Effect of pre-milling treatments and milling mechanisms on dehulling of blackgram.

Abstract

Black gram is mainly used after dehulling. Various types of premilling treatments are applied for proper dehulling. In this study, premilling treatments such as the dry method, chemical and hydrothermal treatments were carried out. It was found that premilling treatments with certain chemicals such as sodium bicarbonate, acetic acid and alcohol were found effective in dehulling black gram. Several vegetable oils at varying concentrations (0.2, 0.4, 0.6, 0.8 and 1.0%) were used; it was found that 0.6% was optimal, except that sesame oil was effective even at 0.2%. Oil treatment gave dhal suitable for use in many traditional products. Although chemicals were effective, they had to be used at relatively high concentrations of approximately 5%. It was also found that a steaming time of 10–15 min was adequate to loosen the hull, resulting in easy dehulling. It was concluded that hydrothermal treatment could be used for dehulling black gram. However, hydrothermally pretreated dhal was not suitable for fermented products, in which case a conventional oil pretreatment method should be used with sesame oil preferred. This study shows the effects of different premilling treatments on dehulling black gram. Black gram dehulling efficiency can be enhanced by premilling treatments such as dry method, chemical method or hydrothermal treatment. For practical application, it is important to give due consideration to the end product use of dehulled black gram. Hydrothermal treatment for 10 min is suitable for dehulling black gram if the finished product is used for nonfermented products, and dry method with sesame oil concentration of 0.4% w/w would suit both fermented as well as nonfermented products. This study could be used by black gram processors for optimizing process conditions and premilling treatment.