MSc

The research programme entitled “Quality assessment of coconut oil and
detection of adulteration” was undertaken at the Department of Plantation Crops and
Spices, College of Agriculture Vellayani during the period 2018-2020. The study was
conducted in order to assess the quality parameters of coconut oil and to detect
adulteration by different techniques and to validate an easy and efficient method for
the detection.
Coconut oil was adulterated with 1, 5, 10, 15, 20 and 30 per cent of palm
kernel oil and mineral oil. Apart from this pure coconut oil, pure palm kernel oil, pure
mineral oil and five branded coconut oils were also collected altogether contributing
twenty samples. These samples were analysed for physical and chemical
characteristics, microbial contamination, thin layer chromatography, fatty acid
composition by GCMS and FTIR spectroscopy to detect adulteration and to find an
easy and efficient method for detection of adulteration.
Physical and chemical characteristics analysed revealed refractive index and
relative density of pure coconut oil, branded coconut oil and coconut oil mixed up to
30 per cent palm kernel oil were within the codex standard range. The apparent
density of pure coconut oil differed significantly from adulterated samples. Insoluble
impurities of all the samples were in the range 0.024-0.047 per cent which was within
the standard prescribed by Codex (< 0.05 per cent). Saponification value of pure
sample and all the branded coconut oil samples showed a value above 250 mg KOH g
of oil-1 which was in tune with standard specified by FSSAI. Palm kernel oil and
mineral oil as adulterant in different percentage showed less than 250 mg KOH g of
oil-1. FSSAI standard for iodine value of coconut oil is in the range 7.5-10g and the
iodine value of pure sample and all the branded coconut oil samples tested were
within the range 7.5-10g. Iodine value of coconut oil adulterated with 5 per cent palm
kernel oil and above exceeded the standard value (10) while adulteration with mineral
oil above 1 per cent showed less than 7.5g. Standard Polenske value as prescribed by
FSSAI and Codex (not less than13) was noticed in all samples except coconut oil with
palm kernel oil 5 per cent and above and all mineral oil combinations. Pure sample,
branded coconut oil and coconut oil mixed with varying percentage of palm kernel oil
had unsaponifiable value within the limit of standards (not more than 1 per cent)
while that of coconut oil mixed with even 1 per cent mineral oil and above exceeded
the limit (1.18 per cent). Acid value of not more than 6 was the standard put forward
by FSSAI and Codex and all oil samples except palm kernel oil and coconut oil mixed
with 15 per cent palm kernel oil and above recorded values above 6. FSSAI standard
for peroxide content in fresh coconut oil is below 10 meq/Kg and higher peroxide
value were obtained from coconut samples mixed with palm kernel oil at 5 per cent
and above and mineral oil at 15 per cent and above. Codex standard for matter volatile
at 105°C is < 0.2% and all samples were within the limit.
Principal component analysis (PCA) performed on physical and chemical
characteristics of oil revealed high coefficient in PC1 for unsaponifiable matter and it
contributed to maximum variation followed by relative density, apparent density,
Polenske value, refractive index, saponification value and iodine value. In PC2, high
coefficient was noticed for acid value followed by peroxide value and iodine value .
Microbial contamination assessed by total plate count was within the APCC
standard of less than 10 (< 10) colony forming units/ml. Fungal and actinomycete
population was however not detected in the oil samples.
Thin layer chromatography revealed yellow streaks in the profile of pure
coconut oil sample, branded coconut oil samples and coconut oil mixed with different
concentrations of palm kernel oil while yellow streaks were absent in coconut oil
samples mixed with mineral oil.
Gas chromatography coupled with mass spectrometry revealed the fatty acid
composition in the oil samples. Principal component analysis carried out to analyze
the variation contributed by the fatty acids revealed C16:0, C 12:0 and C 14:0
contributed the maximum variation in PC1. In PC2 high coefficient was noticed for
C8:0 and C10:0. Percentage of oleic (C18:1) and linoleic (C18:2) acids were found to
increase with increase in concentration of palm kernel oil and fatty acids were not
detected in mineral oil.
FTIR spectra formed peaks at regions of 2800-2900 cm-1, 1743 cm-1, 1465 cm-
1, 1417 cm-1, 1377 cm-1, 1229 cm-1, 1155 cm-1, 1111 cm-1, 962 cm-1, 722 cm-1 in pure
coconut oil sample. Branded coconut oil samples and palm kernel oil adulterated
samples obtained peaks at similar regions. Intensity of the peak at 3006 cm-1 increased
with increasing concentration of palm kernel oil. The peaks for mineral oil were
obtained at 2954 cm-1, 2923 cm-1, 2854cm1, 1466 cm-1, 1378 cm-1 and 721 cm-1.
Intensity of the peaks at 1743 cm-1, 1229 cm-1, 1155 cm-1 and 1111 cm-1 were found
to decrease with increase in percentage of mineral oil which indicated the absence of
carbonyl group in mineral oil.
Economics of adulteration of coconut oil by palm kernel oil and mineral oil
revealed that maximum of Rs 4800/- per quintal was obtained by adulteration when
30 per cent of coconut oil was substituted by mineral oil followed by 20 per cent
mineral oil ( Rs 3200/- per quintal) and 30 per cent palm kernel oil ( Rs 3150/- per
quintal).
The present study implies that among the physical and chemical parameters,
unsaponifiable matter, relative density, apparent density, Polenske value and
refractive index could be used to identify the adulteration in coconut oil by mineral
oil. Similarly thin layer chromatography could also detect the presence of mineral oil.
Saponification value, iodine value and Polenske value could detect the adulteration
due to palm kernel oil. The use of FTIR spectroscopic technique is an easy method to
identify adulteration in coconut oil through identification of specific peaks. GCMS
analysis could provide information about the fatty acid composition.