1. Introduction
Palm oil is the utmost consumed vegetable oil worldwide due to its lower production cost, nutrition values, and higher per hectare yield than any other oilseed crop [
1,
2]. Generally, the palm oil produced from oil palm fruits consists of palm kernel and mesocarp fiber. Palm oil’s most outstanding feature is the presence of a saturated and unsaturated fatty acid ratio of 1:1, which is a nutritionally favorable fatty acid content for human consumption [
3]. Palm oil’s relatively high melting point enables it to have widespread application in the food industry. However, crude palm oil (CPO) cannot be consumed directly due to its containing undesirable substances, including free fatty acids (FFAs), gum, color, waxes, phosphate, toxic metal ion, and odoriferous substances [
2,
4]. Thus, there is a call for an effective refining process to remove palm oil’s undesirable impurities. There is also an increasing concern on GE and 3-MCPDE in refined palm oil. The European Food Safety Authority (EFSA) has categorized GE and 3-MCPDE in vegetable oil as genotoxic and carcinogenic, respectively [
4]. However, both GE and 3-MCPDE are found as process contaminates, since these form in vegetable oil during the deodorization process due to the presence of triacylglycerol and diacylglycerol in degummed and bleached palm oil [
5,
6,
7]. Both triacylglycerol and diacylglycerol present in degummed and bleached palm oil react with the chloride at high temperature of the deodorization process, resulting in producing GE and 3-MCPDE in refined palm oil [
4,
7]. Due to the genotoxic nature of GE, the EFSA in 2017 has set the limit of the presence of GE in vegetable oils is ≤1 mg/kg. Subsequently, the GE limit in palm oil has been followed by major food manufacturers companies, including Nestle and Unilever [
3]. The 3-MCPD limits were set by EFSA to be at 2.5 ppm for palm oil and palm oil derivatives in 2018. However, the limits of 3-MCPDE in palm oil would be revised by consumers and are believed to be more stringent in the future [
8].
The refining process of CPO could be conducted physically or chemically [
9,
10]. However, the physical refining process is preferable because of its substantial advantages over the chemical refining process, including higher oil yield, preventing excessive oil loss, minimizing the use of chemicals, and lowering the environmental impact of palm oil processing [
2,
8,
11]. The physical refining process consists of three major processes: degumming, bleaching, and deodorization [
8,
11]. Degumming is the first step of the refining process of palm oil. The bleaching process is needed to extract the color pigments, protein degradation, traces of metal, and catalysts after the hydrogenation process [
7]. The last unit process is the deodorization process. It is needed to eliminate the volatile components or the impurities that cause odor and off-flavor using steam distillation [
8].
Although the formation of GE and 3-MCPDE in palm oil occurred during the deodorization process due to the high-temperature operation, an effective degumming process of the palm oil may minimize 3-MCPDE and GE formation during the deodorization process [
8]. The prime goal of the degumming process is to eliminate gums or phospholipids from the oil. Usually, the crude palm oil extract from oil palm fruits contains phospholipid by about 0.5 to 2 wt% [
9,
12]. Without the degumming of the CPO, the phospholipids may present in the palm oil and interfere with the oil stability and undue darkening during the deodorization process [
13]. Several types of degumming processes have been employed in the physical refining of palm oil, including water degumming, dry degumming, enzymatic degumming, acid degumming, membrane degumming, and EDTA degumming [
12,
13]. Among these degumming processes, acid degumming using a small amount of phosphoric acid (0.05 to 0.1 wt%) is the most utilized degumming process in the palm oil industry [
7]. This is because phosphoric acid is an effective chelating agent, leading to the minimal amount of residual phospholipids in the oil [
14]. It converts the nonhydratable gums into the hydratable form and, therefore, is easy to eliminate. In addition, the distinct characteristics of phosphoric acids as a degumming agent, such as chelating divalent metal ions, efficiency in removing phospholipids, and food grade, make it a preferable degumming agent in the palm oil refining process [
8]. So far, there are a few studies available in the literature on the phosphoric acid degumming process and its impact on GE and 3-MCPDE formation in refined palm oil. Sim et al. [
8] utilized the phosphoric acid degumming process in the physical refining of palm oil. The mitigation of the GE and 3-MCPDE formation obtained were 65% and 80%, respectively, at the optimal refining process of palm oil of 50 °C degumming temperature, 0.31% phosphoric dosage, 3% bleaching earth dosage, and 240 °C of deodorization temperature. Hew et al. [
7] implemented the phosphoric degumming of palm oil to mitigate GE and 3-MCPDE formation in RBD palm oil. The study reported that the formation of GE and 3-MCPDE mitigated significantly at 0.06% of 85% phosphoric acid for 20 min. However, these studies reported that phosphoric acid doses, degumming temperature, and reaction time potentially influence the degumming of the palm oil and the mitigation of the GE and 3-MCPDE formation in RBD palm oil. However, there is limited study in the literature on the optimization of the degumming parameters such as phosphoric acid doses, degumming temperature, and reaction time on the mitigation of GE and 3-MCPDE formation in RBD palm oil.
Many variables may influence the degumming process, and therefore, it requires a quantitative assessment to determine the influence of the variables [
15]. The conventional approach in the influence impact of process variable varies for one variable while other variables remain constant. This conventional approach may neglect the interactions between or among the variable studied in the degumming process. Generally, the design of experiments (DoE) is an effective statistical tool for designing experimental conditions, wherein the Response Surface Methodology (RSM) is an effective mathematical tool for optimizing the experimental conditions of a process. The potential feature of RSM is that it determines the influence of variables with minimal experimental trials. Therefore, studies have utilized the RSM to optimize the process variables and determine the interactions between or among the process variables [
16]. In the present study, RSM was utilized to optimize the phosphoric acid degumming process on the minimal content of GE and 3-MCPDE formation in refined palm oil. The RBD palm oil properties such as free fatty acids (FFAs), color, phosphorous content, peroxide value, and fatty acids compositions were also determined to ensure the refined palm oil quality.
4. Conclusions
In the present study, the phosphoric acid degumming process parameters of CPO were optimized using RSM based on the minimal formation of GE and 3-MCPDE in RBD palm oil. Optimal experimental conditions of the degumming process were determined as follows: reaction time of 30 min, phosphoric acid concentration 0.06 wt%, and temperature of 90 °C. Under this optimal experimental condition of the degumming process, the residual GE and 3-MCPDE concentration in RBD palm oil were 0.61 mg/kg and 0.59 mg/kg, respectively, below the European’s recommended concentration Food Safety Authority. Analyses of the adjusted regression coefficient (R2adj), the regression coefficient (R2), and insignificant lack of fit at 95% confidence reveals that the regression model was adequately fitted with the experimental data. The determination of RBD oil quality, treated with the optimum experimental condition of the degumming process, shows the effective removal of the phosphorus, total chlorine and hydroperoxide content, and FFAs. However, the phosphoric acid degumming process did not alter the properties of the fatty acids in RBD palm oil. Based on the finding of the present study, it can be postulated that phosphoric acid degumming is an effective process in the physical refining of CPO to remove phospholipids and FFAs with mitigating the formation of 3-MCPDE and GE in RBD palm oil and maintaining the nutritional value of the palm oil.