Cooking Methods and Duration Affects Calcium Content of Bone Soup

The importance of adequate calcium intake is well recognized for supporting bone growth in children and in preventing bone loss in postmenopausal women. Calcium requirement can be met rather easily with the consumption of calcium-rich dairy products. However, some people have difficulties eating dairy products. Soups made from pork or beef bones may serve as an alternative source of dietary calcium. Others have shown that slowly cooking bones in acidic solution enhanced calcium content of the soup. The objective of this study was to determine the effect of cooking methods and cooking duration on calcium content of bone soups prepared in small batches. Pork ribs from the one pig were used in the study. The bones were cut into 2-inch pieces and freed of all soft tissues before they were divided into six groups. Three groups of bones with total weight of 30 g, 60 g, or 90 g, were cooked with 200 ml distilled water with 5% vinegar, either in a stainless steel soup pot or in a pressure cooker. At 30, 60, 90 and 120 minutes after boiling, the volume, pH, and calcium content of the soups were measured. Calcium content of soups cooked in a pot reached 200 or more mg/L. The pH increased as cooking time increased. Increasing the total amount of bone did not increase the calcium concentration further. With the highest amount of bone, the soup calcium actually declined, possibly due to the fast evaporation of water and precipitation of calcium to the pot wall. Calcium contents of soups made in the pressure cooker were lower than those made in the pot. Our results suggest that bone soups prepared under the conditions of this study did not appear to be a good source of calcium. Adding more vinegar and optimization of water to bone ratio may be needed to make calcium-rich bone soups