Low-Temperature Domestic Deep-Frying of Soybean-Cake Tempe in Vegetable Cooking Oils: How Many Times Are Stable to Use?

Abstract

Tempe has gained global popularity, with local vegetable oils commonly used for frying. This study evaluates the cooking temperature and stability of five vegetable oils (olive [Oo], palm [Po], canola [Cnlo], sunflower [Sfo], and coconut [Cco]) for deep-frying Tempe, using acid and peroxide values (AV and PV), antiradical activity, and saturated and unsaturated fatty acids. AV, PV, and linolenic acid (LNA) were referenced to international standards for vegetable oil (0.6 mg KOH/g, 10 mEq of oxygen/kg oil, and 2% for AV, PV, LNA respectively). The initial oil temperature was 130°C ± 1°C, with final temperatures between 145.7°C ± 6.8°C at the lowest and 156.8°C ± 13.0°C at the highest, well below existing studies (≥170°C–250°C). Based on AV and PV, Oo, Po, and Cco were stable up to the fourth, fifth, and eighth frying repeat (FR). The PV of Cnlo (10.2 mEq of oxygen/kg oil) and Sfo (15.5 mEq of oxygen/kg oil) exceeded the maximum limit after one use. The Fresh Cnlo LNA (7.35%) was higher than the limit, while the rest of the oils remained lower and stable until the seventh FR. Po exhibited the highest average antiradical activity (85.42% ± 4.63%), followed by Oo (31.01% ± 10.26%), Sfo (27.96% ± 9.67%), Cnlo (21.85% ± 5.71%), and Cco (14.40% ± 3.46%). Cco had the highest saturated fatty acids (SFA), Oo had the highest monounsaturated fatty acids (MUFA), and Sfo had the highest polyunsaturated fatty acids (PUFA). No significant SFA, MUFA, or PUFA changes were observed up to the seventh FR. Trans-fatty acids C18:1n 9T and C18:2n 6T were undetected in fresh and used oil, indicating a unique character in low-temperature deep-frying in domestic settings. This study provides a comprehensive analysis of low-temperature deep-frying of Tempe. It suggests that Oo, Po, Cnlo, Sfo, and Cco were stable to deep-fried Tempe for four, five, zero, one, and eight FR, respectively. Deep-frying Tempe at lower temperatures and for a shorter duration may enhance its health benefits and help retain its flavor.”