STUDIES ON THE DETECTION OF SORBITOL ADDITION IN MILK USING THIN-LAYER CHROMATOGRAPHIC APPROACH
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Date
2022
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Publisher
ICAR-NDRI, KARNAL
Abstract
Milk has long been known as a source of various nutrients essential for a proper growth in
human beings. It is considered as a complete food due to its balanced nutritional value in
terms of energy, protein, carbohydrate, fat, vitamins etc. In order to fulfil the ever-growing
demand of milk, the suppliers have found it profitable to dilute milk with water and then
adjust its SNF/ lactometer reading by addition of cheaper chemicals like urea, cane sugar,
starch, saccharin, polyol (such as sorbitol), gelatin, etc. These chemicals are used for
artificial sweetening, as a source of solid not fat (SNF) and milk fat replacers, etc. Sorbitol
is the emerging adulterant in the recent times. Easy availability, low cost, and nonavailability
of the sensitive methodology for its detection are the major factors which
render it to be used as an adulterant in milk. Industry and academia are already working in
this field and looking for the methodology to detect sorbitol in the presence of other
commonly reported adulterants. In the present study, the copper impregnation time and
solvent system optimization was carried out to resolve sugars and polyols on Cuimpregnated
TLC plates. A TLC method using copper impregnated silica gel 60F plate
(impregnation time of 90 sec), n-propanol: ethyl acetate: water (7:1:2) as solvent system
and 0.5% potassium permanganate in 0.1 M NaOH as the detecting reagent was developed
to detect sorbitol in both aqueous as well as in milk system. The minimum level of
detection of sorbitol was 0.2%. Sorbitol in the Cu-impregnated TLC was detected as the
dark yellow, short streak at the point of application whereas other sugars and polyols were
found to be travelled to different distances from the point of application. The presence of
glucose, lactose, sucrose, mannitol and maltitol did not interfere in the separation behavior
of sorbitol on the standardized TLC methodology both in aqueous as well as milk system.
The standardized method was also found to be effective in detecting the sorbitol in the
presence formalin. The method was found to be suitable to detect sorbitol even in the
presence of urea (0.2, 0.5 and 1%). Developed acidity and neutralization (with 0.1 N
NaOH) of milk did not affect the efficiency of the developed TLC method. The developed
method could also detect the presence of sorbitol in the diluted milk wherein SNF content
was adjusted with sorbitol solution. Finally, the standardized method was applied in the
branded (5) and unbranded (2) market milk samples. Results revealed that all the samples
were negative for the sorbitol. These samples were also tested for sorbitol presence using
color-based test (Karra, 2021) and the results were similar to the findings of developed
TLC method. The advantage of the developed TLC based method was its better detection
limit and specificity even in the presence of neutralizer and urea.