Comparative appraisal of Kreis methods for the assessment of incipient rancidity in ghee

Purpose 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. Design/methodology/approach 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. Findings 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. Practical implications 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. Originality/value 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.

A STUDY OF METHODS FOR ASSESSING RANCIDITY IN LARD

Lard from 26 sources was stored in glass jars at 26.7 °C (80° F) until definitely rancid. Spoilage was evaluated at two-week intervals by chemical tests and odour ratings. Correlation coefficients between odour scores and the logarithms of chemical test values were: iodometric peroxide, −.90; alpha-dicarbonyl test, −.85; Stamm test −.82; Kreis test −.81; ferrometric peroxide, −.80; fluorescence,.79; free fatty acids, −.10. Association between chemical measurements was greatest between alpha-dicarbonyl and iodometric peroxide values (r = 97). As peroxides are not thermostable, the measurement of the stable alpha-dicarbonyl compounds, although less precise, is considered the best available chemical method for assessing rancidity.