Semester

Summer

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

P. Brett Kenney.

Abstract

A study was conducted to investigate the effect of rigor development, at time of processing, on weight and length changes, proximate analysis, pH, K-value, color, and texture of rainbow trout (Oncorhynchus mykiss ) fillets. Texture of cooked fillets was characterized using two instrumental methods: Allo-kramer and Variable blade. Forty-five rainbow trout were harvested and immediately slaughtered using percussive stunning they were stored, following evisceration, at 4°C on ice. Fish were processed at 0, 24, and 48 h postharvest, and fillets were vacuumed packaged and stored for 2 days at 4°C. These storage treatments were applauded in the context of a randomized complete block design. Condition factor, whole body weight, head--on gutted (HOG) weight, length, percent butterfly fillet, HOG weight, and separable muscle were not affected (P > 0.05) by processing time. After cooking, dimensional changes were not different as a function of processing time. At 48 h postharvest, fillets were wider and longer (P>0.05), in value than the other groups. The 0-h, postharvest fillets were thicker (P<0.05) than those filleted at 24 and 48h, indicative of dimensional changes associated with muscle contraction in the absence of skeletal restraint.;At 0 h, fillet pH was (P.0.05) higher than at 24 or 48h; it is likely that all tissue glycogen had not been metabolized to lactic acid. Fillets moisture content and cook loss were (P > 0.05) lower at 0 h than at 24 and 48 h fillets, and higher cooked moisture was observed for fillets processed at 0 h. A higher fat content in raw (6.44 +/- 0.40) fillets and a lower fat content in cooked fillets (4.38 +/- 0.35) were measured for 0 h fillets compared to 24 and 48 h product. Ash and protein content was (P ≤ 0.05) higher at 0 h postharvest than at 24 and 48 h. A significant rapid decline in rigor angle from 0-24 h was observed, which is indicative of rigor resolution. Fillets L* value increased (P ≤ 0.05) as processing time, postharvest, increased; it was highest at 48 h processing. Meanwhile, 0 h fillets exhibited a (P ≤ 0.05) higher redness and yellowness value. The 0 h fillets had shorter sarcomere length than fillets produced at 24 or 48 h postharvest. ATP (Adenosine triphosphate) catabolizes and shear force were measured at 48 h postharvest for all processing treatments. Texture of trout fillet were affected (P ≤ 0.05) by time of processing, which might be due to the activity of myofibrillar proteolysis within the fillets' muscle. During rigor development, ATP concentration decreased as fillets went into rigor. Adenosine triphosphate (ATP) gradually decreased (P ≤ 0.05) with processing time. Adenosine diphoshate (ADP) and adenosine monophosphate (AMP) were not affected by processing time. Inosine monophosphate (IMP) and inosine (INO) increased (P ≤ 0.05) to 48 h postharvest. Hypoxanthine remained constant after 0 h postharvest. In conclusion, rainbow trout could be processed at 0 h postharvest without negatively affecting product quality.

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