| Summary: | 博士 === 國立中興大學 === 畜產學系 === 90 === This study was investigated the processing steps and quality changes of traditional Chinese-style pork jerky. The results of present studies would be divided into six categories: (1) The moisture content, water activity (aw), crude protein, crude fat, ash, shear value and residual nitrite of pork jerky varied from different regions and manufacturers. The thiobarbituric acid (TBA) and the volatile basic nitrogen (VBN) values were gradually increased as storage progressed. In addition, the total plate counts were inhibited; the mold and yeast growth were prevented slightly during storage at room temperature for 150 days due to low aw of pork jerky. (2) The moisture content and aw varied in accordance with processing steps. The pork jerky roasted at 200℃ had higher shear value than roasted at 150℃ because the moisture content and aw of the former sample was lower than the later sample. The nitrite losses at heating step may amount to about 50 %. The TBA value of pork jerky varied from 0.34 to 9.25 or 9.83 mg of malonaldehyde depended on processing steps. The VBN value of pork jerky ranging from 0.25 mg/kg to 22.4 mg/kg or 23.5 mg/kg depended upon processing steps. The ATPase activity of myofibrillar proteins came from pork jerky during processing steps were partly or entirely lossed by the heat-drying or heat-roasting treatment. (3) The moisture content and aw of pork jerky decreased with increase of the level of sucrose. Shear values were increased by the decreasing of the moisture content and aw due to osmotic dehydration. However, higher level of sucrose had significantly negative effect on protein solubility and extractability of myosin heavy chain (MHC) of pork jerky due to non-enzymatic browning. (4) Pork jerky treated with sucrose had lower moisture content and aw than those of treated with glucose, those of the samples roasted by far-infrared grill had higher moisture content and aw value than those of the samples roasted by commercial oven and charcoal grill. The protein solubility of pork jerky with glucose was lower than sucrose, and pork jerky roasted by commercial oven had higher protein solubility than those by far-infrared and charcoal grill. Glucose incorporated into pork jerky had slightly higher non-enzymatic browning than sucrose, and non-enzymatic browning of pork jerky roasted by charcoal grill was higher than those of roasted by commercial oven and far-infrared grill. The changes in extractability of MHC showed that the pork jerky with glucose was lower than that of sucrose. (5) During storage at room temperature, the TBA value of all samples declined with the addition of glycerol or sorbitol. After storage at room temperature for 180 days, the VBN of all treated pork jerky were less than the control group. In addition, the mold and yeast growth were inhibited slightly with the addition of glycerol or sorbitol. At aw 0.75, the absorption isotherm of pork jerky with different levels of glycerol, the moisture content (g/solid g) were higher than sorbitol treatments and the control group. The chewiness desirability score of pork jerky with 6% glycerol was higher than the others. (6) The pork jerky roasted by far-infrared grill at 150℃ or 200℃ for 5 min showed that the volatile compounds from pork jerky can be divided into two groups by their possible origins. The first group of volatile compounds were derived from oxidation of lipid. The second group of volatile compounds were generated from degradation of natural spices. Significant differences were found between different roasted temperature at levels (p<0.05) for all volatile compounds.
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