Response surface methodology (RSM) was used to analyse the effect of temperature, screw speed, and feed moisture content on physicochemical properties of quinoa extrudates. A three-level, three-variable, Box-Behnken design of experiments was used. The experiments were run at 16-24% feed moisture content, 130-170°C temperature, and 250-500 rpm screw speed with a fixed feed rate of 300 g/min. Second order polynomials were used to model the extruder response and extrudate properties as a function of process variables. Responses were most affected by changes in feed moisture content and temperature, and to a lesser extent by screw speed. Calculated specific mechanical energy (SME) values ranged between 170-402 kJ/kg which were lower than those observed for other cereals, most likely due to high (7.2%) fat content of quinoa. High levels of feed moisture alone, and in combination with high temperature, resulted in poor expansion. The best product, characterised by maximum expansion, minimum density, high degree of gelatinization and low water solubility index, was obtained at 16% feed moisture content, 130°C die temperature, and 375 rpm screw speed, which corresponds to high SME input. It was demonstrated that the pseudo-cereal quinoa can be used to make novel, healthy, extruded, snack-type food products.

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This article focuses on developing a psychophysical model for sensory crispness and understanding the role of structure and phase behavior of the food polymer matrix in terms of affecting crispness. The core hypothesis of the article is that the number peaks during brittle fracture of food foams is the stimulus for crispness. Accurate mechanical methods were developed to count the peaks and then relate them to sensory crispness scores utilizing magnitude estimation. An excellent correlation was obtained with data that was generated in three independent sets of measurements. Finally, models describing the relationship between structure, mechanical signatures and sensory crispness of extruded cellular foods were developed. PRACTICAL APPLICATIONS Texture is one of the most important quality attributes of food products. The fracture properties of the foods have to be clearly understood, because they are one the most important manifestations of texture. Understanding the fracture process in‐depth can help increase consumer acceptability by generating structures leading a particular breakdown behavior, because the sensory attributes like crispness are directly related to how the fracture occurs in solid food foams. The psychophysical model developed in this study will serve as a very useful tool for assessing the effects of changes in formulation and processing that result in a wide range of structural features leading to the desired crisp sensation in the final product.

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This paper focuses on understanding the role of structural parameters and starch crystallization on the toughness of cake samples. Accurate mechanical measurements were performed to obtain toughness values, and these were related to structural parameters obtained from image analyses. Three-dimensional skeletons of food samples were generated by using X-ray tomography technique. The structural parameters (cell diameter, cell wall thickness, thickness to radius ratio (t/R), fragmentation index) were obtained after processing of the images with CTan software. The basic hypothesis of the paper is to show that the structural parameter t/R is a determinant for predicting toughness, which is a critical indicator of freshness. Freshness in cakes and other baked products is a leading factor in consumer perception. For this purpose three different cake formulations were stored at 37 and 50 °C. Cycling from these temperatures to lower storage temperatures of 25 and 4 °C was done to accelerate the starch retrogradation rate. Experimental results indicated that there was a strong interrelationship between morphological structure and the mechanical properties with regression coefficients of 0.68 and 0.95. Starch retrogradation, which was followed by X-ray diffractometry, was found to be directly proportional to toughness values, where the percent relative crystallinity increased with storage temperature.