Enzymatic Hydrolysis of Salmon Frame Proteins Using a Sequential Batch Operational Strategy: An Improvement in Water-Holding Capacity

Abstract

The meat industry uses phosphates to improve the water-holding capacity (WHC) of meat products, although excess phosphates can be harmful to human health. In this sense, protein hydrolysates offer an alternative with scientific evidence of improved WHCs. Salmon frames, a byproduct rich in protein, must be processed for recovery. Enzymatic technology allows these proteins to be extracted from muscle, and the sequential batch strategy significantly increases protein nitrogen extraction. This study focused on evaluating the WHC of protein hydrolysates from salmon frames obtained through double- and triple-sequential batches compared to conventional hydrolysis. Hydrolysis was carried out for 3 h at 55 °C with 13 mAU of subtilisin per gram of salmon frames. The WHC of each hydrolysate was measured as the cooking loss using concentrations that varied from 0 to 5% (w/w) in the meat matrix. Compared with those obtained through conventional hydrolysis, the hydrolysates obtained through the strategy of double- and triple-sequence batches demonstrated a 55% and 51% reduction in cooking loss, respectively, when they were applied from 1% by weight in the meat matrix. It is essential to highlight that all hydrolysates had a significantly lower cooking loss (p ≤ 0.05) than that of the positive control (sodium tripolyphosphate [STPP]) at its maximum allowable limit when applied at a concentration of 5% in the meat matrix. These results suggest that the sequential batch strategy represents a promising alternative for further improving the WHC of hydrolysates compared to conventional hydrolysis. It may serve as a viable substitute for polyphosphates.

Keywords: byproduct recovery; enzymatic protein hydrolysis; nitrogen extraction; salmon frames; sequential batch; water-holding capacity.

Figure 1

Schematic representation of the conventional hydrolysis process and that used in the double- and triple-sequential batch configuration of SF proteins for a total reaction time of 180 min at 55 °C, native and uncontrolled pH, and 13 AU of total subtilisin per kg SF.

Figure 2

Diagram of the tubes used in the centrifugation of the samples for the determination of WHC. (A) Sample before centrifugation. (B) Sample after centrifugation.

Figure 3

Reaction progress of the free α-NH group concentration (liquid samples) during the hydrolysis of SF in different operational configurations [conventional hydrolysis for 180 min, double- and triple-sequential batch hydrolysis for 180 min (90 and 60 min, respectively)]. (a) Comparison of the double-sequential batch method with conventional hydrolysis. (b) Comparison of the triple-sequential batch method with conventional hydrolysis. The reaction conditions were 55 °C, native pH (6.5) without a control, 100% SF, and 13 mAU/g SF. Each point is the mean of two experimental points, and the error bars are the standard deviations. SB1: sequential batch 1, SB2: sequential batch 2, SB3: sequential batch 3.

Figure 4

Nitrogen extraction after SF protein hydrolysis for different operating configurations [conventional hydrolysis for 180 min, double- and triple-sequential batch hydrolysis for 180 min (90 and 60 min, respectively)]. The experimental conditions were as follows: 100% SF, 13 mAU/g SF of subtilisin distributed in the indicated proportions between SB1/SB2/SB3, 180 min of total reaction time distributed as mentioned above, 55 °C, and an uncontrolled native pH of 6.5. Each point is the mean of two experimental points, and the error bars are the standard deviations. SB1: sequential batch 1, SB2: sequential batch 2, SB3: sequential batch 3.

Figure 5

Characterization of the hydrolysates in the soluble phase at the end of the reaction at 55 °C for different operating configurations [conventional hydrolysis for 180 min, double- and triple-sequential batch hydrolysis for 180 min (90 and 60 min, respectively)]. (a) Degree of hydrolysis (DH′). (b) Peptide chain length (PCL). Each point is the mean of two experimental points, and the error bars are the standard deviations. SB1: sequential batch 1, SB2: sequential batch 2, SB3: sequential batch 3.

Figure 6

Cooking loss of salmon meat cooked with different amounts of SF hydrolysate in different operating configurations [conventional hydrolysis for 180 min, double- and triple-sequential batch hydrolysis for 180 min (90 and 60 min, respectively)]. Each value is expressed as the mean ± standard deviation of three replicates. The dashed line represents the STPP cooking loss for the application of the maximum concentration allowed in the industry, 0.5% (w/w).