Lesson 46. HUMAN MILK SUBSTITUTES
HUMAN MILK SUBSTITUTES
While human milk is superior for the new born infant, human milk substitutes (HMS) play a necessary role in infant nutrition when breast feeding is not possible, desirable or sufficient.
46.2 Human Milk Substitute
Since the advent of first commercial formula developed by scientists of Nestlé’s research group in 1866, a wide range of infant formulas have been developed by the manufacturers as shown in Table 46.1.
However, there are many limitations of these formulas as far as their use for infant feeding is concerned. These include the following:
(1). High casein - low whey protein character of standard formula results in lower nitrogen retention, lower weight gains in premature infants, low blood serum albumin levels, higher urea level and increased renal osmolar loads.
(2). Absorption of dietary fat is lower and makeup of adipose tissue fat is different when qualitatively fat is not similar to human milk fat.
(3). Lower absorption of calcium and iron.
(4). Overgrowth of E. coli in intestine and hence alkaline pH of stools, lower resistance of infant to enteropathogenic bacteria, deconjugation of bile salts leading to reduced fat absorption and higher urinary excretion of tryptophan.
(5). Lack of in-built self regulating mechanism available in breast-fed infants.
(6). More common occurrence of atherosclerotic plaques in bottle-fed infants due to high levels of cholesterol as orotic acid is absent in human milk .
(7). Loose and malodorous stools when soy flour is used in SBMF formula.
(8). Hemolytic form of anemia due to Vitamin E deficiency.
(9). Inhibition of trypsin, enlargement of pancreas and goitogenic effects due to presence of residual activity of antinutritional factors in inadequately processed soy beans.
To overcome these limitations, a new generation of nutritionally superior formulas has been developed, having varying degree of chemical and biochemical similarity with human milk. There are two types of approaches tried for this:
(1). Removal/reduction from cow/buffalo milk substances like αs-casein and b -lg through enzyme treatments. However, αs-casein is hydrolyzed in the digestive tract of the infant and thus formula containing hydrolyzed casein may not serve any useful purpose nutritionally.
(2). Modifications justifiable from nutritional angle-for example adjustment of casein: whey protein ratio in cow / buffalo milk so as to simulate human milk . Infants fed this have shown comparable levels of blood serum albumin, blood urea, nitrogen retention and urinary osmolarity as breast - fed infants.
From nutritional point of vie w, following suggestions are important for humanized milk formula:
(1). Modification of proteins of cow / buffalo milk to make them similar to human milk (whey protein: casein=60:40). This will help in enhancing nitrogen utilization and in minimizing renal osmolar load.
(2). Modification of triglyceride makeup of cow / buffalo milk fats so as to simulate ratios of short, medium and long chain triglycerides as well as that of saturated to unsaturated fatty acids to that of human milk fa t. This will enhance linoleic acid and vitamin E contents.
(3). Adjustment of proteins : fat: carbohydrate ratio. This will reduce t he protein content and increase the carbohydrate content of cow / buffalo milk and make it similar to t hat of human milk.
(4). Modification of calcium: phosphorous ratio as well as reduction in total ash content. This will enhance mineral utilization and minimize renal osmolar loads.
(5). Enrichment of cow / buffalo milk with factor to support growth of B. bifidum in intestines.
(6). Enrichment of cow / buffalo milk with lactoferrins, transferrins and immunoglobulins to promote resistance towards enteropathogenic bacteria and to enhan ce iron absorption.
(7). Partial substitution of cow / buffalo milk f at with oils rich in PUFA, as well as use of carbohydrate sources such as maltodextrins may help in reducing the cost.
46.3 Achievements So Far For Humanization of Buffalo Milk
(1). αs-casein reduced to human milk level by renneting.
(2). Total protein concentration reduced to human milk level by proteolysis.
(3). Calcium level reduced by electrodialysis
(4). Curd tension reduced by ion-exchange
(5). Level of unsaturated f atty acids improved by corn oil fortification with milk fat.
46.4 Research on Formulating Human Milk Substitutes
(1). Adjustment of fatty acid composition : Ratio of unsaturated fatty acids (UFA) and saturated fatty acids (SFA) adjusted to 1.92 (similar to human milk) by incorporation of soybean, oleo and safflower oils (rich in UFA) and coconut and milk fat (rich in SFA). Corn oil may be added to increase oleic acid. Blending of milk fat and vegetable fats enables in improving digestibility of infant formulas. Use of sunflower oil as well as one third milk fat replacement by maize oil has been reported.
(2). Use of goat milk: Major components of goat milk (3% fat, 3% protein 4.5% lactose, 0.8% ash) resemble cow milk in composition, however, levels of potassium, chloride and biotin are higher than in cow milk and folic acid content is less (lack of folic acid may lead to anemia in infants). Goat milk lacks in αs-casein but α-lactalbumin, b -lactoglobulin, κ-casein, b -casein and αs2 casein are similar to that of cow milk. Goat milk is used in treatments of infants sensitive to cow milk protein; fat in goat milk is said to be more digestible (than fat in cow milk) due to higher proportion of short chain fatty acids, smaller size fat globules and lack of fat globule clustering euglobulin. However, no scientific evidence in support of this is available.
(3). Human milk based formula : Lucas et al. (1980) blended whole human milk, human cream, salt and lactose-free human milk protein powder into a high protein, high fat and high energy infant formula for low birth weight infants. The increased concentration of antimicrobial proteins allowed subsequent pasteurization of the formula with minimal loss in antimicrobial activity.
(4). Preparation of immunoglobulin concentrates : The colostrum obtained from hyperimmunized pregnant cows against enteropathogenic E. coli is partially purified, sterilized and freeze-dried to yield a colostral whey protein preparation containing 30-45% immunoglobulins. The product has potent anti E. coli activity. Infants suffering from E. coli mediated diarrhoea have shown better recovery. However, practicality of this procedure is doubtful and even if it is practical, the resultant product may be classified as a pharmaceutical.
(5). Addition of lysozyme: The biological value of human milk is proportional to its lysozyme content. Egg white lysozyme (EWL) has a similar composition, though different antigenic specificity, than human milk lysozyme. Humanized infant formulas containing EWL have been patented in Japan and Russia. Even though increased intestinal levels of bifidobacteria have been reported in infants given lysozyme treated formula, growth of bifidobacteria is not stimulated in cow milk due to lysozyme.
(6). Addition of bifidobacteria : Infant formula fortified with spray dried concentrate of bifidobacteria (final concentration 5.73 log CFU/ml) has been reported (Table 46.2). Feeding trials have shown:
a. Decrease in pH and coliform counts of feces and increase in bifidobacteria to the level obtained with human milk .
b. Significant increase in retention of calcium, phosphorous and iron level.
c. Improvement in the proportion of bifidus organisms have been reported through the application of neuraminidase in infant formulas.
d. In a process involving cultivation of B. bifidum in concentrated milk (20-25% TS), the product is spray dried after development of certain acidity. The survival of organisms during spray drying was found to be satisfactory.
e. In an yet another process, direct incorporation of B. bifidum cells into the liquid concentrate prior to spray drying has been reported. The product was shown to contain 15,000 viable cells of B. bifidum /g and it had bifidus activity 170% higher than commercial formulas and about 80% bifidus activity of human milk . On storage of the product for 6 months at room temperature and at 370C, survival of B. bifidus was 48.4% and 60.4% respectively whereas retention of bifidus activity was 84.6% 77.9% respectively.
(2). Addition of other lactobacilli: A number of other closely related lactobacilli, which inhibit the human intestinal tract, synthesize organic acids (acetic, benzoic, lactic), H202, B -vitamins and enzymes, may provide nutritional and/or therapeutic benefits. The lactobacilli also produce natural antibodies (Table 46.3) with broad spectrum activity against pathogenic and non pathogenic organisms. Significant improvement in weight gain in newborn infants given formula containing viable L. acidophilus have been reported.
Table 46.3 Natural antibodies produced by various lactobacilli
46.5 Baby Food Powders
For storage stability, volume and convenience, powdered baby food of different compositions, to be dissolved in water before use has been developed by the multinational companies in their attempt to resemble mother's milk. They have gained increasing acceptance including formulations made for hyper allergic babies. In modern production of baby food powder each component in whole milk from cows is standardized to be as close to the composition of human milk as possible. For some formulations milk is not even used. Powdered baby food available on the market comprises a large group of products with different compositions, which can be classified in the following groups:
1. Ordinary whole milk powder
2. Whole milk powder with added carbohydrates
3. Fermented milk
4. Humanized milk
5. Products with starch
1. Ordinary whole milk powder
The simplest type of baby food is whole milk powder with 25 to 28% fat in the solids, or half-cream milk powder with about 14% fat. Usually some vitamins are added, e.g. A, B1 and D2, in order to equalize the seasonal variations in the vitamin content of natural milk, and to keep it, throughout the year, at the optimum standard level required for babies. The vitamins are added either to the liquid milk or dosed continuously into the concentrate by means of the dosing pump. To ensure uniform distribution of the vitamins, especially the fat-soluble ones, homogenization of the concentrate is required.
2. Whole milk powder with added Carbohydrates
This group of baby foods is based on full-cream or half-cream milk with added sucrose and maltodextrin. The sucrose is added to the milk prior to the evaporation. This allows for pasteurization of the sucrose as well, and a final product with an acceptable plate count is produced. Today industrial ready-made maltodextrin is available in most places. The maltodextrin is then mixed with partially concentrated milk. Very often vitamins are added. The whole mixture must be homogenized before drying. If the preparation of the feed is a batch process, there will be some storage and delay between the evaporator and the dryer.
3. Fermented milk
The fermented milk product, usually half-cream is made by means of special culture starter strains. The pre-concentrated milk - usually not concentrated to more than 22-25% TS - is inoculated by a starter (which is normally a mixture of streptococcus lactic and lactobacillus) and fermented at a slightly elevated temperature for 6 to 10 hours. After the required acidity has been achieved the fermented concentrate is homogenized, cooled and spray dried.
4. Humanized Milk
The biggest group of baby foods is the so-called humanized milk. Human milk has a very different composition from cow's milk, as it has a higher content of lactose, a lower content of proteins with different protein composition (mainly an albumin milk while cow's milk is a casein milk) and a different fat composition (as it has a considerably higher content of unsaturated fat acids) and a lower content of minerals. There are different steps of humanization.
- The simplest one is merely to increase the content of lactose and add some vegetable fat to increase the amount of unsaturated fat acids. Other additives, such as vitamins, ferric ions or lactulose (galactosido-fructose) are used as well, with the aim of converting cow's milk into a composition as close as possible to human milk.
- Cow's milk contains about twice as much protein as human milk, it contains less carbohydrate and about the same amount of fat. The pre-dominant type of protein is not the same in the two kinds of milk. Thus the curd formed by human milk is soft and flocculent in the baby's stomach, whereas that of cow's milk is more tenacious and elastic. Furthermore, cow's milk contains more mineral salts (especially Ca++) and less vitamins.
- A dilution of cow's milk with carbohydrates and fat until the protein content is 15 g/l is not enough, as the composition of the protein differs to a great extent in the two kinds of milk. WPC is used extensively in baby food manufacture to adjust the protein content.
- Cheese whey, the protein content of which is practically only lactalbumin and β-globulin, is often used for standardizing. It is, however, not recommended to use it directly, as the mineral content would become too large in the final product.
- Removal of part of the salts, by membrane filtration or demineralization either by ion-exchange or electrodialysis, is therefore nowadays used more and more.
- Regarding the fat content, human milk contains more than cow's milk, and furthermore it contains more of the polyunsaturated fat acids, such as linoleic and arachidonic acids being necessary for a better utilization of the supplied energy. It is therefore necessary to add fat after the protein standardization.
- Vegetable fat (often corn, palm or sunflower oil) is therefore added, as it contains above mentioned polyunsaturated fat acids. If the animal fat is replaced completely, the end product would then be short of oleic acid being present in the animal fat.
- The mineral content of cow's milk is about four times that of human milk. During the standardization with especially whey proteins (provided the whey is demineralized) but also with fat and possibly lactose, the mineral content is reduced to an acceptable level. However, in most cases the iron content has now become too low and iron lactate, iron saccharate or iron sulphate are often added.
- The vitamin concentration in cow's milk is usually smaller than in human milk. Furthermore it varies with the season, so vitamins are always added to the baby food, also because the processing destroys part of the vitamins.
- Special products where the soy proteins are replacing the milk proteins are produced for allergic babies. Due to the soy proteins, the concentrate will have a high viscosity, and it is thus necessary to lower the solids content to 40-45%.
1. Products with Starch
Another big group of baby foods, for babies >9 months, contains starch as shown in Table 46.5 typically with the following approximate composition:
Table 46.5 Approximate composition of baby foods for babies > 9 months of age
The starch can be added to the process either by dry dosing or in liquid form together with the remaining components:
- Dry dosing - whole milk and sucrose are mixed and pasteurized, after which it is evaporated to about 45% total solids and spray dried using an inlet temperature of 180ºC. The powdered starch is dosed via the fines return system into the spray dryer and is agglomerated with the concentrate particles. The agglomeration of the starch is very important to avoid separation during storage. As powdered starch often contains bacteria, a gamma radiation can be necessary to ensure an acceptable end product.
- Liquid mixing and pasteurizing offer the advantage that the starch can be pasteurized. If the pasteurization temperature is kept below 60ºC, the starch will not be precooked, and the mixture is dried from a feed with 45% solids and a drying temperature of 180ºC. If the pasteurizing temperature exceeds 72ºC, the starch will be precooked and the viscosity will increase. Due to this the solids content must be reduced to 20-25%. Drying temperatures will be 180ºC. Bag filters on the exhaust air must be used, as the powder loss will otherwise be too high.
Thus, human milk does not only contain nutrients but also has a complete immune system consisting of leucocytes, antibodies, complements, lysozyme, lactoferrin, lactoperoxidase, xanthine oxidase, etc. Artificial milks are, and will continue to be, used in those cases where a mother cannot or will not feed her child. But the model for these artificial milks should be breast milk. The immunological adjustment is essential as protective proteins in bovine milk get usually destroyed during manufacture of infant milk f oods due to heat sensitive nature. Preservation of these proteins or their replacement through isolation from raw milk is essential. However, before any infant milk food formula is introduced in the market with a claim of close resemblance to the breast milk, much more needs to be learnt about the physiological response of the infant.
46.6 Malted Milk
A British pharmacist James Horlick developed ideas for an improved, wheat and malt-based nutritional supplement for infants. In 1873, James and his brother William formed a company to manufacture their brand of infant food. The company originally marketed its new product as “Diastoid,” but trademarked the name “malted milk” in 1887. Despite its origins as a health food for infants and invalids, malted milk found unexpected markets due to its nutritive value, convenience, digestibility and palatability. It is also appreciated for its lightweight, non-perishable and high-calorie qualities worldwide.
Malted milk is a powdered food product made from a mixture of malted barley, wheat flour, and whole milk, which is evaporated until it forms a powder. Malt powder comes in two forms: diastatic and non-diastatic. Diastatic malt contains enzymes that break down starch into sugar; this is the form bakers add to bread dough to help the dough rise and create a good crust. Non-diastatic malt has no active enzymes and is used primarily for flavor, mostly in beverages. It sometimes contains sugar, coloring agents, and other additives.
Malting is a process applied to cereal grains, in which the grains are made to germinate by soaking in water and are then quickly halted from germinating further by drying/heating with hot air. Thus, malting is a combination of two processes: the sprouting process and the kiln-drying process. The term "malt" refers to several products of the process:
- The grains to which this process has been applied, for example malted barley;
- The sugar, heavy in maltose, derived from such grains, such as the baker's malt used in various cereals; or
- A product based on malted milk, similar to a malted milkshake (i.e., "malts").
Malting grains develops the enzymes that are required to modify the grain's starches into sugars, including monosaccharides (glucose, fructose, etc.) and disaccharides (sucrose, etc.). It also develops other enzymes, such as proteases, which break down the proteins in the grain into forms which can be utilized by yeast. Barley is the most commonly malted grain in part because of its high diastatic power or enzyme content.
46.6.2 Drying of malted milk