The effects of dietary lipids and antioxidants on growth performance, meat quality and moisture loss of the South African abalone, Haliotis Midae

[摘要] ENGLISH ABSTRACT: Abalone has become a high valued commodity globally, with South Africa being one of the largest producers. Haliotis midae is the most important aquaculture species produced in South Africa, and is exported to the Eastern markets in a variety of forms, with live export and canned abalone being the two most important products. To meet the high international demand, abalone farmers need to remain competitive by optimizing growth rate, increase water absorption, and minimising the stress and moisture loss experienced by abalone during the live export period. Stress and moisture loss experienced during export can potentially contribute to a decrease in live weight and meat quality, which in turn will result in lower income generated, which will impact negatively on the cost-efficient production of abalone.No literature is available on reducing moisture loss in live abalone during export. Other factors such as diet composition (which can affect the growth rate of abalone), animal health condition (assessed by weight of the abalone per unit shell length), and meat composition and quality, can also affect the cost-efficient production of abalone. The aim of this study was therefore to determine the amount of moisture loss experienced by adult live abalone that have reached an export size, and to formulate a complete balanced diet that will minimize the moisture loss during export. Aspects that were investigated included a) the effect of diet on the growth rate of abalone, b) the effect of diet composition on moisture loss during live export of abalone, c) the effect of diet on the extent of post mortem and post cooking moisture loss, and d) the effect of diet composition on proximate and chemical composition of abalone meat.This study evaluated the effect of ten diets that differed in terms of their Vitamin E, polyunsaturated fatty acid (PUFA), chromium, and green rooibos content, The diets consisted of Control 1 (Abfeed®), Control 2 (NutroScience), LN (low PUFA with no additives), LM (low PUFA with vitamin E (mixed tocopherols)), LR (low PUFA with green rooibos) and LCr (low PUFA with chromium), HN (high PUFA with no additives), HM (high PUFA with vitamin E (mixed tocopherols)), HR (high PUFA with green rooibos), and HCr (high PUFA with chromium). Sunflower oil was used to formulate the high PUFA treatments, whilst rendered beef fat (tallow) was used to formulate the low PUFA treatments. Animals (n=25) from each treatment was sampled monthly to determine the effect of the different treatments on the growth performance (measured as weight and length gain, average daily gain and specific growth rate in terms of weight and length, feed conversion ratio, and condition factor).Proximate and chemical analyses were performed on the abalone meat post mortem to determine the effect of diet composition on moisture loss, water retention, and drip loss. Varying results were obtained for the high and low PUFA diets with added antioxidants, and it was suggested that PUFA levels and antioxidants did not play a significant role in improving the overall growth rate and meat composition of abalone. However, there was a trend for improved growth performance when the control NutroScience diet was fed, indicating that the diet can potentially be considered as a cheaper alternative feed for abalone growth performance. Further research, however, is required in this regard before it can be propagated as such.On completion of the feeding trial, a standard 40 hour export journey for live abalone was simulated under laboratory conditions to determine moisture loss during live export. The results from this experiment indicated that, even though not significant, PUFA and antioxidants tend to play an important role in ensuring the retention of body water, consequently reducing moisture loss. Overall, abalone fed the AquaNutro diet lost the least weight during the live export simulation, which differed significantly when compared to the weight loss experienced by abalone fed the Abfeed® diet. Abalone that gained the most moisture during the purging period (i.e. period where animals are starved to clean out their intestines) tended to lose the least total moisture after transport and cooking, respectively. These findings indicated a potential correlation between the absorption rate of water during purging, and moisture retention during handling, transport and cooking of abalone. Further studies are required to better understand the water loss and retention dynamics in live abalone during transport, and how this affects abalone meat quality, water absorption during purging and moisture retention during handling, transport and cooking.

[发布机构] Stellenbosch University