Adding value to fish backbones by mechanic separation of a mince, or by pH-shift processing to recover protein isolates
Today, the fillet of a fish is in most cases the only part which is value-added into foods. However, since this part only contributes to around 40-50% of the fish weight, 50-60% are lost from the food chain in favor of low value uses such as fish meal. Among the lost parts are e.g. backbones and heads which are very rich in prime quality muscle, and therefore have great potentials in production of minces or protein isolates.
In the BBI-funded WaSeaBi-project and a Swedish national project funded by Leader Bohuskust och Gränsbygd and region Västra Götaland, scientists at Chalmers together with e.g. Sweden Pelagic AB has compared the use of backbones from herring, cod and salmon in classic meat-bone separation yielding a mince, and in the more recent pH-shift process yielding a protein isolate. The raw materials, minces and protein isolates have then been compared for their macro- and micro-nutrient profiles, as well as for their stability towards lipid oxidation. In addition, the protein yield in the two processes was compared.
Overall, mechanical separation led to higher protein recovery compared with the pH-shift process and using both techniques, recovery ranked the species as herring > salmon > cod (Figure 1). Thus, it was evident that the most muscle rich backbone was that from herring processing, from which >80% mince could be recovered! However, despite lower yields, the pH-shift process up-concentrated protein from the two fatty species (herring and salmon backbones) more efficiently than mechanical separation by removing more fat and ash, something which at the same time reduced n-3 PUFA and vitamin D content. Regarding vitamins and minerals, their levels in the two product types differed depending on species.
When storing the two products on ice or at −20 °C, salmon-derived products were very stable during both conditions. Contrary, lipid oxidation products in herring- and cod-derived products increased rapidly during ice storage, with the pH-shift-produced protein isolates being most susceptible to oxidation in case of cod. Adding the rosemary-contaning Duralox MANC antioxidant mix (0.5%) to the two products from herring and cod however largely increased the oxidation lag phase in both protein isolates and mechanically separated meat (MSM); from <1 day to >15 days. At −20 °C, mainly the herring products oxidized, and particularly the mince.
When relating so called “pro- and antioxidative compounds” in the products to the development of oxidation, levels of hemoglobin, total iron correlated positively with lipid oxidation development; while levels of the antioxidants vitamin C and E correlated in a negative manner.
Overall, the two studies showed that there is a major potential for upcycling of fish backbones to food ingredients, but processing technology should be carefully balanced against the desired nutrient profile and final application area. It is also clear that for more blood-rich raw materials, providing a lot of hemoglobin, rosemary-derived antioxidants are good recipes to extend the storage time.
You can find the papers below, which have been published with open access: