Mônica Elisabeth Torres Prado

Caracterização física, físico-química, enzimática e de parede celular em diferentes estádios de desenvolvimento da fruta de figueira

With the objective of evaluating the physical, physical-chemical, enzymic and cell wall characterization during the different developmental stages of the fig tree fruits under irrigation in Northern Minas Gerais, the present work was developed during the 2001/2002 cropping cycle in the Unidade de Producao Fruticola da Escola Agrotecnica Federal de Salinas (Fruit Growing Unit of the Federal Agrotechnical School of Salinas (Eafsal), town of Salinas. Plants of two years and a half after transplanting and with twelve well developed primary branches (pernadas = the first strong branches of a tree) and 2.5x1.5 m spacing were utilized in this experiment. The design applied was completely randomized with two replicates and a total of 40 marked plants. The data collected were concerning 2001/2002 cropping cycle for the June-pruned plants. Evaluated during the different developmental stages of fig tree fruits activity of the enzimes, chemical composition, physical evaluate, neutral sugars and cell wall components. As polyphenoloxidase and peroxidase activity was decreasing, polygalacturonase activity increased throughout the development of the fruits. The fruits reached harvest point for industry and in natura consumption at 30 and 75 days from the differentiation of the buds in syconium, respectively. A significant increase took place in the contents of total soluble solids, total soluble and reducing sugars during the development of the fruit. Both pH and TTA ranged very little during fruit development. The average diameter of the fruits was always inferior to the average length, reaching 51.99 mm and 59.18 mm, respectively at 75 days. The average weight of 53.23 g was reached at 75 days. Predominating neutral sugars were galactose, arabinose and xylose whereas fucose, mannose and glucose and rhamnose were those present in smaller amount in the cell wall during the different developmental stages of the fruits. With the maturation of the fruits, there was a reduction of the chief components of pectic polysaccharides (galactose, arabinose and rhamnose), whilst the components of the hemicellulose fraction (xylose, glucose and mannose) tended to increase. Cellulose solubilization and fall in the contents of hemicellulose took place from 60 days when the fruit already in the physiological maturity, starts softening process, as related with pectin solubilization by the higher activity of the pectinnemethylesterase and polygalacturonase enzymes.

Microstructural changes of frozen strawberries submitted to pre-treatments with additives and vacuum impregnation

Strawberries were submitted to freezing after pre-treatments with hydrocolloid and calcium salts (pectin and calcium chloride) at different concentrations, in the attempt to establish a correlation of the effects of these substances and their processing, on the physical and microstructural characteristics of fruits after thawing. Strawberry halves were submitted to impregnation with controlled vacuum pressure of 84.4, 50.5 and 16.6 kPa; comprising pectin at concentrations of 0, 1.5 and 3%; with the addition of calcium chloride at concentrations of 0, 3 and 6%; and glucose at 20%, for 4 hours. Measurements were made of the total soluble solid contents, cellular fluid loss, texture and viscosity of the solution, before and after the freezing/thawing. Images of the tissue cuts during the freezing, in function of time, were taken in an optic microscope coupled to a cold-stage and controlled temperature system, where the reduction of the cellular area was quantified using an image analyzing software. The pectin concentration had an influence on and demonstrated a potential for protection of the frozen tissue samples. The photomicrographs showed that the loss of cellular fluid occurs during the growth of ice formed in the intercellular spaces and it is retarded through treatments with high pectin concentrations.

Estabilidade da microestrutura e do teor de carotenóides de pós obtidos da polpa de pequi (Caryocar brasiliense Camb.) liofilizada

In this study, food powders obtained from the freeze-dried pequi (Caryocar brasiliense Camb.) pulps (internal mesocarp) were developed by adding alcohols (ethanol and isopropyl alcohol) in concentrations of 0, 5, and 10% and sugars (sucrose and fructose) in concentrations of 0, 5, and 10%. Microstructure analyses by photonic microscopy of the freeze-dried powders were used to evaluate the degree of crystallization. Color analyses using a Minolta colorimeter and the total carotenoid values using a spectrophotometer were also done. The results show that treatments with a sucrose and ethanol combination presented the formation of crystalline structures and the best preservation of the carotenoid contents. The higher the concentration of the alcohol added in the pre-treatments, the better preserved the caretenoids in the freeze- dried powders became. Treatments with fructose and isopropyl alcohol produced freeze- dried powders that were typically amorphous presenting caking phenomena. Pre-treatments with sucrose and ethanol are the solution to these problems since they are able to produce freeze-dried powders of the pequi pulp with physical chemical and microstructural stability.

Thermal Conductivity Measurements and Predictive Models for Frozen Guava and Passion Fruit Pulps

The thermal conductivity of guava and passion fruit pulps was measured at temperatures between −30°C and their initial freezing temperature using the hot wire probe method. The results were compared with those calculated using the parallel, perpendicular, and Maxwell-Eucken models as a function of the ice fraction, and the discrepancies in the results are discussed. Exponential equations were then fit to the experimental data to determine the thermal conductivity of the pulps as a function of temperature. These equations produce mean relative errors of 8.1 and 4.0% in the values estimated for the guava and passion fruit pulp, respectively.

Non-uniform Heat Transfer During Air-Blast Freezing of a Fruit Pulp Model in Multilayer Boxes

Effective heat transfer coefficients were measured using an aluminum test body and compared with the results obtained from a Gnielinski correlation for air-blast freezing of a fruit pulp model in multilayer boxes, with the internal airflow through rectangular ducts and the hydraulic diameter as characteristic dimensions. The quantities of products inside the boxes were varied, and the inlet air velocities and temperature profiles during freezing were measured. The inlet air velocities were applied in dimensionless Gnielinski correlations to estimate the local heat transfer coefficient values. The experimental and predicted heat transfer coefficient values were used to determine an average convective heat transfer coefficient weighted by the heat transfer area. The results from this methodology were used in an analytically derived procedure for freezing-time estimates and then compared with experimental results. The average effective heat transfer coefficient underestimated freezing times and demonstrated a higher level of accuracy than the Gnielinski correlation when applied to boxes containing smaller product amounts. For experiments with greater quantity of products, the use of average heat transfer coefficients from the Gnielinski correlation yielded errors lower than 20%. Based on boundary layer theory, the Gnielinski correlation can be used to explain the isotherm behaviors observed during freezing. Many of the results satisfy the standards of accuracy used in engineering, and the procedure does not require extra computational effort.

Effect of sucrose and pectin addition on physical, chemical, thermal and rheological properties of frozen/thawed pineapple pulps

Pectin (0–1.0 g/100 mL) and sucrose (0–20 g/100 mL) were added to pineapple pulp to improve their rheological properties, thermal properties and stability after freezing and thawing processes. The properties of the mixes were characterized before and after freezing and thawing. Samples were frozen at −20°C, and the freeze concentration was evaluated every 60 min. The thawing rate was evaluated at 19°C and quantified by photographic editing and image analysis software. The thawing rates and values for the freeze concentration were leveled out at pectin concentrations above 0.5 g/100 mL pectin, which indicated that pectin functions to maintain structural homogeneity during freezing. In the thawed samples, the plastic viscosity values were leveled out from pectin concentrations (0.25–0.75 g/100 mL) as the sucrose concentration increased when compared to unfrozen samples. The differences between the rheological parameters of the unfrozen and frozen/thawed pulps, the higher yield stress values after thawing were attributed to the size of suspended particles in the pulp. Applications can specify formulations of frozen products containing pectin, where these properties can be handled after thawing the product.

Transformações bioquímicas de abacaxi minimamente processado armazenado sob atmosfera modificada

Pineapples minimally processed were, stored eight days (5oC and 85% RH) under passive and active atmosphere (MA). Neutral sugars, cellulose, hemicellulose, and total polyuronide analysis in cell wall were done. Two different active MA were tested: 5% of O2 + 5% of CO2 (MA1) and 2% of O2 + 10% of CO2 (MA2) and one passive MA (Control); during eight days of storage. Pineapples minimally processed stored under active modified atmosphere showed degradation of cell wall and less solubilization of hemicelluloses, besides being more effective in control of ethanol production and formation of off flavours. Pineapples minimally processed stored under modified atmosphere, showed life average of 6 days under refrigeration at 5oC.

Induction of crystallization influences the retention of volatile compounds in freeze-dried marolo pulp

ABSTRACT The effects of sucrose, maltodextrin, and ethanol as prefreezing treatments on the retention of volatile compounds in freeze-dried marolo pulp were evaluated. The volatile compounds were extracted using a solid-phase microextraction technique and investigated by gas chromatography combined with mass spectrometry. The transition temperatures, X-ray diffraction-derived microstructures, particle sizes, and scanning electron microscopy images were examined. The optimum inducer concentrations which produced typically amorphous structures were maltodextrin up to 60.0 g/L and lower ethanol and sucrose concentrations, which were optimized to achieve maximum retention of volatile substances compared with the original fruit pulp.

Rheological behavior and stability of emulsions obtained from Pereskia aculeata Miller via different drying methods

ABSTRACT Hydrocolloid powders from Pereskia aculeata Miller were obtained by using drying in a vacuum oven and freeze-drying at different concentrations (0.5–3.0 g of hydrocolloids/100 g of aqueous phase) to produce oil-in-water emulsions. The rheological characteristics of the emulsions and their microstructures were determined. The freeze-dried hydrocolloids and higher hydrocolloid concentrations resulted in emulsions with higher viscosities. The drying method and hydrocolloid concentration influenced the thixotropic behavior, and the resulting emulsions exhibited shear-thinning behavior. Microstructural analysis showed that with increasing freeze-dried hydrocolloid concentration, the emulsions had droplets with lower average diameters and greater uniformity, suggesting greater system stability.

Avaliação do processo de impregnação a vácuo em melão, utilizando diferentes substâncias

Cortes cilindricos de meloes (Cucumis melo var. inodorus Naudin tipo amarelo) foram submetidos a impregnacao com solucoes de cloreto de calcio (0,5 g.100 mL-1 de solucao), adicionadas de amido gelatinizado (0, 5 e 10 g.100 mL-1 de solucao) e glicose (0, 10 e 20 g.100 mL-1 de solucao), com pressao de vacuo (84,4; 50,5 e 16,6 kPa) controlada. Foram feitas medidas do teor de solidos soluveis totais, perda ou incorporacao de componentes e textura de pedacos dos meloes antes e apos impregnacao a vacuo. As variacoes desses parâmetros foram calculadas em relacao aos do fruto original. Alteracoes na viscosidade das solucoes devido aos processamentos tambem foram quantificadas. A existencia de processos sinergisticos entre os fluxos de solutos do fruto e da solucao pode ser constatada e analisada atraves de superficies de resposta para as diferentes pressoes, em funcao das concentracoes de amido gelatinizado e de glicose nas solucoes. A mobilidade molecular dos componentes do fruto e da solucao em relacao a viscosidade foi discutida.