Texture and in vitro starch digestion kinetics of French fries produced from potatoes (Solanum tuberosum L.) pre-treated with pulsed electric fields
Sze Ying Leong, Rebecca Roberts, Zhihao Hu, Phil Bremer, Patrick Silcock, Stefan Toepfl, Indrawati Oey
Abstract
• Whole and steam-peeled potato tubers were PEF-treated before cutting for French fries making. • French fries from PEF-treated tubers had harder outer crust than French fries without PEF. • The in vitro starch digestion kinetics of French fries varied between cultivars. • PEF pretreatment affected starch digestion kinetics of fries from tubers with dry matter ∼21%. The impact of Pulsed Electric Field (PEF) processing pre-treatment on the texture and kinetics of in vitro starch digestibility of French fries made from two potato cultivars ( Solanum tuberosum L.) containing dry matter content ranging from 19 to 22% was investigated. Whole and steam-peeled potato tubers were treated with a pilot scale PEF unit (electric field strength of 1.1 and 1.9 kV/cm with energy input <10 kJ/kg or ∼50 kJ/kg). This trial was carried out in a commercial French-fry plant using an industrial scale cutter, blancher, fryer and blast-freezer to prepare the frozen par-fried French fry samples. After subsequent final batch frying of the frozen fries, at 180 °C for 3 min to mimic the typical preparation practice at restaurant, retail and household, the outer crust of the fries produced from PEF-treated potatoes was significantly harder (9.4–16.3 N) than crust produced from untreated potatoes (6.9–8.5 N). High intensity (1.9 kV/cm with energy input ∼50 kJ/kg) PEF processing was found to cause defects ( i.e. hollowness in the internal core) in the fries. A fractional conversion model was a good fit for the starch digestion kinetics of all French fry samples during the small intestinal phase (based on standardised INFOGEST static in vitro digestion assay). A lower % of total starch hydrolysis was predicted for French fries produced from high dry matter (>21%) tubers pretreated with PEF at electric field strength of 1.9 kV/cm. The findings generated in this study demonstrate PEF pretreatment may influence the texture of French fries and the extent of starch digestion that occurs.