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Consumers' preference for products with reduced levels of fat increased in the last years. Proteins and polysaccharides have an important role due to their functional and interaction properties because, when combined in ratios and pH of higher potential for electrostatic interactions they may act as emulsifiers or stabilizers. This study evaluated the ultrasound impact on the electrostatic interaction between pectin (PEC) and whey protein concentrate (WPC) at different WPC:PEC ratios (1:1 to 5:1), and its effect on the emulsification and stability of emulsions formulated with WPC:PEC blends (1:1, 4:1) at low soybean oil contents (5 to 15%). Zeta potential analysis showed greater interactions between biopolymers at pH 3.5, which was proven in FTIR spectra. Rheology and turbidimetry showed that the ultrasound reduced the suspension viscosity and the size of the biopolymer complexes. Suspensions were Newtonian, whereas the emulsions showed shear-thinning behavior with slight increase in apparent viscosity as a function of oil content, and remained stable for seven days, with small droplets (<8 μm) stabilized and entrapped in a pectin network evidenced by confocal laser microscopy. Sonication was successfully applied to emulsion stabilization, improving the functional properties of WPC:PEC blends and enabling their application as low-fat systems, providing healthier products to consumers.

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ObstractThis study aimed at characterizing the soy protein isolate and high-methoxyl pectin biopolymers individually, and the complexes formed by both at different proportions and pHs in order to find the most suitable pH and biopolymer ratios to food application as stabilizers. The biopolymers were evaluated through solubility, charges, turbidimetry, and optical microscopy analyses; the systems with the pair of biopolymers were analyzed through turbidimetry and optical microscopy. High-methoxyl pectin showed high solubility at all pHs investigated. The soy protein isolate showed low solubility at pH 4.5, which is close to its isoelectric point, and complete solubility at pH 11.0. The formation of complexes suggested an attractive interaction between the biopolymers, with high absorbance reading values and images of complexes from optical microscopy. These complexes were present in systems with pHs below the soy protein isolate's isoelectric point, with positive charges; the high-methoxyl pectin, however, had negative ones.

Considering the importance of texture for food products, we aimed to evaluate viscosity of different liquid and semisolid materials through instrumental analyses (rheometer and texture analyzer), as well sensory descriptive analysis, and establishing correlations between all these analyses. Eight materials were used: water, strawberry yogurt, condensed milk, honey, UHT cream, creamy dairy dessert, petit suisse strawberry flavor (a traditional French cheese from Normandy region, and sold as an infant product), and dulce de leche (obtained through cooking of a can of condensed milk, during 15 min under pressure, resulting in a brownish color product and more consistent than condensed milk). All materials were submitted to rheological analysis, analysis on texture analyzer, and descriptive sensory analysis. All techniques of measurement discriminated the texture of samples. The visual viscosity, defined as a sensory attribute evaluated by visual observation, was negatively correlated to apparent viscosity measured through rheological analysis with shear rate at 10 s . Oral viscosity and body (both defined as sensory attributes evaluated by oral perception) were positively correlated with areas from graphs obtained in the texture analyzer, and with apparent viscosity measured through rheological analysis at shear rate of 10 s , although positive strong correlation was also found between body and apparent viscosity at higher shear rates (50 and 100 s ). The strong correlations enable application of these instrumental tests as indicators of the sensory texture of liquid and semisolid materials. PRACTICAL APPLICATIONS: Texture has a minor importance to liquid and semisolid materials in comparison to meat and crunchy products. However, the relevance of texture to these kinds of products has growing up recently. Therefore, measuring and understanding viscosity of liquid and semisolid materials, using different ways of evaluation, brings relevant information to the area. Moreover, establishing correlations between instrumental and sensory analyses may indicate which instrumental analysis and which analysis condition would be more adequate to correlate with sensory perception of texture, allowing a convergence for future studies and for discussion of results.

The effect of heat-moisture treatment on structural, physicochemical, and rheological characteristics of arrowroot starch was investigated. Heat-moisture treatment was performed with starch samples conditioned to 28% moisture at 100 ℃ for 2, 4, 8, and 16 h. Structural and physicochemical characterization of native and modified starches, as well as rheological assays with gels of native and 4 h modified starches subjected to acid and sterilization stresses were performed. Arrowroot starch had 23.1% of amylose and a CA-type crystalline pattern that changed over the treatment time to A-type. Modified starches had higher pasting temperature and lower peak viscosity while breakdown viscosity practically disappeared, independently of the treatment time. Gelatinization temperature and crystallinity increased, while enthalpy, swelling power, and solubility decreased with the treatment. Gels from modified starches, independently of the stress conditions, were found to have more stable apparent viscosities and higher G' and G″ than gels from native starch. Heat-moisture treatment caused a reorganization of starch chains that increased molecular interactions. This increase resulted in higher paste stability and strengthened gels that showed higher resistance to shearing and heat, even after acid or sterilization conditions. A treatment time of 4 h was enough to deeply changing the physicochemical properties of starch.

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RESUMOProteínas e polissacarídeos estão presentes em conjunto em muitos tipos de sistemas alimentícios e ambos contribuem para a estrutura, textura e estabilidade através de seu comportamento espessante ou gelificante ou de sua atividade de superfície. Misturas de proteínas e polissacarídeos são interessantes, pois o comportamento reológico das misturas pode diferir bastante do comportamento dos compostos puros. Além disso, a aplicação de ultrassom de alta intensidade com o objetivo de alterar propriedades funcionais dos biopolímeros também vem sendo estudada. O objetivo do trabalho foi avaliar a interação eletrostática do par concentrado proteico de soro de leite e pectina de alto teor de metoxilação em função da razão proteína:polissacarídeo com e sem a aplicação de ultrassom, buscando identificar as microestruturas formadas por meio de reologia, microscopia ótica e avaliação visual no pH 3,5. O modelo Lei da Potência ajustou-se bem aos dados (R 2 =0,9) e o par apresentou comportamento pseudoplástico (n<1) tendendo ao Newtoniano (n=0,9), o índice de consistência (K) diminuiu com o aumento da proporção de proteína. A avaliação visual indicou o tipo de interação denominada miscibilidade, pois não foi constatado separação de fases. A microscopia ótica confirmou os dados com a ausência de formação de complexos para todos os pares avaliados e, como na reologia, constatou que a aplicação de ultrassom ocasionou a diminuição de tamanho das partículas, mesmo as soluções sendo aparentemente diluídas.