Effect of cooking method on proximate and mineral composition of Lake Malawi Tilapia (Oreochromis karongae)

Abstract

Fish is a nutritious food and an excellent source of animal protein in the human diet containing many vitamins and minerals that are essential for the human body. In Malawi, fish is the major source of affordable dietary protein for humans. Lake Malawi tilapia (Oreochromis karongae) locally known as Chambo, is the most preferred and highest value commercial food fish species obtained from Lake Malawi. Several methods are used to prepare/cook the fish viz.: boiling, deep frying in edible cooking oil, grilling, and/or roasting over fire. However, the fact that cooking alters the nutrient content in foods underscores the need to understand nutritional effects of different food cooking/processing methods. This study investigated effect(s) of cooking fresh fish (Lake Malawi tilapia) by boiling, roasting, pan frying and, using a locally made fireless cooker) on its proximate (protein, fat, ash and moisture) and mineral (calcium, magnesium, zinc, iron and phosphorus) composition. Highest and lowest values for crude protein were reported in fish processed using the fireless cooker (64.3±0.2%) and roasting (59.9±0.4%), respectively (P<0.05), against (64.4±0.3%) for the fresh fish (control). Fish that were pan fried showed significantly higher crude fat content (25.5±0.1%) (P<0.05) followed by samples prepared using the fireless cooker (15.3±0.1), and lowest values were found in fish that were boiled (12.1±0.2%). Fish from the fireless cooker had significantly high moisture content (10.6±0.1%), ash (17.1±0.3%), zinc (0.0±0.0μg/g), phosphorus (2.6±0.0μg/g) and reasonably, more calcium (54.2±7.0μg/g) and magnesium (0.5±0.0μg/g) (P<0.05). The lowest levels of minerals were recorded in fish that were roasted: calcium (44.8±0.1μg/g), magnesium (0.5±0.0μg/g), zinc (0.0±0.0μg/g) and phosphorus (2.0±0.1%) (P≥0.05). The results suggest that fish processed in the fireless cooker were of higher nutritional quality principally due to the relatively high content of the most needed nutrient - protein. Adopting and encouraging use of the fireless cooker could also be a way of saving energy thus; curbing dependency on fuel wood. The results also showed that cooking does not have significant effect on minerals in fresh fish.

Keywords: Fireless cooker, boiling, roasting, pan frying, tilapia, Lake Malawi, Malawi