Introduction: Due to its high nutritional and bio-functional properties, brown rice, consisting of bran, endosperm, and germ, has great potential in food product development. However, the utilization of brown rice in food processing is limited because of its poor technological properties. Therefore, pretreatment of brown rice for improved quality is imperative. The objective of this study was to evaluate the effect of Rhizopus oligosporus (RO) and microwave radiation (MR) pretreatments on the physicochemical and structural properties of brown rice.

Methods: Brown rice flour (BRF) was pretreated with RO or a combination of RO and MR. The BRF sample that received no treatment served as the control. Physicochemical and structural properties of the pretreated BRF and the control were determined using standard protocols.

Results: Higher water absorption capacity, swelling index, and water solubility index were recorded for the pretreated BRF compared to the control; however, the control has a higher bulk density. The least gelation concentration of the control, RO-treated, and RO+MR-treated BRF was 3.5%, 2.5%, and 1.5%, respectively. RO treatment increased the peak, breakdown, final, and setback viscosities of BRF by 8.33%, 73.47%, 35.54%, and 65.45%, respectively while RO+MR treatment increased the parameters by 76.28%, 33.67%, 86.53%, and 85.82%, respectively. The treatments reduced pasting time and temperature significantly (p < 0.05). There was an improvement in BRF morphology, as evident in increased surface smoothness, following its pretreatment with RO and MR. Similar FTIR and XRD spectra were obtained for the samples; however, there were slight changes in the selected peaks of the pretreated samples, relative to the control, indicating molecular structural re-adjustment.

Conclusion: The physicochemical and structural properties of BRF could be improved consequent to its pretreatment with RO and MW, suggesting improved technological properties that would enhance its applicability in food processing.