Processing black rice grains to obtain flour: Influence of pretreatments on mass transfer, in vitro digestibility, and technological properties

Abstract

Background and ObjectivesThe objective of this work was to evaluate the processing of black rice grains to obtain flour and to verify the influence of pretreatments on mass transfer, in vitro digestibility, and technological properties. The grains were submitted to heat moisture treatment (HMT) with a final humidity of 30% at 110°C for 2 h, black rice pretreatment with ethanol (BRE) in the proportion 1:1 (wt/wt) for 5 min/25°C, and high hydrostatic pressure (HHP) under conditions of 200 MPa for 10 min/25°C. Then, the grains were dried at 60°C at an air velocity of 1.5 m/s and ground in an electric multigrain grinder. Was analyzed the mass transfer, in vitro digestion, water, oil, and milk retention capacity, total phenolic compounds (TPC), total anthocyanins (TA), antioxidant activities by (2,2′‐azino‐bis‐(3‐ethylbenzothiazoline‐6‐sulfonic) acid, 2,2‐diphenyl‐1‐picrylhydrazyl, ferric‐reducing antioxidant power, and oxygen radical absorbance capacity Surface appearance by scanning electron microscopy, and thermal analysis by differential scanning calorimetry was carried out.FindingsThe grains when submitted to the HHP obtained a reduction of 58.82% in the drying time, while the HMT promoted an increase of 23.5% when compared to the control. The pretreatments influenced the in vitro digestibility, where the HHP had the highest value (86.33), as well as the highest water, oil, and milk retention capacities. BRE positively impacted TPC, TA, and antioxidant activities regardless of the methods used. HMT promoted the formation of cavities, fissures, and holes on the surface, resulting in a rough appearance and presenting greater thermal resistance with an enthalpy of 12.35 J/g.ConclusionsThis research paved the way for potential commercial applications of black rice flour as an ingredient in functional foods.Significance and NoveltyThis study adds to the significance and novelty of research on black rice processing by evaluating the influence of different pretreatments on mass transfer, in vitro digestibility, and technological properties.