Pendugaan Kandungan Kimia Minyak Goreng Menggunakan Near Infrared Spectroscopy

Abstract

Indonesia menjadi penghasil minyak kelapa sawit terbesar yang berdampak pada perkembangan industri makanan dan rumah tangga. Tingginya kebutuhan akan minyak goreng tidak diimbangi dengan harga yang terjangkau, sehingga pelaku usaha menggunakan minyak goreng berulang kali bahkan hingga menghitam menyebabkan penurunan mutu. Monitoring penurunan mutu minyak goreng pada umumnya dilakukan dengan metode kimia. Metode kimia dianggap kurang praktis, sehingga diperlukan metode alternatif. Near Infrared Spectroscopy (NIRS) dapat menjadi metode alternatif yang lebih cepat dan akurat untuk menguji penurunan mutu minyak goreng dibandingkan dengan metode kimia. Penelitian ini bertujuan untuk memonitoring penurunan mutu minyak goreng yang digunakan berulang menggunakan metode NIRS dengan menentukan pengolahan data spektrum dan jumlah faktor utama terbaik dengan metode Partial Least Square (PLS) pada panjang gelombang 1000 – 2500 nm. Sampel minyak goreng dihasilkan dari 0 – 15 kali proses penggorengan sehingga terdapat variasi mutu pada setiap tahap penggorengan dengan jumlah sampel keseluruhan sebanyak 32 sampel. Bilangan peroksida dan kadar asam lemak bebas dievaluasi sebagai parameter kandungan kimia utama. Data spektrum diolah menggunakan metode normalisasi, Standard Normal Variative (SNV), Multiplicative Scatter Correction (MSC), dan Detrending, kemudian dikalibrasi dengan data kimia menggunakan Partial Least Square (PLS). Nilai terbaik ditentukan berdasarkan pada nilai koefisien korelasi (r), Standard Error of Calibration (SEC) dan Standard Error of Prediction (SEP). Pendugaan terbaik untuk bilangan peroksida menggunakan pretreatment Detrending dengan faktor 7 diperoleh nilai r 0,93, SEC 0,17%, dan SEP 0,16%. Sedangkan untuk pendugaan terbaik kadar asam lemak bebas menggunakan spektrum original dengan faktor 8 diperoleh nilai r 0,94, SEC 0,016%, dan SEP 0,019%. Hasil ini menunjukkan bahwa Near Infrared Spectroscopy (NIRS) dapat digunakan untuk memonitoring penurunan mutu minyak goreng.

Indonesia is the largest producer of palm oil which has an impact on the development of the food and household industries. The high need of cooking oil is not followed by an affordable price. Thus, industries use cooking oil repeatedly, even it turns black, causing a decrease in quality. Cooking oil quality monitoring is generally carried out by chemical methods. Chemical methods are considered less practical, so an alternative method is needed. Near Infrared Spectroscopy (NIRS) can be an alternative method that is faster and more accurate to monitor deterioration of cooking oil quality compared to chemical methods. This study aims to assess NIR spectroscopy for monitoring the quality change of cooking oil that is used repeatly, especially to determine the best spectrum data processing and the number of main factors of partial least square (PLS) for prediction the quality cooking oil. Cooking oil samples were produced from 0 – 15 times in the frying process so that there were variations in quality at each stage of frying with a total sample of 32 samples. Transflectance of cooking oil was measured by FT NIR spectrometer at wavelength of 1000 – 2500 nm. Peroxide number and free fatty acid content as the main chemical content of cooking oil parameters were determined by chemical method. Absorbance spectrum data are processed using some spectra pretreatments such as normalization, Standard Normal Variative (SNV), Multiplicative Scatter Correction (MSC), and Detrending. The best value is determined based on the value of the correlation coefficient (r), standard error of calibration (SEC) and standard error of prediction (SEP). The best prediction of peroxide number was obtained by detrending pretreatment at a PLS factor of 7 with a r value of 0.93, SEC 0.17%, and SEP 0.16%. Meanwhile, for free fatty acid content was original at 8 factor with a r value of 0.94, SEC 0.016%, and SEP 0.019%. This result indicated that NIR spectroscopy can be used to monitor quality change of cooking oil.