Reducing weight loss of retorted soy protein tofu by using glucose- and microwave-pre-heating treatment

Abstract

Soy protein isolate tofu with or without glucose was subjected to a pre-heating treatment in a microwave oven before being thermally processed at 121 °C for a range of time between 5 and 25 min. The occurrence of the Maillard reaction during the processing of tofu containing glucose was shown by a decrease in pH and a change in colour of the tofu from pale white to brownish yellow. Retorted tofu prepared with glucose had a reduced weight loss and lower solubility in 1% sodium dodecyl sulphate solvent. This effect was most pronounced in the tofu containing glucose which had been preheated. Similarly, a lower percentage of glucose loss during retorting was seen in tofu containing glucose which had been preheated, which indicated that some level of the Maillard reaction may have occurred during the microwave pre-heating treatment. The decrease in solubility in sodium dodecyl sulphate solvent was thought to be due to the formation of the 'Maillard network'. It was hypothesized that this had provided a protection to the hydrophobic regions of the protein against attack from the solvent. The glycation effects and formation of the 'Maillard network' within tofu's internal structure were suggested as the major reasons for the reduced weight loss of tofu containing glucose.