By: Rachana Rathwa and Jana Atanu
Soybean (Glycine max L. Merrill) is a legume that isconsumed worldwide. Soybean is a complex food matrix containing low or no starch, about 20 % oil and 40 % high-quality protein in addition to several bioactive compounds such as lunasin, isoflavones and saponins. Soybean is a low cost source of protein that has been consumed in Asian nations for many centuries. The rapid growing population of the developing countries is facing acute shortage of protein. In this regard, soybean would come to rescue for protein malnutrition.
If you’re allergic to dairy, lactose intolerant or you just are not crazy about the taste of dairy milk, reach for soy milk as a comparable alternative. Soymilk generally has a longer shelf life than dairy milk, and some types of packaged soy milk can be stored at room temperature for months together. Soy milk has a number of nutritional advantages.Soymilk is a high-quality source of soy protein that is an alternate of dairy milk and available in variety of flavoured beverages such as vanilla, chocolate, etc. Such milk can be used to replace milk added to coffee, tea or cereal based snacks.
As an inexpensive and convenient source of high quality proteins, soy milk is one of the most important traditional beverages that are consumed widely in Asian countries, including China, Japan, Korea, Singapore and Thailand. Soymilk is a beverage that is free from cholesterol and lactose.The composition of soymilk is different from those of bovine milk in several aspects, such as fat, fatty acid profile, protein as well as soluble sugar content(Table 1). In general, soy milk contains less fat, sugar and calories, and more iron and fiber than cow’s milk. Furthermore, soymilk has significant content of phytoestrogens (isoflavones) that are absent in cow milk; the former playing an important role in human nutrition and health.The flow chart for preparation of soymilk is provided in Figure 1.
However, the presence of natural anti-nutrients, such as trypsin inhibitors (TI), lectins, phytic acids and indigestible oligosaccharides, has limited the consumption of soybased products.
Health benefits of cow milk
Unlike soy milk, cow’s milk contains 30 % of the daily value of calcium, a supporter of teeth and bone health. One cup (237 ml) of soy milk typically contains 99–119 IU of vitamin D, which can satisfy 30% of the RDI for vitamin D;a vitamin essential for calcium and bone homeostasis. Conversely, cow milk contains greater protein (since soymilk is prepared with 6-9% TS only) and phosphorous content than soy milk, which is important for muscle building or repair of body cells and tissues. Harvard School of Public Health reported that both dairy components and calcium may help to reduce colon cancer and osteoporosis. The National Milk Producers Federation announced that the 2010 Dietary Guidelines for Americans recommends that adults and children (9 years and above)should drink three servings of low-fat milk daily.
However, milk is deficient in vitamin C, iron and dietary fiber.
Health benefits of soy milk vis-a-vis cow’s milk
Soybeans contains more protein than any other legume; soy milk is high in protein. The U.S. Food and Drug Administration (2009) reported that as part of a diet low in saturated fat and cholesterol, consumption of 25 g of soy protein daily can decrease cholesterol, thereby reducing the chances of heart disease. Unlike cow milk, soy milk is low in saturated fat, contains almost no cholesterol and has 10 % of daily value of dietary fiber and 8 % of iron. Soybeans also contain omega-3 fatty acids, which can help reduce lipid levels.
Cow milk is an excellent source of calcium, vitamin D and vitamin A, which are essential for strong bones and superior eye sight. It also contains casein and whey protein which are good for building muscle.
Soy milk is richer in vitamin B and iron when compared to cow’s milk. Soymilk also contains 42 times more manganese, which is necessary for bone formation. Soy protein reduces LDL cholesterol (bad cholesterol) and raises HDL cholesterol (good cholesterol). Soy milk contains fiber, which is lacking in cow’s milk.
A serving size of one cup of soy milk provides 5 g of total fat, 4 g of carbohydrates and 80 calories. Soymilk contains about 30 mg of sodium and 7 g of protein. At 6 % of daily value per serving, soy milk is rich in vitamin B6, and has 10 % of magnesium, phosphorous and riboflavin, and 25 % of our daily thiamin requirement.
Nutritive value of soymilk
There are an array of nutrients in soymilk. These are discussed in separate heads below.
Protein: Soy contains all the nine essential amino acids. The human body assembles these amino acids into new proteins, including antibodies essential for immune system function, structural proteins that hold your tissues together. Each cup of unsweetened, plain soy milk provides about 7 g of protein.
Riboflavin and Vitamin B6: Soy milk consumption helps in intake of B-complex vitamins, especially rich in riboflavin and vitamin B6. The average amount of vitamin B6 contained in 100g of soy milk is 0.07 mg. This average value corresponds to 3.5 % of the recommended dietary allowance (RDA) in our diet. The riboflavin in soy milk helps the cells produce energy, and shields DNA from damage. Drinking a cup of soy milk boosts riboflavin by 0.51 mg; satisfying 39 % of the recommended daily intake of riboflavin for men and 46 % for women.
Calcium and Iron: Drinking soy milk helps boost your calcium and iron. A cup of unsweetened plain soy milk boasts a calcium content of 299 mg, which contributes 30 % toward our recommended daily calcium intake. Each serving of soy milk provides 1.1 mg of iron; meets requirement of 14 and 6 % of the daily iron intakes recommended for men and women, respectively.
Functional component in soybean and soymilk
Isoflavones: Soybean owes its recently acquired ‘functional food’ status to the presence of isoflavones, the phenolic compounds, concentration of which ranges between 1–3 mg/g in the mature seeds.The isoflavone content in soybeans comprise of about 72% of the total phenols and are significantly affected by cultivar and environmental factors. Genistein and daidzein are the isoflavones found in food, in the form of conjugated glycosides. Soy isoflavones may also act as antioxidants.Isoflavones, powerful phytoestrogen chemicals found in soy that work like estrogen in the human body. Consumption of just 3.5 ounces of soy protein confers about 102 mg of isoflavones. Soy milk is reported to contribute about 30 mg of isoflavones per cup.
Interest in soy isoflavones is based on data suggesting its potential in lowering cholesterol levels, preventing prostate and breast cancers, osteoporosis, cardiovascular disease as well as relieving menopausal symptoms.
The major forms of isoflavones present in both UHT and fresh soymilk are ?- glycosides; other one being aglycones. The median total isoflavones per serving (mg) in UHT soymilk was significantly greater than that in fresh soymilk, this does not necessarily indicate that UHT soymilk would provide more absorbable isoflavones after ingestion. However, ?-glycosides were present in greater proportion in UHT soymilk than in fresh soymilk.
Effect of processing on some aspects of soymilk
Soy milk fermented with properly selected microbial species offered advantage in decreasing the indigestible oligosaccharides, like raffinose and stachyose, and beany flavor. Soy milk quality in terms of three classes of components, namely, total phenolic, phytic acid and trypsin inhibitors, was improved by the germination pre-treatment (28 h at 25oC) of soybeans.Treatments such as soaking, grinding and heating decreased the total isoflavone content during the production of soymilk. The content of isoflavones in soymilk was higher in soybean cultivars with higher protein content and such cultivars are more suitable for soymilk production.
A novel soymilk beverage containing a compound with B12 activity-producer strain (Lactobacillus reuteri CRL 1098) has been successfully developed that can be used to prevent the pathologies caused by a B12-deficient diet.
Some disadvantages associated with soymilk
Soy milk contains a high percentage of phytoestrogens, which may decrease fertility in men if they consume more than 3 quarts per day. Too much consumption of estrogen can cause hormone imbalance in women. Soy milk also contains oligosaccharides, a type of carbohydrate the body has difficulty breaking down; flatulence may be a problem with some individuals. Soy milk also contains phytates which is reported to interfere with calcium absorption.
Soy milk is a cheaper milk alternative to cow milk. Soy milk can be a boon for people suffering from lactose intolerance. The isoflavones present in soymilk makes it a ‘functional food’ exerting positive metabolic effects in human body. Soy milk can be used in a manner similar to cow/buffalo milk. Flavouring of soymilk can enhance its sensory acceptability. Soy is a unique, excellent food which can be useful as a supplement also.
Rachana Rathwa – Assistant Professor, and Jana Atanu – Professor and Head, Department of Dairy Technology, SMC College of Dairy Science, Anand Agricultural University, Anand, Gujarat E-mail: email@example.com