Raw cassava starch, having 74.94 and 0.44 g/100 g resistant starch type II and III (RS II and RS III), respectively, was autoclaved at 121 degrees C in water, 1, 10 or 100 mmol/L lactic acid. The formation of RS III was evaluated in relation to variable incubation temperature (-20 to 100 degrees C), incubation time (6-48 h) and autoclaving time (15-90 min). Negligible to low quantities of RS III (0.59-2.42 g/100 g) were formed from autoclaved starch suspended in 100 mmol/L lactic acid, whereas intermediate to high quantities (2:68-9.97 g/100 g) were formed from autoclaved starch suspended in water, I or 10 mmol/L lactic acid, except for treatments with water or 10 mmol/L lactic acid incubated at 100 degrees C for 6 h (1.74 g/100 g). Autoclaving times corresponding to maximum RS III contents were 15 and 45 min for water and 10 mmol/L lactic acid, respectively. Whereas, the RS III fractions from cassava starch suspended in water had melt transitions between 158 and 175 degrees C with low endothermic enthalpies (0.2-1.6 J/g), the thermal transitions of the acid treated samples were indistinct. (c) 2006 Elsevier Ltd. All rights reserved.