than the crude fractions (13-20%). The crude and RDP fractions contained 3-linked fucopyranose 4-sulfate and 6-linked galactopyranose 3-sulfate moieties, although the galactofucans isolated from M05 and J06 contained less 6-linked galactopyranose 3-sulfate than the A05 and N05 fractions.

Improvement and modification of whey protein gel texture using polysaccharides

Abstract Whey proteins (WP) and polysaccharides are two gelling biopolymers used in the food industry for their wide range of rheological and textural properties. Mixed gels containing more than one gelling agent are usually classified into three types: interpenetrating, coupled, and phase-separated networks. Large deformation behavior of whey protein gels mixed with polysaccharides is presented. pH, and the concentration and nature of the cations added in the system, affect both protein and polysaccharide gels. These factors will also modify the mixing behavior of protein-polysaccharide solutions. The effect of cations and pH are respectively explained using WP/κ-carrageenan and WP/pectin systems. Under the conditions studied, two types of mixed systems were obtained: one with two gelling biopolymers (WP/κ-carrageenan), and the other where protein is the only gelling biopolymer (WP/pectin). Conditions favoring incompatibility can lead to spherical inclusions of whey protein.

Alpha-amylase and alpha-glucosidase inhibition is differentially modulated by fucoidan obtained from Fucus vesiculosus and Ascophyllum nodosum.

Fucoidan is a water-soluble, negatively charged, biologically active polysaccharide found in great abundance in brown marine algae. However, the inhibition of α-amylase and α-glucosidase by fucoidan derived from two algal species (Ascophyllum nodosum and Fucus vesiculosus) harvested at different periods (accounting for seasonal and yearly variations) has never been investigated. It was found that fucoidans inhibited α-glucosidase differently, depending on the algal species from which it was extracted and the algaes season of harvest. Fucoidan extracted from A. nodosum was a more potent inhibitor of α-glucosidase, with an IC50 ranging from 0.013 to 0.047 mg/mL, than the inhibition by fucoidan extracted from F. vesiculosus (IC50=0.049 mg/mL). In contrast, fucoidan extracted from F. vesiculosus did not inhibit α-amylase activity, while fucoidan from A. nodosum decreased α-amylase activity by 7-100% at 5 mg/mL depending upon the algae harvest period. An IC50 of 0.12-4.64 mg/mL for fucoidan from A. nodosum was found for the α-amylase inhibition. The ability of fucoidan to inhibit α-amylase and α-glucosidase thus varies according to the algae species and harvest period. A. nodosum is more suitable than F. vesiculosus as a source of fucoidan to inhibit α-amylase and α-glucosidase activities. Their potential benefits towards Type 2 diabetes management should be further investigated.

Effect of season on the composition of bioactive polysaccharides from the brown seaweed Saccharina longicruris

The structural features of laminarans and galactofucans extracted from the brown seaweed Saccharina longicruris were determined for four harvest periods (M05, A05, N05 and J06). Crude laminarans were purified and crude galactofucans were fractionated using DEAE Sepharose anion exchange chromatography with increasing levels of NaCl (0.5, 1 and 2 M). The results showed differences in terms of their monosaccharide compositions. Purified laminaran contained a high proportion of D-glucose, between 45.1% and 69.1%, with a higher amount in M05 and A05, while the amount of D-mannitol remained constant (less than 1.7%). Crude galactofucans from M05, A05, and N05 contained 19.9-21.5% of sulphates, where J06 had only 14.3%. The 2 M fractionated galactofucans contained a higher proportion of sulphate groups, from 27.1% to 36.9%, for each harvest period, while the 1 M fraction contained 9.2% to 15.9% of sulphates. An important variation in the amount of L-fucose and D-galactose was observed for crude and fractionated galactofucans. In M05, a higher content of L-fucose was observed for crude galactofucans compared to that observed for D-galactose (21.5% vs. 11.1%), whereas the opposite was found for A05 (18.5% vs. 36.6%), N05 (20.9% vs. 36.8%), and J06 (12.8% vs. 19.6%). Also, the 0.5 and 2 M fractions were similar to the crude galactofucans. A05, N05, and J06 contained lower amounts of L-fucose than D-galactose, while the M05 fractions showed the opposite behaviour. However, the 1 M fraction showed a higher amount of L-fucose than D-galactose for each harvest period. The next step will be to study the biological activity of the fractions and to attempt to relate this activity to the structure of the galactofucan and laminaran fractions.

The effects of pH on the rheology of β-lactoglobulin/κ-carrageenan mixed gels

Abstract Gelation and melting of single and mixed systems of 10% β-lactoglobulin and 1% κ-carrageenan have been investigated by small-deformation oscillatory measurements over pH 4–7. For single β-lactoglobulin, it was found that the gelation temperature and the storage modulus of the gels were strongly pH-dependent. However, the rheological behaviour was almost the same; the β-lactoglobulin gels were formed upon first heating from 45 to 90°C, reinforced on cooling to 20°C, and then weakened during reheating steps to 70°C. Single κ-carrageenan systems showed also the same behaviour over pH 4–7; gelation occurred at temperatures below 25°C and the melting took place on reheating above 40°C. In contrast, over this pH range, mixed systems showed two distinct types of behaviour: one over pH 5–7 and the other at pH 4.0. Over pH 5–7, the behaviour of β-lactoglobulin and κ-carrageenan, upon gel formation and melting, can easily be identified in that of the mixed systems, thus suggesting that phase-separated gels were formed. While at pH 4.0, the mixed gel showed a peculiar behaviour, similar to that of the pure protein gel. The presence of κ-carrageenan is only evidenced by the significant enhancement of the protein gel strengths. At this pH, below the protein p I , the electrostatic attractive forces between β-lactoglobulin and κ-carrageenan are important. Therefore, these two biopolymers associated and then formed a mixed gel, with one continuous network structures, similar to that of complex coacervate networks.

Rheology, texture and microstructure of whey proteins/low methoxyl pectins mixed gels with added calcium

Abstract Gelation of a whey protein isolate mixed with various industrial low methoxyl pectins (LMPs) has been investigated. Ratios were adjusted to keep whey protein (WP) concentrations constant at 8%. Pectin and calcium concentrations were fixed at 0.1%, 0.5%, 1.0%, 1.5% and 0, 5, 10 m m , respectively. The pH was adjusted to 6.0. Heat treatment at 80°C was used to induce WP gelation. Heating WP solution mixed with LMP allowed gel formation with lower protein concentration than normally observed; syneresis was also reduced. The type and proportion of pectin, as well as the calcium concentration affected gel hardness. Increasing the amount of pectin and the calcium concentration made mixed gels firmer. White gels were observed indicating aggregation of WPs. The gelation of the mixed systems appeared to have occurred through a phase separation and a competition between biopolymers for the binding of water and calcium.

Stabilization of whey protein isolate-pectin complexes by heat.

Protein-polysaccharide complexes formed under electrostatic associative conditions could have interesting functional properties. However, their stability over a wide range of pH limits their widespread application. The aim of this work was to determine the time-temperature combination required to stabilize whey protein isolate (WPI) and pectin (LMP) complexes formed at pH 4.5 to a further pH adjustment to 7. The effect of storage for 28 days at 4 degrees C was also evaluated. Stability was confirmed by quantification of sugar and nitrogen in each phase after centrifugation. Three heat treatments were performed: 73 degrees C/5 min, 85 degrees C/15 min, and 90 degrees C/2 min. At 73 degrees C/5 min, adjustment to neutral pH led to disruption of WPI-LMP complexes. The most severe heating conditions (85 and 90 degrees C) allowed the stabilization of WPI-LMP complexes. Heated complexes (90 degrees C) could be preserved for up to 28 days of storage at 4 degrees C without affecting their stability.