Monitoring of Moisture Content During Stir-Fried of Green Curry Paste using Near-Infrared Spectroscopy

Abstract

In the instant curry production process, the moisture content of curry paste during stir-frying with oil must be controlled to conserve the authentic flavor. Therefore, the manufacturers require a rapid method, such as near-infrared (NIR) spectroscopy, to determine the moisture content. In this study, the stir-frying of green curry with oil at 90°C was cooked for 3 hours 30 minutes. The stir-fried curry sample was taken every 15 minutes and subsequently scanned with an NIR spectrometer in the range of 950 - 1650 nm at 25°C and then analyzed for moisture content by oven method. Partial least squares (PLS) regression with full-cross validation method was applied to develop the NIR calibration model. A total of ninety samples was randomly selected to be part of the calibration set (N = 70 samples) and validation set (N = 20 samples). The result showed that the moisture content ranged between 14.72 and 53.38%. The NIR spectra region shows the signal peaks at wavelengths of 1210 and 1450 nm which was associated with oil and water, respectively. It is clear that in the 1000 –1450 nm range the absorptivity depends on the amount of water, which was affected by the stir-frying time. With the aids of Standard Normal Variate, a spectral pretreatment method, the PLS model yielded a good prediction of moisture content with correlation coefficient and root mean square error of prediction values of 0.996 and 0.899%, respectively.