Cynthia Ditchfield

Rheological Properties of Banana Puree at High Temperatures

Abstract The rheological behavior of banana puree was determined using a dynamic stress rheometer with a pressure couette fixture, which allowed experiments to be conducted at high temperature. The pressure couette was pressurized with compressed air to 206.8 kPa (gage pressure) and experiments were carried out at temperatures ranging from 30 to 120°C. The shear stress values ranged from 10 to 170 Pa and the shear rate values from 10−5 to 103 s−1. The model that best fitted the experimental data at all temperatures was the Herschel-Bulkley model. There was a usual tendency for the apparent viscosity to decrease with increasing temperature but an increase in apparent viscosity with increasing from 50 to 60°C and from 110 to 120°C was found. This could be due to interaction of polysaccharides present in banana puree. There was a slight difference between the apparent viscosity values for increasing shear stress sweeps and those for the decreasing shear stress sweeps suggesting time dependency of the rheological behavior. Models were proposed to correlate the parameters of the Herschel-Bulkley model and viscosity with temperature.

EFEITO DA TEMPERATURA DE PASTEURIZAÇÃO NA ESTABILIDADE DE CALDO DE CANA ACIDIFICADO

O tempo de vida util do caldo de cana in natura e bastante limitado em virtude das elevadas taxas de reacoes microbiologicas e enzimaticas que ocorrem na bebida apos a sua extracao. Visando a avaliacao do impacto da temperatura de pasteurizacao na qualidade e na estabilidade de caldo de cana acidificado, processaram-se nove lotes de caldo adicionados de polpa de maracuja. Os lotes foram pasteurizados a 85, 90 e 95 °C por 30 s, em triplicata, envasados assepticamente em garrafas de polietileno tereftalato (PET) e estocados a 7 °C, na ausencia de luz. Testes fisico-quimicos foram realizados para caracterizar a bebida. Determinaram-se as atividades de polifenoloxidase (PPO) e peroxidase (POD) antes e apos o processamento. Contagens de coliformes e analise de Salmonella foram realizadas para garantir a seguranca microbiologica da bebida. Parâmetros de cor foram medidos durante o periodo de estocagem. Cinquenta provadores avaliaram a aparencia, o aroma, o sabor e a aceitacao global da bebida por meio de testes de escala hedonica de sete pontos. A estabilidade sensorial foi estimada considerando-se medias de notas acima de quatro e porcentagens de aceitacao superiores a 60%. As medias dos valores de pH, de solidos soluveis e de acidez titulavel do produto final variaram entre 3,96 e 4,19;19,7 e 20,1 oBrix, e 0,163 e 0,175 g/100g de acido citrico, respectivamente. Os binomios empregados no processamento foram efetivos na inativacao da PPO; entretanto, a completa inativacao da POD foi alcancada apenas pelo tratamento a 95 °C/30 s. A estabilidade sensorial da bebida processada a 85, 90 e 95 °C/30 s foi estimada em 30, 40 e 50 dias, respectivamente. O aumento da temperatura de pasteurizacao impactou positivamente na estabilidade da bebida.

Effect of Pasteurization Temperature on Sensory Stability of an Acidified Sugarcane Juice Beverage

To evaluate the impact of pasteurization temperature on sensory stability of sugarcane juice with passion fruit pulp, nine batches of sugarcane juice with 4 g/100 g passion fruit pulp were processed at (85, 90 and 95)°C for 30s, in triplicate). The pasteurized beverage was aseptically packaged in Polyethylene Terephthalate (PET) bottles and stored at 7°C in the dark. The beverage was characterized by physicochemical tests. Enzymatic activities of Polyphenol Oxidase (PPO) and Peroxidase (POD) were determined before and after processing. Coliforms and Salmonella counts were performed to ensure safety of the beverage safety. Psychrotrophic bacteria and yeasts and molds counts were carried out to assess the microbiological stability. Color parameters were measured in the processed juice throughout the storage period. A team of fifty panelists evaluated the appearance, aroma, flavor, and overall impression of the beverage using seven-point hedonic scale tests. Sensory stability was estimated by considering score averages above four and percentages of acceptance above 60%. The pH, soluble solids and titratable acidity of end product ranged from (3.96 to 4.19), (19.7 to 20.1) oBrix, and (0.163 to 0.175) g/100 g citric acid, respectively. The three processing binomials were effective for PPO inactivation; however, complete POD inactivation was reached at 95 °C/30 s only. Coliforms and Salmonella counts were in compliance with Brazilian Regulations. The estimated sensory shelf-lives for sugarcane juice with passion fruit pulp processed at (85, 90 and 95)°C/30 s were (30, 40 and 50) days, respectively. Thus, the increase of temperature pasteurization had a positive effect on product’s stability.