Utveckling av en C-vitaminberikad tofuprodukt : Studie av C-vitaminhalt under process och förvaring

Sammanfattning: Tofu is a plant based product made from soybeans, water and a coagulant. The coagulant together with heating enables the formation of a soy curd (tofu). The proteins that dominates in soybeans are β-conglycinin (7S) and glycinin (11S). The composition of the proteins differs between soybean cultivars, which also affects the formation of the tofu. The object in this study was to evaluate the vitamin C content and the stability of vitamin C during processing and storage in an ecological tofu-product after enrichment of Sea Buckthorn to increase the vitamin content. Furthermore, the use of germinated soy beans instead of soaked soybeans in the production of tofu was evaluated. When Sea Buckthorn was added to the soymilk it resulted in a decrease in pH from 6.3 to 5.5, which affected the formation of the soy curd negatively as the optimal pH is between 6.0 and 6.5. By adding alkali to reach pH 6.3 it was possible to achieve a soy curd when Sea Buckthorn powder was added. Sea Buckthorn increased the vitamin C content in the product to 32 mg/250 g but only 10% (about 3 mg) remained after four weeks storage. The loss of vitamin C was large in both processing and storage of the tofu. An additional loss of 7- 14% was detected during 10 minutes heating (60°C). Germination of soybeans did neither affect the amount of protein, nor the vitamin C content in tofu. To produce a tofu with more than 15% of RDI for vitamin C in one serving (100 g) the amount berry powder to be added in the production of 250 g tofu must not be less than 31 g (400 mg vitamin C), based on losses up to 90-95% during the process and storage. Hence the huge amount of berry powder that must be added, other ways to decrease the degradation of vitamin C is necessary to be investigated.