Casca de ovo como fonte de cálcio: composição mineral e biodisponibilidade em ratos

Abstract

Most of the people do not reach the recommended intake for calcium (Ca), which is a mineral essential for bone development, muscle contraction, blood coagulation, cell permeability and several other functions. Hen eggshells are composed of around 40% Ca, and could be an easily obtainable low-cost option to meet the nutritional needs of the population. This study aimed to evaluate the influence of rearing laying hens systems and eggshells color in the composition of essential and toxic minerals of eggshell’s powder, to determine the microbiological safety of samples subjected to distinct hygienization methods and compare the bioavailability of eggshell with different particle size to purified calcium carbonate (CaCO3). The shells were washed, cleaned, oven-dried and milled. The mineral composition of 28 samples was evaluated by atomic absorption spectroscopy after previous digestion with nitric acid. Ca remained at similar concentrations in the different samples (approximately 365 mg/g). Eggshells from confined laying hens showed higher concentration of magnesium (Mg) and lower concentration of strontium than free-ranged laying hens egg shells. No significant amounts of iron, chromium, manganese, molybdenum, nickel, selenium, aluminum, cadmium or lead were found in the analyzed samples. Microbiological evaluation consisted of counting coagulase-positive Staphylococcus, total and thermotolerant coliforms, and detecting Salmonella sp. in three eggshell samples sanitized by immersion in 1% sodium hypochlorite followed by boiling in water, and three eggshell samples in which the step of immersion in hypochlorite was suppressed. The samples submitted to both treatments showed no microbial contamination. The bioavailability of Ca was evaluated in growing male Wistar rats fed during 28 days with AIN-93 diet, containing eggshell fractions of different granulometry (ES L, large particle size; ES M, intermediate particle size; and ES S, small particle size), or purified CaCO3 as the Ca source. Mineral absorption, bone mineral concentration and bone biomechanical properties were evaluated. Ca absorption in rats fed with eggshell diets was 56.2%, which is considered high. However, we found a lower Ca absorption in groups ES L and ES S, but the absorption of Ca was similar in the ES M group when compared to CaCO3. Rats that received ES M and ES L had greater absorption of phosphorus and magnesium (Mg) than CaCO3 group. No changes in the mineral deposition, weight or bone biomechanical properties were observed. It was concluded that the eggshell is rich in Ca, shows no contamination by toxic metals, has good sanitary quality if properly processed and is a Ca source that has good intestinal absorption and good retention in bones of growing rats.