Physico-chemical basis of puffing and microstructure-texture relationships of a puffed crispy snack product

A process was developed for producing a fat-free crispy snack product by drum drying sweetpotato-tapioca pastes (1:1, dry solids ratio) into thin sheets and cutting into 2.6 x 2.6 cm squares. This dry dense half-product was made crispy by puffing 15 s in a high temperature fluidized bed drier at 200Pasting of starch from 13 sweetpotato genotypes including cv. Jewel was studied by measuring apparent viscosity (A method for determining proportion of gelatinized starch in a dry material was developed. DG of starch in the drum dried half product was measured from the amount which dissolved in 0.2N KOH. The dissolved starch was complexed with 0.1 N iodine and quantitated from absorption at 600 nm. DG varied with the initial moisture of slurry (60, 70 & 80%), speed of drum rotation (1, 6 & 11 rpm) and drum surface temperature (100, 110 & 120Puffed product specific volume (SV) was related to starch gelatinization, soluble solids content, initial moisture and how the half-product was prepared. SV was maximum (490% increase) and most uniform (3.94% coef. of variation) when 70% moisture paste was drum dried at 100High correlation was found among structural attributes, of cell size (CS), number of cells per unit area (CN), cell wall thickness (CW) and product SV. High correlations were also found among sensory attributes of crunchiness, hardness and density. The process of making the half-product strongly influenced the puffed product microstructural attributes. When the half-product was prepared the same way, puffing by frying or baking resulted in product with the same microstructural attributes. The method of puffing, whether frying or baking had an significant effect on sensory scores. Structural attributes and sensory scores had low R values. Compression force by Instron had high R values against all sensory attributes and microstructural attributes of CS, CW and SV. Higher compression force values reflected lower values of sensory scores for fried products.