Effects of protein isolate prepared from hyacinth bean (Lablab purpureus (L.) Sweet) seeds on cake characteristics were studied. The addition of up to 1% of the protein isolate from hyacinth bean seeds could improve the baking properties of the cake. The volume development and specific volume of the cake with 1% protein isolate were 206.0%, and 2.63 ml/g, whereas those of the control were 160.3% and 2.17 ml/g. Isolate additions of up to 1% softened the cake, as indicated by decreases in texture values, i.e., 184, 112, 100 and 89 g of force for the control, 0.5, 0.75 and 1.0% protein isolate, respectively. However, when more than 1% protein isolate was added, the cake quality tended to decrease compared with that at 1%. Moreover, the more protein isolate was added, the more vivid the colour and the lower the staling rate. Therefore, the protein isolate from hyacinth beans merits further assessment as a practical food additive.Keywords: cake improver, hyacinth bean, protein isolate
IntroductionIndonesia is rich in non-oilseed legumes, such as hyacinth bean (Lablab. purpureus (L.) Sweet), which is commonly planted in marginal land with less of attention. According to Stephens (1994), hyacinth bean has many local names, such as lablab, bonavist, Chinese flowering, Egyptian, Pharao, shink, wild field, and Indian bean. In Indonesia, the local name of this bean is koro komak. It is generally considered to have originated in Southeast Asia. However, some authorities place its origin in Africa, where it has been known since the eighth century. Presently, it is widely cultivated throughout the tropics and subtropics. According to Indonesian farmers, productivity of hyacinth beans plant on dry land can reach to 1000 -1200 kg of dry seeds/ha. Unfortunately, no data is available for the total production of the seeds in Indonesia. In some hyacinth bean-producing areas, the young pods are boiled separately as a vegetable, or together with corn as an soup. The dry seeds are cooked together with rice after soaking water for one night to supply protein. The seeds are also *To whom correspondence should be addressed. E-mail: subagio@ftp.unej.ac.id used as raw materials of tempeh, an traditional Indonesian fermented food usually made from soybeans.Previous study (Subagio, 2006) has reported that hyacinth bean seeds have a moderate protein content (17.1 ± 1.5%), and low concentration of HCN (1.1 ± 0.1 mg/100 g). However, before the seeds can be used as food, treatment is needed to reduce their anti-nutritional components, such as trypsin inhibitor (0.15 ± 0.02 TIU/mg) and phytate (18.9 ± 0.2 mg/g). Using an isoelectric method followed by washing with ethanol, protein isolate produced from the seeds had light colour, neutral odour, high protein content (89.78 ± 0.82 %), and low ash (2.97 ± 0.36 %). The protein isolate had also good functional properties such as solubility, foaming capacity, and emulsifying activity. However, the yield was low (7.38 ± 0.2 g per 100 g of the seeds) (Subagio, 2006).Cake is a food system that requires go...