Physicochemical properties of apple juice during sequential steps of the industrial processing and functional properties of pectin fractions from the generated pomace

- The impact of industrial processing on properties of apple juice is scarcely known.
- The sugar content in apple juice was not altered by any processing step.
- The pasteurization step altered the levels of individual phenols and acids.
- Concentration step favored the formation of 5-HMF.
- Pomace pectins showed less functionality than commercial apple pectin.

The impact of processing at industrial scale on properties of apple juice and pectin fractions extracted from the generated pomace is scarcely known. In this study, apple juice was collected at selected steps of the industrial production process and evaluated for physical and chemical properties. The generated pomace was recovered and subjected to extraction of pectins according to their solubility. They were evaluated for physicochemical and functional properties. The transmittance for color and clearness of juice increased during clarification step but decreased during concentration. The sugar content was not altered by any step. The content of individual acids showed some changes during the pasteurization. The levels of total and individual phenols tended to increase during the production process. Low levels of 5-HMF (4.0 mg/L) were detected only in the concentrated juice while patulin was absent. The pomace contained only chelator and alkali soluble pectin. In comparison to commercial apple pectin, extracted pectins were of low degree of esterification (67% vs 22.8-44.6%), GalA (654.1 vs 393.5-436.6 mg/g) and Gal (228.6 vs 71.3-115.0 mg/g) content but rich in Ara (27.5 vs 103.4-166.3 mg/g) and of high molecular weight (644.5 vs 1559.6-2360.6 kDa). Their viscosity was lower than that of commercial apple pectin (k values of 0.03-0.05 vs 0.14 Pa·sn, respectively). They showed lower thermal stability than commercial apple pectin. The production steps involving high temperature or enzymes effected the properties of apple juice and extracted pectins.