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Cold-set whey protein isolate (WPI) gels formed by sodium or calcium chloride diffusion through dialysis membranes were evaluated by mechanical properties, water-holding capacity and microscopy. The increase of WPI concentration led to a decrease of porosity of the gels and to an increase of hardness, elasticity and water-holding capacity for both systems (CaCl 2 and NaCl). WPI gels formed by calcium chloride addition were harder, more elastic and opaque, but less deformable and with decreased ability to hold water in relation to sodium gels. The non linear part of stress-strain data was evaluated by the Blatz, Sharda, and Tschoegl equation and cold-set gels induced by calcium and sodium chloride addition showed strainweakening and strain-hardening behaviour, respectively. The fractal structure of the gels indicated a weaklink behaviour. For WPI gels results suggest intrafloc links, formed at heating step, which were more rigid than the interfloc links, promoted by salt addition.

Cold-set whey protein (WP) gels with addition of xanthan or guar were evaluated by mechanical properties and scanning electron microscopy. Gels were formed after the addition of different amounts of glucono-δ-lactone to thermally denatured WP solutions, leading to different acidification rates and final pH values. At lower acidification rates and higher final pH, gels showed more discontinuous structure and weaker and less elastic network, which was attributed to a predominance of phase separation during gel formation due to slower gelation kinetics. In contrast, at higher acidification rates and lower final pHs, gelation prevailed over phase separation, favoring the formation of less porous structures, resulting in stronger and more elastic gels. The gels' fractal dimension (D f ; structure complexity) and lacunarity were also influenced by the simultaneous effects of gelation and phase separation. For systems where phase separation was the prevailing mechanism, greater lacunarity parameters were usually observed, describing the heterogeneity of pore distribution, while the opposite occurred at prevailing gelation conditions. Increase in guar concentration or lower final pH of xanthan gels entailed in D f reduction, while the increase in xanthan concentration resulted in higher D f . Such a result suggests that the network contour length was rugged, but this pattern was reduced by the increase of electrostatic interactions among WP and xanthan. Guar addition caused the formation of gel network with smoother surfaces, which could be attributed to the guar-protein excluded volume effects leading to an increase in protein-protein interactions.

The effect of pH and high-pressure homogenization on the properties of oil-in-water (O/W) emulsions stabilized by lecithin and/or whey proteins (WPI) was evaluated. For this purpose, emulsions were characterized by visual analysis, droplet size distribution, zeta potential, electrophoresis, rheological measurements and their response to in vitro digestion. Lecithin emulsions were stable even after 7 days of storage and WPI emulsions were unstable only at pH values close to the isoelectric point (pI) of proteins. Systems containing the mixture of lecithin and WPI showed high kinetic instability at pH 3, which was attributed to the electrostatic interaction between the emulsifiers oppositely charged at this pH value. At pH 5.5 and 7, the mixture led to reduction of the droplet size with enhanced emulsion stability compared to the systems with WPI or lecithin. The stability of WPI emulsions after the addition of lecithin, especially at pH 5.5, was associated with the increase of droplet surface charge density. The in vitro digestion evaluation showed that WPI emulsion was more stable against gastrointestinal conditions.

RESUMO -O fruto do pequizeiro (Caryocar brasiliense Camb.) apresenta considerável variabilidade em suas características físicas e químicas, segundo a região de origem, e pesquisas com frutos procedentes do Estado de Mato Grosso são escassas na literatura. Neste estudo, foram analisadas as características físicas, a composição químico-nutricional e os constituintes voláteis da polpa de pequi coletado em diferentes locais do Estado de Mato Grosso. Os frutos foram analisados quanto à cor (L*, a*, b*, h° e C*), à massa e ao rendimento do mesocarpo externo, pirênios e polpa. Foram determinados a composição centesimal, os teores de carotenoides totais, o perfil de ácidos graxos e de constituintes voláteis da polpa, e analisada a composição físico-química do solo dos locais de coleta.. Constatou-se que o fruto é composto por 80-85% de mesocarpo externo, 11-15% de pirênios e 4-7% de polpa, que é rica em lipídios (46-51g 100g -1 ), carotenoides totais (15-27mg 100g -1 ) -que foram associados à tonalidade e à intensidade da cor (h° e C*) da polpa -e fibra alimentar (8-15g 100g -1 ). Os principais constituintes voláteis da polpa de pequi foram o hexanoato de etila, (E)-β-ocimeno e octanoato de etila. O isobutirato de alila, 3-hexanol, 4-metil-2-pentanol, mirceno, (Z)-di-hidroapofarnesol, β-eudesmol e (E-E) geranilalinalool foram descritos pela primeira vez nos óleos essenciais da polpa de C. brasiliense. Grande parte da variância total dos voláteis foi explicada pelo conjunto de variáveis do solo, destacando-se o silte, o P e o Mg 2+ . Termos para indexação: Pequi, composição centesimal, carotenoides, ácidos graxos, substâncias voláteis. PHYSICAL CHARACTERISTICS, CHEMICAL-NUTRITIONAL COMPOSITION AND ESSENTIAL OILS OF Caryocar brasiliense NATIVE FROM THE STATE OF MATO GROSSOABSTRACT -The fruit of pequi tree (Caryocar brasiliense Camb.) presents a considerable variability in both physical and chemical characteristics, according to the sampling region, and research with fruits collected in the state of Mato Grosso are scarce in the literature. In this study, it was analyzed the physical characteristics, the chemical-nutritional composition, and the volatile compounds of pequi pulp, collected from different places of the state of Mato Grosso. The fruits were analyzed according to color (L*, a*, b*, h° and C*), mass and external mesocarp, seed (pyrenes) and pulp yield. The proximate composition, total carotenoid content, fatty acids profile and volatile compounds of the pulp were determined, and the physicochemical composition of the soil was also analyzed. It was found that the fruit is composed by 80-85% of external mesocarp, 11-15% of pyrenes and 4-7% of pulp, that is rich in lipids (46-51g 100g -1 ), total carotenoids (15-27mg 100g -1 ) -which were related to the color tonality and intensity (h° and C*) of the pulp -and dietary fiber (8-15g 100g -1 ). The main volatile compounds of pequi pulp were ethyl hexanoate, (E)-β-ocimene and ethyl octanoate. The allyl isobutyrate, 3-hexanol, 4-methyl-2-pentanol, myrcene, (Z)-dihydroa...

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Cold-set whey protein isolate gels (7% w/w) were produced by the addition of different amounts of glucono-δ-lactone to thermally denatured protein solutions. After 48 h of incubation at 10 • C, different final pH values were obtained (5.2 to 3.9). The gels were analysed by uniaxial compression measurements, water-holding capacity and protein solubility. The water-holding capacity of the gels decreased at pH values near the pI, this being associated with the lower protein solubility at this pH value. Protein solubility in the presence or absence of denaturing and reducing agents indicated that electrostatic interactions were responsible for the maintenance of the acidified gel structure at pH values from 5.2 to 4.6, but at pH 4.2, more hydrophobic interactions were present in relation to other final gel pHs, in spite of β-lactoglobulin (β-Lg) and BSA being far from their pI values. Complementary PAGE assays showed that disulphide bonds were associated with internal stabilisation of the protein aggregates formed during heat treatment. The mechanical properties of the gels were influenced by the final system pH value, showing that the strongest network was observed at pH 5.2. The results allowed the conclusion that although the interactions amongst the aggregates in the network of cold-set whey protein gels were essentially the same at the pH values evaluated, β-Lg played an important role in gel stabilisation due to its high concentration in WPI, strengthening the structure at its pI and, at the same time, providing good water-retention capacity. whey proteins / glucono-delta-lactone / cold gelation / protein interactions

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