Chemical, Sensory and Microbiological Changes of Spotted Grunter (Pomadasys commersonnii) Under Ice Storage

Abstract

The effects of two types of ice on the quality of Pomadasys commersonnii with storage time were conducted. The overall sensory evaluation otherwise known as quality index (QI) ranged from 3 – 0, the scores of 3 was for very fresh fish while zero implied deterioration. The QI for fish stored in ice block ranged from 2.9 – 1.0, 2.0 – 0.0, 2.2 – 0.0, 3.0 – 0.0, 2.8 – 0.2 and 3.0 – 1.0 for skin, gill, belly, odour, eyes and colour, respectively and for fish samples stored in ice cube were 2.9-1.0, 2.5 -0.0, 2.2-0.0, 2.9-0.0, 2.2-0.0 and 3.0-1.0 for skin, gill, belly, odour, eyes and colour respectively from the 4th to the 22nd day. The QI of the fish stored in ice block at 18th day which is the shelf life were 1.6, 1.4, 1.2, 1.1, 1.4 and 2.0 while that of fish samples stored in cube ice were 1.6, 1.3, 1.0, 0.6, 1.5 and 2.0 for texture of skin, gill, belly, odour, eyes and colour along vertebra column. The odour was fresh until after the 8 days; the belly/ gut has the least QI scores and this corresponded with the microbial load that has the highest count. The shelflife of the fish species was estimated to be 18 days. At this time, the fish was still acceptable by the panel members. The microbial load of the skin, flesh, gut and gill at day zero was less than 0.5 x 10² and 8.5 x 10² -1.56x105, 5.5 x10²- 1.25x107, 8.5x10²-3.78 x10⁷ and1.3x10² - 1.89 x107 cfu/g and 1.22 x10⁵, 1.82 x10⁵, 2.48 x10⁷ and 2.22 x 10⁷ cfu/g, respectively for samples stored in block and cube ice. Trimethylamine for fish samples stored in block ice ranged from 0.6 -15.1 mg/100g while that of cube ice was from 0.6 to 16.3 mg/100g. Total volatile nitrogen ranged from19.5- 42.1 mg/100g and 19.5 - 43.7 mg/100g for samples stored in block and cube ice, respectively. The pH increased steadily throughout storage from an initial pH of 7.0 to 7.48 and 7.56 for block and cube ice, respectively. Moisture and protein range for samples stored in block ice were 81.3-80.6%, and 19.5-17.02% while for samples stored in cube ice were 81.3- 83.9% and19.5-15.5%, respectively. Ash remained constant at 1% for all the samples. Results showed a non-significant difference (p = 0.05), which is an indication that they have the same storage or preservative capacity.

Keywords: Ice, grunter, sensory, microbiological, proximate