Vacuum-frying processing technology improves quality attributes of fried sweetpotato chips.

Abstract

Abstract Sweetpotato (Ipomea batatas) is a very important crop in developing countries. Orange-fleshed varieties provide beta-carotene, a key antioxidant and source of provitamin A. However, sweetpotato does not store for a long period unless properly cured; hence the need for processing into shelf-stable forms such as fried snacks. This study investigated the effect of sweetpotato cultivars (EX-OYUNGA, 440216 and SPK 004), type of frying oil (groundnut oil, refined, bleached and deodorized oil (RBDO) and palm oil) and vacuum frying conditions (temperature - 108°C, 122°C and 136°C, vacuum pressure - 6.54 kPa, 13.21 kPa and 19.88 kPa and time - 3 min, 6 min and 9 min) on some quality attributes of fried sweetpotato chips. The response surface methodology technique based on the Box-Behnken design was used to optimize vacuum frying processes and study the effects of the variables on quality of fried chips. Twenty-eight combinations including five replicates of centre points were performed in random order. Seven responses such as oil and moisture content, beta-carotene, texture, lightness, redness and yellowness were considered to evaluate effects of independent variables on sweetpotato chips. Fried sweetpotato chips from optimized vacuum frying conditions were compared with atmospheric fried samples using the concept of equivalent thermal driving force (ETDF). Significant differences (P<0.05) were observed among sweetpotato varieties and frying oil type. EX-OYUNGA and groundnut oil produced chips with acceptable quality attributes. Frying temperature and time as well as vacuum pressure have significant effect on beta-carotene, texture, lightness, redness and yellowness with coefficient of determination (R2) of models for responses investigated varying between 0.7179 and 0.951. The optimized coded vacuum frying conditions for the adopted cultivar (EX-OYUNGA) and frying oil (groundnut oil) were -0.64, 1 and -1 for frying temperature, vacuum pressure and frying time, respectively, based on the desirability concept of 0838. This choice was based on fried chips of lower oil and moisture contents, higher level of beta-carotene retention, lower breaking force, lighter and intense yellow colouration. When the optimized vacuum fried samples were compared with atmospherically fried ones, the former retained about 35% beta-carotene, had improved texture, were lighter and had a more intense golden yellow colour. Hence, vacuum frying could be an alternative for producing more nutritious deep-fat fried sweetpotato chips compared with atmospheric fried samples, the dominant current practice.