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In the present work, we have developed a set of sequential and complementary alternatives to valorise five fish discards in order to recover and produce fish mince, oils, gelatins, fish protein hydrolysates (FPHs) with antioxidant and antihypertensive properties and marine peptones. In this last case, microbial bioconversion of marine peptones was studied by Pediococcus acidilacti growth, a well-known valuable lactic acid bacterium, and the concomitant production of lactic acid and pediocin SA-1. Highly digestible FPHs with a good quality of amino acids composition and antioxidant and antihypertensive properties were easily produced. In the same bioprocess, fish oils with a healthy ω-3/ ω-6 ratio were also isolated. The use of peptones derived from FPHs as bacterial media nutrient (source of organic nitrogen) led to reduction of bioproductions costs between 2-5 folds in comparison with commercial culture medium.

A new proteolytic activity assay was devised to avoid the interference of paramyosin which causes gelling during the enzymatic assay. Extremely high autolytic activity was observed in octopus arm muscle, which was 40–500 fold higher than those of various other fish species. The proteinase was inhibited strongly by leupeptin and iodoacetic acid and, to a lesser degree, by transepoxysuccinyl‐L‐leucylamino (4‐guanidono)butane (E‐64), indicating the class as a thioi proteinase. The proteinase exhibited optimum activity at pH 2.5 and 40C, although it contained a sulfhydryl group in the active site. Myosin heavy chain was the primary myofibrillar protein which was hydrolyzed during the autolysis of octopus arm followed by paramyosin. Actin showed no signs of hydrolysis during the incubation of up to 8 h. Due to its high affinity for myosin, the enzyme activity should be controlled during processing octopus to ensure the functionality of myosin.

Samples were subjected to continuous and step-pulsed pressurization, in both cases at 7 and 40 ЊC. There was a reduction of microbial flora (total viable count and lactic bacteria) after pressurization and during storage at 2.5 to 3.0 ЊC, chiefly in the lot pressurized by step-pulse at 400 MPa, 40 ЊC. Pressure-induced modification of the microbial flora resulted in a lower level of nitrogenous compounds. Pressurization reduced autolytic activity, but shear strength values remained stable throughout storage. There was less drip loss in the pressurized lots at 7 ЊC that at 40 ЊC, and the WHC values decreased during storage. Shelf life of the pressurized octopus overall was 43 d longer than unpressurized.

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Various hydration properties (solubility, water binding capacity and viscosity) of collagenous material from muscle connective tissue and skin are analysed in terms of pH and NaCl concentration in the medium. In general terms it is found that functionality is at its greatest where pH is between 2 and 4, and that the addition of NaCl reduces functionality, except in the case of viscosity. Both collagenous materials react similarly to changes deriving from pH and the addition of NaCl. The data are relevant to the possible utilisation of waste products from the fish industry as functional ingredients in other foodstuffs.

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