The highest value of aw was found for the AF, and the lowest was found for DPP (Table 2); all were below the limit recommended to control microbial growth, which is 0.6. The AF was darker, reddish and yellowish compared to the EPP and DPP. The EPP had the lower value of L* and higher values of a* and b* compared to the DPP, which indicated a darkening of the product due to the extrusion process. The water absorption index and water solubility index analysis of DPP showed a 76.5% and 99.3% decrease compared to EPP, respectively. Thus, the extrusion significantly increased these
parameters (starch gelatinization). These outcomes are often observed in extruded materials (Day & Swanson, 2013). The micrographs of AF flour indicated that the granules exhibited irregular polygonal shapes with lengths ranging from 2.2 to 3.6 106 m
(Fig. 1A and B), which was different from the values reported in
literature (1e3 106 m). The DPP and EPP can be observed in the
micrographs of Fig. 1C and D, respectively. The grain size of the DPP
starch ranged from 2.3 to 90 106 m, with a predominance of
medium to large granules with irregular oval shape. The starch
granules were intact, and there was a presence of non-starch particles,
which consisted of small pieces of potato peel from processing.
No granular structure was found in the EPP; it consisted of
a compact and solid material resulting from the extrusion.