Model-suspensions rheology : effect of solids concentration and matrix characteristics

Orientador: Rosiane Lopes CunhaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosResumo: A influência das características físicas e químicas do meio dispersante sobre a reologia de suspensões-modelo foi avaliada visando o entendimento do comportamento de sistemas reais como as polpas de frutas. Para isto, o trabalho foi dividido em duas etapas: 1) estudo do efeito da composição de sistemas-modelo de soro de polpas de frutas no comportamento reológico, e 2) estudo de suspensões-modelo de diferentes partículas dispersas em matrizes com diferentes propriedades físicas e químicas. Na primeira etapa, foi verificado o efeito da presença de pectinas de alto e baixo grau de metoxilação, assim como de suas misturas. Os resultados mostraram um efeito sinergístico da mistura destes diferentes tipos de pectinas, devido à maior viscosidade e pseudoplasticidade dos sistemas mistos quando comparados aos sistemas com um único tipo de pectina. Assim, ressaltou-se a importância dos diferentes tipos de ligação no comportamento reológico destes sistemas. A segunda etapa permitiu a compreensão das interações entre partículas e partícula-solvente e a sua influência no comportamento reológico de suspensões-modelo. De um modo geral, as interações entre partículas e partícula-solvente foram maiores nos meios menos viscosos e polares. Tais resultados foram refletidos pelo valor ajustado da fração máxima de empacotamento (fm) por diferentes modelos, dado que foi possível a adição de maior quantidade de sólidos para os sistemas com menos interações. Xantana foi adicionada às matrizes dispersantes para promover pseudoplasticidade, indicando comportamentos distintos quando adicionadas em água pura e em soluções aquosas de glicerina. No primeiro caso, as matrizes apresentaram comportamento altamente pseudoplástico, enquanto que a adição de mesma quantidade de xantana nas soluções aquosas de glicerina levou a um grande aumento na viscosidade, com menor influência no valor do índice de comportamento de escoamento. A adição de sólidos nestes dois tipos de matrizes levou a comportamentos distintos. No primeiro caso verificou-se uma leve desestruturação do sistema, refletido principalmente pela maior influência do módulo complexo com a freqüência e menor variação na viscosidade relativa das suspensões. Por outro lado, o aumento na fração de sólidos nos sistemas compostos com xantana, glicerina e água levou a suspensões mais estruturadas. Assim, os resultados apresentados mostram que além das características das partículas, as propriedades químicas e reológicas da matriz dispersante são essenciais na determinação do comportamento estrutural e de escoamento de suspensões e portanto, não deveriam ser desprezadas pelos modelos existentesAbstract: The influence of the physical and chemical properties of dispersing matrices on the rheological behavior of model-suspensions was evaluated, aiming the understanding of real suspensions such as fruit pulps. The present research was divided into two parts: 1) influence of composition of serum of fruit pulps on their rheological characteristics, through the study of model-systems, and 2) evaluation of model-suspensions of different particles dispersed into matrices with distinct characteristics (physical and chemical). In the first part, the effects of low and high methoxy pectins were evaluated, as well as their mixture. Results indicated a synergistic effect on the mixture of different sorts of pectin, which was observed by the higher viscosity and pseudoplasticity of mixed systems as compared to pure pectin ones. Such results allowed emphasizing the importance of different binding characteristics on the rheological properties of these systems. The second part allowed for the comprehension of interparticle and particle-matrix interactions, and their influence on the rheological behavior of model suspensions. Generally, interactions were more pronounced at low viscous and polar matrices, which reflected the lower maximum packing fraction (fm) fitted by different models. Xanthan was added to dispersing matrices to impart pseudoplasticity, showing distinct behaviors when mixed in pure water and aqueous glycerin solutions. In the first case, matrices showed highly shear thinning behavior, while the addition of the same amount of xanthan in glycerin aqueous solutions promoted a significant increase on viscosity, with lower influence on the flow index behavior (n). Thus, distinct behavior was observed when increasing solids concentration on these two matrices. In the first case, the increase of the dependency of complex modulus with frequency and the lower influence of the relative viscosity reflected a slight loss of structure with solids addition. On the other hand, increasing solids content on systems composed with xanthan, glycerin and water increased structuring. Thus, results indicated that beyond particles characteristics, which have already been widely studied in literature, the knowledge of the chemical and rheological properties of dispersing matrix is of great importance on structural behavior of suspensionsDoutoradoDoutor em Engenharia de Alimento

Influencia do tamanho de particulas no comportamento reologico da polpa de jabuticaba

Orientador : Rosiane Lopes da CunhaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosMestradoEngenharia de AlimentosMestre em Engenharia de Alimento

Structure of gellan gum-hydrolyzed collagen particles : effect of starch addition and coating layer

In this work, we developed biopolymeric structures, based on electrostatic attraction, through dripping gellan gum into hydrolyzed collagen (HC), to deliver hydrophilic compounds. Moreover, we evaluated the influence of starch addition on the polymeric network as well as the coating effects promoted by an outer gellan layer. The lowest tested gellan gum concentration in the core (0.5% w/w) was the best one to build spherical beads, with high retention of bioactives (> 84% for anthocyanin and > 68% for HC). Moreover, the minimum HC concentration (2.5% w/w) in the gelling bath allowed the saturation of active sites of gellan gum presented in the core, as regardless of the HC concentration in the peptide bath, particles presented the same amount of adsorbed peptide. Starch disturbed the interactions between HC and gellan, increasing porosity and pore size, but it presented an important role in retaining anthocyanin in the particles core. Finally, we demonstrated that addition of a gellan coating layer affected the structure of beads: Peptide molecules (positively charged), already adsorbed onto the beads, diffused out of the core, attracted by the negatively charged gellan coating layer. Consequently, it decreased particle size and increased pore size in the outer part of the particles, which was associated with a reduction in the retention of bioactives. These findings bring important contributions to particle engineering: A new process for particle production was proposed, in which hydrogels were produced by dripping the polysaccharide into the protein bath to be externally gelled, without previous crosslinking with salts121394403CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP141112/2018-2; 573913/2008-00535/2018EMU 2009/54137-

Sonication technique to produce emulsions : the impact of ultrasonic power and gelatin concentration

The production of food emulsions has increased the demand for processes, natural emulsifiers and stabilizers that provide reasonable stability. This study approaches the influence of parameters that affect the stability of emulsions produced by sonication, such as ultrasonic power (150, 225 and 375 W) and gelatin concentration, when producing alginate, potato starch and gelatin stabilized emulsions. The results showed that sonication reduced viscosity, surface charge and improved the interfacial properties of biopolymeric solutions. Emulsions presented visual kinetic stabilization after 7 days of storage. The increase of sonication power reduced particle size but increased flocculation. The use of ultrasonic power at 225 and 375 W and gelatin in a concentration above 0.5% resulted in stable emulsions with smaller particle size, which is desirable for its application in food systems52286293FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2007/58017-5; 2009/54137-1; 2011/06083-0; 2015/11984-

Effect of process variables on the osmotic dehydration of star-fruit slices

The objective of this work was to study the effect of blanching and the influence of temperature, solution concentration, and the initial fruit:solution ratio on the osmotic dehydration of star-fruit slices. For blanching, different concentrations of citric and ascorbic acids were studied. The samples immersed in 0.75% citric acid presented little variation in color in relation to the fresh star-fruit. Osmotic dehydration was carried out in an incubator with orbital shaking, controlled temperature, and constant shaking at 120 rpm. The influence of process variables was studied in trials defined by a complete 23 central composite design. In general, water loss and solids gain were positively influenced by temperature and by solution concentration. Nevertheless, lower temperatures reduced water loss throughout the osmotic dehydration process. An increase in the amount of dehydrating solution (initial fruit:solution ratio) slightly influenced the evaluated responses. The process carried out at 50 ºC with a solution concentration of 50% resulted in a product with lower solids gain and greater water loss. Under these conditions, blanching minimized the effect of the osmotic treatment on star-fruit browning, and therefore the blanched fruits showed little variation in color in relation to the fresh fruit

From solvent extraction to the concurrent extraction of lipids and proteins from green coffee: An eco-friendly approach to improve process feasibility

The production of green coffee oil by mechanical pressing of green coffee beans has been precluded by low extraction yields, which generates a protein-rich byproduct (cake) containing variable amounts of lipids. Subsequent utilization of the cake requires the removal of the residual cake oil by solvent extraction. An eco-friendly extraction strategy, using water, enzymes, and mechanical treatments, was evaluated to concurrently extract lipids and proteins from green coffee flour, without the use of harsh solvents. Among the enzymatic treatments evaluated, the use of 0.5% alkaline protease led to higher protein (62.2%) and oil (47.7%) extractability in a shorter time (30 min). This enzymatic treatment was optimized with respect to solids-to-liquid ratio (SLR) (1:17.5-1:7) and concentration of enzyme (0.1-0.9% w/w). Although optimum extraction conditions (1:17.5 SLR and 0.1% enzyme) achieved high protein (70%) and oil (48%) extractability and reduced enzyme use by 80%, a higher water usage was required. Therefore, a two-stage countercurrent extraction was developed to reduce water usage in the process. The countercurrent extraction strategy not only reduced the amount of water used in the process by 60% but promoted higher protein (72%) and oil (58%) extractability, compared with the single-stage process (62.2 and 47.7%, respectively)