Jaime Vilela de Resende

Effect of calcium chloride addition on ice cream structure and quality.

The influence of calcium fortification by the addition of calcium chloride on quality parameters of ice cream based on physical properties was investigated, as was the effect of kappa-carrageenan at modifying the effects of this calcium fortification. Four ice cream mixes of conventional composition, with added kappa-carrageenan (0 or 0.025%) and added calcium chloride (0 or 4.4 g L(-1) = 40 mM of added Ca(2+)), were prepared. Modulated temperature-differential scanning calorimetry was used to investigate the effect of calcium chloride on the nucleation temperature, enthalpy of melting, and freezing point depression. The protein composition of 15.4% (wt/wt) reconstituted skim milk powder solutions with or without 4.4 g L(-1) added CaCl(2) and in the supernatant after ultracentrifugation was determined. Fat particle size distributions in ice cream were characterized by light scattering. Ice crystal sizes before and after temperature cycling were determined by cold-stage light microscopy. The results demonstrated that the addition of calcium chloride led to a substantial increase in ice crystal sizes and in fat partial coalescence, which were exacerbated by the addition of kappa-carrageenan. These results can be explained by the interaction between Ca(2+) ions and casein micelles, rather than any effects on freezing point depression. The calcium ions led to a more compact micelle, less serum beta-casein, and high fat destabilization, all of which would be expected to reduce macromolecular structure and volume occupancy in the unfrozen phase, which led to increased rates of ice recrystallization.

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.

Frutos de melão submetidos a pré-tratamentos com hidrocolóides: efeitos do processo de congelamento sobre a microestrutura celular

Neste trabalho, o uso de hidrocoloides constituidos de pectina (1%), carboximetilcelulose (CMC 0.5%) e amido gelatinizado (5%) adicionados ou nao de sacarose (15%) e nitrato de calcio (0.5%) foi testado com o objetivo de se avaliar a influencia destes sistemas sobre os parâmetros de qualidade de meloes congelados com diferentes velocidades de resfriamento. Foram avaliados parâmetros tais como solidos soluveis totais, perda de fluido celular por exsudacao e capacidade de retencao de agua apos o descongelamento. As rupturas do tecido causadas pelo crescimento de cristais de gelo foram visualizadas por fotomicrografias obtidas por microscopia otica e as disposicoes dos sistemas de hidrocoloides junto a parede celular puderam ser analisadas por microscopia eletronica de varredura (SEM) do material congelado e liofilizado. Os parâmetros avaliados e as analises microscopicas da estrutura celular permitiram estabelecer alguns efeitos interativos entre os sistemas de hidrocoloides e a parede celular, responsaveis pela obtencao de estruturas menos danificadas. Estudos histologicos por microscopia otica permitiram verificar os efeitos das interacoes sobre a resistencia da parede ao rompimento celular. Os tratamentos com sistemas constituidos de amido gelatinizado e pectina, adicionados de sacarose e ions calcio foram os que apresentaram os melhores resultados na manutencao da estrutura, menor perda de fluido e melhor textura do material descongelado. Os tratamentos com calcio foram os principais responsaveis pela manutencao da firmeza dos frutos.

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.

Medidas da condutividade térmica efetiva de modelos de polpas de frutas no estado congelado

As propriedades termofisicas de alimentos, necessarias nas simulacoes e calculos do processo de congelamento, incluem principalmente a densidade, condutividade termica e calor especifico. Neste trabalho, as difusividades e condutividades termicas da solucao, usadas como modelo para o congelamento de polpas de frutas, foram medidas pelo metodo da sonda com aquecimento. Os experimentos foram conduzidos na faixa de -25 a 0oC com modelos alimenticios constituidos de 0,5% de K- carrageenan + 10% de sacarose (massa/volume de agua). Modelos estruturais foram usados para as avaliacoes da conducao de calor, combinada com a fracao de gelo predita para as amostras a partir dos modelos de Heldman e foram comparados com os valores das condutividades termicas efetivas medidas. Os modelos estruturais empregados foram: em serie, paralelo e Maxwell-Eucken, com o gelo considerado como a fase dispersa. Em todos os ensaios, o modelo de Maxwell-Eucken apresentou os melhores resultados (erro maximo de 6,13% quando comparado com os valores experimentais medidos) e foi escolhido para a predicao da condutividade termica efetiva de solucoes-modelo de polpas de frutas congeladas. Os valores calculados da condutividade termica foram ajustados em termos de funcoes polinomiais, divididas em quatro faixas de temperatura e podem ser usadas na resolucao dos problemas de transferencia de calor, nos processos de congelamento.

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.

Relação entre o comportamento reológico e a dinâmica do congelamento e descongelamento de polpa de morango adicionada de sacarose e pectina

The physicochemical and rheological properties of strawberry (Fragaria ananassa) pulps with the addition of sucrose (0; 2.91; 10.0; 17.09; 20% weight/weight) and pectin (0; 0.15; 0.50; 0.85; 10% weight/ weight) were characterized. The relationship in rheology, freezing and thawing dynamics and the ice crystal microstructures were established. The characterizations were performed before and after the freezing/thawing process. The samples were frozen in a water-bath at -20 oC, in a stainless steel recipient with a thermal insulation at the bottom to establish the radial heat flow in an infinite cylinder. The ice fractions were calculated using mathematical equations and the polarized concentrations were evaluated at every 60 minutes. The thawing process was assessed by the relationship between time and surface area growing with the thawing process at 19 oC. The strawberry pulp was a pseudoplastic fluid. The pulps showed a sucrose and pectin synergic effect in acid environment and this fact confirmed the variation in the viscosity, thawing rate and freezing front velocity. The thawing process of the strawberries was faster for the higher concentrated samples. The microstructure of strawberry pulps was influenced by the factors studied, increasing the freezing front velocity on the most concentrated samples.

Escoamento de ar através de embalagens de polapa de frutas em caixas comerciais: efeito sobre os perfis de velocidade em túneis de congelamento

The changes in air velocity, as a function of stacking of fruit pulp packages (100g), offering a resistance to air flow in commercial boxes were evaluated and the air flow rates estimated during blast freezing operations. Velocities were initially measured prior to passing the air through the multi-layer stacks of boxes in the chamber. Processing of the data was accomplished by applying a non-linear regression routine. Air flow rates were determined by numerical integration from adjusted air flow velocity profiles and appeared to be 10% higher than those obtained by the traditional procedure. Under constant operating conditions of the fan, the results for the 7-layer arrays of boxed products exhibited a 62% reduction in the flux of chilling air, in relation to the 3-layer arrays, and 50.9% decrease with respect to the 5-layer array. These values were directly proportional to the void space available for air flow.

Evaluation of the adsorption behavior of freeze-dried passion fruit pulp with added carriers by traditional biospeckle laser techniques

ABSTRACT This work was aimed to evaluate the potential of the biospeckle laser technique to monitor the sorption behavior of freeze-dried passion fruit pulp. For this purpose, passion fruit pulp with carriers (sucrose, fructose, maltodextrin, and ethanol) was added at different concentrations and combinations were freeze dried, and their sorption behavior was monitored in environments with relative humidities of 0.113, 0.529, 0.753, and 0.903 by gravimetric and biospeckle laser analyses. The thermal and structural stabilities of the powders were evaluated using differential scanning calorimetry and scanning electron microscopy. The biospeckle laser tool was capable of monitoring the water activity present in the passion fruit powders at relative humidities of 0.113, 0.529, and 0.753. In a relative humidity of 0.113, adsorption was slow, and the speckle pattern was altered regardless of the added carrier. Relative humidities of 0.529 and 0.753 resulted in an adsorption behavior and altered speckle pattern, which were variable, i.e., they were dependent upon the added carriers. At a relative humidity of 0.903, the adsorbed mass of water and alterations in the speckle pattern over time were intense. Ethanol furthered the degree of organization of the structures in the crystallization process. Maltodextrin was effective at stabilizing the passion fruit powders, resulting in poorer water adsorption and increased vitreous transition temperature. Fructose promoted typically amorphous freeze-dried powders, due to the high glass transition temperature and the formation of highly sticky tubular and roundish structure.

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.