Endogenous lipolysis in feedstuffs and compound feeds for pigs: effects of storage time and conditions and lipase and/or emulsifier addition

Besides the chemical structure of the triacylglycerols (U/S, unsaturated/saturated fatty acids), the content and the source of FFAs (free fatty acids) in mixed feed are very important chemical variables, influencing the subsequent nutritive value (oxidative rancidity (soapy) taste, efficiency of digestion and absorption) of nutrients. The present paper concentrates on the extent of endogenous lipolysis in selected (milled) raw materials and mixed feeds for pigs, as influenced by heat treatment, storage time and conditions and lipase and/or emulsifier addition. In 10 commercial compound feeds (closed formula, containing 20 to 50 g/kg fat) analyzed within 4 months after production, lipolysis (g FFAs/ kg TFAs, total fatty acids) ranged from 2 10 to 770. In nine compound feeds (open formula) used in our own digestion experiments, lipolysis ranged from 250 to 850 g FFAs/kg TFAs, after 6 months of storage at 20 degreesC. In diets containing no exogenous lipases, lipolysis was less pronounced. The type of lipase added, greatly influenced the extent of lipolysis. In addition, the kinetics of lipolysis were followed during storage of compound feeds for piglets and growing pigs (storage from zero to 56 days at -25, 5 and 20degreesC) containing either soy oil, medium chain triacylglycerols or rendered fats and all or not exogenous lipases. The data revealed that freezing could eliminate lipolysis, while at 5 degreesC, only small differences in lipolysis compared with storage at room temperature were noted. Lipolysis amounted to 600-700 g FFAs/kg TFAs at day 56. The highest values were noted for diets containing an exogenous lipase and/or an emulsifier. Lipolysis was further studied in 29 milled feedstuffs, during storage from 0 to 56 days at room temperature. The extent of lipolysis was most pronounced for cereals (high, up to 600 g FFAs/kg TFAs), intermediate for thermal treated materials (e.g. soy products, 150 g FFAs/kg TFAs) and low for fish products (80 g FFAs/kg TFAs) and milk products (50 g FFAs/kg TFAs). Both endogenous and added fat was hydrolyzed, while no obvious substrate specificity was noted. Appropriate measures should be taken to delay or retard endogenous lipase activity in test feeds if long-lasting experiments (e.g. several weeks or months, to measure digestibility or energy content of fat; performance tests) have to be done with the same batches of prepared feeds. Also, the addition of lipases to manipulate fat digestion, should be carefully advised, in order to prevent an excessive endogenous lipolysis, already in the feed. (C) 2002 Elsevier Science B.V. All rights reserved.