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There are various Kreis tests reported in the literature with wide variations in the procedure. The purpose of this paper is to select the most suitable and reliable method for the rancidity evaluation in ghee.

Ghee samples were prepared from butter by the direct cream method. They were assessed for early-stage oxidative deterioration by four Kreis tests in an accelerated storage trial at intervals of 48 h. The amount of ghee samples, amount of reagents (chloroform, 30 percent trichloroacetic acid, 1 percent phloroglucinol, and ethanol), incubation temperature and duration were different in the four tests. For each method, the ghee samples were also monitored for changes in flavor at intervals of 48 h by sensory evaluation. Relationships among the Kreis values determined by the four different Kreis tests and flavor scores were established using a correlation analysis.

The correlation coefficient of the Kreis values determined by different Kreis tests was in decreasing order of: Kreis test-2 (−0.904) > Kreis test-4 (−0.792) > Kreis test-3 (−0.648) > Kreis test-1 (−0.469). Thus, among the four different Kreis tests, Kreis Test-2 reported by Pool and Prater (1945) was found to be more sensitive and more consistent, and have the highest coefficient of correlation (−0.904) with flavor score of ghee during storage at 80±2°C.

The finding of this study will be useful for the selection of an appropriate and reliable Kreis test that can be used for detecting rancidity in ghee at an incipient stage. The development of rancidity in the ghee leads to formation of off-flavor and such an oxidized product is not accepted by the consumer; this leads to economic loss to the manufacturer. Detection of traces of rancidity at an early stage provides an opportunity for industry personnel to take suitable control measures and/or make decisions regarding utilization of the product.

The use of a reliable Kreis test that detects traces of rancidity in a ghee can be very useful for enabling suitable measures to be taken to prevent further oxidative deterioration or to dispose of the ghee as early as possible.

Ghee, anhydrous milk fat, is chemically highly complex in nature. The authentication and characterization of edible fats and oils by routine chemical methods are highly laborious and time consuming. Fourier transform-mid-infrared (FT-MIR) spectroscopy has emerged as a predominant analytical tool in the study of edible fats/oils. However, sufficient attention has not been paid so far to spectral characterization of milk fat obtained from cow and buffalo milk. The purpose of this paper is to fill this void.

Ghee samples were prepared from cow and buffalo milk by the direct cream method. From each type of milk (cow and buffalo), 35 samples of ghee were prepared; thus, in total, 70 samples of ghee were obtained for the study. For assigning absorption bands in the IR spectrum, spectra of cow and buffalo ghee samples were acquired in the MIR region (4,000-650 cm⁻¹).

In FT-MIR spectra of ghee, 14 peaks were obtained at different positions and with varying intensities. They were at 3,005, 2,922, 2,853, 1,744, 1,466, 1,418, 1,377, 1,236, 1,161, 1,114, 1,098, 966, 870 and 721 cm⁻¹ for cow and buffalo ghee with almost equal intensity of absorption.

The finding of this study will be useful for characterization and authentication of ghee.

Application of IR spectral bands of ghee in the MIR region using a FT-infrared spectrometer to monitor the quality of ghee is suggested.