Microwave assisted dehulling of black gram (Vigna mungo L)

Abstract

This article summarises the results of the investigation of application of microwave exposure on the dehulling characteristics of the black gram and the properties of the dehulled grains. Black gram was exposed to 3 microwave power levels, viz., 450, 630 and 810 W for 7 different exposure, ranging from 60 to 150 s at an interval of 15 s with a view to determine the suitable combination of dosage in order to get the maximum yield with little change in colour. Related changes in properties were also studied. It was observed that the surface temperature of the grain increased with the increase in microwave power level from 450 to 810 W as well as exposure time from 60 to 150 s in the range from 58 to 123°C while the dehulling time reduced from 445 to 170 s. The dehulling yield increased with increasing microwave dosage in the beginning and reached to the maximum value followed by decreasing trend. The colour of the dehulled grain changed slowly up to a microwave dosage of 972 J/g after that it changed vividly darker than the control. The dehulling and dhal yields and colour change were polynomial functions of microwave dosage. The highest yield of 73.7 % was achieved at about 972 J/g with a little change in colour (CIELAB ΔE* value of 2.58). The corresponding dehulling time, cooking time and losses during dehulling were respectively 185 s, 10 min and 15.1 % as compared to 492 s, 20 min and 31.5 % for control respectively. It is concluded that a dosage of about 972 J/g was the best for the black gram dehulling at a rate of 630 W or higher power level.

Effect of ultrasound treatment on dehulling efficiency of blackgram

“…The sample of 100 g was taken in a glass beaker and kept on the turn table of the microwave oven. The sample was treated at 810 W power level for 120 s, which was selected from the earlier research findings (Joyner and Yadav 2013).…”

“…Different pre-milling treatments such as chemical treatments (acetic acid, sodium bicarbonate and alcohol etc. ), urea solution, vegetable oil treatments, heat treatment and microwave application have been followed and tested by different researchers (Phirke and Bhole 2000;Narasimha et al 2003;Tiwari et al 2007Tiwari et al , 2008Joyner and Yadav 2013;Pal et al 2017).…”

Effect of microwave treatment on cooking time, colour, sensory and nutritional properties of Bambara groundnut (Vigna subterranea)

“…Furthermore, the microwaving treatment also facilitated the dehulling process. The dehulling time for black gram was reduced by 62.3 % when compared to the control sample (Joyner and Yadav, 2015). Bambara groundnut is becoming a crop of importance that may be explored for various nutrition interventions and for enhancing the nutritional value of traditional products.…”

“…The HTC defect also affects the dehulling of grains (Mubaiwa, et al, 2017). For example, dehulling of black gram has been reported to be a very difficult operation due to the presence of vitreous layer of gums and mucilages, which makes bond between hull and cotyledon stronger (Joyner and Yadav, 2015). Earlier attempt to reduce cooking time of some legumes focused on the use of soaking solutions such as sodium chloride (NaCl) (Huma, et al, 2008;Paredes-López, et al, 1991), water (Huma, et al, 2008), sodium hydrogen trioxocarbonate IV (NaHCO 3 ) (Paredes-López, et al, 1991) and sodium bicarbonate (Huma, et al, 2008).…”

“…Thus, promising methods such as microwave heating that would not require soaking prior to cooking are required to reduce nutrient losses associated with soaking. According to Joyner and Yadav (2015) microwave heating results in the disruption of bond between hull and cotyledon of pulses by denaturing the protein and gums present in between them. These authors found that microwaving of black gram at varying microwaving power and time resulted in significant reduction in cooking time.…”