Dairy Food Fortified/Enriched with Micronutrients
Dairy products are important dietary sources for micronutrients such as calcium, iodine, phosphorus, vitamins B2 and B12. On the contrary, they usually contain scarce amounts of potassium, magnesium, vitamin A, zinc, selenium, folate and no vitamin D at all (Bates et al., 2012). Fortification/enrichment of food with micronutrients represents an alternative or complementary strategy to supplementation (defined as the provision of micronutrients in capsule, tablet, or syrup form).
Some advantages of fortification over supplementation are easier technology, better cost-effectiveness and higher sustainability, and consumer acceptance (Bhutta et al., 2013). Several international organizations have endorsed large-scale fortification of staple foods in order to reduce multiple micronutrient deficiencies in high- burden countries (including, among others, Brazil, China, India, and Russia) (Horton et al., 2008).
Food fortified with micronutrients may also be targeted for specific population segments, such as infants, women of reproductive age, and individuals suffering from chronic diseases (Allen et al., 2009). The main criticism is that in higher-income countries, markets offer products fortified with micronutrients that are not necessarily deficient in the diet (Popkin et al., 2006). This may lead consumers to excessive consumption of a given food perceived as aprioristically beneficial to health (Aaron et al., 2015).
Dairy products (especially fermented milk beverages) are among the most common food fortified with vitamin D. A dairy product defined as “vitamin D fortified” should contain more than 0.5 pg of vitamin D per 100 g. Such fortified foods are targeted for children, because vitamin D, along with calcium, benefits healthy bone development, especially for populations whose diet includes small amounts of oil-rich fish (the best dietary source of vitamin D) and in countries where exposure to sunlight is limited (Williams et al., 2015). Long-term (24 months) administration of milk fortified with vitamin D3 (at least 10 pg of vitamin per day) resulted in increased (from +7.4 to +25.0%) concentrations of calcitriol, the biologically active form of vitamin D, compared to baseline (Chee et al., 2003; Daly et al., 2006). Diabetic patients fed for 12 weeks with a yogurt drink fortified with vitamin D3 (25 pg/die) showed more than 67% increase of calcitriol (Nikooyeh et al., 2011). Unexpectedly, consumption of cheese fortified with vitamin D by elderly resulted in an 8.7% decrease of calcitriol, probably because the subjects enrolled had higher baseline value of calcitriol (Johnson et al., 2005). On the opposite, calcitriol increased of 120% after consumption of one weekly dose (30-40 g) of cheese containing 700 pg of vitamin D (100 pg/die) (Wagner et al., 2008).
Some dietary components (e.g., vitamins B, C, E, folic acid and selenium) improve health outcome of people living with the human immunodeficiency virus (HIV) (Hummelen et al., 2010). Furthermore, since these patients show a dramatic decline of gut lactobacilli and bifidobacteria and high cell density of pathogenic species (Gori et al., 2008), they may benefit from administration of prebiotics and probiotic bacteria (Hummelen et al., 2010). Fortification of a probiotic yogurt with a blend of micronutrients targeted for HIV-positive patients taking highly active antiretroviral therapy allowed maintaining the cell density of the probiotic L. rhamnosus CAN-1 above the supposed therapeutic level, even after three weeks of storage. The fortified yogurt was appreciated by untrained panelists and, after appropriate in vivo trial, could be used as functional food benefiting nutrition and immune function for people living with HIV (Hemsworth et al., 2011).
Among micronutrients, selenium has antioxidant and anti-inflammatory activity, and protects against toxicity of anticancer drug, chemotherapy, and radiotherapy (Rayman, 2012). Different forms of selenium are present in nature. Inorganic forms (selenite and selenate), organic selenium, and elemental selenium are commonly used in dietary supplements. Elemental selenium is characterized by the highest bioavailability and the lowest toxicity (Benko et al., 2012; Yazdi et al., 2013). The enrichment of fermented milk with sodium selenite is a tool for creating a functional food targeted as adjuvant for patients treated with chemotherapy or radiotherapy (Alzate et al., 2010). However, the sodium selenite concentration should be below 0.01 mM (2 pg/g) in order to allow starter lactic acid bacteria to grow during milk fermentation. This would limit the use of fermented milk as dietary source of elemental selenium (Xia et al., 2007). Higher concentration of selenium in yogurt was obtained by pretreating sodium selenite with L. brevis CGMCC no. 6683 isolated from kefir and tolerant to high selenium concentration (Deng et al., 2015). The selected strain reduced sodium selenite into elemental selenium during growth in MRS broth added with selenite (0.5-20 mM) and the sele- nium-enriched-L. brevis cell biomass was added to milk before fermentation. In this way, the starter lactic acid bacteria were not inhibited, the selenite concentration in the yogurt was increased to 24 pg/g, and elemental selenium was detected in the yogurt by scanning electron microscope equipped with energy dispersion X-ray spectrometry (Deng et al., 2015).