ORIGINAL ARTICLE Optimization of preconditioning process of pressure parboiled brown rice (unpolished) for microwave puffing and its comparison with hot sand bed puffing Ajay Kumar Swarnakar | Prem Prakash Srivastav | Susanta Kumar Das Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India Correspondence Ajay Kumar Swarnakar, Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India. Emails: aksw11@gmail.com or aksw11@agfe.iitkgp.ernet.in Abstract Puffing of pre-conditioned brown rice using microwave energy replacing the traditional puffing of preconditioned polished rice on hot-sand-bed has higher nutritive value and produce required amount of puffed rice as per consumer's wish. Preconditioning temperatures (60, 70, 80, 90  C) and salt contents (0, 2, 4, 6% [w/w]) have been chosen to puff brown rice using microwave energy, and quality aspects have been evaluated and compared with those obtained with hot- sand-bed puffing. Optimization of processing variables was carried out for maximizing puffing percentage, expansion ratio, whiteness index, overall sensory score, and minimizing the bulk density and hardness of puffed brown rice. The sensory analysis for the product was carried out using fuzzy logic technique to obtain overall sensory score. Optimum preconditioning tempera- ture and salt content were found to be 76.74  C and 3.74% (w/w) in microwave and 76.16  C and 2.76% (w/w) in hot-sand-bed puffing, respectively. Practice applications Puffing of brown rice (unpolished rice) using microwave oven provides an option in obtaining nutritious, fresh and hygienic puffed product on instant demand. Puffing of brown rice elimi- nates the energy-intensive polishing step of the rice milling process. Optimization of the pro- cess variables can be implemented for making preconditioned brown rice in obtaining desired quality of the puffed rice using microwave energy. The prepacked preconditioned rice can be directly put inside the domestic microwave oven to get required amount of puffed product. 1 | INTRODUCTION Puffed rice, a popular snack in Southeast Asia, is commonly prepared from polished parboiled rice. In rice polishing, the bran part is removed in a process that consumes around 43% energy of the whole rice mill- ing operation (Ekasilp, Soponronnarit, & Therdyothin, 2007). Removal of bran decreases the nutritive quality of the rice considerably (Lamberts et al., 2007) as it contains dietary fiber, fat, minerals, and bioactive components. Thus, puffing of brown rice can save time, energy, and cost. Recently, Mir, Bosco, Shah, and Mir (2016) and Mir, Bosco, Shah, Mir, and Sunooj (2016) have reported effects of puffing on the antioxidant property and optimized the process for popping of brown rice. The puffing of rice comprises parboiling, preconditioning, and roasting (high-temperature short time treatment, HTST) steps. Various methods of parboiling are practiced for obtaining rice suitable for puffing, viz., normal parboiling (at normal atmospheric pressure), sand parboiling (high-temperature heating of moist paddy on sand bed), and pressure parboiling. Chandrasekhar and Chattopadhyay (1991) reported less expansion of rice parboiled at normal pressure compared to rice parboiled by other two methods. Puffing of rice and popping of paddy using microwave energy have been reported by several workers (Devi & Das, 2017; Maisont & Narkrugsa, 2009; Mohapatra & Das, 2011; Swarnakar et al., 2014). According to them, puffing using microwave energy is convenient and hygienic. Similar to commercially available microwavable popcorn Received: 19 June 2018 Revised: 18 November 2018 Accepted: 30 December 2018 DOI: 10.1111/jfpe.13007 J Food Process Eng. 2019;e13007. wileyonlinelibrary.com/journal/jfpe © 2019 Wiley Periodicals, Inc. 1 of 11 https://doi.org/10.1111/jfpe.13007