WORLD AQUACULTURE 65 (CONTINUED ON PAGE 66) Protease inhibitors are present in many plant-derived ingredients used in aquafeeds, particularly legumes. Their potency depends upon their origin and the target enzyme. Soybeans have two groups of protease inhibitors: the Kunitz soybean trypsin inhibitor, which is relatively heat and acid sensitive, and the more stable Bowman-Birk protease inhibitor. Commercial soybean products have concentrations of trypsin inhibitors of 2-6 mg/g. Common culture fishes differ in their tolerance of dietary trypsin inhibitors. Moist heat treatment (autoclaving for 15-30 min) is recommended to reduce the concentration of trypsin inhibitor below critical levels. Glucosinolates are thioglucosides commonly found in plants in the family Cruciferae. They are always accompanied by the thioglucosidase enzyme in plants, but the two are separated in different cell components. When cells are damaged, the contents of these two components come together and breakdown products (e.g., isothiocynates and nitriles) that are capable of causing potentially harmful effects to animals are released. Over the long term, thyroid dysfunction induced by continuous consumption of glucosinolates containing feed is certain to affect metabolism and growth in fish. Glucosinolates are the main anti-nutrients present in rapeseed (Brassica spp.) meal TABLE 1. Classification of major anti-nutritional factors commonly present in plant-derived feedstuffs used in aquafeed (Francis et al. 2001). Anti-nutritional factors Plant-derived nutrient source Means of alleviation Interaction with protein nutrition Protease inhibitors Soybean, Jatropha kernel meal, rapeseed meal, Heat, autoclaving lupin seed meal, pea seed meal, sunflower oil cake, alfalfa leaf meal, sesame meal Heamagglutinins (lectins) Soybean, Jatropha kernel meal, pea seed meal Heat, autoclaving Saponins Peas, alfalfa, Jatropha kernel meal, lupin seed meal, pea seed meal, sunflower oil cake, alfalfa leaf meal Polyphenols (Tannins) Tannins, sorghum, Jatropha kernel meal, pea seed meal, mustard oil cake Chlorogenic compounds Supplementary methionine or choline Interaction with mineral availability Phytic acid Soybean, Jatropha kernel meal, pea seed meal, Supplementation, cottonseed meal, sesame meal use of phytase Oxalic acid Leaf proteins Heat treatment Glucosinolates Rapeseed, mustard oil cake Genetic improvement of plants with low content Gossypol Cottonseed meal Genetic improvement of plants Interaction with vitamin availability Vit A (lipoxygenase) Soybean Heat treatment Vit D Soybean Autoclaving Vit E (oxidase) Kidney beans Autoclaving, addition of Vit E Anti-nicotinic acid (niacinogen) corn Anti-pyridoxine Linseed meal Water extraction, heating Anti-vitamin B12 Raw soybean Heat treatment Cyanogens Cassava, sorghum, pea seed meal, Heat treatment Mimosine Leucaena leaf meal - Arginase inhibitor Sunflower oil cake - cyclopropenoic acid Cottonseed meal - antivitamins Alfalfa leaf meal, cottonseed meal, pea seed meal, soybean meal - Alkaloids Lupin seed meal - Phytoestrogens Soybean meal, lupin seed meal - Allergens Soybean meal -
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