Preservation of South African steamed bread using hurdle technology

Abstract

To transform traditional South African steamed bread, a dumpling-like product, into a convenient ready-to-eat form in a can, the application of various hurdles was investigated. Prevention of the growth of Clostridium botulinum in this low acid product by lowering a(w) was the most important aspect sought, since the internal temperature reached during processing (90 degrees C) was not sufficient to kill spores. The issue of staling was also addressed. The hurdles included use of fat, salt, acid, preservative, glycerol, packaging material, heat and the processing technique. Low pH resulted in poor bread volume. Fat had no effect on a(w). Increasing the salt content from 8 to 24 g/kg flour slightly reduced aw from 0.960 to 0.949. Use of glycerol was the most effective hurdle. Glycerol levels of 150 and 180 g/kg flour produced a(w) levels of 0.908 and 0.880, respectively, which were sufficient to inhibit C. botulinum yeast and moulds were effectively inhibited during the shelf life study. Staling was not sufficiently retarded despite addition of high levels of fat. A consumer sensory panel (focus group) preferred yeast leavened to chemical leavened steamed breads.