BY-PRODUCTS TECHNOLOGY

Lesson 47. NUTRITONAL CHARACTERISTICS OF SKIM MILK AND ITS BY-PRODUCTS, BUTTERMILK AND GHEE RESIDUE

Module 8. Nutritional characteristics of by-products

Lesson 47
NUTRITIONAL CHARACTERISTICS OF SKIM MILK AND ITS BY-PRODUCTS, BUTTERMILK AND GHEE-RESIDUE

47.1 Introduction

Skim milk, buttermilk, ghee-residue and further derived by-products from them contain valuable milk nutrients. Each and every component of milk that is passed on to these by-products has its unique nutritional value. Skim milk and buttermilk are rich in solid-not-fat portion of milk, while ghee-residue is rich in all the milk components, but in modified forms.

47.2 Nutritional Characteristics of Skim Milk & Its By-products

Skim milk lacks the fat and the accompanying vitamin A of whole milk, but is rich in protein, lactose, calcium, phosphorus, and riboflavin. It is nutritionally important for those people, who are suffering from heart diseases. It is valued largely for its high quality proteins, which make up 41% and 37% of total solid content in buffalo and cow milk, respectively. Casein is the major protein in skim milk. With a content of 0.7-0.9% phosphorus, covalently bound to the casein by a serine ester linkage, casein as a phosphoprotein is a member of a relatively rare class of proteins. The phosphate groups bind bivalent minerals such as Ca²⁺. Skim milk is an important source of calcium in readily available form. It provides up to 75% of total calcium intake in western countries. Increased calcium intake results in significant reduction in blood pressure by (i) increasing the urinary excretion of sodium, (ii) preventing the rise in vitamin D hormone, which increases blood vessel resistance, (iii) relaxing smooth muscle cells that line the blood vessels, (iv) suppressing the renin-angiotensin system and (v) increasing production of endothelial relaxing factors. The nutrition provided by skim milk accounts for 55% of the total energy of whole milk. Various by-products are prepared from skim milk.

47.2.1 Casein

Casein is nutritionally an excellent protein due to its high proportions of essential amino acids. Essential amino acid composition of various casein products is given in Table 47.1. Casein contains 45% essential amino acids. The Biological Value (BV), Net Protein Utilization (NPU) and Protein Efficiency Ratio (PER) for casein are 77, 76 and 2.5, respectively, which are mostly unaffected by the processing conditions usually employed during the dairy operations. PER value of lactic and rennet casein is 2.51 and 2.45, respectively. Casein has the primary function in the nutrition of the new born, supplying not only amino acids, but also minerals mainly calcium and phosphorus. Casein also has been demonstrated to be possessing anticarcinogenic properties. Casein inhibits feacal β-glucuronidase, an enzyme produced by intestinal bacteria, which deconjugates procarcinogenic glucuronides to carcinogens. Casein derived peptides isolated from the microbial fermentation of milk inhibit colon cancer by altering cell kinetics. Several peptides with opium like (sleep inducing) activity have been extracted from the casein include ß-casomorphins (from ß-casein) and exorphin (from α_S1 casein). These opium-like peptides have been shown to prolong gastrointestinal transit time exerting anti-diarrhoeal effect. These also stimulate secretion of insulin and somatostatin.

Table 47.1 Essential amino acid composition (in mg amino acid/g N) of FAO reference protein and various casein products

47.2.2 Caseinates

Nutritional characteristics of casein remain similar when it is prepared in its solubilized form e.g. sodium and calcium caseinates. In addition to provide casein, calcium caseinate also provides the valuable and highly bioavailable mineral calcium. Calcium is important to bone, tendon as well as muscle growth. The protein efficiency ratio (PER) of sodium and calcium caseinates is reported to be 2.57 and 2.59, respectively.

47.2.3 Casein hydrolysates

Casein hydrolysates are partly to fully digested casein. Nutritionally, protein hydrolysates are particularly useful to people suffering from protein allergy and for the management of patients with various digestive disorders as a result of pancreatic malfunction, pre-and post-operative abdominal surgical patients, patients on geriatrics and convalescent feeding and other who for various reason are not able to ingest a normal diet. Absorption of short-chain peptides (mainly, di- and tripeptides) is considered a more efficient compared to an equivalent amount of free amino acids. Hydrolysates containing peptides with a high ratio of branched-chain amino acids (BCAA) to aromatic amino acids (AAA), referred to as Fischer's ratio, are used in specific medical diets.

47.2.4 Co-precipitates

Co-precipitates of milk proteins contain not only casein, but also whey proteins, which contain a relatively high concentration of sulphur-containing amino acids, cysteine and cystine, contributing to the higher biological value of co-precipitates. Calcium concentration is in the range of 0.1-3.0% and depends on the thermal treatment, the added quantity of CaCl₂, and the pH value of the medium. A high calcium co-precipitate is nutritionally much superior to casein.

47.3 Nutritional Characteristics of Buttermilk

Buttermilk is luscious, low-fat and loaded with health benefits. It contains all the non-fat components present in milk like casein, whey protein, lactose, minerals, vitamin A, α-tocopherols and cholesterol. It is a good source of valuable milk proteins, lactose and larger proportion of milk fat globule membrane (MFGM) proteins; Phospholipids component of MFGM is considered beneficial for its various health-related properties. The nutritive value of buttermilk is as high as fermented milk and favours the opinion of diet conscious people, since it contains very less quantity of fat but has high content of phospholipids that perform a wide range of biological functions and are significant in human nutrition. Phospholipids have anti-ulceral properties, work as anti-tumor-promoters and aid in the cure of intestinal illness. The phospholipids of buttermilk have more or less equal proportion of lecithin, sphingomyelin, and cephalin together with small proportion of cerebrosides. Lecithin is widely used to stabilize the fat components of the products and has health benefits such as prevention and curing of memory loss, high blood cholesterol and nervous disorder (Brown, 1990). Sphingomyelin prevents water loss through skin and genetic disease and lowers blood cholesterol level. Successful attempts were made by Corredig et al. (2003) to isolate the phospholipids rich MFGM material. Such isolates can be used as functional ingredients in the development of nutraceuticals.

The consumption of buttermilk has been found to lower blood pressure and reduce the serum cholesterol level. Buttermilk is sometimes, recommended for the prevention and treatment of diarrhea in infants. The famous classified Ayurvedic medicine “Takrarishta”, in which buttermilk is the chief ingredient, is helpful in many diseases such as gastrointestinal upsets, acute and chronic condition and first-degree piles with bleeding or non-bleeding. In jaundice and alcoholic liver diseases, regular use of buttermilk immensely helps the patients to regain appetite (Anon, 2003). In addition, buttermilk has recently gained attention as a potential source of functional ingredients.

Desi buttermilk (lassi) has therapeutic value in addition to being nutritive. In addition to normal milk constituents, lassi is also a rich source of vitamins. Buttermilk's active cultures fight undesirable bacteria and help to stimulate the immune system. Many people, who are lactose-intolerant, can use desi buttermilk because the cultures convert lactose partially into more digestible lactic acid. Lassi has a similar place in the diet as other cultured milk products, but over and above, it has beneficial effects in the treatment of patients suffering from acute hepatitis and from a sepsis of the mucous lining of the stomach. Irish folklore claims- a glass of buttermilk will cure a hangover, and when heated with cloves and garlic, it was sure to cure any variety of ailments.

Buttermilk powder is low in fat and provides an excellent source of all nutrients of buttermilk in concentrating form.

47.4 Ghee-Residue

Ghee-residue contains good quantities of milk fat, protein and minerals. Therefore, it can be used as human dietary supplement. But it has poor quality of protein because of its lower lysine content. When it is treated at high temperature (105-110°C), some of lysine and other essential amino acids are lost. The lack of lysine in ghee residue is the most dominant factor in depressing the PER of ghee-residue and damage of some essential amino acids is responsible for low protein nutritional value of ghee residue. Relwani (1978) reported that supplementation of ghee residue with some good quality protein such as skim milk powder (SMP) sharply increased its protein efficiency ratio (PER) from 0.66 to 2.4. Supplementation with 8% lysine, 2.5% methionine and 1.4% tryptophane strikingly improved its nutritive value which was even slightly higher than SMP (Table 47.2).

Table 47.2 Nutritive value of ghee-residue

Selected references

Corredig, M., Roesch, R.R. and Dalgleish, D.G. 2003. Production of a novel ingredient from buttermilk. J. Dairy Sci.,86: 2744-2750.
Kumar, J. 2006. Admixing of buttermilk to buffalo milk for production of Channa and Channa based sweets. A Ph.D. Thesis submitted to N.D.R.I Deemed University, Karnal.
Pagote, C.N. and Bhandari, V. 1988. Antioxidant properties and nutritive value of ghee residue. Indian Dairyman, 40 (2): 73-77.