No abstract

Some physical measurements were applied to silver bananas (Musa paradisiaca) during natural ripening, at room temperature. Changes in fruit weight, fruit diameter and skin thickness were determined, using gravimetric methods and a pachymeter. Both fruit pulp and skin experienced substantial weight loss during ripening. The average of skin thickness was reduced from almost 4.0 mm to 1.5 mm. The results were correlated to the most important chemical changes in the fruit, such as total acidity. starch, reducing and nonreducing sugars and soluble solids.

The water uptake of freeze-dried citrus juices (orange, tangerine and lemon) in powdered form was studied under different relative humidities (13 -98%) at 25°C. The empirical equation proposed previously by Pilosof et al. (1985) to predict water uptake by animal and vegetable proteins and starch materials was tested against the experimental results and good agreement was obtained.

* RESUMONeste trabalho, o uso de hidrocolóides constituídos de pectina (1%), carboximetilcelulose (CMC 0.5%) e amido gelatinizado (5%) adicionados ou não de sacarose (15%) e nitrato de cálcio (0.5%) foi testado com o objetivo de se avaliar a influência destes sistemas sobre os parâmetros de qualidade de melões congelados com diferentes velocidades de resfriamento. Foram avaliados parâmetros tais como sólidos solúveis totais, perda de fluido celular por exsudação e capacidade de retenção de água após o descongelamento. As rupturas do tecido causadas pelo crescimento de cristais de gelo foram visualizadas por fotomicrografias obtidas por microscopia ótica e as disposições dos sistemas de hidrocolóides junto a parede celular puderam ser analisadas por microscopia eletrônica de varredura (SEM) do material congelado e liofilizado. Os parâmetros avaliados e as análises microscópicas da estrutura celular permitiram estabelecer alguns efeitos interativos entre os sistemas de hidrocolóides e a parede celular, responsáveis pela obtenção de estruturas menos danificadas. Estudos histológicos por microscopia ótica permitiram verificar os efeitos das interações sobre a resistência da parede ao rompimento celular. Os tratamentos com sistemas constituídos de amido gelatinizado e pectina, adicionados de sacarose e íons cálcio foram os que apresentaram os melhores resultados na manutenção da estrutura, menor perda de fluido e melhor textura do material descongelado. Os tratamentos com cálcio foram os principais responsáveis pela manutenção da firmeza dos frutos. Palavras-chave: alimentos congelados; qualidade; microestrutura. SUMMARY PRETREATMENT OF MELONS WITH HYDROCOLLOIDS: EFFECT OF THE FREEZING PROCESS ON THE CELL MICROSTRUCTURES.In this research, the use of hydrocolloid constituted of pectin (1%), carboxymethylcellulose (CMC) (0.5%) and gelatinized starch (5%), added to sucrose (15%), was tested to evaluate the influence of these compounds on the quality parameters of frozen melons under various cooling rates. The evaluation parameters were soluble solids, loss of cellular fluid by exsudation and water holding capacity after thawing. Tissue disruption due to ice crystal growth was determined by optical microscopy and the physical distribution of gels on the cell wall was examined by Scanning Electron Microscopy (SEM) on frozen and freeze-dried materials. Evaluation parameters and microscopic analyses of cellular structure, permitted to detect the existence of interactive effects between hydrocolloid systems and the cell wall, which appears responsible for less damaged fruit structures. In addition, histological studies by optical microscopy permitted the verification of a possible increase of the wall resistance. Treatments with pectin and gelatinized starch added of sucrose and calcium ions presented the best results in the maintenance of the structure, minor loss of cellular fluid and better texture of the material after thawing. The treatments with calcium appeared to be responsible for the maintenance of the fruit firmne...

The kinetics of water vapour sorption of drum-dried banana was determined at several conditions of temperature (10, 22, 30 and 40°C) and relative humidity (31-97%). For relative humidities below 7.5% there was a large reduction in sorption rate for a small amount of water absorbed. This type of product presents a very porous structure.