The Curing Process Of Collagen Casing And The Resulting Effects On Performance

Artificial collagen casings are a kind of packaging materials for sausages,which are usually made from the dermis layer of pigs and,cattle.Compared with natural casings,collagen casings offer several advantages including wider sources,easier commercial production and more stable qualities,so that natural casings are being gradually replaced by collagen casings.Nevertheless,the collagen casings made in China are suffered from many problems,especially the poor adhesion between casing and meat stuffing when cooked in hot water.Meat adhesion is a key parameter to evaluate sausage quality.To improve the meat adhesion,the thermal shrinkage and shrink force of collagen casings in hot water should be reduced.Curing process is a key procedure to control the thermal shrink by inducing irreversible thermal denaturation of collagen fibers.Though gradient increase of curing temperature has been employed to control the shrink of collagen fibers,few attentions have been paid to the humidity of curing environment.It is proved that water molecules could improve the stability of collagen structure through forming hydrogen bonding between collagen molecules.Accordingly,we assume that humidity is a key factor to control the structural stability of collagens by regulating the content of associated water,so that the thermal shrink of collagen casings is reduced.To verify the above hypothesis,we introduced relative humidity(RH)as a process parameter in the curing process.The appearance,semi-perimeter,water content,shrinkage and shrink force of the casings were detected to preliminarily screen the suitable RH values,and then optimize the process parameters including RH,temperature and time.Finally,the water-retention of various casing were detected and the potential mechanism was clarified by using DSC and ATR FTIR.The obtained results can provide valuable guidance for improving curing process.The main works and conclusions are listed as follows.(1)First,the constant humidity 60%,70% and 80% were introduced,and at every constant humidity,the curing process included three phases: 50 oC for 24 h,70 oC for 48 h,and 80 oC for 4h.It was found that RH of > 80% produced yellowish collagen casings and led to too much shrinkage of semi-perimeter,while RH of < 60% resulted in serious wrinkles in casings.Therefore,a RH range of 60% ? RH < 80% was selected for the following optimization tests.(2)The process parameters including humidity,temperature and time were further optimized.1)RH: Compared with dry curing,the wet curing at constant RH could effectively reduce the longitudinal shrinkage while the curing at gradient RH could reduce the transversal shrinkage.A wet curing at gradient RH of 60% at 50 oC for 24 h,70% at 70 oC for 48 h,75% at 80 oC for 4 h(S(60/70/75%))was the optimal RH parameters.2)Temperature: Curing temperature had no obvious effects on the water content of the collagen casings yet markedly affected the shrinkage.S(65/75 oC)demonstrated the minimal longitudinal shrinkage and longitudinal/transversal shrinkage ratio,suggesting the optimal curing temperature is S(65/75 oC).3)Time: The denaturation of collagen casings increased with extended curing time.S(48/2~6 h)led to the minimal shrinkage force,indicating the optimal curing time is 2~6 h.(3)Finally,the water retention of various collagen casings was detected and DSC and ATR FTIR were employed to clarify the potential mechanism by which wet curing affected the water retention.1)The water content of casings during 89 days preservation at room temperature was detected.It was found that the water retention of various casings presented an order of: wet cured > dry cured > uncured casings,suggesting that wet curing is helpful to increase water retention.2)According to the DSC detections,curing influenced the glass transition temperature of collagen films;longer curing time led to higher transition temperature.In addition,curing regulated the evaporation temperature of water in casings,presenting an order of S(48/6 h)> S(48/2 h)> S(60/70/75%)> uncured casings,suggesting that the curing parameters influence the bonding of water with collagen.3)ATR FTIR spectra demonstrated that wet curing changed the characteristic peaks of collagens and led to some new peaks,further suggesting that wet curing may promote or alter the bonding of water with collagen and thus improve the water retention of wet cured casings.