PRESERVATION OF BLUE-JACK MACKEREL (TRACHURUS PICTURATUS BOWDICH) SILAGE BY CHEMICAL AND FERMENTATIVE ACIDIFICATION

Abstract

We compared acidified and lactic acid fermented silage approaches for the preservation of blue-jack mackerel. Silages acidified with formic and propionic acids had stable pH (3.8) and low (19 mg/g N) levels of volatile nitrogen compounds (total volatile basic nitrogen, TVBN), but relatively high (82 g/100 g) final non-protein-nitrogen (NPN) values. The silage was fermented with Lactobacillus plantarum LU853, a homofermentative lactic acid bacterium with a high growth (0.51/h) and acidification rate at 37C (optimum temperature), able to grow in the presence of 40 g/L NaCl and to ferment sucrose and lactose. The silages at 37C reached safe pH <4.5 values within 48?72 h, either (F2a) or not (F0), in combination with 20 g/kg salt addition; F2a acidified more rapidly, which may be an advantage for its microbiological stability. Proteolysis resulting in 53?59 g NPN/100 g N was lower in fermented than in acidified silages; however, in fermented silages, the levels of TVBN were much higher (50?80 mg TVBN/g N) than generally considered acceptable.