BY-PRODUCTS TECHNOLOGY

Module 7. Ghee-residue

Lesson 45
GHEE-RESIDUE AND ITS CHARACTERISTICS

45.1 Introduction

Ghee-residue is the by-product of ghee manufacturing industry. It is partially charred (burnt) light to dark brown and moist residue that is obtained on the cloth strainer after the ghee is filtered. During the manufacture of ghee, the solids not fat (SNF) present in cream or butter appears in the form of small particles known as ghee-residue. It is obtained after molten ghee has been either strained out with bag filters or muslin cloth or separated by continuous centrifugal clarifiers. The yield of ghee-residue varies with the method of preparation of ghee. This is due to the variation in the non-fatty serum constituents of the different raw materials used for the preparation of ghee. The average yield of ghee-residue is maximum in direct creamery (DC) method (12%) followed by about 3.7% yield in creamery butter (CB) and desi butter (DB) method. Ghee-residue, particularly one obtained from creamery-butter, has higher content of phospholipids 17.39% of its total fat. Higher phospholipids (a good emulsifier) content of ghee-residue is beneficial in developing certain products where emulsification of fat and aqueous phase is desired. Keeping quality of all types of GR clarified at 120°C is 3 months. Its shelf life can further be increased to more than 4 months by pressing it in cake form.

45.2 Physico-chemical and Functional Properties of Ghee-Residue

Depending on the intensity of the heat treatment used during the ghee manufacture, colour of ghee-residue (GR) may vary from light to dark brown. It has smooth to granular texture with glossy exterior due to the presence of excessive free fat. The average particle diameter of ghee-residue is about 105 microns and average density is 1.14 g/cm³.

45.2.1 Chemical composition

There are considerable variations in the chemical composition of ghee-residue (Table 45.1) depending upon the method of preparation of ghee. The approximate composition (%) of ghee-residue varies as fat (32-70), protein (12-39), moisture (8-30), lactose (2-14) and ash (1-8). Moisture, protein and ash contents are more in CB and DB ghee-residue than in DC ghee-residues. Fat content is higher in DC residues than in butter ghee-residue. Lactose content is highest in DB followed by DC and CB ghee-residues. Thus ghee-residue is a rich source of lipids, proteins and carbohydrates.

Table 45.1 Chemical composition and yield of ghee-residue (Hand pressed)

45.2.1.1 Lipids in ghee-residue

The lipids of ghee-residue have lower Reichert Meissl value and Polenske value (24.4, 1.3) but higher iodine value (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 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 of ghee-residue is dependent upon the method of preparation. It is highest in CB ghee-residue lipids (17.39%) followed by DB ghee-residue lipids (4.95%) and the least in DC ghee-residue lipids (1.57%). These levels are much higher than those in ghee (0.004-0.08%). Phospholipid acts synergistically with reducing substances in ghee-residue and protects it from oxidative defect. The phopholipid content of ghee-residue decreases as the period of heating increases due to the transfer of phospholipids from ghee-residue to ghee. While heating cream/butter, only a small fraction of the phospholipids get transferred to ghee, most of the phospholipids remain with the residue because of their polar character. The differences observed in the physico-chemical constant, fatty acids and PUFA contents between lipids of ghee-residue and ghee are due to the high phospholipid content of ghee-residue.

45.2.1.2 Proteins in ghee-residue

Soluble nitrogen content of ghee-residue prepared from cream or creamery butter decreases with heating time. This decrease is due to the denaturation of almost all the proteins. The total reducing capacity expressed as mg of cysteine hydrochloride/g of CB ghee-residue (26.0) and free sulphydryl content (µm/g) of ghee-residue (2.90) are much higher than those in ghee (0.075 and 0.02, respectively). These substances are liberated from protein during heat treatment and because of their polar nature are mostly retained in the ghee-residue. Whey proteins, especially ß-lactoglobulin are the main source for these sulphydryl compounds.

45.2.1.3 Milk sugars in ghee-residue

Main sugars (wt %) in ghee-residue prepared at 120°C are lactose (76.6), galactose (14.1), glucose (5.3), and two more unidentified spots, one at the origin (4.0) and second of faster mobility. As the period of heating is increased, the lactose content of ghee-residue decreases with a corresponding increase in galactose and glucose content. The unidentified spots are also found to increase as the period of heating is increased. The unidentified spots might be due to some of the breakdown products or sugar fragments formed during browning or caramelization reactions.

45.2.2 Flavouring properties

Ghee residue is also a rich and natural source of flavour compounds viz. FFA, carbonyls and lactones. The level of FFA, carbonyls and lactones in ghee-residue are respectively 11, 10 and 132 times those in ghee as shown in Table 45.2.

Ghee flavour can be induced in vanaspati and butter oil etc. by adding 10% ghee-residue and clarification at 120°C/flash (10%). This treatment also enhances their keeping quality because of the antioxidant property of ghee-residue. Further, ghee, especially prepared from fresh creamery-butter (without ripening) has mild flavour. GR can be used to enhance flavour in such ghee. Creamery butter is mixed thoroughly with ghee-residue (10%) and clarified at 120°C, filtered through 4-fold of muslin cloth and subsequently centrifuged to get ghee with enhanced flavour.

Table 45.2 Flavour potential of ghee and ghee-residue

45.2.3 Antioxidant properties

Ghee-residue is a rich source of natural antioxidants. It is rich in phospholipids and nitrogenous compounds, which contribute towards its antioxidant properties. Other constituents discharging the same function include free amino acid and reducing substances like free sulphydryls from denatured proteins and free sugars from lactose. The antioxidant properties of ghee-residue are affected by method of preparation. CB ghee-residue has the maximum antioxidant properties followed by DB and DC ghee-residues. The overall antioxidant properties are due to both lipid and non-lipid constituents. In lipid constituent of ghee-residue, phospholipids show the maximum antioxidant activity followed by α-tocopherol and vitamin A. Among the various phospholipid fractions, cephalin shows the greatest antioxidant activity. The oxidative stability of ghee can be increased by increasing its phospholipid content to 0.1% either through heat treatment process or through solvent extraction process. It has been observed that heating ghee-residue with ghee in the ratio of 1:4 at 130°C have maximum transfer of phospholipids from ghee-residue to ghee. These antioxidant concentrates can be added to ghee to give about 0.1% phospholipids so as to increase the keeping quality of ghee.

Among the non-lipid constituents, the amino acids, proline, lysine, cysteine hydrochloride and tryptophan show the antioxidant properties. Further, the addition of lactose, glucose, galactose and their interaction products with protein and phospholipids to ghee also increase the oxidative stability of ghee. As ghee-residue contains large amount of reducing substances including free sulphydryls, such compounds may also contribute to the antioxidant properties of ghee-residue.

Selected references

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 (2): 73-77.