Processing Improvement Of Dry-Cured Duck And Effects On The Flavor And Quality

Dry-cured duck is a traditional meat product of china which has a large market for this product.The fresh air was used in the processing of traditional dry-cured duck and it took twenty days to produce it in winter.Up to now,with the control of temperature, moisture and air,the processing period had shorten to three days which changed the shortcomings of fresh air drying in winter.The existing information in scientific literature related to dry-cured duck is very scarce and no theory can be used in optimizing the duration and parameters in practice.The aim of this research is to study the proteolysis,lipolysis,oxidation during traditional processing,investigate the processing improvements and their effects on flavor forming and quality,provide a theory basis for studying and accommodating the flavor, improving the processing technology,optimizing the parameters dry-cured duck.The contents and results are as follows:1 Study on dry-cure duck proteolysis,lipolysis and oxidation during traditional processingRaw ducks(Cherry valley duck) were processed following the traditional methods. Time-related concentration changes of non-protein nitrogen(NPN),free amino acid(FAA) in breast and TBARS value,carbonyl compounds and conjugated dienes,free fatty acid (FFA) in breast and subcutaneous fat during processing were assayed.The results showed that muscle NPN and FAA contents increased gradually during processing while NPN decreased(P＞0.05) at the stage of drying for 15 days and FAA increased significantly (P＜0.05)at the stage of drying for 20 days.More than 28%of NPN in breast muscle of the final product was composed of FAA among which Glu,Ala,Leu,Lys and Arg were dominant in concentration.Since the concentrations of most FAA in breast muscle of the final product were several times of their corresponding sensory thresholds,it might have make an important contribution to the formation of traditional dry-cured duck flavor.The TBARS in breast increased significantly(P＜0.05) at the stage of salting and a reduction followed by an increase was found at the stage of drying.The contents of carbonyl compounds and conjugated dienes in breast and subcutaneous fat increased steadily during the drying periods but with reductions at the end.The SPUFA contents significantly decreased after salting and increased steadily during the drying periods with a highest content at the stage of drying for 20 days while SSFA and SMUFA had non-significant increasing trends during the whole drying periods.C18:2,C20:4,C18:1 and C16:0 were dominant in concentration of FAA and more than 76%in FAA were SMUFA and SPUFA.2 Study on processing improvement of dry-cured duckThe effects of temperature(10℃,14℃,18℃),relative humidity(60%RH,66%RH,72%RH) and wind speed(4 m/s,5 m/s,6 m/s) on drying were studied by orthogonal test L₉(3⁴).The NPN,L^* value of surface and sensory sensory evaluation were used as parameters to optimize the drying conditions.It showed that the best condition of temperature,relative humidity and wind speed for drying were 18℃,66%RH and 4 m/s respectively.The ending point of drying processing was with 15%dehydration rate.3 Study on dry-cure duck proteolysis,lipolysis,oxidation and flavor quality during processing.Raw ducks(Cherry valley duck) were processed following the methods that had been optimized It showed that the proteolysis,lipolysis and oxidation of breast during processing and their effects on flavor were assayed.The results showed that the TVBN value,NPN,TBARS value,POV value,carbonyl compounds and conjugated dienes had increase tendencies and the process of curing had a significant effect on them.Most FAAs decreased significantly(P＜0.05) during curing and increased significantly(P＜0.05) during drying.The content of FAA increased 50%compared with raw which Glu,Val,Leu,Phe and Arg were dominant.FAA contents increased steadily during the drying periods with a highest content at the stage of drying for 2 days then decreased gradually at the stage of drying for 3 days in which SMUFA and SPUFA decreased significantly (P＜0.05).It also showed that 40 compounds were identified in raw duck,42 during the processing of cured,while 51 compounds during the first day of drying,45 during the second day,49 during the third day.The flavor compounds included 13 kinds of hydrocarbons,14 kinds of ketones,21 kinds of alcohols,16 kinds of aldehydes,4 kinds of acids,2 kinds of esters,2 kinds of furans,4 kinds of S-containing compounds and 3 kinds of N-containing compounds.The total area of the flavor compounds of dry-cured duck increased dramatically during the processing and was over 3 times as much as in the raw duck after 3 days drying.All these compounds could play important roles for the specific flavor of dry-cured duck.