The design of a shelf-stable sausage for Thailand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Biotechnology at Massey University

Abstract

Sai Krok Prew is the naturally fermented sausage in Thailand made from pork, fat, cooked rice, sugar and spices. This sausage has a very short shelf life of three days, and inconsistent quality. Studies were carried out to find the basis for a process to increase the shelf life without using refrigeration, and to give a consistently high quality product. Simulated commercial conditions as found in Thailand were used in the laboratory, by mixing in a bowl chopper, mechanical stuffing, storage at 30-32°C, 75% R.H. for two days (factory conditions), and then further storage at 30-32°C, 97-99% R.H. (transport and retail sale). Lactic acid and GDL were used to produce chemically acidified Sai Krok Prew. Lactic acid gave a completely unacceptable flavour and texture; GDL gave a satisfactory texture but a harsh flavour. There might be a good possibility of producing a low quality Sai Krok Prew by using GDL. A satisfactory process for microbiologically fermented sausage was developed using starter culture, straight nitrite and sugar. The starter culture did not give a quicker rate of pH reduction than chance fermentation, as used commercially in Thailand, but suppressed the growth of other microorganisms. An extreme vertices designs were used to study the effect of pork, fat and rice composition upon texture acceptability. Texture was improved with increased pork and fat and decreased with increased rice and an optimum composition was obtained. This would have to be related to cost before commercial production could be considered. Sensory costing was used in an attempt to correlate the attributes of texture - firmness, rubberiness, juiciness, oiliness, smoothness, stickiness. Only rubberiness was correlated directly with fat content; a decrease in fat caused an increase in rubberiness. The other texture attributes appeared to have complex relationships with chemical composition. Generally, pork increased firmness and rice increased grittiness. The shelf life was increased by dipping the sausage in 4% potassium sorbate solution for one minute and/or vacuum packaging. Over 14 days shelf life was obtained with potassium sorbate, and ten days with vacuum packaging.