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The objective of this study was to investigate the effect of chemical oxidation on myofibrillar protein digestibility. Myofibrils were prepared from pig M. longissimus dorsi and oxidized by a hydroxyl radical generating system. Oxidative modifications of proteins were assessed by the carbonyl content, surface hydrophobicity, electrophoresis, and immunoblotting. Oxidized or nonoxidized myofibrillar proteins were then exposed to proteases of the digestive tract (pepsin, trypsin, and alpha-chymotrypsin). Results showed a direct and quantitative relationship between protein damages by hydroxyl radical and loss of protein digestibility.

The present study aimed to evaluate the digestion rate and nutritional quality of pig muscle proteins in relation to different meat processes (aging, mincing, and cooking). Under our experimental conditions, aging and mincing had little impact on protein digestion. Heat treatments had different temperature-dependent effects on the meat protein digestion rate and degradation potential. At 70 °C, the proteins underwent denaturation that enhanced the speed of pepsin digestion by increasing enzyme accessibility to protein cleavage sites. Above 100 °C, oxidation-related protein aggregation slowed pepsin digestion but improved meat protein overall digestibility. The digestion parameters defined here open new insights on the dynamics governing the in vitro digestion of meat protein. However, the effect of cooking temperature on protein digestion observed in vitro needs to be confirmed in vivo.

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BACKGROUND Proteasomes are nonlysosomal proteolytic structures that have been implicated in cell growth and differentiation. Abnormal expression levels of proteasomes have been described in tumor cells, and proteasomes can be detected and measured in plasma. The objective of this study was to characterize differences in proteasome levels between normal, healthy donors and patients with neoplastic disease and to correlate the findings with clinical status and other biologic markers of disease spread. METHODS Plasma proteasome levels were measured using a sandwich enzyme‐linked immunosorbent assay in normal donors (n = 73 donors) and in patients with solid tumors (n = 20 patients), acute leukemia (n = 35 patients), myeloproliferative (n = 37 patients) and myelodysplastic (n = 19 patients) syndromes, chronic lymphocytic leukemia (n = 44 patients), non‐Hodgkin lymphoma (n =104 patients), Hodgkin disease (n = 14 patients), other lymphoid disorders (n = 17 patients), and multiple myeloma (n = 27 patients). RESULTS In the normal donors, the plasma proteasome concentration was 2356 ng/mL ± 127 ng/mL. Patients with solid tumors exhibited a significantly higher value (7589 ng/mL ± 2124 ng/mL), similar to the patients with myeloproliferative (4099 ng/mL ± 498 ng/mL) and myelodysplastic (2922 ng/mL ± 322 ng/mL) syndromes. Patients with lymphoproliferative disorders, in contrast, had significantly lower values than normal donors (1751 ng/mL ± 107 ng/mL), except those in aggressive phase of the disease. This low level persisted in patients who were in complete remission. Proteasome levels decreased during the initial phase of treatment. Although there was a significant correlation with serum lactic dehydrogenase levels, frequent discrepancies were noted. There was no correlation with C‐reactive protein or β2‐microglobulin levels, even in the group of patients with multiple myeloma. CONCLUSIONS The plasma proteasome level is a potential new tool for the monitoring of patients with neoplastic disease. It is not correlated solely with cell lysis and may be involved in the pathophysiology of disease progression. Cancer 2001;92:2493–500. © 2001 American Cancer Society.

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