Three rice-type popcorns (red, white and yellow) and one pearl-type popcorn (yellow) were used in this study. All types were sized into three fractions (5 < D < 6 mm, 6 < D < 7 mm and D > 7 mm) by screening with round-hole sieves. Samples were tested for popping quality and suitability for popping, and the sensory properties of the popcorns were evaluated. A popcorn popper with a maximum operating temperature of 226°C was used for popping the samples (25 g). Both kernel type and size affected the expansion volume and the number of unpopped kernels. Yellow pearl-type (YPT) and white rice-type (WRT) popcorns showed good popping performance. The popping properties of the smallest-sized kernels were better than those of the other fractions. Popcorn type signi®cantly affected the¯ake size uniformity,¯ake shape uniformity,¯ake colour, crispness and taste of the products. Analysis of variance (ANOVA) and principal component analysis (PCA) showed that that kernel size was of great importance for the expansion volume, which was negatively correlated with number of unpopped kernels, 1000-kernel weight and diameter ratio and positively correlated with¯ake size, kernels per 25 g, crispness and tenderness.

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Response surface methodology was used to evaluate the effects of ingredients on popcorn popping characteristics. The effects of different ingredients on the expansion volume and unpopped kernel ratio of popcorn in a conventional popper and a microwave oven were evaluated and optimized by response surface methodology. The regression models were significant and had R 2 value in the range of 0.919-0.956. The optimum levels of ingredients for microwave popping were 4.4% salt, 5.9% vegetable oil, 0% sodium bicarbonate and 16.4% butter, this formulation giving an expansion volume of 33.1 mL g )1 . In the case of conventional popping, the maximum expansion volume of 37.3 mL g )1 was obtained for 3.5% salt, 6% vegetable oil, 0.10% sodium bicarbonate and 12.9% butter.