Application of compression test in analysis of mechanical and color changes in grapefruit juice powder as related to glass transition and water activity

Physicochemical and structural properties of grapefruit juice powder were studied as affected by water activity. Powdered juice was obtained by freeze-drying and equilibrated at different water vapor pressure atmospheres in order to give samples with water activity in the range of 0-084 The mechanical properties of the powder were measured by confined compression tests and the compressed samples, which presented uniform surface and thickness, were subjected to color analysis The maximum force attained during the compression tests and the color coordinates could be quantified with good reproducibility. The results were related to water activity and to glass transition temperature The occurrence of mechanical changes in the powder was shown to precede significant color changes with increasing water activity. Considering the susceptibility to stickiness, the stability limit was observed at T-T(g) approximate to 2 degrees C, with a high degree of mechanical changes being detected at T-Tg 16 degrees C, whereas for significant color changes this critical temperature difference was around 32 degrees CAuthors thank the Ministerio de Educacion y Ciencia and the Fondo Europeo de Desarrollo Regional (FEDER) for the financial support throughout the projects AGL2002-01793 and AGL 200505994. Vania R. N. Tells acknowledges the support of the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) as an external grant (Proc. BEX 4452/06-2).Telis, VRN.; Martínez Navarrete, N. (2010). Application of compression test in analysis of mechanical and color changes in grapefruit juice powder as related to glass transition and water activity. Food Science and Technology. 43(5):744-751. https://doi.org/10.1016/j.lwt.2009.12.007S74475143

Predicting lamp spectrum effects at mesopic levels. Part 2: Preferred appearance and visual acuity

Laboratory tests were carried out to investigate lighting for pedestrians at mesopic levels under lamps of different spectral power distribution. This paper reports an evaluation of lamp spectrum effects on visual acuity, using Landolt ring charts of high and low luminance contrast, and forced choice judgements of the preferred appearance of human hands, a colour array and an illuminated space. These were carried out alongside judgements of brightness reported in a previous paper. Five types of lamp were used, including standard high pressure sodium, two metal halide and a fluorescent lamp of broader spectral distribution and a two-colour solid state device (LED). It was found that lamp spectrum affected judgements of preferred appearance, with the high pressure sodium and LED lamps being considered poor compared with the two metal halide lamps; these results correlated better with the CIE General Colour Rendering Index than other metrics of lamp spectral characteristics. It was also found that acuity was affected by lamp spectral power distribution, with the high pressure sodium (HPS) lamp enabling more Landolt rings to be correctly read than lamps of higher S/P ratio