ENZYMATIC DIGESTION OF MUSCLE FROM MENHADEN (BREVOORTIA SPP.) AT DIFFERENT pHs

Abstract

Solubilization of muscle from South American menhaden, Brevoortia spp., was done with and without added proteolytic enzymes. Pepsin and trypsin were isolated from the stomach and the pyloric caeca of croaker (Micropogonias furnieri) respectively, and used for enzymatic solubilization. Digestion of muscle proteins was carried out at 8C for 20 h with the pH maintained at either 3, 4, 5, 6, 7, 8, 9 or 10. The hydrolytic action was evaluated by measuring the concentration of peptides and proteins solubilized from previously frozen muscle or from lyophilized muscle. The protein solubility of menhaden muscle was optimum at basic pH; approximately 50–60% of the previously frozen or lyophilized muscle was soluble after incubation without added enzyme at pH 9.0. All of the protein was solubilized from lyophilized menhaden muscle with purified trypsin at pH 10.0. Addition of croaker pepsin to menhaden muscle increased protein solubility by only 10–15%. Digestion of menhaden muscle with both pepsin and trypsin from croaker resulted in a similar increase in protein solubility as obtained by addition of only trypsin. Similar results were obtained with crude croaker stomach extracts and with purified pepsin, and also with crude pyloric caeca extract and with purified trypsin. Complete solubilization of menhaden muscle with croaker pyloric caeca extract may be an inexpensive way to separate the protein from lipids and prepare a protein isolate from this underutilized specie. Additional work is needed to characterize the functional properties of the menhaden protein extract obtained by digestion of the flesh at alkaline pH with croaker trypsin.