Introduction
Frying with cooking oil is a widespread technique for preparing foods. The frying process degrades oil because it creates a series of chemical reactions, such as hydrolysis and thermo-oxidative degradation, that reduce nutritional contents and form undesirable compounds. Thus, it is essential from both an economic and health perspective for producers and consumers to use oil that is capable of withstanding repeated frying cycles. Many parameters can be used to measure the quality of cooking oil, and the most frequently measured include acidity, peroxides, total polar materials (TPM), and oxidative stability index (OSI). Used cooking oil also has uses in manufacturing, such as being the carbon source in the production of polyhydroxyalkanoates (PHA). This occurs through fermentation in a bioreactor. The current reference methods for both cooking oil quality and reaction monitoring are expensive, time-consuming, and labor-intensive, creating the need for a fast, cheaper alternative for monitoring the parameters of interest. One such method that has been examined is NIR spectroscopy.
Analytes
- Acidity (AV)
- ρ-Anisidine (pAV)
- Total Polar Materials (TPM)
- Peroxide Value (PV)
- Oxidative Stability Index (OSI)
- Biomass
- Used Cooking Oil
- Polyhydroxyalkanoates (PHA)
Summary of Published Papers, Articles, and Reference Materials
Measurement of chemical parameters for quality control purposes has been studied using NIR spectroscopy for cooking oil. One study examined measuring parameters of interest for thermo-oxidative degradation of cooking oil. Numerous reactions take place while cooking oil is used for frying and they are grouped into oxidative, hydrolytic, and thermal degradation. The correlation between calibration models of some parameters used to monitor these reactions and the reference method was good enough to show NIR spectroscopy as a potential replacement for traditional reference tests. Another study examined monitoring a bioreactor producing a PHA using used cooking oil as a carbon source. NIR spectroscopy was used to monitor the fermentation and results were good enough to show it is a suitable method for online monitoring and assistance of bioreactor control.
Scientific References and Statistics
Evolution of Frying Oil Quality Using Fourier Transform Near-Infrared (FT-NIR) Spectroscopy – Calero, Munoz, Perez-Marin, et al., Applied Spectroscopy 2018, Vol. 72(7) 1001-1013
Fourteen types of vegetable oil were used and were subjected to successive frying processes. After each frying, a sample was scanned for NIR spectra, and reference tests were performed for the parameters of interest. Spectra were collected using a transflectance probe from 12500 cm-1 to 4000 cm-1 using 8 cm-1 resolution. Thirty-two scans were collected per spectrum. A total of five hundred sixty-two samples were collected. 80% of the samples were used to build calibration models using the NIR spectra and reference values and 20% were used as a validation test set.
| Acidity (AV) | R² = 0.96 |
| ρ-Anisidine (pAV) | R² = 0.95 |
| Total Polar Materials (TMP) | R² = 0.99 |
| Peroxide Value (PV) | R² = 0.93 |
| Oxidative Stability Index (OSI) | R² = 0.91 |
Correlation coefficients were high for all parameters and validation set predictions proved the validity of the calibration models. Some samples did show chemical anomalies in the reference testing, and before implementing these calibrations in a real-time setting, more such samples will be needed in the models. The study showed the potential to replace traditional methods for monitoring thermo-oxidative degradation in frying oils using NIR spectroscopy.
https://journals.sagepub.com/doi/pdf/10.1177/0003702818764125
Online Monitoring of P(3HB) Produced from Used Cooking Oil with Near-Infrared Spectroscopy – Cruz, Sarraguca, Freitas, et al., Journal of Biotechnology 194(2015) 1-9
Polyhydroxyalkanoates (PHA) are polyesters produced in nature by numerous microorganisms, including through bacterial fermentation of sugar or lipids. The simplest and most commonly occurring form is the fermentative production of poly-3-hydroxybutyrate (P3HB). There is high interest in the creation of PHA-based materials on an industrial scale because they are biodegradable while having properties of plastics as well as a way to create plastics from non-fossil fuel sources. Oil containing feedstocks are used as alternative substrates to glucose and sucrose for PHA production because high conversion yields can be obtained. Used cooking oil is one option for the substrate. A batch reactor was operated producing P(3HB) using used cooking oil as the sole carbon source. NIR spectroscopy was used for online monitoring of the fermentation. Spectra were collected using a transflectance probe from 10000 cm-1 to 4000 cm-1. Resolution was 8 cm-1 and sixteen scans were collected and averaged per spectrum. Samples were pulled from the reactor and reference tests were performed for Biomass, Used Cooking Oil (UCO), and Polyhydroxyalkanoates (PHA).
| Biomass | R² = 0.86 |
| Used Cooking Oil (UCO) | R² = 0.96 |
| Polyhydroxyalkanoates (PHA) | R² = 0.78 |
The results prove the feasibility of using NIR spectroscopy and calibration models as an on-line monitoring tool for Biomass, UCO, and PHA. This study was the first to successfully use NIR as a method for monitoring these specific parameters in a bioreactor. Further work will be needed for full implementation of the method but it was validated as a way to estimate these three important parameters with no significant analytical, operational costs.
https://www.sciencedirect.com/science/article/pii/S0168165614010207