Preservation of Aloe vera and soybean flour fortified Granny Smith apple through optimised quartz-halogen radiated vacuum drying: kinetics and quality evaluation.

Background: Granny Smith (GS) apple has low protein content and poor antimicrobial properties; hence it has been blended with Aloe vera (AV; high ascorbic acid, antimicrobial and antioxidant properties) and soybean flour (SF; rich in phenols, flavonoids, ascorbic acid, total antioxidant and protein) in different proportions to obtain fortified GS, i.e. GSAVSF. Moreover, GS being a perishable fruit, its moisture content should be reduced to enhance shelf life. Accordingly, this GSAVSF was osmotically pre-dehydrated and finally dried through energy-efficient quartz-halogen radiation (QHR) assisted vacuum-drying (QHRVD) to produce dried GSAVSF i.e. (DGSAVSF) under optimized conditions.

Results: The optimally dehydrated DGSAVSF product resulted in minimum moisture (4.85% w/w) and maximum protein (6.24 g kg ) content. The application of osmotic dehydration and QHRVD afforded acceptable colour of DGSAVSF compared to GSAVSF (ΔE * = 10.07 ± 0.21). A parametric drying model was formulated that corroborated well with Fick's equation. QHRVD rendered high moisture diffusivity (1.49 × 10 m s ) and low activation energy (27.64 kJ mol  K ). Appreciable quality improvements with respect to fresh GS concerning ascorbic acid (176.05%), total phenolic (579.07%), total flavonoid (333.33%) contents and 2,2'-diphenyl-1-picrylhydrazyl radical scavenging activity (446.71%) could be achieved. The product demonstrated satisfactory shelf life (1 × 10 CFU g : aerobic mesophilic; 1 × 10 CFU g : mould and yeast) and high rehydration ratio (4.25 ± 0.1).

Conclusion: The enrichment of GS with AV and SF along with optimal drying protocols could provide a quality fortified DGSAVSF through an energy-proficient sustainable process. The highly nutritious product with suitable colour, microbial stability and rehydration ratio also satisfied a 9-point hedonic scale, thus confirming consumer acceptability. © 2020 Society of Chemical Industry.