Abstract The aim of this investigation was to evaluate the impact of multiple freezing and thawing cycles on the physicochemical properties of Nile tilapia fillets. For this purpose, 72 fresh Nile tilapia fillets were packed and stored in a freezer at -18 °C. The frozen samples were submitted to five freeze-thaw cycles; in each cycle, the freezer was switched off during 14 hours. The consecutive freeze-thaw cycles resulted in a fillet’s total weight loss of 9.48%, with a quadratic regression (P < 0.0001) for thaw loss, with a greater loss percentage in cycle 3 (2.68%). pH values differed between the cycles (P < 0.0001), being observed an increment in this parameter only from cycle 4. The lipid oxidation remained constant in cycles 1, 2, 4 and 5, however in cycle 3 the lowest value (P < 0.0002) was observed. The luminosity, and intensity of the red and yellow colours increased linearly (P < 0.0001) as the cycles increased. Thereby, the tilapia fillets’ quality were adversely affected by the freezing cycles. The unfavourable alterations included weight loss, lipid oxidation and elevated pH, as well as the increasingly augmentation of brightness and red and yellow colorations of fillets as the progressive cycles occurred.

ABSTRACT: This study evaluated pre-slaughter stress and its influence on the stress indicators, quality characteristics and sensory characteristics of Nile tilapia fillets. To this end, two experiments were conducted: (1) two transportation times (60 and 240 min), with a density of 200 kg m−3, were compared to control treatment fish (in which the fish were removed from the net cage and immediately euthanized); and (2) two transportation densities (100 and 400 kg m−3), transported for 180 min, compared with control treatment fish. In experiment 1, the transportation time of 60 min resulted in higher levels of serum cortisol and plasma glucose compared to the transportation time of 240 min and the control. Fish fillets transported for 240 min had higher water-holding capacity, less water loss by pressure and higher levels of juiciness compared to fish transported for 60 min. Color, pH and water loss during cooking were not affected by transportation time. In experiment 2, transportation densities of 100 and 400 kg m−3 did not significantly affect the stress indicators nor the instrumental quality parameters of the fillets, but fish transported at 400 kg m−3 showed better visual acceptance by panellists.

Resumo O objetivo deste trabalho foi avaliar o efeito do peso de abate e do sexo sobre os rendimentos do processamento e sobre a composição centesimal do jundiá (R. voulezi). Foram calculados os rendimentos percentuais em relação à massa do peixe inteiro (rendimentos da carcaça, tronco limpo, músculo abdominal, filé, partes comestíveis, cabeça, pele, gônadas e gordura visceral). Não houve diferença estatística nos rendimentos entre as classes (P>0,05). Entretanto, ao se avaliarem os rendimentos entre os sexos, foi observada diferença significativa (P<0,05) para os rendimentos da carcaça, tronco limpo, músculo abdominal e gordura visceral, sendo que os machos obtiveram os maiores valores nestes itens. As fêmeas apresentaram maior (P<0,05) rendimento das gônadas. Os teores de proteína bruta, cinzas e carboidratos não diferiram (P>0,05) entre as classes, porém, a umidade, lipídeos e valor calórico tiveram diferença significativa (P<0,05) entre as classes, sendo que a umidade diminuiu com o aumento do tamanho dos peixes e o teor de lipídeos e valor calórico foi maior nos peixes da classe 301-400 g. Concluiu-se que os rendimentos do processamento do jundiá (R. voulezi) com massa entre 100 e 400 g são iguais, sendo que os peixes de 301 a 400 g apresentam maior teor de lipídeos no filé.

Abstract The aim of this study was evaluate the effect of slaughter weight and sex on processing yield and on the proximate composition of Rhamdia voulezi. We calculated the percentage yield of the whole fish (carcass, clean trunk, abdominal muscle, fillet, edible parts, head, skin, gonads and visceral fat yield). There was no statistical difference in yields among weight classes (P>0.05). However, when assessing the income between sexes we observed significant difference (P<0.05) for carcass, clean trunk, muscle and abdominal visceral fat yield, and males presented the highest values for these items. Females had higher (P<0.05) gonads yield. Crude protein, ashes and carbohydrates did not differ (P>0.05) among the classes, however, moisture, lipids and calories had significant difference (P<0.05) among the classes, and humidity decreased with increasing size of the fish, and lipid content and calorific value were higher for fish weighing 301-400 g. We concluded R. voulezi with mass between 100 and 400 g presents equal yield processing, and fish weighing 301-400 g have higher lipid content in the fillet.