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

Abstract

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−1) content. The application of osmotic dehydration and QHRVD afforded acceptable colour of DGSAVSF compared to GSAVSF (ΔEI* = 10.07 ± 0.21). A parametric drying model was formulated that corroborated well with Fick's equation. QHRVD rendered high moisture diffusivity (1.49 × 10−8 m2 s−1) and low activation energy (27.64 kJ mol−1 K−1). 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 × 104CFU g−1: aerobic mesophilic; 1 × 104CFU g−1: 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