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

Abstract

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 (SGDAGS) and Differential Scanning Calorimetry (DSC). The process conditions used were related to some physical quality characteristics of the pelleted feeds as well. Physical pellet quality was evaluated for hardness and durability, which incorporated tests that are also used in the feed industry. The processing line used in the experiment consisted of a conventional barrel type conditioner where steam pressure (100–180 kPa) and tap water addition were varied (0–52 g kg−1 of the feed debit). Subsequently, expander processing was carried out and the screw speed of the expander was varied (60–140 rpm) as well as the amount of dissipated (expander) motor power (1.3–5.7 kW). Response surface regression methodology was used to assess the directions and relative magnitude of changes in processing conditions on starch modification, physical pellet quality and some system variables. The results show that no combination of independent factor levels can be found that satisfies one common maximum or one common minimum value for all of the dependent variables tested. Hardness and durability values of the pellets 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. © 1999 Society of Chemical Industry