Effect Of Papain-Tenderizing And Curing-Drying Process On Proteolysis And Quality Of Spent Hens

There are nearly two billion hens to be spent for meat every year in China. However, the meat quality of spent hen meat is of hardness and poor tenderness, which, to a large extent, affects its edible quality. Therefore, various methods have been used to tenderize the muscle of spent hen by the researchers at home and abroad in order to make the spent hens be well reused, among which tenderizing with papain have also been reported. Salting and drying-ripening is a Chinese traditional processing of chicken processing, and the corresponding dry-cured chicken are deeply favored by consumers because of their aroma. The papain-tenderizing and dry-ripening processing of spent hens have been studied preliminarily in our laboratory. This paper further studied the effect of papain-tenderizing combined with dry-ripening on proteolysis and quality characteristics of spent hens by Response Surface Methodology, and explored a new process suiting the deep processing utilization of spent hens. The detailed contents are as follows:1. Effect of papain-tenderizing and drying-ripening process on proteolysis of spent hens:Fourty five spent hens were used as the experimental materials. To investigate the effect of drying-ripening process on the tenderizing effect of papain for breast meat of spent hens and to optimize the processing conditions of dry-cured chicken, a central composite response surface experiment using enzyme dosage, drying-ripening temperature and time as experimental factors and proteolysis index (P.I.%) as responses was carried out based the single factor tests. The results showed that effect order of three factors influencing the P.I.%were enzyme dosage> drying-ripening temperature> drying-ripening time, and all the three factors had significant interactive effect on proteolytic index (P.I.%) between each other (p<0.01); The optimum processing conditions for dry-cured chicken processing were: enzyme dosage3.5U/g, initial drying-ripening temperature14℃(14-17-20-23-26℃) and drying-ripening time99.33hours, under these conditions the proteolysis index was measured as10.30%; Time-related concentration changes of proteolytic indices during processing and comparison of tenderized and non-tenderized muscle were assayed; Total nitrogen (TN) was decreased gradually until drying-ripening24h, and thereafter increased (p<0.05). Non-protein nitrogen (NPN) and P.I.%also decreased initially and then increased (p<0.05). Compared with the control, TN and NPN decreased by12.27%and7.21%, respectively, while the P.I.%increased by5.76%in the chicken breast muscles tenderized with papain.2. Research on mechanism of proteolysis for breast muscle of spent hens by papainUsing the brest meat of spent hens tenderized by papain as materials, the time-related changes of the residual activitie of papain, myofibrillar fragmentation index (MFI) and free amino acids (FAA) during processing of dry-ripened spent hens were determined. The degradation of breast sarcoplasmic protein and myofibrillar protein were analyzed using SDS-PAGE. The results showed that the papain activity increased gradually during processing but was not statistically significant(p>0.05); Papain tenderizing could markedly promote myofibrillar fragmentation of the breast meat of spent hens. And the sarcoplasmic protein and myofibrillar protein were degraded to small molecular products such as peptides and FAAs during the processing of spent hens; Most of the FAAs in breast muscle of final product were several times of their corresponding sensory thresholds, indicating that the nutritional value of spent hen was increased significantly through papain tenderizing, which had important contributions to the development of dry-cured chicken produced by spent hens.3. Effect of papain-tenderizing and drying-ripening process on tenderizing effectiveness and quality characteristic of spent hensSpent hens were used as the experimental materials, and a central composite response surface experiment using enzyme dosage, drying-ripening temperature and time as experimental factors and Warner-Bratzler Shear force (WBS) as response was carried out to investigate the tenderizing effect of papain as well as the effect of salting and air-drying on it. The results showed that effect order of three factors influencing the WBS were drying-ripening time> enzyme dosage> drying-ripening temperature; The optimum processing conditions for dry-cured chicken processing were:enzyme dosage3.5U/g, initial drying-ripening temperature14℃(14-17-20-23-26℃) and drying-ripening time99.33hours, and under these conditions WBS was determined as3.50kg/cm2. All the quality indices of flavor and tenderness of final products have reached designed requirement after the spent hens were tenderized by papain. The briskets WBS decreased by25%and cooking loss increased by34.67%compared with those of control, respectively, furthermore sensory evaluation results was aslo better than control.