Stroage and Deffects of Ghee and Butter Oil

The storage temperature of ghee in India ranges from 5 to 38oC depending upon the season of the year and region. Higher temperature of storage (> 30oC)accelerates chemical, particularly oxidative deterioration, whereas, the low storage temperature (< 10oC) though delays the chemical spoilage, it impairs the texture of ghee. At low temperature, ghee becomes greasy and pasty. Best temperature for storage of ghee and butter oil is between 20-30oC. The various defects normally encountered in ghee and their causes are discussed as below:

Acidic: Slight to moderate acidity in ghee, as produced by desi or indigenous method is highly desirable but too much acidity is considered as a defect. Use of raw materials, viz. milk, cream or cooking butter with high acidity along with high initial moisture in ghee is responsible for development of high acidity. This is not a very serious flavour defect.

Curdy: This flavour (referred as defect when pronounced intensity) can be found when cream or butter is undercooked during ghee preparation and all the SNF content (curd) not completely removed. Kachcha ghee prepared under rural conditions by heating makkhan or butter at low fire normally contains curdy and acidic flavour. Sometimes curdy defect resembles to acidic ghee. Ghee packers
normally collect the kachcha ghee having either acidic or curdy flavour and convert it into good ghee by further heat processing.

Smoky: Use of smoky fire, such as of wood/animal dung, for making ghee is responsible for smoky flavour defect in ghee. Storage of ghee under smoky environment may also be responsible for absorption of this flavour. The intensity of this defect, however, decreases on storage.

Burnt: Heating of butterfat, particularly at the last stage of preparation, at a very high temperature (normally at about 125oC and above) is responsible for development of burnt flavour defect in ghee.

Flat or lacking: When there is no flavour in ghee it is criticized as bland or flat or lacking. Butter oil has typically this type of flavour. The use of butter having very low curd content, or maintaining low temperature of heating under vacuum are responsible of producing ghee with flat flavour. This type of ghee, though not completely rejected, but receives lower preferences by consumers.

Rancidity: This is the most serious defect of ghee. It is of two types, viz. hydrolytic and oxidative rancidity. Normally this defect develops in ghee during storage, but in case the raw material used for ghee making is rancid, the freshly prepared ghee will also have this defect. Rancidity in ghee is caused by the formulation of volatile compounds, which exhibit unpleasant odours even when present in small quantities.The nutritive value of ghee is also adversely affected due to rancidity in ghee. Milk fat hydrolysis is faster in liquid state than in solid state. Because of more solid fat in buffalo milk its rate of fat hydrolysis is slower than cow milk fat. Therefore, the cow ghee is more prone to developing rancid flavour during storage.

Hydrolytic rancidity: The fat splitting enzyme, lipoprotein lipase found in milk fat globule membrane, is responsible for hydrolysis of milk fat and production of lower molecular weight fatty acids (butyric, caproic and caprylic). These fatty acids, particularly butyric, impart rancid off flavour in ghee. During manufacture of ghee a very high heat treatment is employed which inactivates the lipase enzyme.Therefore, the hydrolytic rancidity, in ghee is not of much problem, provided raw material of good quality (having no rancidity) is used. Rancid flavour defect is found more commonly in butter oil.

Oxidative rancidity: Oxidation of butterfat (ghee) is a more common problem and caused by oxidation of poly-unsaturated fatty acids in presence of oxygen. The reaction of oxygen with poly-unsaturated fatty acids involves free radical initiation,propagation and termination. In ghee and butter oil the chain reaction is catalyzed by heat, light, ionization reaction and trace metals (copper and iron), etc. The end products of lipid auto-oxidation are ketones, aldehydes, alcohols, hydrocarbons,acids, epoxides, etc.

Greasy texture: Good quality ghee should have well developed and uniformly dispersed ghee grains. Improper storage of ghee, particularly frequent thermal shocks, destroys the granularity of ghee and causes greasiness. Prolonged storage of ghee under refrigeration also leads to developing greasy texture in ghee.

Note: Amongst the above-discussed defects, acidic, curdy, smoky and burnt are normally not encountered in butter oil, whereas flat or lacking is not a common defect of ghee.

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