No abstract

β‐glucan films with different plasticizer concentrations (glycerol and water) were deformed in tension and various mechanical characteristics (modulus of elasticity, yield stress, strength, and strain at rupture point) were evaluated. The influence of both plasticizers was of additive nature describable by the total plasticizer content. The influence is reflected by an exponential decrease of either modulus of elasticity or yield stress with increasing total plasticizer content. The film strength decreased linearly with plasticizer concentration, whereas the decline in strain at the rupture point followed a power function. It was also found that the stress parameters can be expressed via modulus of elasticity: the strength as linear function of the square root of the elasticity modulus and the yield stress as a linear function of the latter parameter. On the basis of such relations a quadratic function between strength and yield stress was proposed. This relation well describes the character of the deformation curves that were obtained at different deformation conditions. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

A new CPEM method was developed and used to study the cooking curves of two potato varieties showing differences in texture and of one variety cultivated in four different regimes. The two main cooking curve stages (i.e., cooking and disintegration) can be described by simple linear equations, with density as an independent parameter. The parameters in the equation describing the cooking stage were reformulated to express directly the role of starch. The two new parameters obtained were weakly correlated and expressed separately cooking time sensitivity to starch content and the basic potato characteristic in relation to sloughing. Data obtained indicate only a minor role of starch content during the first part of cooking that is determined primarily by basic potato characteristics probably related to the cell wall properties. In the second stage of disintegration, starch content plays a more important role.

The new CPEM (cooked potato effective mass) method was used to study the sloughing of a potato variety grown in two successive years in six regimes given by different levels and forms of fertilisation and irrigation. The sloughing process is characterized by the cooking time, i.e. the starting point of disintegration, and by the speed of disintegration. Both parameters are also evaluated in dependence on tuber density in linear models of cooking and disintegration stages. Effects of different cultivation regimes were observed in both stages. The sloughing sensitivity to tuber density expressed via the cooking time seemed to be a relatively stable variety parameter independent of growing conditions. The fertilisation reduced the level of sloughing, i.e. higher cooking time values (P < 0.0023), and at the same time lower disintegration rates (P < 0.006) were indicated for fertilised tubers. No influence of irrigation was observed in our study.

Two cultivars (Nicola and Saturna) largely distinguishing from each other in cooking behaviour and one cultivar (Agria) grown in six different cultivation regimes were tested by the CPEM (cooked potato effective mass) method for the potato sloughing assessment. The sloughing process is characterised by two cooking and disintegration stages, from which two basic CPEM parameters are derived: cooking time as the starting point of disintegration and the rate of the disintegration. Both parameters are analysed as functions of the tuber density in linear models of both stages. Significant differences in CPEM parameters and in the linear models were observed between different varieties. The data from two-year measurements were in basic agreement with our previous concept of the limited contribution of starch in the first cooking stage and of its more important role in the second disintegration stage of sloughing. The results indicated a close association between the mechanisms controlling sloughing and the tuber density in the cultivars Agria and Saturna. A different cooking behaviour was observed in the case of the typical salad cultivar Nicola with a considerably lower cooking time sensitivity to the tuber density.