Effects of process conditions during expander processing and pelleting on starch modification and pellet quality of tapioca

In this study the effect of processing conditions during the manufacture of pelleted animal feed is related to the degree of gelatinization of tapioca starch as measured by the amyloglucosidase method (SGD(AGS)) and Different ial Scanning Calorimetry (DSC), The process conditions used were related to some physical quality characteristics of the pelleted feeds as well. Physi cal pellet quality was evaluated for hardness and durability, which incorpo rated tests that are also used in the feed industry. The processing line us ed in the experiment consisted of a conventional barrel type conditioner wh ere steam pressure (100-180kPa) and tap water addition were varied (0-52gkg (-1) of the feed debit). Subsequently, expander processing was carried out and the screw speed of the expander was varied (60-140rpm) as well. as the amount of dissipated (expander) motor power (1.3-5.7kW). Response surface r egression methodology was used to assess the directions and relative magnit ude of changes in processing conditions on starch modification, physical pe llet quality and some system variables. The results show that no combination of independent factor levels can be fo und that satisfies one common maximum or one common minimum value for all o f the dependent variables tested. Hardness and durability values of the pel lets were most affected by steam pressure and the amount of expander motor power used, whereas starch modification was most affected by steam pressure and water addition. (C), 1999 Society of Chemical Industry.