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During the manufacturing of food and dairy products, there invariably arises the problem of the utilization of by-products. Due to great as well as unique nutritive value, most of the by-products are utilized as food products. Conversion of by-products into edible food products is profitable and preferable to countries like India which have a variety of food cuisines and food lovers. Milk is indeed the greatest gift given by nature to humans. Each and every component of milk must be processed judicially into edible form. This utilization can not only prove profitable but also prevent environmental pollution. Ghee residue refers to moist charred light to a dark brown residue which obtained on strainer after ghee is filtered. The colour of ghee residue is depending upon the intensity of heat treatment during ghee making. Chemically, it is heat-denatured milk proteins, caramelised lactose and varying amounts of entrapped fat. It has a granular body, glossy exterior due to the presence of free fat and crispy texture. It is used to make chocolate burfi, samosa filling, chapatis, etc.
It contains a considerable amount of milk fat, protein and minerals. It is largely made up of the solid-not-fat (SNF) portion of butter or cream which appears in the form of small particles during ghee processing. Thus, it can be seen clearly that the composition of the residue is influenced by the composition of non-fatty constituents of butter or cream. Further, it may be affected by the process of separation from ghee. Residue obtained from cow milk cream (sweet-unwashed) contains 3.0% water, 62.5% fat, 24.1% protein, 8.2% lactose and 2.2% ash. Fat content is higher in the one prepared from direct cream as compared to that of butter ghee-residue. The shelf life of ghee residue clarified at 110 to 120°C is about 3 months. However, its keeping quality can be increased to about 4 months by packing it properly in a cake form. The average particle diameter of the residue is about 105 microns and the average density is 1.14 g/cm3.
Yield is highly influenced by the percentage of SNF in butter or cream, the process of ghee manufacturing and separation technique applied. Ghee residue obtained from cow milk cream (sweet-unwashed) has an average yield of 12.0 kg per 100 kg butter/cream. The average yield of ghee residue is about 12% by the direct cream method and 3.7% by creamery butter and Desi butter method. As per research, higher the SNF content in raw material, lower the final temperature of clarification, lower the pressure applied in squeezing out surplus fat from the residue, higher the yield and vice versa. Ripening of cream prior to heat clarification tends to decrease the yield of ghee residue.
‘Lipid-Profile’ of the residue
The lipids of ghee-residue have lower Reichert Meissl value and Polenske value (24.4, 1.3) but higher iodine number (43.4) in comparison to those of corresponding ghee (30.1, 1.6, and 33.9 respectively). The lipids of ghee-residue have lesser lower chain fatty acids C4 to C12 (5.3%) and total saturated fatty acids (58.7%) and more of unsaturated fatty acids (41.3%) in comparison to those of ghee (10.1, 66.8, 33.2%, respectively). Irrespective of the method of preparation, PUFA (polyunsaturated fatty acids) content of ghee-residue lipids (4.4%) is higher than those of corresponding ghee (2.8%). The fatty acid composition of phospholipids shows that it has no fatty acids lower than 12 carbon atoms.
Ghee-residue is rich in phospholipids (1-9%). The phospholipid content depends on the method of preparation. These levels are much higher than those in ghee (0.004-0.08%). Due to the polar characteristics, most of the phospholipids remain in it during processing.
Ghee residue is a rich and natural source of flavouring compounds viz. FFA (free fatty acids), carbonyls and lactones. Interestingly, the levels of FFA, carbonyls and lactones in ghee-residue are respectively 11, 10 and 132 times those in ghee.
Ghee residue can be used as a flavour enhancer for vanaspati ghee, ghee and butter oil by adding @ 10% and clarifying (filtering) at 120°C. This treatment has also reported increasing the keeping quality of the product as ghee residue has antioxidant property.
It’s a rich source of nitrogenous compounds, free sugars (from lactose), free sulphydryls and phospholipids. These constituents make ghee residue as a good antioxidant. The antioxidant properties of ghee-residue are affected by the method of preparation. Ghee residue obtained from the creamery butter method has the highest antioxidant properties as compared to others. The overall antioxidant properties are due to both lipid (phospholipids,α-tocopherol and vitamin A) and non-lipid constituents(amino acids, proline, lysine, cysteine hydrochloride and tryptophan). However, the antioxidant properties decrease with increase in temperature of clarification.
Fat recovery process
It is a common practice in most of the dairies to recover fat from the residue. Methods employed for this are as follows:
- Centrifugal process:
It consists of heating in water (65°C). The fat is then recovered by centrifuging the water-fat phase. This method has 46% efficiency (recovering about 25% fat)
2. Pressure technique:
This technique consists of heat treatment (65-70°C) along with a limited pressure in hand screw or hydraulic press. This method has an efficiency of 67% (recovering about 45% fat).
It has a poor quality of protein because of its low lysine content. Supplementing it with skim milk powder can increase its protein efficiency ratio (PER) from 0.66 to 2.4. Ghee residue is produced in large quantity in India but not utilized properly. Most of the dairy plants have not used it profitably except for fat extraction. Every year a huge quantity of this residue goes as waste. A sincere R & D work and strong willingness on the part of the manufacturer is needed to put it in the market place develop its food uses.
- Galhotra, K.K. and Wadhwa, B.K. 1993. Chemistry of ghee-residue, its significance and utilisation – A review. Indian J. Dairy Sci., 46: 142-146.
- Pagote, C.N. and Bhandari, V. 1988. Antioxidant properties and nutritive value of ghee residue. Indian Dairyman, 40
- Shivashraya Singh. 2014. Dairy Technology Volume 2 Dairy Products and Quality Assurance.
- Sukumar De. 2013. Outlines of Dairy Technology.
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