Abstract: The effect of high temperature cooking in water and acetic acid solution on the hardness of pork bones was studied under the conditions of 120 ℃ and different cooking times (40, 50, 60, 70 and 80 min) in water, and different acetic acid concentrations (0.0%, 0.2%, 0.4%, 0.6%, 0.8% and 1.0%, V/V) and 80 min in acetic acid solution. The protein content of raw and cooked pork bones were determined by the Kjeldahl method, and calcium and phosphorus contents as well as the amount of calcium and phosphorus release by inductively coupled plasma atomic emission spectrometry (ICP-AES). The microstructure of comminuted bones was examined by scanning electron microscope (SEM), and the structure of chemical components in bone powder samples was characterized by infrared spectroscopy. It was found that high temperature cooking resulted in a decrease in bone hardness, which decreased from (16 445 ± 867) to (10 995 ± 546) g with increasing the cooking time from 40 to 80 min, and from (10 995 ± 546) to (6 003 ± 153) g with increasing the acetic acid concentration from 0.0% to 1.0%. After cooking in water, the protein content in pork bone decreased by 7.4% to (28.5 ± 2.3) g/100 g, the apparent contents of calcium and phosphorus increased by 11.8% and 8.9% to (210.0 ± 8.2) and (96.0 ± 4.0) mg/g, respectively, and the amounts of calcium and phosphorus released were (0.57 ± 0.04) and (0.17 ± 0.01) mg/g, respectively. After cooking in acetic acid solution, the protein content decreased by 10.0% to (25.9 ± 0.9) g/100 g, the apparent contents of calcium and phosphorus increased by 18.3% and 14.8% to (230.0 ± 6.4) and (100.0 ± 2.3) mg/g, respectively, and the amounts of calcium and phosphorus released were (1.73 ± 0.01) and (0.75 ± 0.01) mg/g, respectively. Cooked pork bone was easily ground, especially the one cooked in acetic acid. The mid infrared absorption spectrum of cooked pork bone was simpler than that of the untreated one, with the former being similar to synthesized hydroxyapatite. Thus, the chemical components of pork bone were changed after cooking. We concluded that high temperature cooking in both water and acetic acid solution can change the contents of protein, calcium and phosphorus in pork bone, leading to a significant decrease in hardness (P < 0.05).

Key words: pork bone, acetic acid, cooking, hardness, chemical composition