EFFECT OF HEAT-TREATMENT UPON THE CHEMICAL-COMPOSITION OF COTTONSEED MEAL AND UPON THE REACTIVITY OF COTTONSEED CONDENSED TANNINS

The effects of heat treatment on the chemical composition of cottonsee d meal (CSM), with or without the addition of cottonseed hulls (contai ning condensed tannins; CT), and upon reactivity of the CT were studie d. Heat was applied in a forced draught oven at 100 degrees C for 2 h. Fluorodinitrobenzene (FDNB)-available lysine, free gossypol, extracta ble- and bound-CT concentrations, in vitro total nitrogen (N) solubili ty and the in vitro rumen degradation of the two major seed proteins ( 52 and 48 kDa) present in cottonseed kernel (which does not contain CT ) were determined. The reactivity of CT was assessed by determining N solubility and rumen degradation of cottonseed kernel proteins in the presence or absence of polyethylene glycol (PEG; molecular weight (MW) 3500), which binds and inactivates CT. Heat treatment reduced the con centrations of free gossypol and FDNB-available lysine by small amount s, reduced measurable total CT content by 13%, reduced the solubility of total N, and reduced potential degradability of the 52 and 48 kDa c ottonseed storage proteins by mixed rumen microorganisms. Addition of hulls further depressed solubility of total N and ruminal degradation of the two major storage proteins in cottonseed kernel. The action of PEG in vitro indicated that only part of the depression caused by hull addition could be explained by the presence of CT in the hulls, and t hat the effects of CT upon N solubility and potential degradability in heated CSM were similar to that in unheated CSM. Addition of hulls al so substantially reduced FDNB-available lysine. In commercially produc ed materials, CSM from the Brisbane mill had a lower total CT content, lower N solubility and lower ruminal protein degradation rate than CS M from the Narrabri mill, but a similar level of FDNB-available lysine . Although application of heat inactivated 13% of the total CT, such t hat it could no longer be extracted and detected with butanol/HCl, it did not seem to change the overall effects produced by CT in reducing N solubility and protein degradation. The effect of hull addition in r educing available lysine has considerable relevance for feeding CSM to monogastric livestock. Interactions involving heat, hulls and CT need to be further studied.