MODEL PENDUGAAN KANDUNGAN AIR, LEMAK DAN ASAM LEMAK BEBAS PADA TIGA PROVENAN BIJI JARAK PAGAR (Jatropha curcas L.) MENGGUNAKAN SPEKTROSKOPI INFRAMERAH DEKAT DENGAN METODE PARTIAL LEAST SQUARE (PLS)

LADY C. E. CH. LENGKEY, I WAYAN BUDIASTRA, KUDANG B. SEMINAR, BAMBANG S. PURWOKO

Abstract


ABSTRAK
Jarak pagar berpotensi sebagai sumber biodiesel karena kandungan
lemak yang tinggi (>40%) dan belum ada penggunaan lainnya.
Spektroskopi (Near Infrared) NIR adalah metode yang cepat untuk
mengukur spektrum sampel dan tidak terdapat limbah kimia. Tujuan
penelitian adalah mengembangkan metode pendugaan komposisi kimia
beberapa  provenan  jarak  pagar  berdasarkan  spektroskopi  NIR
menggunakan kalibrasi PLS. Pengujian dilakukan menggunakan tiga
provenan jarak pagar yaitu IP-3A, IP-3M, dan IP-3P masing-masing 85
sampel. Spektrum reflektansi diukur menggunakan alat NIRFlex Solids
Petri pada panjang gelombang 1000–2500 nm. Sekitar ⅔ jumlah sampel
digunakan untuk mengembangkan persamaan kalibrasi dan ⅓ jumlah
sampel untuk validasi. Pra perlakuan data spektrum dilakukan dengan
normalisasi antara 0-1, turunan pertama Savitzky-Golay 9 titik dan
gabungan keduanya. Hasil penelitian menunjukkan spektroskopi NIR
dapat menduga kadar air, lemak, dan asam lemak bebas . Koefisien
korelasi (r) antara komponen kimia metode acuan dengan dugaan NIR
>0,83 menunjukkan ketepatan model cukup baik (r kadar air=0,96, r kadar
lemak=0,92, dan r ALB=0,89 ). Konsistensi model kalibrasi kadar
air=94,85%, lemak=82,56%, dan ALB=87,80%. Koefisien keragaman
dugaan (Prediction Coeficient Variability/PCV) ketiga model <10%
menunjukkan model yang dibangun cukup handal. Ratio of standard error
prediction to deviation (RPD) menunjukkan metode spektroskopi NIR
dapat digunakan untuk menentukan kadar air (RPD=3,30) dan lemak
(RPD=2,06). Model-model yang dikembangkan secara umum layak
untuk menentukan kadar air dan lemak biji jarak pagar, tetapi belum
optimal untuk penentuan kadar ALB biji jarak pagar.
Kata kunci: NIR , jarak pagar, kadar air, kadar lemak, kadar asam lemak
bebas

ABSTRACT
Physic nut is a potential source of biodiesel. It is high in fat content,
above 40% and has not been usesed for other purposes. Moisture, free fatty
acid, and fat content are the chemical compounds and determinant factor
for physic nut seed quality. The objective of this study was to develop a
method to predict chemical composition of physic nut by NIR
spectroscopy and PLS calibration. The study was conducted using three
provenances of physic nut, i.e. IP-3A, IP-3M, and IP-3P, with 85 samples
each. The wavelengths of near infrared reflectance ranged from 1000 to
2500 nm, and measured by NIR Flex Solids Petri Apparatus.
Approximately ⅔ of total samples were used for developing calibration
equation, while ⅓ of total samples for performing validation. Pre-treatment
of spectrum data was done by applying normalization, first derivative of
Savitzky–Golay 9 points, and as well as their combination. The results
showed that NIR spectroscopy performed acceptable prediction for
moisture and fat content. Correlation coefficients (r) between the reference
method and NIR prediction were 0.96 for moisture content, 0.92 for fat
content, and 0.89 for FFA and the consistency of the model were 94.85%
for moisture content, 82.56% for fat, and 87.80% for FFA. Prediction of
coefficient of variability (PCV) of the three models ≤10 % shows that the
models are reliable. Ratio of standard error prediction to deviation (RPD)
for moisture content has the potential to be used for screening (RPD=3.30)
though the fat content model has rough screening (RPD=2.06).
Key words: NIR, physic nut, moisture, fat, free fatty acid contents.


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DOI: http://dx.doi.org/10.21082/jlittri.v19n4.2013.203-211

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