FULL UNIAXIAL COMPRESSION CURVES FOR PREDICTING SENSORY TEXTURE QUALITY OF COOKED POTATOES

The prediction of six different sensory texture attributes of twenty-seven potato samples based on uniaxial compression curve features and full uniaxial compressions curves is reported. The data set comprised five varieties, sorted in dry matter bins, and sampled at two storage times. The predictions of most of the sensory texture attributes from full compression curves performed better than just using curve features. Furthermore, force-deformation curves are shown to give slightly better predictions than stress-strain curves. For most of the texture attributes better predictions were obtained using uniaxial compression data from raw potato samples as compared to cooked samples. This study is meant to open up a debate on interpreting the information in uniaxial compression curves in relation to sensory texture quality. Multivariate analysis can handle this and can further give insight about where in the curve the information relevant for the predictions of the sensory attributes is found.     

INSTRUMENTAL AND SENSORY CHARACTERIZATION OF COOKED POTATO TEXTURE

Uniaxial compression, Texture Profile Analysis (TPA) and chemical measurements were related to sensory texture evaluation of potato quality during storage. Principal component analysis grouped the varieties into three types of variation: mealiness versus firmness and springiness (PC1), moistness versus adhesiveness (PC2) and hardness versus adhesiveness and moistness (PC3). In uniaxial compression the variable 'stress', 'work up to fracture' and 'total work during compression' described the same type of information in the data. These uniaxial data and most of the TPA data were highly correlated. Uniaxial compression data (stress, strain, modulus of deformability), starch structural data (area, roundness, aspect ratio), specific gravity and pectin methyl esterase activity discriminated between the varieties and harvest times. Partial Least Squares Regression showed stress, strain, modulus of deformability and specific gravity to be the most important variables in distinguishing between two groups of sensory texture attributes explaining 65% of the total variance in the sensory data. Coefficients of correlation between predicted and measured sensory attributes were in the range 0.36–0.79. The TPA data were not found to be relevant substitutions for the sensory attributes.     

Texture and Microstructure of Steam Cooked, Vacuum Packed Potatoes

Uniaxial compression tests combined with light microscopy and scanning electron microscopy were used to study textural properties of vacuum packed, steam cooked (VPS-cooked) potato tubers. Comparisons were made with conventionally water cooked tubers for cooking intervals of 0–60 min. In the VPS-cooked potatoes the gelatinized starch formed dense clusters. In contrast, water cooked cells were filled with gelatinized starch. The textural attributes declined with increased cooking time, faster for water cooked potatoes than for VPS-cooked. After >30 min cooking, firmness of VPS-cooked potatoes increased, while cell separation and disintegration of tissue made the water cooked tubers less firm. Textural properties and cell structure were directly affected by processing conditions.     

DEVELOPMENT OF A SENSORY TEXTURE PROFILE OF COOKED POTATOES BY MULTIVARIATE DATA ANALYSIS

A sensory texture profile of cooked potatoes ( Solanum tuberosum ) was developed through two training periods in 1995 and 1997. Training time necessary to obtain a reliable sensory panel in assessing texture attributes was studied by the use of univariate and multivariate data analysis. The panel was interviewed and introduced to the Texture Profile Method. A list of texture attributes, ranging from non oral terms to terms evaluated after the first bite and the following mastications, was developed resulting in 14 texture attributes, Analysis of variance (ANOVA), discriminant partial least squares regression (DPLSR) and principal component analysis (PCA) was used to reduce the texture profile to 8 reliable sensory attributes covering the geometrical (reflection, mealiness, graininess), mechanical (firmness, hardness, springiness chewiness) and moistness characteristics. These variables explained 89% and 86% of the total variance in 1995 and 1997, respectively. Relevant criteria for studying panel performance are discussed. Training for more than one day did not significantly improve panel performance. Geometrical attributes as well as moistness were found easier to evaluate than the mechanical attributes.     

QUALITY OF PRECOOKED VACUUM-PACKED POTATOES (Solanum tuberosum L.) IN RELATION TO COOKING METHODS AND OXYGEN PERMEABILITY OF THE PACKAGING MATERIAL

Precooked vacuum-packed potatoes are widely used in catering. The influence of different processing temperatures on texture kinetics of water and steam cooked vacuum-packed potatoes was studied. At temperatures above 90C the initial decline in cohesion of steam cooked vacuum-packed potatoes was followed by an increase in cohesion when processed for more than 30 min. Preheating of vacuum-packed potatoes at 70C and 75C increased their cohesion and thereby firmness. Steam cooked vacuum-packed potatoes processed in multilayer barrier pouches having a low oxygen permeability (0.9 cm³/m²/24h/atm) compared with standard pouches had a more intense and stable yellow surface color, as well as they developed significantly less off-flavor after storage. The oxygen permeability of the pouches had no effect on the content of vitamin C, neither during processing nor after storage. The vitamin C content of steam cooked vacuum-packed potatoes was unaffected by processing time.     

The incidence of Clostridium botulinum in Danish trout farms: I. Distribution in fish and their environment

Examination of four Danish trout farms demonstrated the presence of Clostridium botulinum in trout, the wet-fish feed, farm waters, pond muds and invertebrates and in the soil of the area surrounding the farm. The incidence in 530 trout examined varied from 5-100% in winter to 85–100% in late summer. Clostridium botulinum type E was the predominant type found.     

INFLUENCE OF UNIAXIAL COMPRESSION RATE ON RHEOLOGICAL PARAMETERS AND SENSORY TEXTURE PREDICTION OF COOKED POTATOES

The effect of uniaxial compression rate (20–1000 mm/min) on the parameters: Stress (σ_ftrue), strain (ε_fHencky) and work to fracture (W_f), modulus of deformability (E_d), maximum slope before fracture (E_max) and work during 75% compression (W_total) was investigated for ten potato varieties. Multivariate data analysis was used to study the correlation between and within the sensory and nonsensory measurements by Principal Component Analysis (PCA) which showed σ_ftrue, E_max, W_f, and W_total to explain the same type of information in the data, and ε_fHencky versus E_d another type of information in the data. The deformation rate had a large effect on ε_fHencky. Nine sensory texture attributes covering the mechanical, geometrical and moistness attributes were evaluated. Relationships between uniaxial compression data at various deformation rates and the sensory texture attributes were studied by Partial Least Squares Regression (PLSR). A minor effect of deformation rate on the correlation with the sensory texture properties was obtained. Mechanical properties were predicted to a higher extent than the geometrical attributes and moistness. The prediction of the mechanical, geometrical and moistness attributes increased largely by using uniaxial compression supplemented by chemical measures such as dry matter and pectin methylesterase, but here no relevant effect of deformation rate was obtained.