[4-1015-A] Postharvest/Food Technology and Process Engineering (1)

[4-1015-A-05] Effects of Ultrasound Pretreatments on the Texture and Colour Kinetics of Sweet Potato (Ipomea batatas) during Deep Fat Frying

*Ayobami Olayemi Oladejo¹, Haile Ma², Cunshan Zhou² (1. University of Uyo, Uyo.(Nigeria), 2. Jiangsu University, Zhenjiang(China))

Keywords:frying, ultrasound, kinetics, texture, colour, sweet potato

The effects of ultrasound pretreatment prior to frying on the texture and colour kinetics of deep fat fried sweet potato were investigated. Three different pretreatment methods (UD-ultrasound with distilled water, OD-Osmotic dehydration without ultrasound and UOD-ultrasound assisted osmotic dehydration) and the untreated (control) were employed in the experiment. Pretreated and untreated samples were fried in a deep fat fryer at 130-170 ^oC for 2-10 min. The kinetic models for texture and colour fitted the experimental data with high coefficient of determination (> 0.700). The normalized maximum force (F*) of samples pretreated by UD showed no significant difference with that of the untreated, while samples pretreated by UOD and OD were significantly higher than that of the untreated. The rate of hardening process was significantly enhanced in sweet potato pretreated by UOD and OD during frying. For colour, samples pretreated by UOD showed high lightness (L/L_o), low redness (a/a_o), moderate yellowness (b/b_o) and low total colour difference (ΔE/ΔE_o) compared to other pretreatment methods at 150 ^oC. The rate of formation of lightness and yellowness of fried sweet potato was enhanced in samples pretreated by UOD. The texture and colour kinetics of pretreated and untreated fried samples were temperature dependent and expressed as activation energy. Therefore, ultrasound pretreatment is a good technology that could be applied to positively influence the texture and colour of sweet potato during deep fat frying.