A real case study on the physicochemical changes in crude palm oil (<em>Elaeis guineensis</em>) during the deep-frying of <em>akara</em>, traditional cowpea-paste balls, in Brazil

Abstract

The objective of this study was to evaluate the physicochemical changes in crude palm oil during a real case of deep-frying of akara, cowpea-paste balls, fried and sold in the streets of Brazil. Discontinuous frying over five consecutive days, using 5-h frying a day, was performed according to traditional practices. The formation of polar compounds was evaluated by the IUPAC official method and by quick tests based on measures of physical properties, Testo 270 and Fri-check. In addition, 1H-NMR spectroscopy was applied to evaluate physicochemical changes. The results showed that after 15-h frying the total content of polar compounds (TPC) exceeded the limit of 25% established in most of the recommendations and regulations on heated oils. Such a level was reached quickly due to the high content of hydrolytic compounds present in the fresh oil and to the inappropriate use of blends of fresh and used oil in the oil replenishment. The two quick tests presented significantly lower values for TPC than the official method, probably due to the elevated hydrolysis of the fresh oil. In contrast, 1H-NMR results exhibited changes in the fatty acid composition which were similar to those provided by the common GC analysis. The use of crude palm oils of better initial quality and replenishment with fresh oil only are recommended to improve the quality of the oil absorbed by akara.

Physicochemical parameter based estimation of discarding points for frying oil using data interpolation and principal component transformation

“…A few rapid measurements, such as piezoelectric (using sensors) and optical property measurements (Ali, Angyal, Weaver, Rader, & Mossoba, 1996; Xu, Zhu, Yu, Huyan, & Wang, 2018), are not suitable to be conducted at high temperatures; moreover, certain parameters cannot be measured because of the limited detection area of the employed equipment. Other rapid measurement methods such as gas chromatography (GC) separation and liquid chromatography (LC) separation (Ali et al, 1996; Feitosa, Boffo, Batista, Velasco, & Silva, 2019; Fritsche et al, 1998; Zribi et al, 2016) also have limitations in measuring the types of parameters because of the different physical and chemical properties. Moreover, these rapid methods cannot directly measure the parameter values; instead, they compute them through conversion between the characteristic values of the piezoelectric frequency, spectra or chromatograms, and the parameter values.…”