Compositional and morphological properties of pretreated orange and plantain peels: effect on apple juice clarification efficacy of polygalacturonase

Abstract

This study evaluated the effect of alkaline and microwave pretreatments on the chemical composition and morphology of orange peel powder (OPP) and plantain peel powder (PPP), and the application of polygalacturonase, produced using the pretreated peels, in apple juice clarification. The pretreatment caused a significant (p < 0.05) reduction in hemicelluloses and lignin, while pectin, cellulose, and the total sugar increased. The morphological evaluation showed disruption in the structures of OPP and PPP following their pretreatment with NaOH and microwave radiation. The most pronounced modification was recorded in the peels pretreated with the combined use of NaOH and microwave as compared to their separate use. Significantly higher (p < 0.05) titratable acidity, total solids, sugars, degree of lightness, and color intensity were recorded for the apple juice clarified with polygalacturonase produced using pretreated peel (PUEA) as compared to the one clarified with polygalacturonase produced using untreated peel (CREA). Also, PUEA was more preferred than CREA and compared significantly (p < 0.05) with the apple juice clarified with a commercial polygalacturonase in terms of colour, consistency, clarity, mouthfeel, and overall acceptability. This study showed that the pretreatment of OPP and PPP improved their chemical composition and morphology, and enhanced apple juice clarification efficacy of polygalacturonase.